ET-based Irrigation Scheduling Research Articles

Comparative analysis in selecting best irrigation method to maximize tomato yield from various irrigation approaches in water scarce regions

It is now essential for farmers to evaluate and compare different irrigation scheduling strategies in order to operate their irrigation systems in accordance with their resources and achievements. For tomato crops, a rigorous comparison was made between the yield of soil moisture and irrigation scheduling systems based on evapotranspiration. The experimental setup used a randomized complete block design (RCBD) with three replications, with water requirements of 100%, 75%, and 50%. Using a ReplogleBos-Clemmens (RBC) flume with an input rate of 1.62 l/s, water was applied to the furrows. The total applied amount in the Soil Moisture (SM) and Evapotranspiration (ET) based methods was 229.1 mm, and 280 mm, respectively. The collected data were assessed using ANOVA at a 5% significance level. For every technique, yield values, yield attributes, and agronomic traits were computed. The result indicates that there is no appreciable variation among the factors. The net yield advantage was highest at 75% SM and lowest at 25% SM. Furthermore, compared to the ET-based approach, it was demonstrated that the SM-based method conserved approximately 18.2% of irrigation water. As a result, when producing crops that require a lot of water, like tomatoes, in areas with limited water resources, SM-based irrigation scheduling is preferable to ET-based irrigation scheduling.

Effect of Different ET-Based Irrigation Scheduling on Grain Yield and Water Use Efficiency of Drip Irrigated Maize

The development of irrigation schedules based on water balance implies a study of daily plant water requirements. A properly selected irrigation method is also of most importance. The objective of this study was to find out how surface drip irrigation (SDI) and shallow subsurface drip irrigation (SSDI), as well as different ET-based irrigation scheduling for maize (reference evapotranspiration (ETo), pan evaporation (Eo), and local climatic coefficients (lc)), affect grain yield, water use efficiency (WUE), and yield response factor (Ky) of maize. The field experiments were conducted in Vojvodina, a northern part of the Republic of Serbia, on the calcareous gleyic chernozem soil, using a complete block design in three replicates in 2019–2021. The water balance method was used for irrigation scheduling. The nonirrigated treatment was used as a control. The yield in irrigation conditions was statistically higher as compared with the nonirrigated control variant. Concerning the tested parameters, especially the maize yield, reference evapotranspiration (ETo) should be recommended as the most acceptable method for assessing maize evapotranspiration. Preference should be given to SSDI compared to SDI because the installation of laterals can be performed together with the sowing, which can ensure the uniform and timely emergence of plants. Based on the Ky coefficient of 0.71, it can be concluded that maize is moderately tolerant to water stress in Vojvodina’s temperate climate. The results can contribute to precise planning and efficient irrigation of maize in the region, implying high and stable yields.

Short-Term Evapotranspiration Forecasting of Rubber (Hevea brasiliensis) Plantations in Xishuangbanna, Southwest China

Rubber (Hevea brasiliensis) plantations have high water consumption through evapotranspiration, which can contribute to water scarcity. In addition, there is a lack of spatial observation data and estimation methods for evapotranspiration (ET) for rubber plantations. To alleviate the water stress of expanding rubber plantations caused by seasonal drought in Xishuangbanna, Southwest China, an up to 7 days crop evapotranspiration (ETc) forecast method, “Kc-ET0” for rubber plantations with limited meteorological data, was proposed by using rubber crop coefficient Kc and public weather forecasts. The results showed that the average absolute error (MAE) of forecasted ETc was 0.68 mm d−1, the root mean square error (RMSE) was 0.85 mm d−1, and the average correlation coefficient (R) was 0.69 during the rainy season, while during the dry season these metrics were 0.52 mm d−1, 0.68 mm d−1, and 0.85, respectively. The accuracy of ETc forecast in the dry season was higher. Additionally, Kc was the main factor influencing the accuracy of rubber plantations ETc forecast, while the accuracy of the temperature forecast and the chosen Hargreaves-Samani (HS) model were also considerable. Our results suggested that the “Kc-ET0” short-term rubber plantation ETc forecasting method shows good performance and acceptable accuracy, especially in the dry season. The study provides an important basis for creating ET-based irrigation scheduling for improving regional-scale water management in high water consumption rubber plantations.

Evapotranspiration Based Irrigation Trials Examine Water Requirement, Nitrogen Use, and Yield of Romaine Lettuce in the Salinas Valley

Cool season vegetables require adequate soil moisture to assure that maximum yield and quality are achieved. On California’s central coast, where the majority of cool season vegetables are produced in the US, long-term overpumping of irrigation water has reduced groundwater levels and led to environmental degradation. Two evapotranspiration (ET) based irrigation field trials were performed near Salinas CA (USA) to determine if ET-based irrigation scheduling could conserve water while producing romaine lettuce (cv. Sun Valley) of commercially viable yield. Sprinklers were used for seed germination and crop establishment. Four drip irrigation treatments were then imposed using a randomized complete block design with six replications. The CropManage decision-support model was used to estimate the full (100%) crop water requirement based mainly on ET replacement. Other treatments included 50% 75% and 150% of the full water requirement. The 100% treatment received 185 mm of water in 2015 and 247 mm in 2016, both of which were well below prior guidance and grower reports. Yields from the 100% and 150% treatments were not significantly different and were similar to industry average, while yields were significantly lower for the 50% and 75% treatments. The 100% treatment had the highest water use efficiency, and the 100% and 150% treatments together had the highest nitrogen recovery efficiency. Irrigation of romaine near the 100% ET replacement level can potentially reduce environmental impacts associated with nitrate leaching and surface runoff.

Evaluating deficit irrigation scheduling strategies to improve yield and water productivity of maize in arid environment using simulation

Water scarcity and rising temperatures are creating serious concerns over the sustainability of agriculture systems in arid regions of the Middle East and North Africa. The aims were (i) to calibrate and evaluate the Decision Support System for Agrotechnology Transfer (DSSAT) model using detailed experimental datasets on maize (Zea mays L.) yield and water productivity in an arid Mediterranean environment and (ii) to determine the impacts of various irrigation scheduling strategies on maize yield and water productivity in arid sandy soils and produce irrigation scheduling recommendations that maximize the marginal benefit per unit water applied. The goodness-of-fit statistics comparing the observed and simulated crop phenology, grain yield, dry matter, evapotranspiration (ET), and soil water content indicate that the model simulates these crop and soil variables reasonably well for a medium-maturity maize hybrid (~ 110 days to physiological maturity) commonly grown in the study region. Long-term simulations (1984–2018) using the well-calibrated model were performed and included three irrigation scheduling strategies: (i) soil water-based irrigation scheduling, (ii) ET-based threshold irrigation scheduling, and (iii) growth-stage ET-based irrigation scheduling. In the soil water-based, four levels of maximum allowable depletion (MAD) of available soil water content (AWC) were tested using the auto-irrigation option of DSSAT. Results indicated that MAD 50% is recommended for scheduling irrigation in arid sandy soils for potential irrigation water saving without unacceptable yield loss. The ET-based threshold consisted of a combination of four cumulative net ET threshold (ETH) triggers of 14, 21, 28, and 35 mm and five ET replacement levels of 50%, 70%, 90%, 110%, and 130% ET using the DSSAT ET-based auto-irrigation option. Based on this irrigation strategy, it is more favorable to irrigate at the high frequency of ETH 14 or 21 mm than low frequency of ETH 35 mm, even when replacing 130% ET, as high drought-stress during the crop development and reproductive stages were observed for ETH 35 mm due to the omission of key irrigation events. In the growth-stage ET-based, two levels of irrigation of 100% ET and 60% ET estimated based on the crop coefficient approach were tested with different combinations of targets during the vegetative and reproductive growth stages. Results indicated that meeting crop ET requirements during the reproductive stage is more essential than during the vegetative stage for greater yield and enhanced WUE, particularly when available seasonal irrigation water is less than seasonal full crop ET requirements. In water limited environments, reasonable yield and enhanced WUE can be achieved by applying a deficit rate of 40% ET during the vegetative stage and 80% ET during the reproductive stage or scheduling irrigation based on soil water content to ensure AWC of 30% in the top 0–30 cm soil layer throughout the growing season. Concepts developed in the present study can be adapted to effectively manage irrigation scheduling for medium-maturity maize hybrids in arid sandy soils with low AWC and organic C content.

Evapotranspiration-Based Irrigation for Agriculture: Sources of Evapotranspiration Data for Irrigation Scheduling in Florida

This article is part of a series on ET-based irrigation scheduling for agriculture. The rest of the series can be found at http://edis.ifas.ufl.edu/topic_series_ET-based_irrigation_scheduling_for_agriculture.

ET-Based Irrigation Scheduling for Papaya (Carica papaya) in Florida

Three irrigation scheduling methods (set schedule, ET-based, and tensiometer-based) were tested for papaya production in south Florida. ET-based irrigation scheduling was found to conserve water effectively. This 6-page document primarily focuses on the ET-based irrigation scheduling techniques for papaya under Florida conditions. Written by Haimanote K. Bayabil, Jonathan H. Crane, Kati W. Migliaccio, Yuncong Li, and Fredy Ballen, and published by the UF/IFAS Department of Agricultural and Biological Engineering, March 2020. https://edis.ifas.ufl.edu/ae540

Kansas Center Pivot Uniformity Evaluation Overview

Abstract. Center pivot irrigation systems are the most common system type in Kansas for a variety of factors – one of which is the ability to deliver a uniform depth of water application for a variety of crops and field conditions. Uniform applications are dependent on properly designed, installed and operated sprinkler nozzle packages. Uniformity evaluations were conducted as part of the Mobile Irrigation Lab (MIL) project to promote adoption of improved irrigation management practices with an emphasis on ET based irrigation scheduling. Since efficient and uniform water applications are critical to successful irrigation scheduling; MIL assessment included evaluation of sprinkler package performance using a single line catch can test. Catch can data was used to calculate the coefficient of uniformity (CU) and average application depth. The average CU value of the tested systems was 78.7 with a range of from 91.9 to 53.2. Many of the factors affecting pivot uniformity could have been identified and corrected with a visual inspection and/or comparison to the manufacturer’s sprinkler design specifications. Some of the catch tests indicated poorly designed and/or maintained sprinkler systems with reduced uniformity directly impacting crop performance, water use efficiency and economic results. Initial information was used in extension programs to illustrate the effect of various correctable sprinkler package deficiencies on performance and to encourage irrigation farmers to examine their nozzle packages and operating conditions. Keywords: Center pivot irrigation, Sprinkler packages, Uniformity.

New Approaches to Irrigation Scheduling of Vegetables

Using evapotranspiration (ET) data for scheduling irrigations on vegetable farms is challenging due to imprecise crop coefficients, time consuming computations, and the need to simultaneously manage many fields. Meanwhile, the adoption of soil moisture monitoring in vegetables has historically been limited by sensor accuracy and cost, as well as labor required for installation, removal, and collection of readings. With recent improvements in sensor technology, public weather-station networks, satellite and aerial imaging, wireless communications, and cloud computing, many of the difficulties in using ET data and soil moisture sensors for irrigation scheduling of vegetables can now be addressed. Web and smartphone applications have been developed that automate many of the calculations involved in ET-based irrigation scheduling. Soil moisture sensor data can be collected through wireless networks and accessed using web browser or smartphone apps. Energy balance methods of crop ET estimation, such as eddy covariance and Bowen ratio, provide research options for further developing and evaluating crop coefficient guidelines of vegetables, while recent advancements in surface renewal instrumentation have led to a relatively low-cost tool for monitoring crop water requirement in commercial farms. Remote sensing of crops using satellite, manned aircraft, and UAV platforms may also provide useful tools for vegetable growers to evaluate crop development, plant stress, water consumption, and irrigation system performance.

Optimizing Et-Based Irrigation Scheduling for Wheat and Maize with Water Constraints

Abstract. Deficit irrigation has been shown to increase crop water use efficiency (WUE) under certain conditions, even though the yield is slightly reduced. In this study, the Root Zone Water Quality Model (RZWQM) was first calibrated with measured data from a large weighing lysimeter from 1998 to 2003 at the Yucheng Experimental Station in the North China Plain for daily evapotranspiration (ET), soil water storage (0-120 cm), leaf area index (LAI), aboveground biomass, and grain yield. The calibrated model was then used to explore crop responses to ET-based irrigation management using weather data from 1958 to 2015 and identify the most suitable ET-based irrigation schedules for the area. Irrigation amount was determined by constraining irrigation to a percentage of potential crop ET (40%, 60%, 80%, and 100% ETc) at the various growth stages of wheat [planting to before winter dormancy (P-D), green up to booting (G-B), booting to flowering (B-F), and flowering to maturity (F-M)] and of maize [planting to silking (P-S) and silking to maturity (S-M)], subject to seasonal water availability limits of 100/50, 200/100, 300/150, and 400/200 mm and no water limit for wheat/maize seasons, respectively. In general, wheat was more responsive to irrigation than maize, while greater influence of weather variation was simulated on maize than on wheat. For wheat with seasonal water limits, the highest average WUE was simulated with the highest targeted ETc levels at both the G-B and B-F stages and lower targeted ETc levels at the P-D and F-M stages. However, the highest average grain yield was simulated with the highest targeted ETc levels at all four growth stages for no water limit and the 400 mm water limit, or at both the G-B and B-F stages for the 300 and 200 mm water limits. For maize, lower targeted ETc levels after silking did not significantly affect maize production due to the high season rainfall, but irrigation of 60% ETc before silking was recommended. These results could be used as guidelines for precision irrigation along with real-time weather information. Keywords: Deficit irrigation, Evapotranspiration, Growth stage, RZWQM, Water use efficiency, Wheat and maize.

Evapotranspiration-based Irrigation Scheduling of Head Lettuce and Broccoli

Estimation of crop evapotranspiration supports efficient irrigation water management, which in turn supports water conservation, mitigation of groundwater depletion/degradation, energy savings, and crop quality maintenance. Past research in California has revealed strong relationships between fraction of the ground covered by photosynthetically active vegetation (Fc), crop coefficients (Kc), and evapotranspiration (ET) of cool-season vegetables and other specialty crops. Replicated irrigation trials for iceberg lettuce and broccoli were performed during 2012 and 2013 at the USDA Agricultural Research Station in Salinas, CA. The main objective was to compare crop yield and quality from ET-based irrigation scheduling with industry standard practice. Sprinkler irrigation was used to germinate and establish the crops, followed by surface drip irrigation during the treatment period. Each experiment compared three irrigation treatment schedules replicated five times in a randomized block design. Two decision-support models were evaluated as follows: 1) an FAO-56-based algorithm embedded in NASA’s prototype Satellite Information Management System (SIMS) based on observed Fc, and 2) CropManage (CM), an online database-driven irrigation scheduling tool based on modeled Fc. Both methods used daily reference ETo data from the California Irrigation Management Irrigation System (CIMIS) to translate Kc to crop ET, with a target of 100% replacement of water use during the drip irrigation phase. A third treatment followed an irrigation schedule representing grower standard practice (SP) at 150% to 175% ET replacement during the drip irrigation phase. No significant treatment differences were seen in lettuce head weight or total biomass. Marketable yields of lettuce (near 45.4 Mg·ha−1) and broccoli (near 17.4 Mg·ha−1) were in-line with industry averages during both years and all treatments. During 2012, CM yield was below lettuce SP, and above broccoli SP, while in 2013 no treatment differences were detected for either crop. No significant differences were detected between SIMS and SP yields during any trial.

Comparison of traditional and ET-based irrigation scheduling of surface-irrigated cotton in the arid southwestern USA

The use of irrigation scheduling tools to produce cotton under-surface irrigation in the arid southwestern USA is minimal. In the State of Arizona, where traditional irrigation scheduling is the norm, producers use an average of 1460mm annually to grow a cotton crop. The purpose of this paper was to determine whether or not the use of ET-based irrigation scheduling methods could improve lint yield and irrigation water use productivity over traditional cotton border irrigation scheduling practices in the region. A field study with four irrigation scheduling treatments replicated in 4 blocks was conducted for two cotton seasons (2009 and 2011) in 16, 12-m×168-m cotton borders at the Maricopa Agricultural Center (MAC), in Arizona, USA. Remotely-sensed vegetation indices (VI) were used to estimate basal crop coefficients (Kcb) at 40, 4-m×8-m zones within borders for two treatments, denoted as VI_A and VI_B, whereas a single Kcb curve was applied to all zones in borders for a third treatment (FAO). Daily ETc for these three treatments was estimated using FAO-56 dual crop coefficient procedures with local weather data and irrigation scheduling for the three treatments were based on soil water balance predictions of soil water depletion (SWD). For the VI_A and FAO treatments, irrigations were given when predicted SWD of all 160 zones in the treatment averaged 45% of total available water (TAW). For the VI_B treatment, irrigations were given when 5% of the 160 zones in the treatment were predicted to be at 65% SWD. A fourth treatment (MAC) represented the traditional irrigation scheduling treatment and was scheduled solely by the MAC farm irrigation manager using only experience as a guide. The study showed that the lint yields attained under the MAC farm manager’s irrigation scheduling equaled or exceeded the yields for the three ET-based irrigation scheduling treatments. Although the MAC irrigation scheduling resulted in somewhat higher irrigation input than for the other treatments, the MAC treatment maintained or exceeded the irrigation water productivity attained for other treatments that had lower irrigation inputs. A major conclusion of the study was that present-day irrigation water use for cotton in surface-irrigated fields could be substantially reduced. When compared to Arizona state cotton averages, any of the four treatments presented in the study could potentially offer methods to significantly reduce cotton irrigation water use while maintaining or increasing current lint yields levels.

Modeling the Effect of Cistern Size, Soil Type, and Irrigation Scheduling on Rainwater Harvesting as a Stormwater Control Measure

Urban stormwater runoff could have negative impacts on water resources and the environment. Rainwater Harvesting (RWH) can serve both as a stormwater control and water conservation measure. Cistern size and irrigation scheduling are two of the factors that directly impact the total runoff from a residential unit with a RWH system and the amount of potable water used for irrigation. The effectiveness of RWH was evaluated for four soil types; Sand, Sandy Loam, Loamy Sand, and Silty Clay, with a root zone of 15.2 cm using three irrigation scheduling methods (Evapotranspiration (ET)-based, soil moisture-based, and time-based), and five cistern sizes. Total runoff volumes and total supplemental potable water used were compared among the three irrigation scheduling systems and a control treatment without RWH. A model was developed to simulate the daily water balance for the treatments. Irrigation and runoff volumes were compared for the various scenarios. Silty clay soil resulted with 83 % more runoff than Sandy soil, while Sandy soil required on average 58 % more supplemental water than Silty Clay soil. On average, the 833 L cistern resulted with 41 % savings in water supply and 45 % reduction in total runoff. Results showed that the greatest volumes of runoff predicted were for the silty clay soil Control Treatment using a time-based irrigation scheduling method, while the least volumes calculated were for the sandy loam soil time-based irrigation scheduling treatment with 833 L cistern size. The greatest volumes of total supplemental water predicted were for sandy loam soil Control Treatment, while the least volumes were for silty clay soil ET-based irrigation scheduling treatment with 833 L cistern size. Regression equations were developed to allow for users to select a RWH cistern size based on the amount of water they want to save or runoff to reduce.

Efficient Irrigation for Optimum Fruit Quality and Yield in Apples

Use of crop evapotranspiration (ETc), when a precise crop coefficient value (Kc) is used, provides a reliable tool (irrigation scheduling) for determination of water requirement. In this process, Kc should be modified by percentage of ground shade (GS) and tree canopy maturity (M). In an experiment in Idaho with ET-based irrigation scheduling, each tree with a full microjet sprinkler system received an average of 6461.7 L (994 mm), whereas each one with a full drip system used 3996 L (614.1 mm) of irrigation water. In general, deficit drip irrigation was shown to initially increase yield as a result of induction of stress and the production of a higher number of fruit spurs. However, production declined if the extreme water deficiency was repeatedly applied to the trees over several years. Using a microjet sprinkler system, a partial root zone drying regime reduced fruit size but slightly improved fruit color. Application of water at 65% full drip rate, applied on both sides of the tree row (DD), reduced fruit size. However, when the 65% of full drip rate was applied to only one of the alternating sides of the tree every other week (PRD), fruit size was larger than those with DD treatment.

Evapotranspiration-Based Irrigation Scheduling for Agriculture

AE457, a 6-page fact sheet by Isaya Kisekka, Kati W. Migliaccio, Michael D. Dukes, Jonathan H. Crane, and Bruce Schaffer, focuses on the main concepts related to ET-based irrigation scheduling and reviews the use of "smart" irrigation scheduling controllers for agricultural applications. Includes references. Published by the UF Department of Agricultural and Biological Engineering, January 2010. AE457/AE457: Evapotranspiration-Based Irrigation Scheduling for Agriculture (ufl.edu)

Water-use patterns of tall fescue and hybrid bluegrass cultivars subjected to ET-based irrigation scheduling

In turf industry, the ability of a cultivar to use less water is an important consideration, especially where rainfall and irrigation water are insufficient. Knowledge of turf grass water-use patterns is therefore important for developing efficient water management practices and also for selection of drought-resistant cultivars. We evaluated the soil water‐use patterns of tall fescue and hybrid bluegrasses cultivars irrigated at different rates. Field experiments were conducted at the Turfgrass Research Facility, Auburn University, AL, in 2005 and 2006. Two tall fescue (Festuca arundinacea Schreb.) cultivars (‘Kentucky 31’ and ‘Green Keeper’) and four hybrid bluegrass (Poa pratensis L. × Poa arachnifera Torr.) cultivars, viz., HB 129 [‘Thermal Blue’], HB 130 (Experimental line), HB 328 (Experimental line) and HB 329 [‘Dura Blue’] were included in this study. Plots were irrigated based on the potential evapotranspiration, viz., 100% ET, 80% ET and 60% ET replacements. Tensiometers were installed at 0.075, 0.15 and 0.30 m depths, and their readings used to calculate the matric head, water content and water-use values. Turf color quality was determined from turf canopy digital images. Analysis of variance (ANOVA) for a random complete block design (RCBD) was conducted for available water, water-use and turf color quality values. Hybrid bluegrasses revealed significantly (P = 0.05) higher turf color indices compared to the tall fescue cultivars, but there was no indication of differential responses to irrigation among cultivars. Based on water-use data, hybrid bluegrass cultivars revealed significantly (P = 0.05) lower water-use compared to tall fescue cultivars.

Use of the modified atmometer to estimate reference evapotranspiration in Mediterranean environments

Reference crop evapotranspiration (ET 0) estimates on the basis of FAO recommended methodology require the knowledge of several meteorological data. An alternative approach is the use of the modified atmometer which reduces the work and the complexity associated with ET-based irrigation scheduling. To establish relationships between Penman Monteith (PM), atmometer and Class ‘A’ pan ET 0 in Mediterranean environments, field tests were carried out during five irrigation seasons in different east and west coast sites of southern Italy. In all sites, high values of the correlation coefficient were found when comparing daily estimates of atmometer versus PM ET 0. Scattering of experimental data was the result of atmometer readings taken manually. Linear regression models yielded intercept coefficients which did not differ from zero, in any of the sites. A unique relationship could be established between atmometer and PM when data from all sites were pooled, providing a slope coefficient of 1.034. When comparing with a high resolution weighing lysimeter across a complete irrigation season, a slope not different from unity was found. Comparisons with Class ‘A’ mean weekly ET 0 during two consecutive irrigation season, indicated a slight underestimation of pan ET 0 by the atmometer. On the basis of experimental evidence, atmometer may be used for reliable ET 0 estimates under Mediterranean conditions, at both the farm and the extension level, whenever standard meteorological data are not available.