Cotton Water Use Research Articles

Evaluating the Effect of Deficit Irrigation on Yield and Water Use Efficiency of Drip Irrigation Cotton under Film in Xinjiang Based on Meta-Analysis.

Water scarcity constrains the sustainable development of Chinese agriculture, and deficit irrigation as a new irrigation technology can effectively alleviate the problems of water scarcity and water use inefficiency in agriculture. In this study, the drip irrigation cotton field under film in Xinjiang was taken as the research object. Meta-analysis and machine learning were used to quantitatively analyze the effects of different farm management practices, climate, and soil conditions on cotton yield and water use efficiency under deficit irrigation, to investigate the importance of the effects of different factors on cotton yield and water use efficiency, and to formulate appropriate optimization strategies. The results showed that deficit irrigation significantly increased cotton water use efficiency (7.39%) but decreased cotton yield (-15.00%) compared with full irrigation. All three deficit irrigation levels (80~100% FI, 60~80% FI, and 40~60% FI; FI: full irrigation) showed a significant decrease in cotton yield and a significant increase in water use efficiency. Under deficit irrigation, cotton yield reduction was the smallest and cotton water use efficiency increased the most when planted with one film, two tubes, a six-row cropping pattern, an irrigation frequency ≥10 times, a nitrogen application of 300~400 kg·ha-1, and a crop density ≥240,000 per hectare, and planted with the Xinluzhong series of cotton varieties; deficit irrigation in areas with average annual temperature >10 °C, annual evapotranspiration >2000 mm, annual precipitation <60 mm, and with loam, sandy soil had the least inhibition of cotton yield and the greatest increase in cotton water use efficiency. The results of the random forest showed that the irrigation amount and nitrogen application had the greatest influence on cotton yield and water use efficiency. Rational irrigation based on optimal management practices under conditions of irrigation not less than 90% FI is expected to achieve a win-win situation for both cotton yield and water use efficiency. The above results can provide the best strategy for deficit irrigation and efficient water use in drip irrigation cotton under film in arid areas.

Comparison of Infrared Thermometry and Soil Water Derived Stress Indices and Crop ET in Cotton

HighlightsA crop water stress index (CWSI) was calculated using a theoretical approach.Averaged daily rather than one to two hour daily maximum CWSI correlated better with soil-based crop water stress.Crop ET scaled with the CWSI accurately predicted ET for a dissimilar canopy and irrigation level.Sub-hourly canopy resistance and transpiration were inferred from canopy temperature measurements.Abstract. Upland cotton (Gossypium hirsutum L.) is increasingly being managed under subsurface drip irrigation (SDI) in the semiarid Texas High Plains (THP). Scheduling irrigation using a thermally based crop water stress index (CWSI) has the potential to overcome limitations of soil water-based methods and facilitate efficient use of water. The objectives of this study were to develop a CWSI calculation procedure using stability correction, determine an appropriate window for averaging CWSI during daytime hours, compare CWSI with soil water-based indicators of crop water stress, and evaluate methods for estimating crop evapotranspiration (ET) using measured canopy temperatures. Infrared thermometer measurements of canopy temperature and corresponding cotton water use derived from soil water measurements were acquired under two irrigation levels (100% and 33%) under SDI during three growing seasons. A theoretical approach was used to calculate the CWSI using the Businger-Dyer stability correction. Basing daily CWSI on short 1- or 2-h periods in the afternoon overestimated crop water stress. In contrast, CWSI averaged during daytime periods with 0.25-h solar radiation and air temperature exceeding 0.3 MJ m-2 and 24°C, respectively, was strongly correlated (R2=0.76) with the soil water depletion-based stress coefficient Ks with a plausible lower canopy resistance of 25 s m-1. The CWSI was weakly correlated (R2=0.48) to the fraction of plant available water, with the CWSI exhibiting the greater increase of these two indices in response to irrigation events. Using the proposed CWSI scaling at different locations for canopies with dissimilar cover fractions yielded satisfactory estimates of crop ET (RMSE=0.74 mm d-1) compared with soil water balance-calculated ET (ETswb). When summed over weekly intervals, energy balance predictions of 0.25-h crop transpiration inferred from canopy temperature measurements had an acceptable agreement with ETswb (RMSE=0.92 mm d-1). Employing the CWSI to trigger irrigation will require targeted field studies to evaluate thresholds and strategies to optimize water management. Keywords: Canopy temperature, Crop water stress index, Evapotranspiration, Subsurface drip irrigation, Upland Cotton.

Changes in cotton water use efficiency and its mechanism during drought and subsequent rehydration

There is limited information on the changes in cotton water use efficiency and its affecting factors under drought and rehydration. To end this, a greenhouse experiment was conducted with Dexiamian 1 (a drought-tolerant cultivar) and Yuzaomian 9110 (a drought-sensitive cultivar) under three different soil relative water content (SRWC) including well-watered SRWC(75 ± 5)%, mild drought SRWC(60 ± 5)% and moderate drought SRWC(45 ± 5)% during the reproductive stage. The changes of characteristics associated with instantaneous water use efficiency (WUEi) were studied at 10-, 17-, and 24-day of drought treatments and subsequent rehydration. Under 10-day drought, the decreased osmotic potential and increased GhPIP2;3 expression helped maintain root water uptake, while the increased total root length and root surface area also participated in mediating water uptake under 17-day drought. Besides maintaining root water uptake, cotton also closed stomata to reduce transpirational water loss, thus WUEi was increased under 10- and 17-day drought. However, under 24-day drought, the weakened osmotic adjustment, down-regulated GhPIP2;3 expression and suppressed root growth inhibited water uptake, and photosynthesis was more suppressed compared with transpiration, resulting in the decreased WUEi. When rehydrated after 10- and 17-day drought, the compensatory effects of root growth and physiological characteristics enhanced water uptake, and photosynthesis was also promoted, contributing to the WUEi improvement. However, under the rehydration after 24-day drought, root water uptake was irreversibly inhibited, and photosynthesis was still suppressed because of the weak recovery of stomatal conductance, thus WUEi was not restored. In addition, more efficient water transport mediated by increased root vessel numbers improved cotton WUEi, which effect was pronounced during the rehydration period rather than the drought period. In brief, under dynamic drought and subsequent rehydration, the changed water uptake and transport regulated by root morphological and anatomical traits, osmotic adjustment and aquaporin expression, and the varied transpiration efficiency for carbon fixation which was mediated by stomatal conductance, coordinately affected cotton WUEi.

Nitrogen rate for cotton should be adjusted according to water availability in arid regions

Recent reports on cotton water use and root-canopy relationship responses to nitrogen (N) fertilizer management under varying water supply in arid regions are limited. This experiment was conducted to estimate cotton water use, root-canopy development, canopy photosynthetic rate (CAP), and yield responses to N application rates under varying water supply levels and to quantify associations between water use processes and N-induced variation in root systems. A two-year field experiment was conducted from 2019 to 2020 at a field site in Xinjiang, China. Cotton root traits and agronomic responses to three N fertilizer application rates (320, 272, and 224 kg N ha −1 ) under two water supply levels (sufficient water supply: 400 mm; limited water supply: 267 mm) were evaluated. Root length density and root dry matter were maximized at 272 kg N ha −1 under sufficient water supply and 320 kg N ha −1 under limited water supply. CAP was strongly associated with crop stage water use induced by root-canopy variation. Under sufficient water, 272 kg N ha −1 substantially increased water use and root growth, slightly inhibited leaf expansion, and substantially improved crop yield compared to 320 and 224 kg N ha −1 . Although net root productivity and live root length declined for 320 kg N ha −1 under limited water supply, yield increase was not limited because of higher CAP and water use induced by the establishment of strong shallow roots. The results demonstrate that moderate N rate (272 kg ha −1 ) under sufficient water supply improves yield through reducing LAI and promoting root growth, while higher N rate (320 kg ha −1 ) under limited water supply achieves high yield through higher CAP, sufficient leaf area, and efficient water uptake under shallow root systems. These findings suggest that both N management strategies and water availability levels should be considered in future efforts to scale from canopy to root level responses in cotton. • The development of roots and canopy jointly determined the water use capacity in crops. • Improving the water use promoted aboveground CAP, dry matter accumulation, and seed cotton yield. • Two N strategies for high cotton yield were proposed under sufficient water and limited water supply. • Root length dynamics from minirhizotron can reflect the crop stage water use during growing season.

Soil Water Dynamics and Cotton Production Following Cover Crop Use in a Semi-Arid Ecoregion

Conservation management practices such as no-tillage and cover crops can decrease soil’s susceptibility to wind erosion, but adoption of these practices has been limited on the Texas High Plains (THP) where producers are concerned with cover crop water usage. The objective of this study was to evaluate the impact of no-tillage and cover crops on cotton (Gossypium hirsutum L.) lint yield and soil water content in a deficit irrigated cropping system. Soil water was observed bi-weekly in long-term, continuous cotton systems established in 1998 that included (1) conventional tillage, winter fallow, (2) no-tillage with rye (Secale cereale L.) cover, and (3) no-tillage with mixed species cover located in Lamesa, TX, USA. Results include observations from 2018–2020 (years 21–23 of the study period). The adoption of conservation practices did not significantly reduce cotton lint yield compared to conventionally tilled, winter fallow cotton. Soil water was initially depleted with cover crops but was greater throughout the growing season following cover crop termination. Throughout the soil profile, water depletion and recharge were more dynamic with conservation practices compared to the conventionally tilled control. There were no differences in cotton water use efficiency between treatments. Results from this study indicate cover crop water usage is likely not the cause of cotton lint yield decline in this deficit irrigated semi-arid production system.

Simulated effects of plastic film-mulched soil on surface energy fluxes based on optimized TSEB model in a drip-irrigated cotton field

The value-added by plastic film mulches are numerous in agricultural productivity and its global acceptance is unprecedented. However, its disturbing effects on the natural water cycling, surface energy fluxes and partitioning of evapotranspiration (ET) in drip-irrigated fields with plastic film mulch are often overlooked or not investigated due to deficiencies in existing process-based ET models. This study optimized the simulation of plastic film-mulched soil effects on surface energy fluxes by incorporating a thermal contact resistance component into a satellite derived Land Surface Temperature-based Two-Source Energy Balance (i.e.,TSEBPM) model, in a drip-irrigated cotton field for two consecutive growing seasons (2009 and 2010). The optimized model agrees better with Eddy Covariance (EC) flux tower observation and showed reduced error biases than the original TSEB model. The RMSE values decreased for the net radiation, latent, sensible and ground heat fluxes by 10.85, 1.93, 4.84, 0. 81 (Wm−2), respectively. Moreover, ET partitioning by TSEBPM revealed the actual contribution of evaporation (E) and transpiration (T) in cotton water use at different growth stages. When cotton growth reaches the ball-opening stage (i.e., harvesting period or cotton canopy coverage > 75%), the mean E/ET value was 0.20 ± 0.05, while T/ET was 0.79 ± 0.05 during the irrigation seasons. Meanwhile, the plastic mulching altered the reflected shortwave radiation, thereby impacting on surface albedo reflectance under well saturated cotton canopy. As such, the transpiration sub-model parameters such as fractionalvegetationcover and vegetationgreenfraction had influential effects, and are the most sensitive in the TSEBPM model parameterization. This study showed that TSEBPM can provide robust insights into the effects of plastic mulching on surface energy fluxes and cotton ET, therefore can be explored further across arid agroecosystems.

Determining water use and crop coefficients of drip-irrigated cotton in south Xinjiang of China under various irrigation amounts

Crop evapotranspiration (ETc) and crop coefficient (Kc) can vary among various geographical locations and cultivated species. Therefore, determining regional- and species-specific crop coefficients is fundamental for rational irrigation water management. A two-year field study was conducted in south Xinjiang of northwest China to estimate periodic ETc and reference evapotranspiration (ET0), and thus develop the regional crop coefficient (Kc) at various growth stages of fertigated cotton (Gossypium hirstum L. Xinluzhong No 67) under various irrigation amounts. ETc was determined by the soil water balance method, while ET0 was obtained using the FAO (Food and Agriculture Organization of the United Nations) Penman-Monteith model. The results indicated that increasing irrigation amounts resulted in increased seed cotton yields, but reduced crop water productivity (WP). The water consumption at flowering and boll setting stages accounted approximately for 60% of the seasonal water use of cotton under various irrigation amounts. The average locally developed Kc (Kc-local) values over two seasons were 0.38, 1.30 and 1.09 for initial, mid-season, and end-season stages, respectively. The locally developed initial Kc (Kc-local-ini) (0.38) was higher than the optimized initial-stage Kc (Kc-opt-ini) (0.23) and similar to the FAO recommended Kc (Kc-FAO) (0.35). The optimized Kc (Kc-opt) did not significantly differ from Kc-FAO at mid-season and end-season stages. The locally developed middle-stage Kc (Kc-local-mid) was 10% higher than the optimized middle-stage Kc (Kc-opt-mid) and the FAO recommended middle-stage Kc (Kc-FAO-mid), and the locally developed end-stage Kc (Kc-local-end) was approximately 82% higher than the optimized end-stage Kc (Kc-opt-end) and the FAO recommended end-stage Kc (Kc-FAO-end). The difference between Kc-local, Kc-opt and Kc-FAO was attributed to the variations of climate condition, cultivated variety and field management. Kc-local determined by the soil water balance method in the present study fully considered the regional conditions including weather, species and management practices, which can be adopted to guide the irrigation management in this region. This study provided credible cotton periodic Kc in the arid and semiarid regions of northwest China. A second-order polynomial relationship between cotton Kc and t/T (the days after emergence/the days of total cotton growth period) was established, which can provide a reference for the determination of local cotton Kc and irrigation management.

Irrigation-Water Management and Productivity of Cotton: A Review

A decrease in water resources, as well as changing environmental conditions, calls for efficient irrigation-water management in cotton-production systems. Cotton (Gossypium sp.) is an important cash crop in many countries, and it is used more than any other fiber in the world. With water shortages occurring more frequently nowadays, researchers have developed many approaches for irrigation-water management to optimize yield and water-use efficiency. This review covers different irrigation methods and their effects on cotton yield. The review first considers the cotton crop coefficient (Kc) and shows that the FAO-56 values are not appropriate for all regions, hence local Kc values need to be determined. Second, cotton water use and evapotranspiration are reviewed. Cotton is sensitive to limited water, especially during the flowering stage, and irrigation scheduling should match the crop evapotranspiration. Water use depends upon location, climatic conditions, and irrigation methods and regimes. Third, cotton water-use efficiency is reviewed, and it varies widely depending upon location, irrigation method, and cotton variety. Fourth, the effect of different irrigation methods on cotton yield and yield components is reviewed. Although yields and physiological measurements, such as photosynthetic rate, usually decrease with water stress for most crops, cotton has proven to be drought resistant and deficit irrigation can serve as an effective management practice. Fifth, the effect of plant density on cotton yield and yield components is reviewed. Yield is decreased at high and low plant populations, and an optimum population must be determined for each location. Finally, the timing of irrigation termination (IT) is reviewed. Early IT can conserve water but may not result in maximum yields, while late IT can induce yield losses due to increased damage from pests. Extra water applied with late IT may adversely affect the yield and its quality and eventually compromise the profitability of the cotton production system. The optimum time for IT needs to be determined for each geographic location. The review compiles water-management studies dealing with cotton production in different parts of the world, and it provides information for sustainable cotton production.

Net positive soil water content following cover crops with no tillage in irrigated semi-arid cotton production

Conservation management practices such as no-tillage and cover cropping can reduce soil erosion, enhance soil biological activity, increase water capture and storage, and sequester C. Cover crops, however, utilize stored soil water during the winter months, and the water depletion is thought to have negative impacts on the subsequent cotton (Gossypium hirsutum L.) crop in semi-arid ecoregions where water resources are limited. The objective of this research was to quantify the long-term impacts of conservation tillage and cover crop use on volumetric water content of soil in an irrigated cotton production system. Soil water was measured in a long-term (established 1998) conservation system in Lamesa, TX and water dynamics during the 2015–2017 growing seasons are presented here. Volumetric water content was reduced by cover crops prior to their termination but was replenished by spring precipitation and deficit irrigation prior to planting cotton. A stepwise regression analysis was used to determine changes in soil water at depth. In each of the study years, soil water increased more with no-tillage following cover crop termination and decreased less during cotton growth than the conventionally tilled system. Cotton water use efficiency was not significantly different between treatments in any year. Results from this study challenge the concept that winter cover crops result in reduced in-season soil water in irrigated systems, a supposition that has limited adoption of conservation tillage and cover crop use on the Texas High Plains.

Temporal and Spatial Changes in Crop Water Use Efficiency in Central Asia from 1960 to 2016

Water resources among five Central Asian countries are distributed unevenly. Since the collapse of the Soviet Union, the conflict between water and land use has become increasingly serious. Due to limited data, the temporal and spatial characteristics and trends of crop water use efficiency in Central Asia over the past 60 years remain unclear. This paper combines state-level agricultural statistics data and cultivated land data (1975, 2005 and 2015) from remote sensing imagery and calculates crop water use efficiency based on the FAO crop coefficient method. The results are as follows: (1) the development of crop cultivation in Central Asia is divided into an expansion period (1960–1990), a reduction period (1990–2000), and a recovery period (2000–2016); (2) the grain yield in Central Asia increased from 0.9 to 1.9 t/ha during 1960–2016, with Uzbekistan having the highest, reaching 4.2 t/ha in 2016. Cotton yield increased during 1960–1990 and decreased from 1990 to 2016. (3) The grain water use efficiency in Central Asia increased from 0.22 kg/m3 to 0.39 kg/m3 during 1960–2016. The cotton water use efficiency increased from 0.23 kg/m3 to 0.30 kg/m3 during 1960–1990, has decreased since 1990, and is currently close to the 1960s level.

Water–Nitrogen Coupling and Multi-Objective Optimization of Cotton under Mulched Drip Irrigation in Arid Northwest China

Cotton is the most important cash crop in Xinjiang but low utilization rate of water and fertilizer is restricting healthy development of this industry. At present, there is a lack of water and nitrogen management optimization methods based on multi-objectives of cotton water use efficiency (WUE), nitrogen use efficiency (NUE), yield, and income. A continuous field experiment was conducted during 2017–2018 to study the effects of water–nitrogen coupling on cotton growth, WUE, NUE, nitrogen partial factor productivity, yield, quality, and economic benefits under drip irrigation in northern Xinjiang. Using multiple regression and spatial analyses, the water and nitrogen management strategy for multi-objective optimization was determined. Three irrigation levels were used—low (I1), medium (I2), and full (I3)—Representing 75%, 87.5%, and 100% of cotton water demand, respectively. The three nitrogen application levels were low (N1, 210 kg/ha), medium (N2, 280 kg/ha), and high (N3, 350 kg/ha), representing 75%, 100%, and 125% of the local nitrogen application, respectively. Among all treatments, the leaf area index, boll weight, dry matter quantity and yield reached respective maxima of 4.43 m2/m2, 4.73 g, 16,623 kg/ha, and 6333 kg/ha for the I3N2 treatment. Cotton fiber quality was the best for I3 irrigation, but too little or too much nitrogen reduced fiber quality. The economic benefit under I3 irrigation was 1.93–4.81 times that for I1. For a single optimization objective, WUE reached a maximum of 1.78 kg/ha·mm for irrigation of 415.80 mm and nitrogen application of 295.71 kg/ha; corresponding single maxima follow: NUE of 37.65% for 418.27 mm and 278.57 kg/ha; yield of 6416.42 kg/ha for 470.12 mm and 304.29 kg/ha; and economic benefit of 15,338.55 RMB/ha for 470.12 mm and 307.14 kg/ha. Multiple regression and spatial analysis showed that for irrigation of 430.71–440.12 mm and nitrogen application of 270.95–318.45 kg/ha, the WUE, NUE, yield, and economic benefits of cotton simultaneously exceeded 90% of their maxima, which was an efficient and reasonable water and nitrogen management mode in this location. The results provide a scientific basis for effective integrated management of water and fertilizer in drip irrigation cotton fields in northern Xinjiang.

Determination of crop water use and coefficient in drip-irrigated cotton fields in arid regions

A 3-year field experiment was conducted in Aksu region in Northwest China to determine crop water use, suitable irrigation mode and actual crop coefficient (Kc) in drip-irrigated cotton fields. In the experiment, 12 non-weighing large lysimeters were used to measure cotton water use under various irrigation modes. Then a micro-lysimeter was placed in each large lysimeter to monitor soil evaporation (E). Adjustments were done for a number of factors (including irrigation, meteorology, plastic mulching, water stress and salinity stress) in order to compare FAO-adjusted Kc (Kc-FAO) with the local actual Kc (Kc-loc). The results showed that: 1) plastic mulching with 0.6 cover ratio and 37.5 mm drip irrigation quota gave a crop water requirement of 536.4 mm; which was suitable for the study area. Also Kc-loc were respectively 0.28, 0.97 and 0.31 for early, middle and late growth stages. 2) Kc-FAO generally reflected the trend in Kc-loc for the entire growing season. The suggested 0.1 adjusted coefficient under plastic mulching for the initial growth stage was relatively low, and was most rational for the study area when increased to 0.25. 3) E/ET ratio was low (19.1–24.5%) under mulching treatment and relatively high (27.7–32.7%) under non-mulching treatment. 4) While change in E/ETo ratio was linear or logarithmic, that in T/ETo ratio was a power function of the canopy cover. Also the two rates responded to the interaction effects of canopy cover and soil water content. The results could lay the basis for developing scientific, data-driven water-saving strategies in the study area and elsewhere.

Irrigation Timing and Rate Affect Cotton Boll Distribution and Fiber Quality

Core Ideas Timing of water deficit stress affects boll production.Stress timing influences fiber quality.Multiple timings of water deficit stress interact. Decreased aquifer water in the Texas High Plains has increased the risks associated with irrigation, including lower irrigation volume and the need to balance seasonal water demands among crops, requiring management of both irrigation rate and timing. Boll distribution measurements in cotton (Gossypium hirsutum L.) can be used to quantify the effects of irrigation on productivity and were used in a study of irrigation rate × timing from 2011 to 2013 in Halfway, TX. Field experiments quantified cotton boll distribution using three in‐season irrigation levels (maximums of 0, 3.2, and 6.4 mm d−1) during three different irrigation periods determined by accumulated growing degree days (GDD) based on the threshold of 15.6°C: period 1 (P1, &lt;525 GDD), period 2 (P2, 525–750 GDD), and period 3 (P3, &gt;750 GDD). Combinations of these factors resulted in 27 irrigation treatments, applied with a low energy precision application (LEPA) pivot. Heavy irrigation early in the growing season used more water, did not increase boll number, and was often detrimental to yield. Mid‐ and late‐season irrigation improved yield and fiber quality, with P2 irrigation influencing yield in the middle of the plant and P3 irrigation controlling yield at the top of the plant. Moderate irrigation later in the season minimized effects of short‐term water deficit observed in other similar studies. These results provide insight into optimizing cotton water use in a region with declining crop water availability, increased pumping restrictions, and a challenging climate.

Determination of evapotranspiration for cotton in Alabama by the Penman method

Cotton irrigation is increasingly becoming a challenge because of climate change effects such as the variations in rainfall, temperature, and cloudiness during the growing season. Cotton crop characteristics, as well as the prevailing environmental conditions, are critical in determining cotton water use. An efficient method of scheduling irrigation to cotton crop is imperative for optimising time and amount of water to apply for achieving cotton yield potential. In this article, a reliable approach to determine crop water requirement for cotton cultivation is proposed using the Penman method for Gadsden, Alabama, located in the southern part of the USA.

Determination of evapotranspiration for cotton in Alabama by the Penman method

Cotton irrigation is increasingly becoming a challenge because of climate change effects such as the variations in rainfall, temperature, and cloudiness during the growing season. Cotton crop characteristics, as well as the prevailing environmental conditions, are critical in determining cotton water use. An efficient method of scheduling irrigation to cotton crop is imperative for optimising time and amount of water to apply for achieving cotton yield potential. In this article, a reliable approach to determine crop water requirement for cotton cultivation is proposed using the Penman method for Gadsden, Alabama, located in the southern part of the USA.

Modeling the effects of land use change from cotton (Gossypium hirsutum L.) to perennial bioenergy grasses on watershed hydrology and water quality under changing climate

Assessing the impacts of biofuel-induced land use change on hydrology, water quality and crop yield under the current and future climate scenarios enables selection of appropriate land uses and associated best management practices under the changing climate. In this study, the impacts of land use change from cotton (Gossypium hirsutum L.) to perennial grasses in the Double Mountain Fork Brazos watershed in the Texas High Plains were assessed using the Soil and Water Assessment Tool (SWAT). While switchgrass (Panicum virgatum L.) was assumed to replace cotton in irrigated areas, dryland cotton was replaced by Miscanthus×giganteus under the hypothetical land use change scenarios. Climate change impacts were assessed based on the Coupled Model Intercomparison Project Phase 5 (CMIP5) climate projections of 19 General Circulation Models (GCMs) under two Representative Concentration Pathway (RCP) emission scenarios of RCP4.5 and RCP8.5 during two 30-year periods of middle (2040–2069) and end (2070–2099) of the 21st century. Median irrigation water use of cotton was simulated to decrease by 41%–61% in the future when compared to historic (1994–2009) period based on projections by 19 GCMs. Under the future climate change scenarios, when compared to cotton, median annual irrigation water use by switchgrass reduced by 62%–89%. Simulated future median total nitrogen load decreased by 30%–40% under perennial grasses when compared to future cotton land use. The median irrigated switchgrass yield decreased by 16%–28%, but the median dryland Miscanthus yield increased by 32%–38% under the future climate change scenarios.

Cotton Irrigation Scheduling Using a Crop Growth Model and FAO-56 Methods: Field and Simulation Studies

Abstract. Crop growth simulation models can address a variety of agricultural problems, but their use to directly assist in-season irrigation management decisions is less common. Confidence in model reliability can be increased if models are shown to provide improved in-season management recommendations, which are explicitly tested in the field. The objective of this study was to compare the CSM-CROPGRO-Cotton model (with recently updated ET routines) to a well-tested FAO-56 irrigation scheduling spreadsheet by (1) using both tools to schedule cotton irrigation during 2014 and 2015 in central Arizona and (2) conducting a post-hoc simulation study to further compare outputs from these tools. Two replications of each irrigation scheduling treatment and a water-stressed treatment were established on a 2.6 ha field. Irrigation schedules were developed on a weekly basis and administered via an overhead lateral-move sprinkler irrigation system. Neutron moisture meters were used weekly to estimate soil moisture status and crop water use, and destructive plant samples were routinely collected to estimate cotton leaf area index (LAI) and canopy weight. Cotton yield was estimated using two mechanical cotton pickers with differing capabilities: (1) a two-row picker that facilitated manual collection of yield samples from 32 m2 areas and (2) a four-row picker equipped with a sensor-based cotton yield monitoring system. In addition to statistical testing of field data via mixed models, the data were used for post-hoc reparameterization and fine-tuning of the irrigation scheduling tools. Post-hoc simulations were conducted to compare measured and simulated evapotranspiration, crop coefficients, root zone soil moisture depletion, cotton growth metrics, and yield for each irrigation treatment. While total seasonal irrigation amounts were similar among the two scheduling tools, the crop model recommended more water during anthesis and less during the early season, which led to higher cotton fiber yield in both seasons (p &amp;lt; 0.05). The tools calculated cumulative evapotranspiration similarly, with root mean squared errors (RMSEs) less than 13%; however, FAO-56 crop coefficient (Kc) plots demonstrated subtle differences in daily evapotranspiration calculations. Root zone soil moisture depletion was better calculated by CSM-CROPGRO-Cotton, perhaps due to its more complex soil profile simulation; however, RMSEs for depletion always exceeded 20% for both tools and reached 149% for the FAO-56 spreadsheet in 2014. CSM-CROPGRO-Cotton simulated cotton LAI, canopy weight, canopy height, and yield with RMSEs less than 21%, while the FAO-56 spreadsheet had no capability for such outputs. Through field verification and thorough post-hoc data analysis, the results demonstrated that the CSM-CROPGRO-Cotton model with updated FAO-56 ET routines could match or exceed the accuracy and capability of an FAO-56 spreadsheet tool for cotton water use calculations and irrigation scheduling. Keywords: Cottonseed, Crop coefficient, Decision support, Depletion, Evapotranspiration, Fiber, Management, Simulation, Soil moisture, Yield.

Cotton Water Productivity and Growth Parameters in the Humid Southeast: Experimentation and Modeling

Abstract. A global challenge for the coming decades will be increasing food and fiber production with less water. This can be partially achieved by increasing water productivity (WP) or crop water use efficiency (WUE), i.e., yield or biomass produced per unit water used. Cotton ( L.) is a major rainfed and irrigated crop in the U.S. and worldwide. While there is abundant information on cotton water use and yield relationships in drier regions, relevant field data and modeling in humid regions is not well developed. Robust crop models help complement field experimentation and predict the impact of irrigation management on production. The Food and Agriculture Organization (FAO) of the United Nations has developed a crop model (AquaCrop) that has been parameterized for a number of crops including cotton, but not in a humid region. The objective of this study was twofold: (1) to quantify cotton water use and in-season biomass and growth parameters, and (2) to parameterize and validate AquaCrop to simulate cotton water use and productivity in the humid Southeast U.S., where water conservation and sustainability are emerging issues. Irrigation experiments were conducted from 2009 to 2011 under field conditions as well as under a newly installed automated rainout shelter at a Clemson University research site near Blackville, South Carolina. Extensive season-long soil, crop, and climate data were collected under irrigation regimes ranging from rainfed (i.e., no irrigation) to fully irrigated (i.e., meeting 100% of crop water needs). Season-long data collected in 2009 and 2011 under different irrigation regimes were used to parameterize the model. Cotton seasonal water use ranged from 320 mm at 33% irrigation to 718 mm at full irrigation, corresponding to average seed cotton yields of 2134 to 3682 kg ha -1 . Water use efficiency in the three years ranged from 0.48 to 0.71 kg of seed cotton per m 3 of water applied (irrigation and rainfall). Normalized water productivity for the local climate was nearly the same during the three years, averaging 12.5 g m -2 . Model parameterization was less demanding than expected, requiring adjustments of a few model parameters. Using the parameterized model with independent field data from 2010, the model simulated canopy cover, soil water content, aboveground dry biomass, and yield values that were highly correlated with measured values, with coefficients of determination (R 2 ) greater than 0.66. Seasonal crop water use was predicted within 5% for most treatments but underpredicted by as much as 18% for the 100% treatment at the shelter and for all irrigation treatments in 2010. The underprediction of crop water use corresponded to values of deep percolation simulated by AquaCrop. Field measurements were inadequate to verify deep percolation, but such measurements are suggested for future model investigations. Results of this study suggest that a properly parameterized AquaCrop model provides a useful tool to study yield response to water stress and evaluate the effects of drought and alternate management practices on productivity.

Simulating future climate change impacts on seed cotton yield in the Texas High Plains using the CSM-CROPGRO-Cotton model

The Texas High Plains (THP) region contributes to about 25% of the US cotton production. Dwindling groundwater resources in the underlying Ogallala aquifer, future climate variability and frequent occurrences of droughts are major concerns for cotton production in this region. Assessing the impacts of climate change on cotton production enables development and evaluation of irrigation strategies for efficient utilization of groundwater resources in this region. In this study, the CROPGRO-Cotton module within the Cropping System Model (CSM) that is distributed with the Decision Support System for Agrotechnology Transfer (DSSAT) was evaluated for the THP region using measured data from cotton water use efficiency experiments at Halfway over a period of four years (2010–2013). Simulated seed cotton yield matched closely with observed yield during model calibration (average percent error of 0.1) and validation (average percent error of 6.5). The evaluated model was able to accurately simulate seed cotton yield under various irrigation strategies over the four growing seasons. The evaluated CROPGRO-Cotton model was later used to simulate the seed cotton yield under historic (1971–2000) and future (2041–2070) climate scenarios projected by three climate models. On an average, when compared to historic seed cotton yield, simulated future seed cotton yield across the THP decreased within a range of 4–17% when carbon dioxide (CO2) concentration was assumed to be constant at the current level (380ppm) under three climatic model scenarios. In contrast, when the CO2 concentration was assumed to increase from 493ppm (in year 2041) to 635ppm (in year 2070) according to the Intergovernmental Panel on Climate Change (IPCC) A2 emission scenario, the simulated future average seed cotton yield in the THP region increased within a range of 14–29% as compared to historic average yield. When the irrigation amount was reduced by 40% (from 100% to 60%), the average (2041–2070) seed cotton yield decreased by 37% and 39% under the constant and increasing CO2 concentration scenarios, respectively. These results imply that cotton is sensitive to atmospheric CO2 concentrations, and cotton production in the THP could potentially withstand the effects of future climate variability under moderate increases in CO2 levels if irrigation water availability remains at current levels.

Cotton Water Use Efficiency under Two Different Deficit Irrigation Scheduling Methods

Declines in Ogallala aquifer levels used for irrigation has prompted research to identify methods for optimizing water use efficiency (WUE) of cotton (Gossypium hirsutum L). In this experiment, conducted at Lubbock, TX, USA in 2014, our objective was to test two canopy temperature based stress indices, each at two different irrigation trigger set points: the Stress Time (ST) method with irrigation triggers set at 5.5 (ST_5.5) and 8.5 h (ST_8.5) and the Crop Water Stress Index (CWSI) method with irrigation triggers set at 0.3 (CWSI_0.3) and 0.6 (CWSI_0.6). When these irrigation triggers were exceeded on a given day, the crop was deficit irrigated with 5 mm of water via subsurface drip tape. Also included in the experimental design were a well-watered (WW) control irrigated at 110% of potential evapotranspiration and a dry land (DL) treatment that relied on rainfall only. Seasonal crop water use ranged from 353 to 625 mm across these six treatments. As expected, cotton lint yield increased with increasing crop water use but lint yield WUE displayed asignificant (p ≤ 0.05) peak near 3.6 to 3.7 kg ha−1 mm−1 for the ST_5.5 and CWSI_0.3 treatments, respectively. Our results suggest that WUE may be optimized in cotton with less water than that needed for maximum lint yield.