Quantifying evapotranspiration and crop coefficients for cotton (Gossypium hirsutum L.) using an eddy covariance approach
Introduction
Currently, more than 80–90 % of the freshwater resources available globally is used for irrigating crops for producing food, fiber, and energy for the burgeoning population (FAOSTAT, 2006; Morison et al., 2008; Wada and Bierkens, 2014). Groundwater withdrawals from aquifers for crop irrigations above their natural recharge capacities lead to aquifer declines that are threatening the sustainability of irrigated agriculture across the globe (Gleick, 1993; de Fraiture and Wichelns, 2010; Dalin et al., 2017). The ongoing pressure on agriculture for more food production calls for more judicial use of the limited ground water resources available for irrigations (Bruinsma, 2003; Rijsberman, 2006; Saseendran et al., 2014a, b, 2015; Distefano and Kelly, 2017). In this evolving scenario, for enhancing water productivity in irrigated agriculture, it is critical that irrigation we apply is based on accurate information on location-specific ETc demands (Shiklomanov, 2000). The ETc at specific locations is dynamic and depends mainly on the weather, crop type and variety, and soil properties among many other crop characteristics (Farahani et al., 2008; Li et al., 2008; Irmak et al., 2012, 2013, 2014; Anapalli et al., 2018b, 2019).
When crop growth and productivity mainly depend on the water available for meeting their ETc demands, about 1% of the water absorbed by the plant from the soil is only used in its metabolic activities (Rosenberg et al., 1983; Allen et al., 1998; Morison et al., 2008). Most of the water absorbed gets evaporated from plant-soil-residue surfaces by absorbing heat from the surroundings (the latent heat of evaporation), thereby indirectly cooling the crop-environment to safe limits within which most of the metabolic activities take place. The crop environmental demand for water for meeting this ET demand is normally quantified at a potential rate of ET demand of the atmosphere (potential evapotranspiration, PET) and calculated from weather data (Penman, 1948). The PET definition assumes a crop that does not exert any resistance to water flow from the soil-crop canopy surface, that is, evaporation of water is only limited by the energy available for converting the state of water from liquid to vapor. However, in nature, many crop-environmental factors resist water loss at PET rate through plant stomatal control and other soil-residue related resistances to evaporation losses, so the concept of PET by itself restricts its applications in estimating ETc or irrigation water requirements.
For calculations of PET, Monteith (1965) offered a single layer – an extended grass covered soil – Penman-Monteith (P-M) combination equation. This concept was extended to partial canopy-soil by Shuttleworth and Wallace (S-W) (1985), further extended to include the effects of surface residue on soil evaporation by Farahani and Ahuja (1996). Calculation of PET, for a crop in a natural environment, by means of the original P-M and the S-W equations, requires crop growth information on a daily or hourly basis, besides the weather data, to compute aerodynamic and canopy resistances. The values of these resistances differ with the plant species, varieties, and cultivars; climate, soil water, and nutrient status; and crop-management practices that are difficult to quantify accurately for water management applications. Therefore, for irrigation water management, Doorenbos and Pruit (1977) offered a two-step approach to ETc: ET is initially calculated for a single reference crop (ETref) - a hypothetical crop - with known canopy-soil resistances and then modified with experimentally (real-world) obtained crop coefficients (Kc) to estimate ETc of the crop of interest
Allen et al. (1998) standardized the computation of a hypothetical grass reference crop, ETo, defined with given soil-plant-aerodynamic resistances and published Kco for a variety of field and tree crops. Fully irrigated short grass (0.12 m tall), Kco and alfalfa (0.50 m tall), Kcr, with full canopy cover are two mainly accepted reference crops. The ASCE-EWRI (2005) presented ETr computation methods and Kc values for a variety of plants and conditions. When Allen et al. (1998) provide Kco for many crops, including cotton, those values were reported to be inadequate in calculating optimum irrigation water requirements for optimum crop production: Irmak et al. (2013) reported significant differences between the Allen et al. (1998) and measured Kco using lysimeters for soybean in south-central Nebraska’s soil, climate, and management practices; In a lysimetric study with cotton in the Mediterranean region of Northern Syria, Farahani et al. (2008) reported 24 % lower mid-season cotton Kco than Allen et al. (1998) tabulated values; in various studies using either EC or lysimeters with various field crops, Karam et al. (2007); Farg et al. (2012); Payero and Irmak (2013), and Sánchez et al. (2015) also reported significantly lower Kco in experiments, compared to Allen et al. (1998), in various climates across the world. Considering these findings, we conclude that, in general, there is a need for developing location specific, crop-soil-climate specific Kc for crops and their cultivars for limited irrigation water management.
For limited water irrigation management in water scarce environments, Allen et al. (1998) also proposed a dual Kc approach for ETc estimation - a basal crop coefficient (Kcb) representing the plant-transpiration contribution to ETc and a Ks representing the soil surface evaporation during the initial growth of a crop with partial canopy covered dry soil surfaces. However, in the humid climate of the Mississippi Delta, with plenty of spring rainfall during the initial growth period of the crop, plant growth is not normally affected by dry soil surface, so a single Kc is still preferred for optimum growth benefits of the crops (Anapalli et al., 2016a, b).
For quantifying ET exchanges from cropping systems and computing Kc of crops, the eddy covariance (EC) is a cutting-edge, sound micrometeorological theory-based method (Parent and Anctil, 2012; Shurpali et al., 2013; Tallec et al., 2013; Uddin et al., 2013; Baldocchi, 2003; Anapalli et al., 2018a, 2018b, 2019). In the EC method, normally, net ecosystem exchanges of CO2 (NEE) and water vapor (ET) are estimated by tracking and measuring the turbulent transport of eddies carrying CO2 and water vapor in the plant canopy boundary layer of the atmosphere. Numerous methods with varying complexity were reported in the literature for quantifying ET: field lysimeters, Bowen ratio modeling, water balance, residual energy balance, and EC (Wilson et al., 2001; Anapalli et al., 2018a, b, 2019). Among these methods, with the current efficient and cost-effective electronic technologies available for frequent crop-soil-water-air data collection, storage, onsite-computing, and communication, the EC method emerged a scientifically sound and easy to install and maintain technology for quantifying ET in cropping systems.
An important agricultural production region in the USA, the Mississippi (MS) Delta, uses groundwater from the MS River Valley Alluvial Aquifer (MSRVAA) for meeting its irrigation water needs (Heatherly, 2014; Powers, 2007). Typically, over 60 % of all the crops grown in this region are irrigated. Currently, water is drawn from the thin MSRVAA, outside its natural recharge capacities, resulting in significant aquifer depletions, threatening the sustainability of irrigated agriculture in this region (Clark and Hart, 2009: Runkle et al., 2017). Developing and disseminating irrigation schedules based on location-specific crop ETc demands and water supply scenarios can help in conserving the MSRVAA for sustainable irrigated agricultural production (Anapalli et al., 2018a. 2018b).
In this study, we quantified ETc of cotton using an EC approach and then used that information for developing Kc for Allen et al. (1998) grass and ASCE-EWRI (2005) alfalfa reference crop ET data.
Section snippets
Cotton experiment
The experiments for this study were conducted in 2017 and 2018 on a commercial producer’s 250-ha field located about 1 km from the USDA Agricultural Research Service Crop Production Systems Research Unit’s farm at Stoneville, Mississippi, USA (33° 42′ N, 90° 55′ W, ∼32 m elevation above sea level). The data collected in 2017 in this study had been used by Anapalli et al. (2019) for comparing water use efficiencies of Soybean and corn with those of cotton. In this study, we used the data
Weather
In crop fields, about 99 % of the water taken up by plant roots is lost to the air as water vapor through the stomatal opening in the plant epidermal cells, the process known as transpiration. Water is also lost due to direct evaporation from soil, residue, and plant surfaces, and the combined loss of water to air from a crop-soil-residue system is termed ET (Rosenberg et al., 1983; Allen et al., 1998; Morison et al., 2008; Farahani et al., 2008; Irmak et al., 2014). Hence, the rate and amount
Conclusions
Water resources in aquifers across the globe are declining due to unsustainable water withdrawals for irrigated agriculture. For sustaining irrigated agriculture for producing sufficient food, fiber, and fuel for an increasing population, it is critical that irrigations are applied based on location-specific crop water demands for achievable production goals. Crop water demands vary across space and time during the crop season depending on the realized weather and other dynamic
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
References (62)
- et al.
Adaptation and application of an energy balance method for estimating evapotranspiration in cropping systems
Agric. Water Manag.
(2018) - et al.
Quantifying soybean evapotranspiration using an eddy covariance approach
Agric. Water Manage.
(2018) - et al.
Quantifying water and CO2 fluxes and water use efficiencies across irrigated C3 and C4 crops in a humid climate
Sci. Total Environ.
(2019) - et al.
Energy budget closure observed in paired Eddy Covariance towers with increased and continuous daily turbulence
Agric. For. Meteorol.
(2014) - et al.
Satisfying future water demands in agriculture
Agric. Water Manag.
(2010) - et al.
Are we deep in water? Water scarcity and its limit to economic growth
Ecol. Econ.
(2017) - et al.
Gap filling strategies for defensible annual sums of net ecosystem exchange
Agric. For. Meteorol.
(2001) - et al.
Estimation of evapotranspiration ETc and crop coefficient kc of wheat, in south Nile Delta of Egypt using integrated FAO-56 approach and remote sensing data
Egyptian J. Remote Sens. Space Sci.
(2012) - et al.
Trend and magnitude of changes in climate variables and reference evapotranspiration over 116-year period in the Platte River basin, central Nebraska, USA
J. Hydrol.
(2012) - et al.
Evapotranspiration, seed yield and water use efficiency of drip irrigated sunflower under full and deficit irrigation conditions
Agric. Water Manag.
(2007)
Determination of growth-stage-specific crop coefficients (Kc) of cotton and wheat
Agric. Water Manag.
Reflections on the surface energy imbalance problem
Agric. For. Meteorol.
Evapotranspiration and crop coefficient of spring maize with plastic mulch using eddy covariance in northwest China
Agri. Water Man.
Effects of heat storage and phase shift correction on energy balance closure of paddy fields
Atmosfera
Quantifying evapotranspiration of a rainfed potato crop in South-eastern Canada using eddy covariance techniques
Agric. Water Manage.
Daily energy fluxes, evapotranspiration and crop coefficient of soybean
Agri. Water Manage.
Water scarcity: fact or fiction?
Agric. Water Manag.
Developing and generalizing average corn crop water production functions across years and locations using a system model
Agric. Water Manag.
Linking water vapor and CO2 exchange from a perennial bioenergy crop on a drained organic soil in eastern Finland
Agric. For. Meteorol.
Energy and water balances of two contrasting loblolly pine plantations on the lower coastal plain of North Carolina, USA
Forest Ecol. Manag.
Crop´s water use efficiencies in a temperate climate: comparison of stand, ecosystem and agronomical approaches
Agric. Forest Meteorol.
Net ecosystem carbon dioxide exchange of dedicated bioenergy feedstocks: switchgrass and high biomass sorghum
Agric. For. Meteorol.
A comparison of methods for determining forest evapotranspiration and its components: sap-flow, soil water budget, eddy covariance and catchment water balance
Agric. Forest Meteorol.
Crop Evapotranspiration: Guidelines for Computing Crop Water Requirement
Vulnerability and adaptation of cotton to climate change in the Mississippi Delta
Climate
Climate optimized planting windows for cotton in the Lower Mississippi Delta Region
Agronomy
The ASCE standardized reference evapotranspiration equation
Assessing the eddy covariance technique for evaluating carbon dioxide exchange rates of ecosystems: the past, present, and future
Glob. Change Biol.
Introduction to the eddy covariance method: general guidelines and conventional workflow
Li-Cor Biosciences
The Mississippi Embayment Regional Aquifer Study (MERAS): Documentation of a Groundwater-flow Model Constructed to Assess Water Availability in the Mississippi Embayment
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