Broad‐leaved dock (Rumex obtusifolius L.) is a troublesome weed that predominantly grows in pastures and grassland. We hypothesised that frequent defoliation of Rumex will, over time, result in a reduction in root weight and leaf area, to the point where the impact on grass production is negligible. In order to investigate this hypothesis, we conducted three experiments. The objective of the first experiment was to perform a preliminary test of the hypothesis, using potted plants growing in the controlled conditions of a glasshouse. This experiment showed a rapid decline in leaf growth in plants that were defoliated weekly. The objective of the second experiment was to test the hypothesis in realistic outdoor conditions while still being able to collect detailed plant growth information. This experiment confirmed the findings of the glasshouse experiment and provided evidence that leaf growth ceased as a result of a dwindling supply of carbohydrate reserves in the root. Defoliated plants did not exhibit increased mortality. Finally, the objective of the third experiment was to test the hypothesis in a commercial pasture where normal field operations, specifically grass harvesting (three times) and slurry injection (twice), were performed. The results of this experiment were consistent with the results of the other two experiments. We conclude that weekly defoliation, maintained for three or more months, is an effective method to control (reduce the impact on grass production), but not kill, R. obtusifolius in pasture.

Finnish N fertilizer application regulations for forage grasses are based on field experiments mainly conducted in the 1960–1970s with cultivars and management practices typical of the time. In order to update the yield response function of N, to make it better suited to current grassland farming, field experiments were conducted at two sites in 2015–2017 with two cultivars of timothy (Phleum pratense L.) and one of meadow fescue (Festuca pratensis Huds.). Dry matter (DM) yield, nutritive value and N balance were evaluated, with N application levels 0, 150, 200, 250, 300, 350, 400 and 450 kg N ha−1 year−1. The grasses were harvested three times per season. The data indicate that the DM yield response was significantly stronger, and N was used more efficiently for DM production than earlier without compromising the nutritive value, especially during the first two years. The third harvest produced on average 23% of the annual yield, utilizing N efficiently. N application rates below 350 kg N ha−1 year−1 did not cause substantial overwintering losses or lodging. The data indicate that with changing climate and improved cultivars and management practices, there is a need to modify the rates and timing of N application. The results suggest that N application levels could be increased by at least 50 kg N ha−1 year−1 from the current maximum accepted rate (250 kg N ha−1 year−1) without too high NO3‐ or CP concentrations in feed, or too high N balance that indicates increasing risk of N leaching.

A Syrian grassland was subject to 13 years of replicated management treatments, namely a factorial design of 0 or 60 kg/ha annually of phosphate fertilizer, combined with relatively low or high sheep stocking intensities. Previous work found that differences in grazing intensity and phosphate induced changes in the structure of the legume community, presumably due to changes in competitive relationships. The aim of this study was to investigate how the populations of the predominant clover species, Trifolium campestre and Trifolium tomentosum, changed as a consequence of management treatments. We hypothesized that the populations from the fertilized or low grazing intensity treatments would express phenotypic traits associated with increased competitive ability and/or with risk mitigation. Populations of both ruderal‐type clover species provided evidence of evolution but were largely responsive to different management factors. Assuming that heavy grazing and no fertilizer are the natural state of the grassland, addition of phosphate led to T. tomentosum plants that were wider and had larger seeds, traits associated with improved competitive ability. The populations from the fertilized paddocks had increased fecundity and a trend towards greater dormancy, traits associated with risk mitigation. In contrast, T. campestre plants became wider and more erect when stocking intensities were reduced and had greater seed dormancy in fertilized paddocks. The implication of this work is that the collection of germplasm from grasslands with a history of heavy grazing and fertilizer application may assist agronomists to find genotypes that are better adapted to pastures within ley farming systems in Australia.

The evapotranspiration (ET) and crop coefficient (Kc) spatial variabilities are disregarded in traditional methods of evapotranspiration estimation based on lysimeters. With the development of remote sensing techniques, the estimative of ET on agricultural areas, in a specialized way, has become possible through the use of algorithms based on the surface energy balance such as the METRIC and its automated version, featured on the Google Earth Engine Evapotranspiration Flux (EEFlux) platform. This study was carried out at a center pivot irrigated area located in the city of Primavera do Leste, MT, Brazil. One growing season (2016) of the specie Zea mays (maize) was analyzed. Using processed images from the Landsat 8 satellite, within the EEFlux platform, the spatial variability of the actual evapotranspiration (ETa) and the Kc curve of this crop was determined. The water use efficiency (WUE) was also determined. A comparative analysis was performed using different statistical indices: root mean square error (RMSE), the mean bios error (MBE) and the index of agreement (d). The ETa for maize ranged from 1.3–4.1 mm d−1 and the Kc obtained ranged from 0.3 to 1.2. The average WUE of maize was 1.13 kg m-3. The method of estimation of ETa and Kc spatialized using the Google EEFlux platform made possible the understanding the spatial variability of these two variables and, therefore, this application has high potential to estimate the ETa and Kc on different stages of maize crop growth cycle.

Impatiens glandulifera is a globally successful invader that primarily spreads along riparian habitats; however, during the last ~20 years, it has started to colonise forests, but little has been published on impacts of this recent spread. Several factors may have contributed to this phenomenon: (i) high propagule pressure from large and widespread riparian populations, (ii) extensive anthropogenic and natural disturbances in the forest ecosystems, (iii) increased use of forest machinery efficiently spreading the seeds together with (iv) a wide environmental tolerance of the species. The impacts of I. glandulifera on native communities in forests are manifold. Contrasting effects are reported on native plant species diversity, richness and growth of saplings of co‐occurring species, as well as negative effects on soil mycorrhizal fungi. We suggest that the eradication of I. glandulifera populations in forests is more feasible than along watercourses because the recolonisation in forests is limited and, in some cases, populations are outcompeted by woody species during succession.

Phenotypic plasticity, which confers a fitness advantage under heterogeneous and novel environments, has been commonly suggested to contribute to the success of invasive plants in their introduced range. For example, plasticity in response to changes in light availability could facilitate invasiveness by allowing plants to both rapidly establish in unshaded, disturbed habitats, and tolerate shaded or crowded environments. The plastic responses of invasive plants to shade were mostly studied in morphological traits. However, plasticity in physiological traits might provide more rapid and reversible responses and thus be more effective in environments with rapid temporal variations. Here, we compared plasticity in a range of morphological and physiological traits that provide shade avoidance or tolerance between two native and six introduced populations of Impatiens glandulifera. In a common garden, we subjected second‐generation siblings of native and invasive plants to two light availability treatments and measured their morphological, physiological and performance responses. Impatiens glandulifera from invasive populations exhibited greater phenotypic plasticity in response to light availability in four out of 12 measured traits. Moreover, this greater plasticity was mostly limited to physiological traits associated with photosynthetic acclimation. These results suggest high phenotypic plasticity in response to light availability could have facilitated I. glandulifera's spread in both disturbed habitats and woodlands or under intense light competition. The results of this study highlight the importance of considering physiological traits when studying the role of plasticity in the success of invasive plants.

Soil loss from riparian areas supporting the annual invasive weed, Impatiens glandulifera (Himalayan balsam), was measured and compared with equivalent values recorded at nearby, topographically similar areas supporting perennial vegetation over a cumulative seven‐year period, along sections of two separate river systems; one in Switzerland, and one in the UK. Soil loss from colonised locations was significantly greater than from reference locations in four of the seven measurement periods. Despite contrasting results, standard deviations, based on soil losses and gains, were predominantly higher for colonised areas at both rivers over most monitoring periods. These findings indicated that areas colonised by Himalayan balsam experience higher sediment flux in comparison with areas free of invasion. Here, we test those original interpretations by reinterrogating the datasets using a more robust analysis of inequality. Nine datasets were tested, five of which (i.e. 56%) showed that sediment flux was significantly greater at Himalayan balsam‐invaded areas than at reference areas. Three datasets showed no difference in sediment flux between invaded and reference areas (33%), and one (11%) showed higher sediment flux at reference areas. Most results uphold our original interpretations and support our hypothesis that hydrochory probably dictates where colonisation initially occurs, by depositing Himalayan balsam seeds in slack or depressional areas along river margins. Once Himalayan balsam becomes established and sufficient perennial vegetation is displaced, seasonal die‐off and depleted vegetation cover may increase the risk that some areas will experience significantly higher sediment flux.

In 2014, the rust fungus Puccinia komarovii var. glanduliferae, native to the foothills of the Himalayas from Kashmir to Western Nepal, became the first fungal agent to be released into Europe for the classical biological control of a non‐native weed. The target, Impatiens glandulifera or Himalayan balsam, is a prolific invader of riparian habitats in Europe and North America. During the period 2015–2018, a strain of the rust from India was released at a total of 36 sites, in 17 counties in England and Wales. There was limited field infection in 2015 and inoculation experiments conducted under controlled conditions revealed significant variation in the susceptibility of plant populations to the rust, with some showing immunity. Subsequently, a second strain of the rust from Pakistan was released in 2017 and was found to infect a different cohort of Himalayan balsam populations. The rust mass production methodology, and field inoculation and monitoring protocol, are detailed, and plants were tested for susceptibility to both rust strains prior to field release. Levels of foliar infection at selected sites in 2017 and 2018 are presented, as well as seedling infection rates in the spring of 2019. The results show that the rust is able to overwinter and establish populations in stands of Himalayan balsam in England. The issues involved with measuring the impact of the biological control agent are discussed.

The rust fungus, Puccinia komarovii var. glanduliferae, has been introduced into the UK for biological control of the invasive weed, Impatiens glandulifera (Himalayan balsam). However, establishment of the pathogen has differed across the country, which may be partly explained by variation in plant genotype. The aim of this study was to examine whether there is a further layer of phenotypic resistance, provided by indigenous foliar endophytic fungi. Culturable endophytes were isolated from a number of different balsam populations, and the commonest species were inoculated into ‘clean’ balsam plants, to test their interactions with the rust. We found that endophyte communities within balsam are low in diversity and become more dissimilar with increasing distance between populations. Three endophytes (Colletotrichum acutatum, Alternaria alternata and Cladosporium oxysporum) were common and appeared to be antagonistic to the rust, reducing pustule number and mitigating the effect of the pathogen on plant biomass. I. glandulifera thus partially conforms to the endophyte‐enemy release hypothesis, in that as an introduced species, it has an impoverished endophyte complement, acquired from the local environment. However, these endophytes represent a potential barrier to effective biological control and future weed control strategies need to find strains of rust that can overcome plant genetic resistance and the overlaying phenotypic resistance, conferred by endophytes. Future classical biological control programmes of weeds must therefore take into account the fungal bodyguards that invasive species may acquire in their introduced ranges.

The use of bioherbicides containing fungal active ingredients or natural fungal molecules is one of the possible solutions to reduce the use of chemical products. This paper focuses on studies of bioherbicides, including both living fungi and natural fungal molecules, published in the last 45 years, and their associated weed targets; current problems in the development of bioherbicides are also discussed. Bibliometric methods based on the Web of Science database were used to analyse relevant articles published between 1973 and 2018. Overall analysis suggested that interest in bioherbicides extends over the preceding thirty years, when many potential microorganisms and natural fungal molecules were proposed. Furthermore, analysis of about 229 articles indicated an encouraging exploitable potential, although there is a real gap between the number of experimental studies and the small number of products currently on the market. A dozen fungal‐based bioherbicides are on the market in the United States and Canada, while countries, such as China and South Africa, have one, and none is available in Europe. The active ingredients in these bioherbicides are living fungi, but no fungal molecule‐based product is thus far on the market. Reasons for this gap include production hurdles, formulation process, ecological fitness, duration of herbicidal effects, and costly and time‐consuming registration procedures. However, it is clear that analysis of fungus–plant interactions provides a promising source of bioherbicides that may be applied to appropriate cropping systems for environment‐friendly, sustainable weed control.

The perennial weed, Cirsium arvense (creeping, Canada or Californian thistle), is notorious for its ability to tolerate defoliation by mowing, herbivores or herbicides. The tolerance of 36 genotypes of C. arvense was examined by establishing pairs of clonal replicates that were assigned to a clipped or unclipped treatment. Three clippings were applied from spring to early summer to simulate repeated mowing. The average final percentage reduction caused by the repeated clipping was 18%, 72%, 32% and 50% for shoot biomass, root biomass, number of shoots and shoot height respectively. While nearly all genotypes were negatively affected by clipping, some overcompensated, and achieved greater shoot biomass, number of shoots, or increased height than their unclipped counterparts. No genotype was able to overcompensate, or fully tolerate, the lost root biomass due to repeated clipping. Genetic variation for tolerance to defoliation was detected for the number of shoots, maximum shoot height and for relative height growth rate. For relative growth rate, significant genetic variation was not detected until after the third clipping event, indicating that genotypes were equally tolerant to a moderate degree of defoliation, but upon more severe defoliation, genetic differences were evident. Since repeated defoliation is a recommended control technique, selection for more tolerant genotypes is possible and should be considered for the management of this weed.

This paper presents an overview of introduced alien plant species inhabiting natural thermal waters of Serbia. We recorded the presence of six naturalised aquatic plant species, also recognised as weeds in several regions of the world. This was the first time that Heteranthera zosterifolia (Pontederiaceae), Lemna minuta (Araceae) and Rotala rotundifolia (Lythraceae) were recorded in the aquatic ecosystems of Serbia. In addition, the presence of H. zosterifolia and R. rotundifolia was previously unknown in other countries of Southeastern Europe. The study includes detailed habitat descriptions and impact assessments for all introduced aquatic species in thermal waters in Serbia. All species were prioritised for pest risk analysis using a modified version of the EPPO prioritisation process within the framework of the EU regulation for invasive species. As a result, four alien species may be considered invasive (three at EU and one at national level), while two other species did not show strong invasiveness, but still need to be monitored. In addition, risk management measures were proposed for all invasive species from this study, and they may provide implications for the theory and practical management of weeds.

Functional diversity of cover crop mixtures is thought to improve biomass production and weed suppression, two key agroecosystem services in organic systems. To test this hypothesis, we selected eight cover crop species belonging to four functional groups: (i) vining growing large‐seeded legumes (field pea, common vetch), (ii) erect growing small‐seeded legumes (crimson clover, squarrosum clover), (iii) grasses (barley, oats) and (iv) Brassicaceae (radish, black mustard). Nine cover crop mixtures were designed to create a gradient of diversity in terms of number of species and number of functional groups. A control treatment and all monocrops were included in the trial. Regarding cover crop biomass, mixtures outyielded monocrops by an average of 37%. Both functional identity and composition (i.e. trait complementarity) influenced biomass production and weed suppression provided by cover crops. Regression analysis showed that increase in both species diversity and functional diversity in cover crop mixtures improved the provision of agroecosystem services. Results from this study show that complementarity of species functional traits in cover crop mixtures can be used as a strategy to ensure high biomass production and good weed suppression in changing agroecosystems.

Maize (Zea mays L.) is an important cereal crop grown worldwide. With the increase in human food demand but limited land and water resources, precise spatially explicit knowledge about the maize production capacity through agricultural management practices (e.g., using recommended nutrient and water inputs, RNWI, by local agronomists) is essential to guide the future policy, research, development, and investment. Here, we used a well-validated crop model (APSIM-Maize) for 1981–2010 combined with actual climatic and soil data to estimate maize yield improvements under RNWI in three main cropping regions in China (the North China Spring Maize Region, NCS; the Huanghuaihai Summer Maize region, HS; and the Southwest China Mountain Maize Region, SCM). Compared with the county-level maize actual yield in the three main cropping regions, the average maize yield could be increased by 33 % (4 Mg ha−1) through RNWI, while the improvements in the coefficients of variation (CVs) of grain yield and reliable grain production (RGP) were 0.11 and 32 % (69 million Mg), respectively. Except for RNWI, the average yield, CVs of yield, and RGP could still be increased by 28 % (3 Mg ha−1), 0.10, and 36 % (80 million Mg) through other management and technologies (OMT). Further analysis in four types of yield level-stability zones (high-stable, low-stable, high-unstable, and low-unstable zones) showed that greater contributions of using RNWI and OMT to improve maize grain yield, yield stability, and RGP were found in zones with low/unstable yield across the three regions. The findings highlighted the focus on increasing maize yield in low/unstable-yield zones could provide a greater return.

The study of alternate bearing based on the seasonal changes pattern of tree carbohydrate is the unreviewed issue in the loading physiology of date (Phoenix dactylifera L.) trees. On the other hand, bunch cutting back is a crop improvement practice used in the date orchards, and it is effective on flower induction and fruit set that regulates the quality and growth of fruit in the On year and the amount and yield of the produce in the Off year. Research on an alternative thinning agent with the bunch cutting back is essential for dates in order to be economical and applicable in harsh climates. For this purpose, the experiment was conducted as a combined analysis across years based on randomized complete blocks on ‘Mazafati’ dates of 10–12 years old with different loading in 2017 (Off2017, Normal2017 and On2017), as well as the On condition trees in 2017 plus bunch cutting back (On2017+Cutting back) or regulated deficit irrigation (On2017+RDI). The main objectives of this study were to investigate the fragmentation of carbohydrate reserves of the tree in the annual rotation cycle in different loading, to evaluate the relationship of sugar reserves with production and abscission of flowers and fruits, to determine the effect of the RDI application in the On year on the pattern of sugar changes, hydrolytic enzymes activity, alternate bearing, quantity and quality of the product, and the possibility of replacing it with cutting back. The results confirmed the significant effect of loading rate on the seasonal fragmentation and fluctuation of carbohydrates and the hydrolytic enzymes activity. The results also showed that the RDI treatment, due to the decrease of bunch length, reduced the biennial bearing index (BBI) and improved the qualitative and quantitative traits of fruit better than the cutting back. According to the results of this study, the irrigation condition of trees has the potential to change the marketability and abscission of date fruits and this is a pioneer study of the RDI role as a thinning potential and moderating of date alternate bearing. However, further research is needed to justify the time and duration of this treatment application.

Efficiency is one of the most important assessment indicators in irrigation systems. Classical efficiency (CE) is not an exact index due to the lack of consideration of the return flows. Therefore, the neoclassical concepts of the efficiency are considered to take a part of losses of irrigation water as a return flow into account. Quality of the return flows may change in their path and it must be considered in evaluating the efficiency and productivity of irrigation water. This research was carried out to investigate this challenge. Sustainable efficiency (SE) was applied based on the water balance and quality of return flows. The methodology and detail for computing different parameters and their quality and beneficial coefficients in water balance equation were presented. Moghan irrigation and drainage network in the northwest of Iran was selected as the study area and CE and SE were calculated in meso and micro levels using the meteorological data, cropping pattern, irrigation water volume, natural and artificial drainages, infiltration and return flow quality. In addition, the irrigation water productivity was calculated by considering the volume of water based on the different concepts of efficiency. Quality coefficient related to return flow had different values in different months (0.85 in August and 1 in November and December). The results showed that about 87 % of inflow, 91 % of the rainfall, 89 % of the evapotranspiration, 13 % of the non-reusable water, and 91 % of the return flow were useful in the study area. The highest and the lowest efficiencies are occurred in September and November, respectively. The average of meso and micro Sefficiencies were 72 % and 47.5 %, respectively, and the CE was 37.9 %. The results showed that water productivity based on the SE is more than that of the CE. The water productivity at the meso level also showed a higher value than at the micro level.

Assessment of agricultural drought risk is significant for risk division and management. Nevertheless, the drought risk dynamic evolution characteristics have not been revealed. To this end, the agricultural drought conditions are characterized by the standardized precipitation index (SPI), and the time scale of SPI is determined based on agricultural damage data. The joint return periods of various drought severities and durations under different agricultural drought scenarios are calculated by using copula functions. Moreover, drought risk factors (resilience, vulnerability, and exposure) are also used to characterize drought risk. Subsequently, based on the moving window, the joint return period and risk factors in each window are calculated, and agricultural drought dynamics are explored. The Pearl River Basin (PRB) is selected as a case study. Results indicated that: (1) the 4-month most appropriate timescale for the SPI in characterizing agricultural drought based on agricultural damage data in the PRB; (2) risk factors method is more suitable than joint return period in assessing agricultural drought risk; (3) most of the PRB exhibit a significant increasing agricultural drought risk, while the drought risk of the Pearl River Delta has a decreased trend within the past 50 years. Generally, this study show new insights into agricultural drought risk assessment, thus promoting local agricultural drought preparedness and mitigation.

Irrigation systems have in recent years attained a higher level of variety in as such that the selection and implementation of an irrigation system is based on the physical constraints of the site area thus giving way to a much more adequate irrigation efficiency. With due regards to the water crisis in Iran and subsequent drought conditions, the implementing of similar irrigation systems in different regional conditions lacks any justification. In the Izeh plain the use of surface irrigation systems with minimal efficiency is very common. In order to implement and operate modern irrigation systems and maximize water saving, the site selection of pressurized irrigation systems was evaluated through the fusing of AHP and GIS maps for a variety of pressurized irrigation systems followed by the selecting of the best irrigation system for each region. In the current study physical and socio-economic criteria were selected as the main criterion and were then classified into several sub-criterions.A Drip irrigation system, a Gun irrigation system, a center pivot irrigation system and a linear irrigation system were selected as the options utilized when using the AHP method. The Gun and center pivot irrigation systems had the least value as they were not suitable for mountainous area. Drip and linear irrigation systems were given a higher value and were suitable for implementation in most regions. After comparing different sub-criterion, the drip irrigation system was identified as being the most suitable pressurized irrigation system for the Izeh plain.

Effective indicators of plant nitrogen (N) nutrition are needed to improve N management in grasslands. This is particularly the case for mixtures that rely on N fixation by legumes as a major N input, because no reference tool such as the nitrogen nutrition index (NNI) exists under these conditions. The aims of this study were to test the reliability of a plant‐based index, the N concentration of upper leaves in the canopy (Nup), as a possible alternative for NNI in both pure and mixed grasslands. Data were gathered from four experiments covering a range of pure and mixed grasslands under different N fertilization levels. A cross‐validation of Nup predictions against NNI in pure stands, and against two NNI‐derived indices in mixtures, was performed. The Nup values appeared to be linearly related to NNI in pure stands of both grasses and legumes. The relationship was identical for the two groups of species and explained up to 86% of NNI variability. In mixtures, Nup also displayed a linear relationship with the two other tested indices, explaining 65% and 78% of variability. The conclusions of the three indices diverged with respect to strongly unbalanced mixtures, where the assumptions regarding the computation of NNI‐derived indices were not met. Excluding these situations, the overall relationship between Nup and NNI proved to be identical for mixtures and pure stands. The results suggest that Nup is a valid criterion for plant N nutrition which applies to a broad range of grassland species and to mixture conditions.

Recent years have seen a decline in herbage production and tiller populations in New Zealand's perennial ryegrass (Lolium perenne) dairy pastures. One hypothesis is that modern genotypes are less suited to the warmer, drier weather experienced under changing climate patterns. In this study, a combination of long‐term trial data (2011–2017) and a process‐based pasture model (BASGRA) was used to explore the causes and possible mitigation of the observed production and population loss at three sites (dryland sites in Northland and Waikato and an irrigated site in Canterbury). Bayesian calibration was used to identify the model parameter sets that were consistent with the trial data and to identify differences in plant morphology and responses between sites. The model successfully simulated the observed differences in tiller numbers between the dryland sites, where populations and production declined rapidly after the second year and the irrigated site where populations and production were maintained. Analysis of the model calibrations along with preliminary scenario simulations suggests that increased tiller mortality associated with drought was the main cause of persistence failure at the dryland sites and that decreasing grazing pressure or breeding for tolerance to higher temperatures may not be successful in preventing this.

Efficient agricultural water use is required for food safety and water alleviation on a global scale. Combining the water footprint and agricultural water use paradigms and enveloping water resource movement and its impact on the environment in the agricultural production process, a hybrid framework for agricultural water utilization and efficiency evaluation was constructed in the current paper. The indicators water resources use (WRU), efficiency (WRE) and productivity (WRP) are used in this framework for the total water exploitation, the effective utilization rate and the production capacity measurement, respectively. An empirical study on the framework was conducted with major cereals (wheat, maize and rice) in 31 provinces, autonomous regions and municipalities (PAMs) of China. The national WRU, WRE and WRP values of integrated cereal were calculated to be 669.0 G m³, 0.633 and 0.679 kg/m³, respectively, from 1996 to 2015. The PAMs with high WRE values were located in southwestern, northeastern and northern China, while the ones with low values were clustered in northwestern and southeastern China. The spatial distribution pattern of WRP is consistent with precipitation. The water use efficiency (WRE and WRP) of the three specific crops in this framework increased over time. The WRE of maize was significantly higher than that of rice and wheat, while the WRP of wheat was the lowest. WRU measures the total water resource appropriation during crop growth in both quantity and quality; WRP was able to show where water use efficiency needs to be improved; and the function of WRE to indicate water saving potential could not be replaced by notable indices, such as irrigation efficiency or generalized efficiency. Therefore, further research is warranted to evaluate agricultural water use efficiency at different scales using this hybrid framework.

In the arid region of Central Asia, climate change leads not only to changes in water availability generated by glacier/snow melt in the alpine regions, but also to changes in water consumption. This paper evaluates agricultural water demand and water supply (represented by precipitation) for the five Central Asian countries (Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan) under global warming conditions of 1.5 °C and 2.0 °C. As Central Asia is more sensitive to climate change compared to the global average, the temperature is predicted to rise by 1.7 °C and 2.6 °C and precipitation to increase by 9 % and 12 % in global warming scenarios of 1.5 °C and 2.0 °C, respectively. The average crop water requirement (CWR) is expected to increase by 13 mm and 19 mm per year, respectively, under the global warming scenarios of 1.5 °C and 2.0 °C. A widening gap between water supply and water demand is expected compared to the historical period (1976–2005) under global warming scenario of 2.0 °C. Under global warming of 2.0 °C, the anticipated water gaps between precipitation and CWR are projected to increase by 2.8 × 108 m3 and 1.5 × 108 m3 for the rainfed north Kazakhstan region and the irrigated Fergana region while the increase of precipitation could able to meet the increase in CWR under global warming of 1.5 °C. Investigating the water balance for major planting areas in water-limited Central Asia could provide a scientific basis for sustainable development of the entire region.

Aquaculture effluent irrigation has been widely adopted to replace freshwater irrigation to save water and providing additional fertilizer to the crop. There is limited information on the performance of fertilizer supply levels under fishpond effluent irrigation. The objectives of this study were to investigate the effect of reducing a rate of fertilizer on the purification of wastewater from fishponds by paddy fields and the yield of rice under fishpond effluent irrigation in central China in 2015. The treatments included 100 %, 80 %, and 60 % of the normal fertilizer rate (NFR, 150 kg N ha−1, 120 kg P2O5 ha−1 and 75 kg K2O ha−1) with fishpond (freshwater-pond aquaculture) effluent as an irrigation source, designated NFR-E, 0.8NFR-E, and 0.6NFR-E, respectively; with an additional NFR with freshwater as an irrigation source (NFR-F). The results showed that 5700 m3 ha-1 freshwater was saved by the use of the NFR-E, 0.8NFR-E and 0.6NFR-E treatments. The concentrations of total nitrogen (TN), total phosphorus (TP), dissolved phosphorus (DP), ammonia-nitrogen (NH4+-N), nitrate-nitrogen (NO3--N) and particulate phosphorus (PP) in the surface water and seepage water of the paddy field and the residual soil N and P in the 0−60 cm soil depth after the rice harvest decreased with the decreasing NFR. The removal rates of the TN in the surface water across the tillering, booting, heading and filling stages were 25.1 %, 38.9 % and 50.5 % on average for the NFR-E, 0.8NFR-E and 0.6NFR-E treatments, respectively. The corresponding removal rates of the TP were 56.4 %, 71.2 % and 76.2 %, respectively. These increased removal efficiencies were related to the lower N and P concentrations in the surface water of the paddy field and the efficient use of nutrients by rice under the reduced fertilization treatments. Compared to the NFR-F treatment, the 0.8NFR-E treatment resulted in a comparable accumulation of N and P and grain yield of rice, while decreasing the contents of N and P in the water of paddy fields and the residual soil N and P in the 0−60 cm soil depth after the rice harvest. Thus, reducing the normal fertilizer rate by 20 % could improve the water quality of the paddy field without deleterious effects on the rice yield and save 5700 m3 ha-1 of fresh water under fishpond effluent irrigation. These results can also provide a basis for in-depth understanding of the mechanism of aquaculture effluent purification through paddy field ecosystem in response to fertilizer supply levels.

Ridge-furrow farming systems with transparent plastic film have been used extensively for maize (Zea mays L.) production in semi-arid areas. However, with climate warming, problems may arise associated with premature senescence and reduced production. This study examined whether dual mulching of ridges with black plastic film and furrows with straw can delay senescence and increase summer maize yield. Summer maize cultivation experiments were conducted in 2014–2015 by ridge-furrow planting with black (BRM) or transparent (TRM) plastic film mulch over the ridge and wheat straw mulch over the furrow, flat planting with black (BM) or transparent plastic film mulch (TM), and flat planting without mulch (control treatment, CK). The objective of this experiment was to determine the effects of the different mulching treatments on soil water and temperature, evapotranspiration (ET), leaf, photosynthesis rate, yield, and water use efficiency of summer maize. The BRM and TRM treatments were superior to the BM and TM treatments in terms of soil water storage in the 0–200 cm soil profile. The BRM reduced the diurnal variation in the soil temperature and lowered the soil temperature in the root zone. The BRM treatment extended the maize reproductive growth period by 5 days compared with TM, and 2–3 days longer than for the other mulched and control treatments. The BRM also increased the leaf area and dry matter accumulation per plant while significantly increasing the leaf photosynthesis rate. Moreover, BRM increased the 100–seed dry weight and significantly improved yield and water-use efficiency. The 2–year average yield of the BRM treatment was 6.7, 13.4, 18.4, and 72.9 % greater than yield of the TRM, BM, TM, and CK treatments, respectively. The corresponding water-use efficiency improved by 11.2, 13.1, 20.3, and 72.1 %, respectively. Applying the BRM cultivation practice will effectively delay senescence and increase summer maize yield in the agricultural production area of the study region.

The study was conducted to evaluate the economic and environmental impacts of water-saving technologies (WST) on Boro rice (Oryza sativa; var. BRRIdhan 29) farming in Bangladesh. A total of 480 farmers (80 focal and 400 control) were selected as sample from Mymensingh, Comilla, Bogra and Gaibandha districts. Focal farmers were selected purposively and a limited amount of financial support was provided to them to implement WST. On the other hand, control farmers were selected randomly. They did not receive any financial support and continued practicing conventional irrigation methods. For analyzing the data, a combination of descriptive, mathematical and statistical techniques was used. The study revealed that 62.5 and 37.5% of focal farmers adopted alternate wetting and drying (AWD) and system of rice intensification (SRI) methods, respectively, where the majority of them were within the late majority group in terms of adoption. The profitability and productivity of Boro rice, as well as water productivity, were comparatively higher for focal farmers compared to control farmers. Furthermore, focal farmers’ irrigation amount for producing Boro rice was significantly lower than control farmers. The study also revealed that focal farmers’ income from rice production was 24.6% higher than control farmers. Input support, motivation, training programs and extension services are recommended to implement to raise the awareness and enrich the knowledge of the farmers on water-saving technologies.

The Ogallala Aquifer is the main water resource for irrigated agricultural production in much of Western Kansas. It is hypothesized that as crop price expectations increase, producers will apply more water to increase yields in order to maximize profit. Using field-level panel data on groundwater pumped for irrigation in Western Kansas, this paper examines whether irrigated producers’ groundwater pumping decisions are consistent with the profit maximization framework by empirically testing if crop price expectations have a positive impact on the quantity of groundwater pumped. In general, the empirical results indicate that crop price expectations have no statistically significant impact on the quantity of groundwater pumped per acre. This suggests that groundwater pumping decisions are not consistent with the profit maximization framework and that irrigated producers consider groundwater as a fixed input possibly due to limited availability of groundwater in the area. Our econometric analysis also suggests that only a small portion of rainfall is effective.

A higher drought risk in Java Island is generally known than the other regions in Indonesia. Tracking soil moisture can be an alternative way to monitor drought rather than precipitation-based drought indices. The objective of this study was to assess root-zone water storage (defined by root-zone soil moisture contents) based on a linked approach between the generalized complementary relationship (GCR) and a single bucket model in Java Island. Since it does not require precipitation for estimating actual evapotranspiration (ETa), the GCR allowed implementation of a simple single bucket model. The ETa and root-zone soil moisture estimated in this study were compared against the Global Land Evaporation Amsterdam Model (GLEAM) and the root-zone water storage additionally compared with the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis data products. Overall, the GCR ETa estimates were higher than those from GLEAM, and similar patterns of the root-zone water storage were found in the comparisons of both GLEAM and ERA5. The comparative evaluation suggests a further study on the adjustment of Priestley-Taylor coefficient value in Java for better application of the GCR. The soil moisture estimated by the single bucket model and the root-zone soil moisture products of GLEAM were highly correlated (0.8 or greater Pearson correlation coefficients). Low root-zone water storage and high ETa rates were found in eastern Java relative to the other areas, indicating high water shortage risks in dry season. This study found that El Niño clearly contributed to the variability of the root-zone water storage in Java especially in wet seasons (December to February). It is also suggested that the proposed approach can be useful to operationally provide soil water availability in Java from readily available meteorological observations.

Seed priming is known to often alleviate salinity stress during seed emergence and subsequent crop growth. This study compares the effects of salinity stress on the germination and emergence of wheat (Triticum aestivum L.) seeds untreated (control) and primed with ascorbic acid (Asc), potassium silicate (K2SiO3), proline (Pro), spermidine (Spd) and Lake Urmia saline water (LUsw). Saline water from Lake Urmia (Iran) was diluted to produce salinities with electrical conductivities (EC) of 2, 4, 6, 8, 10, 12, 14, 20 dS m−1, while distilled water (EC ≈ 0 dS m−1) was used for the control. Two independent sets of experiments were conducted. The first experiments were used to select the most effective concentration of each priming agent based on the final germination percentage (GP) and germination rate (GR). The second set of experiments aimed to analyze the measured data in terms of salinity response functions in order to quantitatively determine the most effective priming agent(s). The first experiments showed that the most effective concentrations of Spd (0.5 mM), Pro (25 mM), K2SiO3 (1.5 mM) and LUsw (100 mg L−1) mitigated the negative impacts of salinity on GR by 32, 18, 17 and 22 %, respectively. The second experiment showed that the Maas and Hoffman (1977) and van Genuchten and Hoffman (1984) salinity response functions provided effective descriptions of seedling and early growth response to salinity stress. Mean values of the salinity threshold (EC*) and the salinity at which a given trait was reduced by 50 percent (EC50) in these functions were 3.4 and 10.8 dS m−1 for the control, respectively. By comparison, the EC* values for the K2SiO3, Pro, Spd and LUsw primed seeds were 5.3, 4.5, 4.7, and 4.2 dS m−1, respectively, and the EC50 values were 12.4, 11.4, 11.9, and 9.4 dS m−1, respectively. The beneficial effects of K2SiO3 on seedling growth were more evident than those of the other priming agents. K2SiO3 had the highest effect on EC* and EC50 of the vitality index (VI), showing increases of 151 and 34 %, respectively. The highest increases of EC* and EC50 for seedling dry weight (72 and 24 %, respectively) were obtained with Spd and K2SiO3. The findings provide much insight on relieving the negative effects of salinity through cost-effective seed priming operations so as to improve the production of wheat under saline conditions.

Cover crops are a potential component of agroecological cropping systems, since they may render crop rotations more sustainable. They simultaneously provide multiple ecosystem services, such as decreasing nitrate leaching, decreasing erosion, and increasing soil organic matter. However, cover crops increase evapotranspiration and reduce drainage, which results in a potential disservice for groundwater recharge. Little attention has focused on management of cover crop residues after destruction or their influence on water flux dynamics, particularly in dry and temperate climates. The objective of our study was to analyze and quantify the impact of cover crop management on soil water content and water flux dynamics to understand the main mechanisms of system functioning. We combined a two-year field experiment with crop-model simulations. We performed the field experiment in southwestern France that compared three cover crop treatments, with bare soil as the control. The treatments included (1) living cover crops lasting ca. 9 months from August-April, (2) crushing cover crops in November and leaving them as mulch on the soil, and (3) plowing up cover crops in November to promote residue decomposition and the green manure effect. The STICS soil-crop model was used to predict water fluxes that were not measured and to perform a 20-year independent simulation study based on recent climate series for the experimental site. Our main results indicated that cover crops (1) always reduce water drainage by 20-60 mm compared to that under bare soil; and (2) could significantly reduce soil water content (0-120 cm deep) for the next cash crop by a mean of 20-50 mm, and up to 80 mm in dry spring conditions, but early destruction could decrease this negative impact. The simulations clearly showed that the interaction between climate variability, i.e., rainfall distribution during the fallow period, and cover crop management should be considered to explain the impact of inter-annual variability on the water balance. Thus, destroying cover crops mechanically in late autumn and retaining the residues as mulch could be a good compromise between the multiple services the cover crop provides during the fallow period and avoiding the negative impact on soil water availability for the next cash crop.

Wheat, triticale and common bean are planted in both irrigated and rainfed conditions and may suffer the effects of water stress in both situations. The objective of this work was to evaluate the effect of water stress on the physical and chemical qualities of wheat (Triticum aestivum), triticale (Triticosecale wittmack) and common bean (Phaseolus vulgaris L.) grains. The experiment was conducted at the Embrapa Cerrados experimental station, in Planaltina, DF, Brazil. The experimental design was in randomized blocks with four replications. The treatments were composed of four water regimes (187 mm, 304 mm, 410 mm, 535 mm) applied to common bean (BRS Realce), two wheat genotypes (CPAC 0544 and BRS 404) and triticale (BRS Ulisses). The physical quality of grains was evaluated by the weight of a thousand grains (WTG) and color of the grains (represented by the luminosity (L*), chroma (C*) and hue angle (h*); the chemical quality was determined by protein, carbohydrate, lipid, ash, macro and microminerals contents. Water stress reduced grain yield of all species, however it did not reduce the weight of one thousand grains of the wheat genotype BRS 404, showing the potential of this cultivar, though it did lead to reduced WTG in common bean, triticale and the wheat genotype CPAC 0544. There was also a reduction of luminosity (L*) in the grains for both studied wheat genotypes, and chroma (C*) and hue angle (h*) for triticale. Water deficit also affected protein, carbohydrate, lipid and ash contents, with an increase in the protein content and a reduction in the carbohydrate and ash contents in common bean. In general, water stress reduced macro and micromineral contents in the grains, caused an undesirable change in the physical quality of the grains, and affected the chemical quality of the grains.

Drip irrigation has been gradually adopted for winter wheat production in the North China Plain (NCP) due to significant saving from using irrigation water and improving water and nitrogen use efficiencies. However, the optimal water and nitrogen application rates for drip-irrigated wheat are still unclear. A field experiment with five nitrogen application rates (0, 120, 180, 240, and 300 kg ha−1, referred as N0, N1, N2, N3, and N4) and three irrigation levels (40, 30, and 20 mm per irrigation, referred as I1, I2, and I3) was conducted during the 2015–2016 and 2016–2017 winter wheat seasons to study the effects of irrigation and nitrogen rates on crop growth, yield, and the water and nitrogen use efficiencies. Results showed that increasing irrigation and nitrogen application rates notably improved actual evapotranspiration, leaf area index, aboveground biomass, grain yield, and water use efficiency (WUE) of winter wheat. However, nitrogen application rates exceeding 240 kg ha−1 were not beneficial for wheat growth, grain yield, WUE, and irrigation water use efficiency (IWUE). The maximum grain yields of 8034 and 8760 kg ha−1 were achieved in N3I1, which had WUE of 2.08 and 2.23 kg m−3, and IWUE of 4.46 and 4.87 kg m−3 in 2015–2016 and 2016–2017, respectively. At the same time, N3I1 did not result in much reduction of nitrogen partial factor productivity (NPFP) (average of 34.99 kg kg−1 in N3I1 for two seasons). Considering comprehensively growth, yield, WUE, IWUE, and NPFP, combination of N rate of 240 kg ha−1 and irrigation quota of 40 mm per irrigation was optimal pattern for drip-irrigated winter wheat. These results may provide a scientific basis for water and nitrogen management of drip-irrigated winter wheat in the NCP.

The Ningxia Hui Autonomous Region (NX) in Northwest China has been challenged by water scarcity and drought for decades. In this study, to understand the spatio-temporal variation, cause analysis and relationship with atmospheric circulation of ET0 in Ningxia, ET0 and other climate factors at 20 national climate stations from 1957 to 2018 were analyzed. Results showed that ET0 in NX (Ningxia), NYR (Northern Yellow River Irrigation Area) and SMA (Southern Mountain Area) had increased significantly at annual scale, whilst the CAZ (Central Arid Zone) was the opposite trend, and ET0 had a trend of first rise and then decline from north to south in spatial distribution. ET0 was most sensitive to RH and Tmax at annual scale in Ningxia, while the greatest contribution rates were Tmax and SD. Ningxia was becoming drier in the past decades. The abrupt change in ET0 at approximately 1990, and it’s long and short period were 25a(15a) and 10a(5a) at annual scale, respectively. The four teleconnection indices could be used to predict changes in ET0 at annual and autumn scale, while the ENSO and PDO could predict changes in ET0 of summer and IOD and AO could predict changes in ET0 of spring and winter.

Drought is a major limiting factor for rainfed spring wheat production on the semiarid Loess Plateau of China. Suitable tillage practices are important for improving precipitation use efficiency (PUE), which is the ratio of grain yield to annual precipitation. To obtain a better understanding of the effects of conservation tillage practices on PUE on the semiarid Loess Plateau, PUE was divided into five steps: precipitation storage efficiency, farmland water consumption rate, ratio of transpiration to evapotranspiration, crop transpiration efficiency, and harvest index. Six tillage practices were assessed in this paper, including conventional tillage with no straw (T), no-till with straw cover (NTS), no-till with no straw (NT), conventional tillage with straw incorporated (TS), conventional tillage with plastic mulch (TP), and no-till with plastic mulch (NTP), based on a long-term experiment initiated in 2001. The impact of tillage practices on soil quality, soil water storage, soil evaporation, biomass yield, and grain yield of spring wheat were monitored in 2015 and 2016. The results show that NTS improved soil quality and soil water storage before sowing. No-till with plastic mulch and NTS increased evapotranspiration but decreased evaporation, thus optimizing precipitation storage efficiency, the farmland water consumption rate, the ratio of transpiration to evapotranspiration, and crop transpiration efficiency, which gave rise to greater aboveground dry matter accumulation and more dry matter accumulation in grain. As a result, grain yield under NTS and NTP was significantly increased by 45 and 41 % compare to T, respectively, with corresponding improvements in PUE of 43 and 39 %. Therefore, both NTS and NTP have potential to substantially increase grain yield of spring wheat and PUE. However, for sustainable intensification in the long-run, NTS is the best combination of tillage and soil surface management for spring wheat production on the semi-arid Loess Plateau of China.

Elevation of mean air temperature related to climate change speeds up plant maturity, which influences mostly forage feed value. The objective of the study was to assess variation in hay quality harvested over 32 years at the same experimental site, and whether feed value is better predicted by combining agro‐climatic variables with chemical composition. From 1979 to 2010, the in vivo digestibility (OMd) and voluntary dry matter intake (VDMI) of 271 hays, harvested during the first vegetation cycle on permanent grasslands, were measured in sheep. Over 32 years, the mean air temperature between February and August increased significantly by 1.34°C. Cutting date was advanced by 6 days, but the average sum of temperature at cutting (ST) increased significantly by 13%. Crude protein (CP) content declined (−22%, p < .001), crude fibre content increased (+8%, p < .001), OMd decreased (−3%, p = .012) and VDMI increased (+9%, p = .011). Changes in the chemical composition and OMd were consistent with the increase in ST. Finally, the prediction of OMd from CP and crude fibre contents (R2 = .57, RMSE = 2.99) was slightly improved by the addition of ST and hay drying time (R2 = .60, RMSE = 2.83). Climate change may have a negative indirect effect on hay quality if an earlier cutting date does not compensate for its effect on the faster maturation of the plants. Moreover, agro‐climatic criteria could help to monitor and predict hay quality in relation to intra‐ and inter‐annual climatic changes.

The sustainability of spate-irrigated agriculture in a semi-arid climate depends on efficient use of irrigation water. Thus, efficient capture and storage of soil moisture in the field are crucial for sustained productivity. The main objective of this study is to examine the performance of improved field design strategies to manage variable irrigation water supply and application time in the Gash agricultural scheme (GAS) in eastern Sudan where open-end border irrigation is practiced to irrigate large fields with variable sizes that range from 250 to 1250 ha. Irrigation performance was examined using the WinSRFR model for a large-sized field (8400 m × 500 m), continuously irrigated for 25 days but also under alternative designs and irrigation times. The performance was evaluated using efficiency, adequacy and uniformity criteria. The results demonstrate that the current irrigation practices are quite inefficient but could be substantially improved by adopting alternative design and operational strategies. A vertical division of the field (8400 m × 250 m) under the average inflow condition could result in a substantial increase in application efficiency (from less than 50% to over 70%), distribution uniformity (from 0.34 to 0.87), and irrigation adequacy (from 0.68 to 1). Additionally, the fields could be irrigated in considerably less time when an alternate irrigation schedule between two equally divided fields is followed, which indicated time savings of 40 % under a high inflow rate scenario (occurring during a large flood season), and a 20% reduction in time under an average inflow rate scenario (occurring during a medium flood season). Therefore, this modelling study has demonstrated a great potential to significantly improve irrigation performance by applying alternative field designs and operation strategies in the GAS. The modelling outcomes confirmed that the farmers’ indigenous experiment, though without a scientific study, on the vertical division of a large-sized field is indeed successful in improving irrigation performance, and could be adopted in other similar conditions.

Water scarcity, climate variability and continuing growth in water demand have put severe pressure on high‐quality freshwater sources. This challenge exacts the necessity to explore alternative water sources for agricultural irrigation. The objective of this study was to implement the integrated geospatial Multi-Criteria Decision Analysis (MCDA) with the Analytical Hierarchy Process (AHP) to evaluate the potentiality of reclaimed water use for agricultural irrigation in California. Five evaluation criteria included in this study were agricultural land (crop type), climate conditions, water policies, irrigation status, and proximity to wastewater treatment plants (WWTPs) respectively. The suitability maps for reclaimed water use were generated for three cases in terms of accessibility to WWTPs, their discharge volume and appropriate treatment processes respectively. In addition, a composite suitability map was produced using the hybrid model considering all three cases together. Results from this study led to a better understanding of sustainable reclaimed water use for crop irrigation at a regional level. It provided supporting evidence of the applicability of the GIS-MCDA method integrated with AHP technique for a larger geographical scale with a diverse crop pattern. This study established the importance of using both knowledge-based and data-driven criteria and sub-criteria in the decision framework. The results also highlighted how the spatial distribution of suitable areas for reclaimed water reuse is closely linked to the agricultural areas.

Interreplicate variability—the spread in output values among units of the same sensor subjected to essentially the same condition—can be a major source of uncertainty in sensor data. To investigate the interreplicate variability among eight electromagnetic soil moisture sensors through a field study, eight units of TDR315, CS616, CS655, HydraProbe2, EC5, 5TE, and Teros12 were installed at a depth of 0.30 m within 3 m of each other, whereas three units of AquaSpy Vector Probe were installed within 3 m of each other. The magnitude of interreplicate variability in volumetric water content (θv) was generally similar between a static period near field capacity and a dynamic period of 85 consecutive days in the growing season. However, a wider range of variability was observed during the dynamic period primarily because interreplicate variability in θv increased sharply whenever infiltrated rainfall reached the sensor depth. Interreplicate variability for most sensors was thus smaller if comparing θv changes over several days that excluded this phenomenon than if comparing θv directly. Among the sensors that also reported temperature and/or apparent electrical conductivity, the sensors exhibiting the largest interreplicate variability in these outputs were characterized by units with consistently above or below average readings. Although manufacturers may continue to improve the technology in and the quality control of soil moisture sensors, users would still benefit from paying greater attention to interreplicate variability and adopting strategies to mitigate the consequences of interreplicate variability.

Abstract Laboratory experiments were used to estimate the hydraulic performance of emitters, i.e., the emitter flow variation (qvar) and manufacturer’s coefficient of variation (CVm), by measuring the discharge of different labyrinth-channel emitters at different operating pressures (P) and water temperatures (T). Considering the importance of the structural parameters of the labyrinth-channel emitters in drip irrigation design, which has been experimentally confirmed, artificial neural network (ANN) and gene expression programming (GEP) models were developed to predict qvar and CVm. The ANN and GEP models were trained and tested using structural parameters (including the number, height (H), and spacing of trapezoidal units and the flow path width and length) of different labyrinth-channel emitters, P and T as the input variables, and qvar and CVm as the outputs. Statistical criteria, including the coefficients of correlation (r), relative root-mean-square error (RRMSE), and mean absolute error (MAE), were used to examine the accuracy of the developed models. The ANN models exhibited good correlation with experimental values, with high r values 0.995 and 0.969 for qvar and 0.997 and 0.947 for CVm in the training and testing processes, respectively. The ANN models had lower RRMSE and MAE values than the GEP models. Furthermore, H was the dominant variable for obtaining the most accurate prediction model. The results confirm that the ANN models are superior to the GEP models for the prediction of the hydraulic performance of emitters.

This study evaluated the effects of salicylic acid (SA), beeswax waste extract (BWE) and licorice extract (LE) as novel biostimulants, on drought-induced oxidative stress on sesame. The treatments consisted of three drought stress conditions (full irrigation, 90 % field capacity (FC); moderate stress, 60 % FC; and severe stress, 30 % FC) together with four exogenous foliar applications (control, water; LE, 5000 ppm; BWE, 2000 ppm; and SA, 1.5 mM). Plants subjected to drought stress displayed significant reduction in plant height, leaf area index, biological and seed yield, chlorophyll a and b content, quantum efficiency of photosystem II (Fv/Fm), net photosynthetic rate (Pn), stomatal conductance (gs), transpiration (Tr) and water use efficiency (WUE). Drought stress stimulated Malondialdehyde (MDA), proline, protein and carotenoid contents, and catalase (CAT), ascorbate peroxidase (APX), Guaiacol peroxidase (GPX) and glutathione reductase (GR) activity, while the exogenous foliar application of substances mitigated the oxidative damages. The alleviated effect of BWE on drought stress was more effective than those of LE and SA. In conclusion, it could be recommended that the application of the natural substances may lead to overcoming the negative effects of drought stress by regulating osmoprotectants content and antioxidant defense system, increasing mineral nutrients in plant organs and adjusting photosynthesis systems; consequently, contributing to improving the sesame productivity.

Determining methods for increasing irrigation water productivity is important for sustaining high wheat grain yields in the irrigated region of the Loess Plateau in China. Plastic-covered ridge and furrow planting has been widely applied in dryland farming, as it markedly increases precipitation productivity and crop yields. However, whether this planting system can significantly increase irrigation water productivity and whether it can reduce the irrigation volume for high-yielding wheat production in irrigated regions of the Loess Plateau are unclear. In the present study, plastic-covered ridge and furrow planting and traditional flatbed planting were performed at four irrigation levels. The objective was to investigate whether applying plastic-covered ridge and furrow planting to an irrigated farmland system could reduce the irrigation water requirements and increase water productivity for high-yielding wheat production. The results suggested that plastic-covered ridge and furrow planting significantly increased soil moisture content and increased both grain yield and water productivity of wheat. At the 0, 400, 1200, and 2000 m3 ha−1 irrigation levels, compared with that resulting from traditional flatbed planting, the grain yield resulting from plastic-covered ridge and furrow planting was 51.7 %, 64.8 %, 25.5 %, and 5.84 % greater, respectively. At the high-grain-yield level (6–7 t ha−1), the plastic-covered ridge and furrow planting system at 1200 m3 ha−1 irrigation conserved 40 % of irrigation water during wheat production. And it coordinated the relationships among grain yield, quality, water protuctivity and for wheat production. These findings show that the plastic-covered ridge and furrow planting system with 1200 m3 ha-1 irrigation is suitable for sustainable high-yielding wheat production in the irrigated regions of the Loess Plateau of China.

Two major irrigation challenges of cotton producers in the Texas High Plains (THP) include the depletion of the Ogallala Aquifer and the highly evaporative, semi-arid environment during late spring and early summer. A recent cotton experiment using center pivot irrigation at deficit irrigation capacities showed the reduction in seasonal irrigation by 20% with minor yield loss by reducing irrigations during the vegetative period instead of attempting to store soil water during this period of high evaporative losses. Due to its method of delivery, subsurface drip irrigation (SDI) should reduce evaporation losses during the preplant and early-season periods and improve water storage efficiency and crop yield even at low irrigation capacity. Two experiments having different SDI installation designs and irrigation capacities were conducted in adjacent fields on clay loam soils over 4- and 5-year periods. Treatments included levels of preplant (PP) and vegetative (Veg) period irrigations. In both experiments, under seasonal growing conditions ranging from favorable to unfavorable, yields and crop values were only modestly increased by additional PP irrigations above that required for germination. Among treatments with common PP amounts, larger irrigation amounts during the vegetative period did not significantly (p < 0.05) increase yield or crop value in any individual year or any group of years. In three growing season groupings, with unfavorable to favorable weather conditions, as seasonal irrigation increased, gross irrigation value decreased. Results suggest that in most years, on heavy soils within the THP, SDI productivity can be improved by limiting PP and early-season irrigations under deficit irrigation conditions.

Abstract Growing crops in cities is challenging due to many factors including space restrictions, busy lifestyles, cost and availability of water. Wicking beds (WBs) have been identified as a simple, potentially water- and labour-efficient irrigation method compared to hand irrigation. However, limited studies exist to validate claims of the effectiveness of WBs with respect to water use efficiency (WUE) and crop productivity. The effectiveness of WBs to grow shallow-rooted crops was scientifically investigated for the first time in this study using a small-scale glasshouse experiment to identify the gaps in WB research and to reveal benefits or problems with the application. Specifically, the growth of lettuce (Lactuca sativa, var. ‘cos’) and two radishes (Raphanus sativus, var. ‘mars’, and (Raphanus sativus var. ‘white long icicle’) was examined. The performance of WBs was compared with a precise hand irrigation treatment based on WUE, yield, biomass, crop type and the presence or absence of mulch. WUE, yield and biomass were always higher in WBs than the hand-irrigated treatments. Furthermore, the WUE benefits of WBs may depend on the type of crop grown (specifically the root form), soil bed depth, and the presence of mulch.

Abstract In this study, the volume balance equation and Elliott and Walker’s two-point method were employed to estimate the Kostiakov–Lewis (KL) infiltration equation parameters. The volume balance equation has a maximum point, whose location (distance) is a function of two parameters, r (constant parameter in advance equation) and fo. (final infiltration rate). If the length of the field is less than the distance of maximum point, then parameters of the infiltration equation obtained by the two-point method will have appropriate values. Otherwise, the values of infiltration parameters would depend on the values of r and fo, and there would be a possibility of their values being inappropriate. In this method, the soil texture of the field is assumed to be homogeneous; so, the relationship between r and fo is ignored, which may render the two-point method unsuitable in heterogeneous soils. By investigating the effect of soil heterogeneity on the values of r and fo, it was found that in the two-point method, point information is used for the estimation of parameters of the KL infiltration and that there is no clear relationship between these two points. As a result, a novel method was developed in this study to estimate the KL infiltration equation parameters and applied in three irrigation fields. The infiltration parameters obtained by the proposed method had appropriate values. The infiltration depth computed with the use of parameters so obtained was in close agreement with observed infiltration depth. Thus, the proposed method is potentially useful for estimating the KL infiltration equation parameters.

Pressurized irrigation systems, center pivots, and linear moves are used worldwide on a large scale. Accurate predictions of wind drift and evaporation losses (WDEL) could help in improving the system’s uniformity and efficiency. The current study evaluates data analysis techniques for accurately estimating WDEL under moving sprinkler irrigation systems. A total of 72 experiments (2015–2017) were conducted at the research and extension center in Prosser, WA, under a wide variety of climate conditions. Two data analysis techniques, namely linear mixed modeling (LMM) and artificial neural networks (ANN), were used to identify the significant drivers of WDEL from the given weather-related inputs. Four published datasets were also used to check the generalization capabilities of the developed models. The results revealed an average of ~ 20% WDEL under Prosser, WA, conditions. Vapor pressure deficit and wind speed were the only significant weather variables at a 0.05 level of significance. Both in training and in testing, the ANN models (root mean squared error (RMSE = 2%)) worked better than the LMM (RMSE = 5%). Testing results revealed the high generalization and predictive power of ANN models with a RMSE of 1% for the (Yazar 1984) datasets. The best LMM model was with the Sanchez et al. (2011) dataset with a RMSE of 14%. The above results showed that ANN models can be used to accurately predict WDEL. This should help in further research for efficiency improvements in sprinkler irrigation systems.

Abstract This study addresses water-saving irrigation strategies, including deficit irrigation (DI) at 70% and 50% crop evapotranspiration, ETc (DI70 and DI50, respectively), and partial root-zone drying (PRD) at 70% and 50% ETc (PRD 70 and PRD 50, respectively) to investigate the response of the tomato (Lycopersicon esculentum L.) using a surface drip system in the field on a sandy loam soil during years 2017 and 2018. Full irrigation (FI) at 100% ETc was used as the control treatment. Results revealed that the soil water content values for the DI and PRD treatments were lower than those in the FI treatment. The net photosynthesis rate, stomatal conductance, and transpiration rate decreased with decreasing irrigation water, whereas the xylem abscisic acid content increased. A significant decrease in fresh and dry vegetative parts for DI and PRD treatments was detected compared to the FI treatment in 2017, whereas there were no significant differences in 2018. Both DI70 and PRD70 treatments had fresh and dry tomato yields similar to the ones in the FI treatment, whereas the corresponding yields were significantly lower under DI50 and PRD50 treatments. This resulted in a water productivity increase by, on average, 28.15% and 38.24%, for DI70 and PRD70 treatments, respectively, compared to the FI treatment. The DI and PRD treatments significantly affected the tomato fruit quality. Fruits under DI and PRD treatments accumulated higher amounts of total soluble solids, vitamin C, and titratable acidity compared to FI Fruits. Therefore, the use of water-saving practices is feasible for tomato production in areas where water supply is limited.

Abstract A good hydraulic design of drip irrigation systems requires an accurate evaluation of the friction head loss that occurs in pipes as well as the local head loss induced by the presence of emitters. Previous approaches on theoretical design usually neglect the local emitter head loss or consider it equal to the friction loss produced by an equivalent length of the straight pipe, which may lead to substantial errors. In this study, an improved finite element-based formulation is presented for the hydraulic analysis of drip irrigation subunits. Local head loss is calculated as a fraction of the kinetic head using the results from recent experimental studies on on-line and integrated in-line emitters (Method 1), or by the equivalent length (Method 2). A custom Matlab software script was developed and the two methods are compared for accuracy and convergence speed. For practical purposes, the head loss components along lateral direction are analyzed for two types of in-line emitters and a manifold design example is also provided. Acquired data indicate that considering an equivalent length as a constant value leads to a higher percent error between the numerical solution and the experimental data. The percentage of local head loss to the total head loss varies dramatically from 6.3 to 49.2% and this result is in good agreement with the results from alternative procedures available in the literature. The decrease in the local head loss coefficient allows a slight increase in manifold length. In general, the finite element model with solution method 1 can be a fast, accurate, and convenient way of designing a drip irrigation pipe network system.

The main aim of this study was to investigate the qualitative changes of the rainbow trout effluent as water supply in a drip irrigation system. Two drip irrigation systems with a hydro-cyclone filter, sand filter and screen filter for using freshwater (control treatment) and fish farm effluent were tested in Kurdistan province (northwest of Iran) in 2017. In addition, the effect of lateral drainage at the end of each irrigation event was also studied. Two emitter types with different discharge flows were used for each treatment. In the 16 irrigation events carried out, samples were collected from the different water sources (dam, well, and river), filter outlets and lateral locations for measuring total suspended solids (TSS), particle size, pH, electrical conductivity, different compounds (Fe, Na, K, Ca, Mg, NO3, PO4, HCO3) and the number of coliform bacteria. The results showed changes in the TSS and the number of coliform bacteria, but the remaining parameters had slight changes. In both control and effluent treatments, the filtration system significantly reduced TSS, having the screen filters the greatest effect on this decrease and hydro-cyclone and sand filter the least. To achieve higher removals, it is recommended to use finer grains in sand filters. The filtration of both control and effluent treatments increased the number of bacteria. The highest number of bacteria in the control treatment was measured after the sand filter and in the effluent treatments after the screen filter.

In arid and semiarid environments, with shortage of water resources, maize production is competing for available water. This study analyzed the effect of different irrigation systems on maize yield, crop evapotranspiration and its components, i.e., canopy transpiration (T) and soil evaporation (E). A 2-year field experiment was conducted at the ITAP Research facilities located in Albacete (southeast Spain). Four treatments were assessed: surface drip irrigation with a spacing between drip lines of 1.5 m (SDI_1.5) and 0.75 m (SDI_0.75); subsurface drip irrigation (SubDI); solid set sprinkler irrigation (Sprink). In all treatments, irrigation was applied to refill the estimated potential water demand. Crop evapotranspiration (ETc) and E/T partitioning were estimated using a Simplified Two-Source Energy Balance (STSEB) approach. Although there was an important difference in the irrigation water applied between treatments, ranging from 743 and 722 for Sprink system to 534 and 495 for SubDI system in 2014 and 2015, respectively, yield was unaffected by the irrigation regime, resulting in an increase in the irrigation water productivity (IWP) by an average of 25% when irrigation was applied by the subsurface system. Maize ETc was affected by the irrigation system, with the SubDI achieving in 2015 a 39% reduction of seasonal ETc in comparison with the Sprink system. Similar reductions were obtained for separated E and T components with soil evaporation accounting in general for 15–20% of the total ETc. It is concluded that subsurface irrigation is a water savings strategy for irrigation of maize reducing the consumptive water use and increasing IWP. The final convenience for the widespread adoption of subsurface irrigation will depend on water availability and prices.

Water scarcity is seriously affecting agricultural production, especially in arid and semi-arid areas. Therefore, there is increasing interest in improving water productivity in agriculture. This research aims to study the effects of deficit irrigation on the productive response of sweet pepper plants. Nine deficit irrigation strategies were assayed during two seasons (2017 and 2018) in a randomised complete block design with three replicates. These irrigation strategies consisted of applying 100%, 75% and 50% of the irrigation water requirement (IWR) during the entire growing period (continued deficit irrigation) or applying 75% or 50% of the IWR during one of the following stages (regulated deficit irrigation): vegetative growth, fruit setting, and harvesting. Pepper plants cultivated under deficit irrigation reduced fruit biomass and indicators of plant water status. Applying water deficits during the vegetative growth and fruit-setting stages had minimal effects on the marketable yield but with minimal water savings. Irrigating pepper plants with 75% or 50% of the IWR during the entire crop cycle or with 50% of the IWR during harvesting resulted in a high incidence of fruits affected by blossom end rot, which in turn, led to a drastic reduction of the marketable yield in relation to fully irrigated plants (− 36%, − 55% and − 44%, respectively). These strategies also recorded the highest soluble solid and phenolic contents. Reducing the water applied to 75% of the IWR at harvesting led to a yield reduction (− 19%) but with important water savings (21%) and acceptable levels of soluble fruit solids and phenolic compounds.

There were inadvertent errors in the authorship line and text. The authorship line should read as: Sumantra Chatterjee, Suat Irmak, Jose O. Payero, Ayse Kilic, Lameck O. Odhiambo, Daran Rudnick, Vivek Sharma, and David Billesbach.

Abstract Surface renewal (SR) is a biometeorological technique that uses high-frequency air temperature measurements above a plant canopy to estimate sensible heat flux. The sensible heat flux is then used to estimate latent heat flux as the residual of a surface energy balance equation. SR previously relied on calibration against other methods (e.g., eddy covariance) to obtain accurate measurements of sensible heat flux, and this need for calibration limited the use of SR to research applications. Our group recently showed that compensating for the frequency response characteristics of SR thermocouples causes the calibration factor to converge near the theoretically predicted value of 0.5 (Shapland et al., Agric For Meteorol 189:36–47, 2014). This led to the development of an inexpensive, stand-alone SR system to measure sensible heat flux without the need for calibration, and here we evaluated the SR system in a mature vineyard containing a weighing lysimeter. Vineyard evapotranspiration (ET) measured with SR was strongly and positively correlated with that from the lysimeter, eddy covariance, and a soil water budget approach. ET measured with the various techniques responded similarly to changes in the microclimatic conditions (i.e., day to day variability) and when water was withheld from the entire vineyard for an extended period. A stress index, calculated using reference and actual ET from SR and lysimetry, was correlated to leaf water potential, stomatal conductance, and volumetric soil water content measurements, but some of these relationships were more variable than others. Our results suggest that the new SR method could potentially be used as a low-cost tool to provide growers with field-specific estimates of crop water use and stress for irrigation management in vineyards.

The sustainability of groundwater abstractions for irrigation practices must be monitored to achieve a long-term equilibrium in aquifers. The accounting of irrigation water requirements in river basin management plans is commonly and mainly calculated by combining the average multiannual irrigated surface estimates and the unitary crop water requirements. However, remote sensing approaches allow water managers to incorporate more dynamic knowledge of a territory by monitoring irrigated crops. Hence, time series of biophysical products processed from Earth Observation data for 4 years (2010–2013) were incorporated into a remote sensing-based soil water balance to estimate spatially distributed irrigation water requirements on a monthly time scale over a semiarid environment, where agricultural practices greatly depend on groundwater resources. The simulated monthly water abstractions were then evaluated regarding monthly groundwater level changes recorded from a piezometric network. The results indicated that groundwater level changes on a monthly scale could be explained in more than 75% of the cases. Therefore, a simple remote sensing-based approach brings temporally and spatially distributed information of great practical value to river basin water managers according to their management necessities.

Abstract The operation patterns of drip irrigation fertigation system have significant impacts on the emitter clogging. Exploring the dynamic variation and influence mechanism of mineral components in clogging substances under different operation patterns can provide suitable guidance for fertigation management models. In this study, an emitter clogging experiment was conducted through three operating irrigation patterns (once per day, OP1/1; once every 4 days, OP1/4; once every 7 days, OP1/7) by running high-sediment surface water under the potassium dihydrogen phosphate (PDP) fertigation. The X-ray diffractometer was used to identify the mineral components. The results indicated that the primary mineral components in the emitter clogging materials were quartz, silicate, and carbonate and their contents accounted for more than 97% of the total. The components showed a dynamic process of slow growth followed by rapid growth. And there was a significant correlation between mineral compositions and the clogging degree (R2 > 0.86). The application of PDP fertilizer did not generate phosphate precipitation in the emitters directly, but accelerated the carbonates precipitation through adsorption influence of phosphate fertilizers instead. The contents of quartz, silicate, and carbonate were at their highest levels in OF1/7 followed by OP1/4, and then at their lowest in OP1/1 due to the difference time of applying P fertilizer time in three operating patterns. Both the relative discharge (Dra) and uniformity coefficient (CU) of the drip emitters also showed similar trends for the all eight types of emitters that were tested in this experiment.

Abstract Water productivity has become a key requirement in sustainable crop production and environmental management. Deficit irrigation (DI) and partial root-zone drying irrigation (PRDI) are two strategies that have been exploited to maximize crop production per unit water, with attendant effect on the quality attributes of harvest index. We employed meta-analysis to synthesize evidence for the relative performance of full irrigation (FI), DI and PRDI for three quality attributes of fruits and vegetables, namely, total soluble solids (TSS), titratable acidity (TA) and pH. Overall, TSS, TA and pH of crops under DI and PRDI do not differ significantly. However, TSS in crops under DI and PRDI are significantly larger than that of crops under FI. DI and PRDI improve TSS by 4.1 ± 1.8% and 5.0 ± 2.0%, respectively, relative to FI. Crops under the three irrigation techniques do not differ significantly in TA and pH. The differences in TSS of crops are contextual, depending on type of crop, soil texture and irrigation frequency. The effect of water-saving irrigation on the selected crop quality attributes may, therefore, have the add-on effects of crop, system and/or site characteristics. Therefore, in terms of quality attributes, water-saving irrigation techniques are superior to FI when considering improvement in TSS without significantly altering TA or pH of fruits and vegetables.

Abstract Potential low-cost micro-irrigation emitters appropriate for smallholder farmers in developing countries were the subject of a field experiment. Low-cost micro-irrigation technologies have been introduced with some success; however, further improvements are needed to increase adoption. The experiment evaluated three types of metal screw drip emitters (brass, zinc, and stainless steel), a conventional drip emitter, and a low-cost drip emitter (microtube). The effect of lateral flushing on emitter discharge and emitter uniformity was also evaluated. Emitter discharge, coefficient of variation (Cv), emission uniformity (EU), emitter blockage rates, and crop yield (Lactuca sativa ‘Toronto’) were the evaluation parameters. Screw emitter Cv ranged from 5 to 27%, and the conventional emitter and microtube emitter Cv were 9% and 29%, respectively. Blockage rates were significantly greater in the microtube, brass, and zinc emitters. Individual lettuce plant weight ranged from 0.676 to 0.912 kg/head for the three screw-based emitters, and 0.711 kg/head and 0.816 kg/head, respectively, for the microtube and conventional emitters. The stainless steel and conventional emitter performance were superior in all indices used to evaluate the emitters. Weekly flushing of laterals was found to be beneficial in optimizing emitter discharge and uniformity. Field evaluation demonstrated the potential use of metal-based screws as drip emitters.

Abstract The concept of soil water contents at field capacity (FC at 0.33 MPa) and at wilting point (WP at 15 MPa) is often used to explain plant water availability and as maximal and minimal limits on observed soil water content. Field observations often differ, however, from laboratory-determined FC and WP water content values. Moreover, as more capable sensors have become available and graphical plots of soil water dynamics have become common, plotting of FC and WP lines on such graphs often reinforces these differences and engenders confusion rather than enlightenment. Resolving this confusion has been greatly eased by the introduction of soil water sensors that encapsulate an entire time domain reflectometry (TDR) system in individual sensor heads and the recent availability of a reader for capturing georeferenced values of the TDR waveform and estimated values of soil volumetric water content (VWC), permittivity, temperature, and bulk electrical conductivity. The present study illustrates the typical confusion with season-long graphs of soil water content that greatly exceed the FC values for individual soil horizons, and it resolves the confusion with concurrent and co-located TDR sensor readings and volumetric soil sampling to ascertain sensor accuracy. It was found that sensor readings were reasonably accurate (RMSE = 0.01 m3 m−3) across a range of textures from fine sandy loam to clay, even though some measurements were up to 0.19 m3 m−3 larger than FC values. Water contents in a sandy eluviated horizon above a dense clay were larger than FC due to the clay layer impeding water flow and perching water in the sand, augmented by the capillary fringe in the fine sand. Confusion was in part created by plotting water content for four different depths of different textures but plotting the FC and WP values for only one soil texture. Misperception of water available for crops was greatly reduced by converting the water content values to equivalent water depth values for the four soil layers and plotting only the soil water storage depth for the entire profile depth covered by the sensing network. The ambiguity was further reduced by determining the maximum value of soil water storage for the season and calculating soil water depletion by subtracting the maximum value from the soil water storage throughout the season. When this was done, it was easy to see depths of water removed from the soil and needing replacement, and to see the extra soil water depletion that occurred when a plot was not irrigated.

A SWAT model equipped with an alternative auto-irrigation algorithm was used to evaluate the effects of planting date on hybrid corn yield and seasonal water use in the Texas High Plains. Research field data from the USDA-ARS Conservation and Production Research Laboratory at Bushland, TX and the Texas A&M AgriLife North Plains Research Field near Etter, TX were used for model calibration. A long-term weather data set was used to simulate continuous corn using five planting dates (15-April, 1-May, 15-May, 1-June, and 15-June) for both long- and short-season corn hybrids. Results suggested that delayed planting resulted in a reduction of seasonal water use for both hybrids. Reductions in seasonal irrigation between the 15-April and 15-June were 28 % and 31 % for long- and short-season hybrids, respectively, using an application depth of 25.4 mm. Corresponding reductions in yield were considerably less at 8.9 and 8.8 % for long- and short-season hybrids. Reduced irrigation was attributed to decreased temperature stress and lower evapotranspiration of the later growing season. However, simulation of long season corn for the 15-June planting resulted in late season cold temperature stress. Further analysis of 19.1 mm and 31.8 mm irrigation depths revealed the latter resulted in an average of 4.4 and 4.7 % reductions in seasonal irrigation for long- and short-season hybrids, respectively. Results from this assessment study suggest the delayed planting of corn may result in decreased irrigation while maintaining profitable yields, potentially reducing withdrawals from the Ogallala Aquifer in the Texas High Plains region.

Abstract Clay particles under certain physico-chemical and hydrodynamic conditions can form agglomerates after passing through a filtering system, which favours clogging of the emitters. The main factors interfering with the aggregation potential of clay particles are the type of clay mineral, pH, and ionic strength of the irrigation water. This study analysed the influence of ionic strength and type of clay mineral on clogging, discharge variation, and particle deposition in turbulent-flow non-pressure compensating drippers. Two types of clay (kaolinite and montmorillonite) at a concentration of 500 mg L−1 and four values of ionic strength (0.31, 0.81, 0.02, and 0.01 mol L−1) promoted by the addition of different salts to the solution were used. Clogging tests were conducted with two commercial models of drippers (0.6 and 1.7 L h−1). The deposition zones along the labyrinth channel were analysed using a transparent milli-fluidic system coupled to an optical microscope. Deposition of particles inside dripper labyrinths was observed and this process was strongly influenced by the nature of the clay. The regions of highest particle deposition were vortices zones located in the first baffles of the labyrinths. Kaolinite particles had greater potential of accumulation in the labyrinths than montmorillonite particles. There were fluctuations in the drippers’ discharge during the clogging experiments, but the discharge variations observed were not sufficient to classify the emitters as clogged in any of the test conditions. Clay, as an isolated agent, did not cause full clogging in the emitters evaluated under any of the ionic strength conditions studied. Since particles did not accumulate in the region of the main flow, we suggest that clay particles alone have no potential to cause full clogging of drippers, but may contribute to clogging build-up.

Engineering technologies for site-specific irrigation management (SSIM) have already been developed for applications in precision irrigation. However, further studies are needed to identify scenarios where SSIM leads to better agronomic outcomes than conventional uniform irrigation management (CUIM). The objective was to conduct a long-term simulation study to compare SSIM and CUIM given spatial soil variability at the Maricopa Agricultural Center (MAC) in Arizona. More than 500 surface soil samples were collected across a 730-ha area of the MAC from 1984 to 1987. A more detailed soil data set was more recently obtained across a 5.9-ha area at a MAC location designated for SSIM studies. Ordinary kriging was used for spatial interpolation of soil hydraulic properties within \(10\,\hbox {m} \times 10\,\hbox {m}\) zones across the MAC, and 11 field parcels with an area of approximately 60 ha were delineated on the MAC quarter sections. Using an agroecosystem model, simulations of cotton production at the zone level with a 30-year weather record were conducted using a field-tested algorithm to optimize irrigation schedules for SSIM and CUIM. Long-term seed cotton yield, irrigation requirements, water use efficiency, and marginal net return for SSIM and CUIM strategies were often not different (\(p>0.05\)). Differences in seed cotton yield and irrigation requirements among the tested irrigation strategies were less than 11% and 6%, respectively, and within the typical range of model error. Most soils on the MAC have enough available water holding capacity to sustain cotton production at full potential with weekly CUIM, and advantages of SSIM were not consistently demonstrated by the simulations.