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.

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.

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.

Reasonable regulation of irrigation and drainage is an important way to decrease water resource waste and water pollution, and to ensure the sustainable utilization of water resources. In this study, appropriate irrigation and drainage methods are proposed by optimizing agricultural water and soil resources based on the current status of water resource utilization in irrigation district in Northwest China, and as much as possible to reduce the amount of irrigation and drainage while ensuring the necessary for salt leaching. A two-layer model was considered to maximize economic benefits and relative production through a nonlinear algorithm to optimize the crop acreage, irrigation quota and the amount of irrigation water at each crop growth stage. A support vector machine regression model for predicting drainage was constructed, including drainage and irrigation, precipitation, evaporation and groundwater depth. Additionally, the amount of drainage water was compared before and after the optimization of irrigation. The amount of irrigation water demand in a wet year (2014), normal year (2008) and dry year (2013) decreased by 23.85 million m3, 12.85 million m3 and 17.50 million m3, respectively, after optimization of the crop planting structure and irrigation scheduling. Furthermore, the net economic benefit increased by 3.76 billion yuan, 1.14 billion yuan and 2.34 billion yuan, as compared with the actual output value. The amount of drainage water decreased by 8.60%, 8.93% and 5.21% compared to that with no optimization in a wet year (2014), normal year (2008) and dry year (2013), respectively. This method can scientifically allocate the amount of irrigation and drainage, feasibly improve economic benefits and prevent soil salinization, thus providing guidance for efficient water resource utilization and ecological protection in arid areas.

Abstract Irrigation uniformity, application efficiency and seasonal irrigation uniformity of mobile drip irrigation (MDI) were compared to those of low elevation spray application (LESA) and low energy precision application (LEPA). A center pivot fitted with two sets of MDI (with dripper flow rates of 3.8 L/h and 7.6 L/h), LESA and LEPA was used in this study. Irrigation uniformity tests were conducted in accordance with the American Society of Agricultural Engineers’ standards. Application efficiency was computed as the ratio of depth of water retained in the root zone to that applied. Potential differences in season-long irrigation uniformity were evaluated by analysis of periodically acquired aerial vegetative index data. The coefficient of uniformity of the 3.8 L/h and 7.6 L/h MDI was 93.8% and 93.7%, respectively, and 95.1% for LEPA, and 83.8% for LESA. Application efficiencies for the 3.8 L/h and 7.6 L/h MDI, LEPA and LESA were 76.1, 96.8, 98.4 and 51.2%, respectively. There were no significant differences (p value = 0.5749) in the amount of water stored in the soil profile between MDI, LESA and LEPA, 72 h after irrigation. For three irrigation capacities of 6.2, 3.1 and 1.6 mm/day, there were no significant differences in mean seasonal Advanced Difference Vegetative Index (ADVI) between MDI, LESA and LEPA, with p value = 0.987, 0.999 and 0.999, respectively. A similar observation was made for Normalized Difference Vegetative Index, with p value = 0.998, 0.999 and 0.999, for MDI, LESA and LEPA, respectively. Higher coefficient of uniformity and higher application efficiency for MDI and LEPA indicate that they were more efficient than LESA. These results show that MDI can adapt the high efficiency of traditional drip irrigation to center pivot systems.

Significant efforts have been made recently in the application of high-resolution remote sensing imagery (i.e., sub-meter) captured by unmanned aerial vehicles (UAVs) for precision agricultural applications for high-value crops such as wine grapes. However, at such high resolution, shadows will appear in the optical imagery effectively reducing the reflectance and emission signal received by imaging sensors. To date, research that evaluates procedures to identify the occurrence of shadows in imagery produced by UAVs is limited. In this study, the performance of four different shadow detection methods used in satellite imagery was evaluated for high-resolution UAV imagery collected over a California vineyard during the Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) field campaigns. The performance of the shadow detection methods was compared and impacts of shadowed areas on the normalized difference vegetation index (NDVI) and estimated evapotranspiration (ET) using the Two-Source Energy Balance (TSEB) model are presented. The results indicated that two of the shadow detection methods, the supervised classification and index-based methods, had better performance than two other methods. Furthermore, assessment of shadowed pixels in the vine canopy led to significant differences in the calculated NDVI and ET in areas affected by shadows in the high-resolution imagery. Shadows are shown to have the greatest impact on modeled soil heat flux, while net radiation and sensible heat flux are less affected. Shadows also have an impact on the modeled Bowen ratio (ratio of sensible to latent heat) which can be used as an indicator of vine stress level.

Vineyards in many semi-arid regions globally face limited water resources. Monitoring évapotranspiration (ET) of vineyards is critical for water resource management, but remains difficult due to the complex biophysics of the surfaces. Both measurement and modeling approaches for estimating turbulent water vapor transport rely on implicit assumptions that exchanges occur in a reasonably regular fashion over the time scales generally used for averaging. However, heterogeneous vegetation in semi-arid climates, such as many vineyards, presents inherent factors, including canopy row/row space structure and frequent periods of light wind, unstable conditions, that can create episodic transport characteristics. Eddy covariance data were collected above and within the canopy of two vineyards in the Central Valley of California during the Grape Remote sensing Atmospheric Profile & Evapotranspiration experiment (GRAPEX). The goal was to document and quantify the existence of intermittent turbulence transport of water vapor, and associated episodic canopy venting. These effects were found to correlate with periods light winds and highly unstable/convective conditions. Power and cross-spectra for intermittent periods documented enhancement of low-frequency water vapor exchange events compared to more steady periods, and diminished time scale correlation between humidity within the canopy and above the canopy. Analyses show that intermittent cases can necessitate longer flux-averaging periods (up to 2 h) than more steady conditions. Episodic exchange events were isolated and summed to determine their relative contribution to the overall water vapor flux. Since light wind, unstable conditions are relatively common in many arid vineyard regions, these findings have implications for mechanistic ET models that rely on time-averaged vertical gradients, which implies reasonably steady transport.