Evapotranspiration Requirements Research Articles

Bio-economic analysis of irrigation schedules considering shallow groundwater: lessons from South Africa

Due to the pressure on South Africa’s irrigated agriculture to improve efficiency and optimal water use, irrigators must consider alternative water sources, such as root-accessible shallow groundwater tables, to supply the crop evapotranspiration requirement. Devising irrigation scheduling strategies that will optimize conjunctive water use is difficult because the contribution of shallow groundwater tables is not directly observed and is a function of irrigation management decisions; as a result, very few irrigators use these strategies. This paper aims to evaluate the profitability of using shallow groundwater tables as a source of irrigation water to satisfy crop evapotranspiration requirements. A bio-economic simulation model consisting of the soil–water–atmosphere–plant model and an economic accounting module was developed to calculate the profitability of conjunctive irrigation practices under different states of nature. The bio-economic simulation model was linked to a differential evolutionary algorithm to optimize the irrigation scheduling decisions. The results showed that irrigators could substantially increase profitability and water use efficiency if they consider the shallow groundwater table in their irrigation decision. About 51% of crop evapotranspiration could originate from shallow groundwater tables, reducing the irrigation requirements substantially without impacting crop yields. Sequential adaptive irrigation decision-making does not improve the bio-economic indicators much since using the shallow groundwater table mitigates the risk of undersupplying water. Therefore, conjunctive water use strategies using shallow groundwater tables economically benefit irrigators. However, a complex interplay exists between irrigation adjustments, crop yields and economic performance in different states, emphasizing the careful consideration of context-specific factors in irrigation management decisions.

Internet of things-based rice field irrigation evaporation monitoring system

The urgency for efficient irrigation in Indonesia’s agriculture sector, particularly in paddy fields, is evident. However, existing methods for monitoring water levels are antiquated, often requiring manual measurements with a ruler. This research introduces a comprehensive “monitoring system for light intensity and water temperature as an analysis of evaporation for rice irrigation based on the internet of things”. The system integrates various sensors an anemometer for wind speed, an ultrasonic sensor for water level, a DS18B20 waterproof sensor for water temperature, and a GY-8511 sensor for sunlight intensity. All data are collected by an Arduino Mega controller, connected to an ESP32 for transmitting the readings to the Blynk app and an I2C 20×4 liquid crystal display (LCD) screen. The control mechanism employs a closed-loop system with a direct current (DC) motor actuator to operate the water gate, which can also be manually controlled via a cellphone. The system effectively meets daily evapotranspiration requirements of 1.44 mm, with optimal conditions yielding water levels of 3 cm, water temperatures of 38.53 °C, sunlight intensity of 4.59 mW/cm², and wind speed of 0.21 m/s.

Effect of foliar fungicide application timing on corn yield across different water regimes

ABSTRACT Corn (Zea mays L.) is a major irrigated crop in the Texas High Plains (THP). Inadequate precipitation, declining groundwater resources, and inevitable seasonal drought in the area have led to a greater number of studies on crop hybrids, water regimes, and other yield-enhancing techniques. A four-year field study was conducted to investigate the effect of foliar fungicide timing on corn grain yield, grain moisture, and grain test weight under different irrigation regimes. A fungicide containing QoI + DMI was applied to four to six corn hybrids each year at various growth stages (V5, R1, and V5 + R1). For all years, corn plants were grown under three irrigation regimes to meet the seasonal evapotranspiration (ET) requirements of 50% (I50), 75% (I75), and 100% (I100). Hybrid response to the timing of fungicide application and irrigation regime was not consistent over the years. However, in 2 of the 4 years, timing of fungicide application resulted in yield differences among the hybrids, especially at I75 and L100. For those years, the fungicide applied at R1 resulted in a higher grain yield, grain moisture, and grain test weight followed by the fungicide applied at V5 + R1. Results showed that hybrids reacted differently to the foliar fungicide based on the availability of water under disease-free conditions. This study further revealed that irrigation water could be reduced from I100 to I75 with a limited (5.6% in 2011, 11.3% in 2012, 1.3% in 2013, and 0.3% in 2014) yield penalty in the THP region.

Gas exchange and yield of yellow passion fruit under different irrigated depths, planting hole volumes, and hydroretentive polymer application

Passion fruit cultivation relies on irrigation to increase yields in the semiarid of northeastern Brazil. Water scarcity is one of the factors that most affect crop physiology, leading to lower yields. Therefore, this study aimed to assess the influence of planting hole volume and application of a hydroretentive polymer on physiological and productive aspects of irrigated yellow passion fruit cv. BRS GA1 in the Northeast semi-arid region of Brazil. The experiment was conducted in randomized blocks, in a split-plot design 2 × (2 × 2). Treatments consisted of irrigation depths (100% and 70% of the crop's evapotranspiration requirement - ETc), planting hole volumes (64 dm3 and 128 dm3), and soil with and without application of hydroretentive Polymer (1.5 g dm3), with four replicates and three plants per plot. The analyzed variables included chlorophyll a and b indices, gas exchange, and yellow passion fruit yield. The findings showed that hydroretentive polymer application to the soil increases chlorophyll content and gas exchange in yellow passion fruit. Moreover, photosynthetic rates were not limited by a 30% reduction in irrigation depth and increased in plants grown in 128-dm3 planting holes with hydroretentive polymer. Based on yield results, irrigation depths can be reduced to 70% of the ETc by applying hydroretentive polymer in 64-dm3 planting holes.

Calibration and validation of solar radiation-based equations to estimate crop evapotranspiration in a semi-arid climate

The Abtew and Jensen-Haise solar radiation-based equations were used to estimate evapotranspiration, considering the limited climatic data in many locations. Both equations were proven to successfully predict the potential evapotranspiration (ETO) compared with the standard Penman–Monteith (PM) method in two Mediterranean countries. Calibration of the constant coefficient k of the Abtew equation showed substantial differences compared to recommended values (1.22 vs. 0.53), with the highest values observed during September (1.46). Validation of ETO measurements using calibrated Abtew equation against the PM method indicated a high correlation coefficient (r2 = 0.97, RMSE = 0.61). Further, evapotranspiration requirements, using the calibrated empirical equation, were calculated for olives (449 mm) and citrus (807 mm) showing a good agreement with recommended values for dry climate regions. Therefore, the tested equations could be safely used to predict frequencies and doses of irrigation in semi-arid climates, considering limited climatic data availability.

Effects of different photovoltaic shading levels on kiwifruit growth, yield and water productivity under “agrivoltaic” system in Southwest China

Agrivoltaic systems (AVS) are emerging mixed production systems where crops are cultivated below the photovoltaic (PV) panels. This study investigated the effects of different PV shading levels on kiwifruit growth, yield and water productivity (WPc), with three densities of 19.0% (T1), 30.4% (T2) and 38.0% (T3) of translucent PV panels installed on the South-oriented AVS roof. The AVS perimeter was left open with the full sun treatment outside the AVS as the control treatment (CKL). Results showed that the solar radiation in T1, T2 and T3 was reduced by 43.8 ± 0.6%, 50.5 ± 0.6% and 55.0 ± 0.5%, respectively, compared with CKL, whereas the air temperature was uniform and the relative humidity increased with increased PV shading. The leaf area index and leaf light use efficiency improved, while the leaf transpiration rate, photosynthetic rate and water use efficiency decreased with increased shading. The accumulated transpiration (T) was higher in CKL (419.9 ± 9.9 mm) than shading treatments (380.8 ± 26.7, 319.2 ± 15.1 and 308.8 ± 12.9 mm in T1, T2 and T3, respectively), and shading also reduced soil evaporation (E) (63.4 ± 1.0, 51.9 ± 3.1 and 47.4 ± 3.8 mm in T1, T2 and T3, respectively, compared to 79.4 ± 1.1 mm in CKL) and thus decreased the total evapotranspiration (ETc act=E + T) requirement. The kiwifruit volume and yield were slightly reduced (−7.3 to 5.5% and −6.5 to −2.6%) in T1 relative to CKL (101.4–106.8 cm3 and 17.6–18.9 t/ha), while the negative effects of shading on the volume and yield were significant (p < 0.05) in T2 and T3. The water productivity (WPc) was improved in T1 (8.2 ± 5.7%) and T2 (5.8 ± 1.9%) relative to CKL, however, it was significantly reduced in T3 (−9.8 ± 1.4%). It was concluded that 19% (T1) PV coverage was a suitable shading treatment management in the AVS, as kiwifruit growth and yield were less affected, and WPc was increased with reduced water consumption. The total potential profit can be largely promoted from electricity production, especially for dry rainfed and no electricity remote areas, where they can benefit from using produced electricity locally for irrigation.

Salt and irrigation management of soil-grown Mediterranean greenhouse tomato crops drip-irrigated with moderately saline water

Five integrated experiments, irrigated with water of moderate salinity (about 1.6 dS m−1), were conducted in an Spanish Mediterranean greenhouse to provide a better insight into soil salt accumulation processes in tomato crops and how to leach away these salts by irrigation both during and outside the cropping period. Salts (mostly chloride and sodium coming from the irrigation water) accumulated in the soil wet bulb leading to soil solution electrical conductivities (ECSS) of about 6 dS m−1 or higher during the second half of the crop cycles. During the first phases of these tomato crops it appears to be advisable to apply the crop evapotranspiration (ETc) requirements or slightly higher rates (1.1 ETc). Subsequently, before salts accumulated reach hazardous levels, it is necessary to over-irrigate with a leaching fraction to avoid further salinity increments. Moreover, crop water requirements must be applied with a single daily irrigation, rather than several shorter ones. After the cropping period, the application of 60–70 mm of irrigation water leached away most of the accumulated salts and led to ECSS slightly below 3 dS m−1, considered appropriate for planting a new crop. This amount of water, which has to be adapted to the soil salinity content and characteristics, supplied with daily irrigation rates of about 3–10 mm d−1, led to lower ECSS values, compared with higher irrigation rates. Moreover, the application of crop water requirements with water (11–33% of the irrigation rate) and nutrient solution, instead of nutrient solution over the whole event, substantially reduced the total fertiliser supplied and the concentration of the main nutrients in the wet bulb, but did not negatively affect the biomass, productivity or fruit quality of tomato crop. However, this fertigation strategy requires low-cost, fast monitoring systems of water and nutrients in the soil and/or the plant

Irrigation water requirement of rice in Long Xuyen Quadrangle area, Vietnam in the context of climate change

Climate variability is deeply affecting all aspects of human life including agricultural sector. In the present study the CROPWAT model was used to estimate reference evapotranspiration (ETo), crop evapotranspiration (ETc), effective rainfall (ER) and crop water requirement (CWR) of summer-autumn rice crop and its yield during baseline period (2002-2017) and also under representative concentration pathways (RCPs) 4.5 scenario for 2020s, 2055s and 2090s-time scales for Long Xuyen Quadrangle (LXQ) area of Vietnam. It was found that the ER significantly increased by 6.2, 16.9 and 15.4 per cent, respectively in 2020, 2055 and 2090; ETo and ETc increased by 2.1 and 2.3 per cent, respectively in 2020s; 4.4 and 5.8 in 2055; and 5.8 and 7.7 per cent in 2090 compared to baseline. The CWR also increased approximately 4.6, 4.4 and 3.5 per cent, respectively in 2020, 2055 and 2090 and consequent decrease in rice yield by 6.5, 7.9 and 10.4 per cent, respectively. Results showed that if the crop planting date is delayed by 20 days, the rice yield would increase approximately 4.9, 7.9 and 9.9 per cent, respectively in three-time scales of RCP 4.5 scenario, compared to base line period.

Crop water and irrigation requirements of some selected crops in southwestern hydrological zone of Nigeria

This study was carried out to determine the crop water and irrigation requirement of some selected crops in southwestern Nigeria. The crops are cucumber, water melon, maize, groundnut, eggplant and tomato. Irrigation requirement and crop coefficient for each crops were determined from the interrelationships of the evapotranspiration, soil type, bulk density, field capacity and the effective root zone of the crops at the selected locations using CROPWAT for windows version 8. Soil parameters used for analysis were determined from laboratory experiment. The crop evapotranspiration and water requirement for cucumber varied from 2.52 to 7.21mm/day and 17 to 73.2mm/dec, respectively, for maize from 1.36 to 6.35mm/day and 5.1 to 63.5mm/dec respectively, for watermelon varied from 2.59 to 6.67mm/day and 25.9 to 73.3mm/dec respectively, for eggplant varied from 1.92 to 6.35 mm/day and 15.9 to 64.4mm/dec respectively. The irrigation requirement for water melon and cucumber recorded the highest value of 461.6 and 497.4mm/dec respectively, an indication that the two crops require more water for physiological activities. The reduction in the values of crop coefficient was observed during the study which could be attributed to the reduction in evapotranspiration at the late stage of growth. The findings also showed that known quantities of irrigation water could be used in producing crops optimally.

Estimation of Evapotranspiration and Water Requirements of Strawberry Plants in Greenhouses Using Environmental Data

Farmers routinely determine irrigation requirements from visual observations and cultivation experience, but this can lead to under- or over-irrigation. To establish precise irrigation technology for strawberry cultivation, the average daily evapotranspiration and water requirements were estimated according to the environmental data: air temperature and humidity from the center of the greenhouses and solar radiation from outside greenhouses. Makkink FAO24 equations (temperature and cloudiness) were used to estimate the evapotranspiration and water requirements. The temperature equation showed higher correlation coefficients in solar radiation (R2 = 0.60), evapotranspiration (R2 = 0.76), and water requirements (R2 = 0.69) than other tested equations. The daily irrigation, calculated from the estimated evapotranspiration, was 3.8 tons/10a. It is possible to develop a precision irrigation system from estimated evapotranspiration during the winter cultivation of “Seolhyang” strawberries in South Korea.

Detection of cyanotoxins in irrigation water and potential impact on putting green health

AbstractCreeping bentgrass putting greens require frequent irrigation during summer months to meet evapotranspiration requirements. Golf courses that utilize local water bodies for irrigation may potentially spread phytopathogenic waterborne microbes, or toxins they produce, to putting greens. Cyanobacteria associated with yellow spot and black layer have been detected in water bodies and are known to produce cyanotoxins that may hinder plant growth at high concentrations. Water samples were collected from irrigation heads, irrigation intakes, and the epilimnion of exposed water sources. Anatoxin, cylindrospermopsin, microcystin, and saxitoxin concentrations were analyzed using ELISA kits. Microcystin and saxitoxin were detected in irrigation systems that utilize surface water sources. Anatoxin was detected in every irrigation system, regardless of water source. Cylindrospermopsin was only detected in one system that utilized a local water body as a water source. Only two samples from one site contained cyanotoxin (microcystin) concentrations that exceeded the recommended threshold for recreational water use.

Comparative evaluation of actual evapotranspiration of capsicum inside and outside of naturally ventilated polyhouse

This study was conducted to study the relationship between capsicum crop evapotranspiration inside (ETCin) and crop evapotranspiration outside (ETCout) the naturally ventilated polyhouse (NVPH) using meteorological parameters. Polyhouse has a straightway impact on air temperature and relative humidity while it indirectly influences soil temperature and soil moisture inside the structure. Under this study, crop evapotranspiration was estimated by conventional method i.e., obtaining reference evapotranspiration from weather data recorded inside the polyhouse and multiplying it with crop coefficient values of capsicum crop. Reference crop evapotranspiration inside and outside the polyhouse found as 745.19 mm and 590.22 mm, respectively whereas capsicum crop evapotranspiration inside and outside the polyhouse was 868.40 mm and 694.16 mm, respectively. The results of the study revealed that the relationship between weekly ETCin and ETCout can be expressed mathematically as ETCin = 0.84 ETCout. This implies that, there was approximately 15 % lower crop evapotranspiration requirement for the capsicum crop inside the naturally ventilated polyhouse as compared to outside the polyhouse.

Simulated deficit irrigation and climate change effects on sunflower production in Eastern Colorado with CSM-CROPGRO-Sunflower in RZWQM2

Sunflower (Helianthus annuus L.) has been used as an alternative summer crop in the traditional wheat (Triticum aestivum L.)-fallow rotation in the Great Plains of the USA. However, few studies have been conducted to quantify sunflower productivity and water productivity (WP) under semi-arid conditions and projected climate change. Experiments were conducted in 2008, 2010, and 2011 on sunflowers under deficit irrigation to meet a fraction of crop evapotranspiration (ETc) as estimated by FAO-56 in eastern Colorado. The field data was used to calibrate and validate the CSM-CROPGRO-Sunflower model that is incorporated in the Root Zone Water Qualify Model (RZWQM2). The calibrated model was then used to simulate sunflower production under projected climate conditions with four Representative Concentration Pathways (RCP) scenarios (2.6, 4.5, 6.0, and 8.5) and four irrigation levels (100%, 60%, 40% ETc and rainfed) in the late 21st century. The results showed that the model was able to adequately simulate sunflower biomass, yield, and soil water storage under the different irrigation treatments in all three years. The corresponding relative root mean square deviation (RRMSD) values were between 0.05 and 0.15 for the simulations of soil water storage, yield, and biomass. Under future climate change conditions, the model simulated greater impact of irrigation treatments than RCP scenarios on sunflower production. For example, yield was 3251.3, 2638.85 and 1937.17 kg ha−1 with 100%, 60% and 40% ETc irrigation under baseline (1992–2013) and was 2932.47, 2360.53 and 1810.65 kg ha−1 with these irrigation treatments under RCP8.5 (2070–2091). Simulation results also showed that scheduling irrigations based on 60% of ETc was the best choice for sunflower WP in eastern Colorado. Climate change did not affect sunflower biomass, yield, and WP. There was an increasing trend of irrigation amount was simulated from the baseline to RCP8.5 scenario to maintain a certain percent of ETc due to high temperature projected. For instance, the irrigation amount for 100%, 60% and 40% of ETc irrigation treatment was 16.4%, 17.3%, and 20.0% higher under RCP8.5 than those under baseline conditions with CO2 fertilization. Finally, our results demonstrated that RZWQM2 can be used to effectively schedule sunflower irrigations based on crop evapotranspiration requirement.

Systematic review: Effect of Irrigation Water Quality and Deficit Irrigation on Crop Yield and Water Use efficiency

The main purpose of this paper is to review on the effect of irrigation water quality and deficit irrigation on crop yield and water use efficiency. Low quality water for irrigation can impose a major environmental constraint to crop productivity. If salts become excessive, losses in yield will result. To prevent yield loss, salts in the soil must be controlled at a concentration below that which might affect yield. Irrigation application below the full evapotranspiration requirement is termed as deficit irrigation. Deficit irrigation consists of deliberately applying irrigation water in amounts below the plant‘s water requirements. Deficit irrigation can be applied at certain periods during the crop‘s growing season or throughout its growing season. Yield reductions also occur in a number of crops when subjected to water stress. Yield reductions depend on the crop‘s sensitivity to water stress at its various growth stages. In order for deficit irrigation to be an economically viable practice, the revenue lost due to yield reduction should be lower than savings in total cost of production. The goal of deficit irrigation is to increase crop water use efficiency by reducing the amount of water that is applied or by reducing the number of irrigation events. The interaction effects of water quality and DI illustrated that when the two types of stresses; saline and DI were coupled together, a serious reduction occurred on total dry biomass and total yield. The interaction effects of water quality and deficit irrigation illustrated that when the two types of stresses; saline and deficit irrigation were coupled together, a serious reduction occurred on total dry biomass and total yields.

Spate Irrigation Potential Assessment for Ethiopian Watershed

In the low lands of Logia sub basin, Ethiopia, because of shortage of rain to fully grow crops, irrigation is an obligation in general and the presence of seasonal rivers flowing in the region in particular makes flood utilization ideal for spate irrigation. The subjects of the present study were to assess the spate irrigation potential of Logiya watershed that has been brought under irrigation on the basis of flood water availability and land suitability. A GIS based technique combined with analytical hierarchy process (AHP) was applied to access the potential of the watershed for spate irrigation development. Potentially suitable sites for spate irrigation development were assessed for Maize, Sorghum and Tomato crops. Spate irrigation area was evaluated based on land use/cover, slope and soil suitability. CROPWAT software was used to estimate the reference crop evapotranspiration, effective rainfall, net irrigation and gross irrigation water requirement. The suitability model developed shows that only 26.15% of the total area falls under marginally to highly suitable categories for spate irrigation development. The Logiya seasonal river flow from July to October was 301.64 Mm3. However, the annual flood water available from the river was less than the total GIWR by 8.77 Mm3 during growing period. The surplus water available from the river before July might be stored and used for irrigation during water deficit period during growing seasons.

Soil water storage changes in a small headwater catchment in the central North Island of New Zealand following afforestation with Pinus radiata

The effect of afforestation of pasture with Pinus radiata D. Don on soil water storage was measured in a small headwater catchment (8.7 ha) located in the Central North Island of New Zealand, as part of a larger study of land use effects on streamflow. Soil water content of the pumice soil was measured on an approximately monthly basis at 10 cm intervals to approximately 200 cm depth to the ignimbrite rock layer, using a neutron probe. Measurements occurred between stand ages 2–8 years (1975–1982) during which time the leaf area index of the forest was measured annually. Soil water storage in the profile varied between relatively narrow limits, with annual mean storage ranging from 766 to 878 mm even though annual rainfall and streamflow varied considerably between years. Soil water storage was more variable on a monthly basis, decreasing to approximately 630 mm in the entire profile during the summer drought in 1978 when streamflow almost ceased. The pumice soil at Puruki stored sufficient water in the profile to meet annual evapotranspiration requirements of P. radiata, including during a summer drought when water stored below 100 cm depth was utilised. The root systems of P. radiata trees can extend to below 3 m depth when growing on pumice soils in the Central North Island and plantations will therefore not be water limited unless rooting depth is impeded or annual rainfall decreases substantially in future owing to climate change.

Yield determination of maize hybrids under limited irrigation

ABSTRACTHybrid adoption, irrigation, and planting density are important factors for maize (Zea mays L.) production in semiarid regions. For this study, a 2-yr field experiment was conducted in the Texas High Plains to investigate maize yield determination, seasonal evapotranspiration (ETc), and water-use efficiency (WUE) under limited irrigation. Two hybrids (N74R, a conventional hybrid, and N75H, a drought-tolerant (DT) hybrid) were planted at three water regimes (I100, I75, and I50, referring to 100%, 75%, and 50% of the evapotranspiration requirement) and three planting densities (PD 6, PD 8, and PD 10, referring to 6, 8, and 10 seeds m−2). At I50, drought stress reduced grain yield by 4.78 t/ha for the conventional hybrid but only 4.22 t/ha for the DT hybrid, when compared to I100. Although ETc decreased at I75 and I50, the highest WUE was found at I75. The DT hybrid did not yield more than the conventional hybrid but had greater yield stability at lower water regimes and extracted less soil water. Drought decreased biomass, harvest index, and kernel weight but did not affect kernel number. Higher planting densities increased biomass and kernel number but decreased kernel weight. Kernel number and kernel weight of the conventional hybrid were more sensitive to planting density than the DT hybrid. These data demonstrated that limited irrigation at I75 is an effective way to save water and maintain the maize yield in semiarid areas, and that DT hybrid shows a greater yield stability to plant density under water stress.

Estimating Impacts of Land Use Change on Evapotranspiration for Three Agricultural Crops in Malta—A Preliminary Assessment

Estimating evapotranspiration is crucial for better management of catchment water resources. In this study, the FAO CropWat model was used to estimate reference evapotranspiration (ETo), crop evapotranspiration (ETc), and total gross water requirements for three economically important agricultural crops grown in Malta: potatoes, wheat, and vineyards for three years representative of a typically wet (2003), average (2009), and dry (2013) year. In addition, changes in ETc due to changes in land use were estimated for 2009 and 2013 relative to a 2003 baseline. Across all three years and crops, the average ETo rates were estimated to range between 3.7 mm day -1 (2003) and 4.0 mm day-1 (2013) while average ETc rates were estimated to range between 1.6 mm day-1 and 5.3 mm day-1, respectively. For all three years, the highest total gross water requirement was estimated for wheat, reaching a maximum of 1450 mm in 2013. The results suggest that changes in land use between 2003 and 2013 were the main driver for changes in crop water demand. Differences in water demand compared to 2003 were estimated to range between -38% and 60%. This could have a substantial impact on the future sustainability of Malta&amp;rsquo;s increasingly constrained water resources.

Yield determination in winter wheat under different water regimes

Wheat (Triticum aestivum) is grown in a wide range of water regimes and produces both grain and forage in the U.S. Southern Great Plains (SGP). Despite being relatively adapted to water stress, decreased water supply has become the main abiotic factor limiting wheat yield in the region. A 5-yr field study was conducted to investigate the yield determination in winter wheat under a center pivot irrigation system. Twenty elite wheat cultivars were grown at four water regimes, I100, I75, I65, and I50 to meet 100%, 75%, 65%, and 50% evapotranspiration (ET) requirement, respectively. The 2011 and 2013 seasons had all irrigation levels, while there were only two irrigation levels in 2012 (I50 and I65) and 2014 (I75 and I100), and three irrigation levels in 2015 (I50, I75, and I100). In most seasons, ET, biomass, and grain yield decreased consistently from higher to lower water regime, but water use efficiency (WUE) and harvest index (HI) were the highest at I75. Averaged across all years and genotypes, grain yield was reduced by only 5% from I100 to I75 indicating that reducing irrigation to meet 75% of ET requirement can still achieve similar yield to I100 and maximize HI and WUE. Newer cultivars including Duster, Endurance, Winterhawk, TAM 112, and TAM 113 had greater yield at I50 compared to other cultivars. Grain yield showed a strong relationship with biomass, HI, and ET. At lower water regimes (I50, I65), all three yield components (spikes per square meter, seeds per spike, and kernel weight) were correlated to grain yield. At higher water regimes (I75 and I100) grain yield was consistently related to kernel weight. This study demonstrated that high yield can be achieved at an irrigation level of I75. In addition, planting newer drought tolerant cultivars may provide yield benefits under water-limited conditions in the SGP.

Multispectral satellite imagery to quantify in-field soil moisture variability

As pressure on available water resources increases, the need to exploit technology in order to produce more food with less water becomes crucial. The technological hardware requisite for precise water delivery methods, such as variable rate irrigation, is commercially available. Despite that, techniques to formulate a timely, accurate prescription for those systems are inadequate. Spectral vegetation indices are often used to gauge crop vigor and related parameters (e.g., leaf nitrogen [N] content). However, research heretofore rarely addresses the influence of soil moisture on the indices. The objectives of this study were to determine (1) if vegetation indices derived from multispectral satellite imagery could assist in quantifying soil moisture variability in irrigated maize (<i>Zea mays</i> L.) production, and (2) the period of time that a single image is representative of soil moisture. A variable rate irrigation pivot was used to form six water treatment zones. Each was equipped with tensiometers installed in the center of the plots at 20, 45, and 75 cm depths to individually monitor conditions in the water treatment zones. Water was applied for each treatment as a percentage of the estimated evapotranspiration (ET) requirement: 40%, 60%, 80%, 100%, 120%, and 140%. Data collected from tensiometers was paired with the image pixels corresponding to its ground location. Statistical analysis was performed separately to assess whether vegetation indices are representative of soil moisture at several crop growth stages. Findings from this study indicate that Red Edge Normalized Difference Vegetation Index could quantify soil moisture tension variability at V6 (six leaf; <i>r</i>² = 0.850, <i>p</i> = 0.009) and V9 (nine leaf; <i>r</i>² = 0.913, <i>p</i> = 0.003) crop growth stages. Results suggest that satellite-derived vegetation indices may be useful for creating time-sensitive characterizations of soil moisture variability. Further study is necessary to investigate additional crop growth stages, more crops, and other sources of multispectral imagery.