Irrigation scheduling performance by evapotranspiration-based controllers

Evapotranspiration-based irrigation controllers, also known as ET controllers, use ET information or estimation to schedule irrigation. Previous research has shown that ET controllers could reduce irrigation as much as 42% when compared to a time-based irrigation schedule. The objective of this study was to determine the capability of three brands of ET-based irrigation controllers to schedule irrigation compared to a theoretically derived soil water balance model based on the Irrigation Association Smart Water Application Technologies (SWAT) protocol to determine the effectiveness of irrigation scheduling. Five treatments were established, T1-T5, replicated four times for a total of twenty field plots in a completely randomized block design. The irrigation treatments were as follows: T1, Weathermatic SL1600 with SLW15 weather monitor; T2, Toro Intelli-sense; T3, ETwater Smart Controller 100; T4, a time-based treatment determined by local recommendations; and T5, a reduced time-based treatment 60% of T4. All treatments utilized rain sensors set at a 6 mm threshold. A daily soil water balance model was used to calculate the theoretical irrigation requirements for comparison with actual irrigation water applied. Calculated in 30-day running totals, irrigation adequacy and scheduling efficiency were used to quantify under- and over-irrigation, respectively. The study period, 25 May 2006 through 27 November 2007, was drier than the historical average with a total of 1326 mm of rainfall compared to 1979 mm for the same historical period. It was found that all treatments applied less irrigation than required for all seasons. Additionally, the ET controllers applied only half of the irrigation calculated for the theoretical requirement for each irrigation event, on average. Irrigation adequacy decreased when the ET controllers were allowed to irrigate any day of the week. All treatments had decreased scheduling efficiency averages in the rainy season with the largest decrease of 29 percentile points with a timer and rain sensor (T4) and an average decrease of 20 percentile points for the ET controllers, indicating that site specific rainfall has a significant effect on scheduling efficiency results. Rainfall did not drastically impact the average irrigation adequacy results. For this study, there were two controller program settings that impacted the results. The first setting was the crop coefficients where specific values were chosen for the location of the study when calculating the theoretical requirement whereas the controllers used default values. The second setting was the soil type that defines the soil water holding capacity of the soil. The ET controllers were able to regularly adjust to real-time weather, unlike the conventional irrigation timers. However, the incorporation of site specific rainfall measurements is extremely important to their success at managing landscape water needs and at a minimum a rain sensor should be used.     

Water conservation potential of smart irrigation controllers on St. Augustinegrass

A variety of technologies for reducing residential irrigation water use are available to homeowners. These “Smart Irrigation” technologies include evapotranspiration (ET)-based controllers and soil moisture sensor (SMS) controllers. The purpose of this research was to evaluate the effectiveness of these technologies, along with rain sensors, based on irrigation applied and turfgrass quality measurements on St. Augustinegrass (Stenotaphrum secundatum (Walter) Kuntze). Testing was performed on two types of SMS controllers (LawnLogic LL1004 and Acclima Digital TDT RS500) at three soil moisture threshold settings. Mini-Clik rain sensors (RS) comprised six treatments at two rainfall thresholds (3 mm and 6 mm) and three different irrigation frequencies (1, 2, and 7 d/wk). Two ET controllers were also tested, the Toro Intelli-Sense controller and the Rain Bird ET Manager. A time-based treatment with 2 days of irrigation per week without any type of sensor (WOS) to bypass irrigation was established as a comparison. All irrigation controller programming represented settings that might be used in residential/commercial landscapes. Even though three of the four testing periods were relatively dry, all of the technologies tested managed to reduce water application compared to the WOS treatment, with most treatments also producing acceptable turf quality. Reductions in irrigation applied were as follows: 7–30% for RS-based treatments, 0–74% for SMS-based treatments, and 25–62% for ET-based treatments. The SMS treatments at low threshold settings resulted in high water savings, but reduced turf quality to unacceptable levels. The medium threshold setting (approximately field capacity) SMS-based treatment produced good turfgrass quality while reducing irrigation water use compared to WOS by 11–53%. ET controllers with comparable settings and good turf quality had −20% to 59% savings. Reducing the irrigation schedule (treatment DWRS) by 40% and using a rain sensor produced water savings between 36% and 53% similar to smart controllers. Proper installation and programming of each of the technologies was essential element to balancing water conservation and acceptable turf quality. Water savings with the SMS controllers could have been increased with a reduced time-based irrigation schedule. Efficiency settings of 100% (DWRS) and 95% (TORO) did not reduce turf quality below acceptable limits and resulted in substantial irrigation savings, indicating that efficiency values need not be low in well designed and maintained irrigation systems. For most conditions in Florida, the DWRS schedule (60% of schedule used for SMS treatments) can be used with either rain sensors or soil moisture sensors in bypass control mode as long as the irrigation system has good coverage and is in good repair.     

利用气象资料指导膜下滴灌棉花灌溉的试验研究

利用气象资料指导膜下滴灌棉花灌溉的试验于2007年5~10月份在新疆生产建设兵团灌溉中心试验站的试验基地进行。试验共设置7个处理,分别按生育期ET0的不同比例进行灌水。试验结果表明,为了获得经济合理的产量,膜下滴灌棉花全生育期耗水量应控制在360~405 mm之间。用实时气象资料指导膜下滴灌棉花的灌溉具有很好的可行性,蕾期和花铃后期10 d灌1次水,灌水定额为60%ET0;花铃前期7 d灌1次水,灌水定额为75%ET0,是一种适宜北疆地区膜下滴灌棉花的灌水模式。     

Soil matric potential-based irrigation scheduling to rice (Oryza sativa)

About half of the total fresh water used for irrigation in Asia is used for rice production. Decreasing water resources and increasing water costs necessitates increasing water use efficiency for rice. The most common method of irrigation in northwestern India is through alternate wetting and drying with a fixed irrigation interval, irrespective of soil type and climatic demand resulting in over-irrigation or under-irrigation under different soil and weather situations. Soil matric potential may be an ideal criterion for irrigation, since variable atmospheric evaporativity, soil texture, cultural practices and water management affect rice irrigation water requirements. A 4-year field study was conducted to assess the feasibility of rice irrigation scheduling on the basis of soil matric potential and to determine the optimum matric potential so as to optimize irrigation water without any adverse effect on the yield. The treatments included scheduling irrigation to rice with tensiometers installed at 15–20 cm soil depth at five levels of soil matric suction viz. 80, 120, 160, 200 and 240±20 cm, in addition to the recommended practice of alternate wetting and drying with an interval of 2 days after complete infiltration of ponded water. The grain yield of rice remained unaffected up to soil moisture suction of 160±20 cm each year. Increasing soil matric suction to 200 and 240±20 cm decreased rice grain yield non-significantly by 0–7% and 2–15%, respectively, over different years compared to the recommended practice of the 2-day interval for scheduling irrigation. Irrigation at 160±20 cm soil matric suction helped save 30–35% irrigation water compared to that used with the 2-day interval irrigation. With a soil matric potential irrigation criterion the total amount of irrigation water used was a function of the number of rainy days and evaporation during the rice season.     

Landscape irrigation by evapotranspiration-based irrigation controllers under dry conditions in Southwest Florida

Due to high demand for aesthetically pleasing urban landscapes from continually increasing population in Florida, new methods must be explored for outdoor water conservation. Three brands of evapotranspiration (ET) controllers were selected based on positive water savings results in arid climates. ET controllers were evaluated on irrigation application compared to a time clock schedule intended to mimic homeowner irrigation schedules. Three ET controllers were tested: Toro Intelli-sense; ETwater Smart Controller 100; Weathermatic SL1600. Other time-based treatments were TIME, based on the historical net irrigation requirement and RTIME that was 60% of TIME. Each treatment was replicated four times for a total of twenty St. Augustinegrass plots which were irrigated through individual irrigation systems. Treatments were compared to each other and to a time-based schedule without rain sensor (TIME WORS) derived from TIME. The study period, August 2006 through November 2007, was dry compared to 30-year historical average rainfall. The ET controllers averaged 43% water savings compared to a time-based treatment without a rain sensor and were about twice as effective and reducing irrigation compared to a rain sensor alone. There were no differences in turfgrass quality across all treatments over the 15-month study. The controllers adjusted their irrigation schedules to the climatic demand effectively, with maximum savings of 60% during the winter 2006-2007 period and minimum savings of 9% during spring 2007 due to persistent dry conditions. RTIME had similar savings to the ET controllers compared to TIME WORS indicating that proper adjustment of time clocks could result in substantial irrigation savings. However, the ET controllers would offer consistent savings once programmed properly.     

Evaluating irrigation applied and nitrogen leached using different smart irrigation technologies on bahiagrass (Paspalum notatum)

Irrigation technologies [i.e., automatic timer, automatic timer with rain sensor, automatic timer with soil water sensor (SWS), and evapotranspiration (ET) controller] were compared in a bahiagrass plot study by measuring irrigation applied, water volumes drained, and NO₃–N and NH₄–N leached. All irrigation technologies were scheduled to irrigate on Sunday and Thursday. Three different irrigation depths were evaluated with the automatic timer: 15, 19, and 32 mm. SWS treatment allowed scheduled irrigation if soil water content was estimated to be below 70 % of water holding capacity, while the ET treatment allowed scheduled irrigation if soil water content was estimated to be below 50 % of plant available water. The rain sensor, SWS, and ET controller treatments applied significantly less water (p < 0.05) than the automatic timer treatment (which irrigates on specific days and times without regard to system conditions), reducing water by 17–49, 64–75, and 66–70 %, respectively. NO₃–N and NH₄–N were only significantly different after the second fertilizer application, which coincided with the 32 mm per event irrigation rate for the automatic timer treatment. Under these conditions, the automatic timer treatment had significantly greater NO₃–N and NH₄–N leachate than other treatments due to greater occurrence of soil water content exceeding water holding capacity, which resulted in drainage. Findings suggest that water can be saved using rain sensors, SWSs, or ET controllers and that leachate NO₃–N and NH₄–N can be reduced using rain sensors, SWSs, or ET controllers.     

Integrating satellite-based evapotranspiration with simulation models for irrigation management at the scheme level

Improvements in irrigation management are urgently needed in regions where water resources for irrigation are being depleted. This paper combines a water balance model with satellite-based remote-sensing estimates of evapotranspiration (ET) to provide accurate irrigation scheduling guidelines for individual fields. The satellite-derived ET was used in the daily soil water balance model to improve accuracy of field-by-field ET demands and subsequent field-scale irrigation schedules. The combination of satellite-based ET with daily soil water balance incorporates the advantages of satellite remote-sensing and daily calculation time steps, namely, high spatial resolution and high temporal resolution. The procedure was applied to Genil–Cabra Irrigation Scheme of Spain, where irrigation water supply is often limited by regional drought. Compared with traditional applications of water balance models (i.e. without the satellite-based ET), the combined procedure provided significant improvements in irrigation schedules for both the average condition and when considering field-to-field variability. A 24% reduction in application of water was estimated for cotton if the improved irrigation schedules were followed. Irrigation efficiency calculated using satellite-based ET and actual applied irrigation water helped to identify specific agricultural fields experiencing problems in water management, as well as to estimate general irrigation efficiencies of the scheme by irrigation and crop type. Estimation of field irrigation efficiency ranged from 0.72 for cotton to 0.90 for sugar beet.     

Responses of winter wheat (Triticum aestivum L.) evapotranspiration and yield to sprinkler irrigation regimes

The North China Plain (NCP) is one of the main productive regions for winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) in China. However, water-saving irrigation technologies (WSITs), such as sprinkler irrigation technology and improved surface irrigation technology, and water management practices, such as irrigation scheduling have been adopted to improve field-level water use efficiency especially in winter wheat growing season, due to the water scarcity and continuous increase of water in industry and domestic life in the NCP. As one of the WSITs, sprinkler irrigation has been increasingly used in the NCP during the past 20 years. In this paper, a three-year field experiment was conducted to investigate the responses of volumetric soil water content (SWC), winter wheat yield, evapotranspiration (ET), water use efficiency (WUE) and irrigation water use efficiency (IWUE) to sprinkler irrigation regimes based on the evaporation from an uncovered, 20-cm diameter pan located 0-5 cm above the crop canopy in order to develop an appropriate sprinkler irrigation scheduling for winter wheat in the NCP. Results indicated that the temporal variations in SWC for irrigation treatments in the 0-60-cm soil layer were considerably larger than what occurred at deeper depths, whereas temporal variations in SWC for non-irrigation treatments were large throughout the 0-120-cm soil layer. Crop leaf area index, dry biomass, 1000-grains weight and yield were negatively affected by water stress for those treatments with irrigation depth less than 0.50E, where E is the net evaporation (which includes rainfall) from the 20-cm diameter pan. While irrigation with a depth over 1.0E also had negative effect on 1000-grains weight and yield. The seasonal ET of winter wheat was in a range of 206-499 mm during the three years experiments. Relatively high yield, WUE and IWUE were found for the irrigation depth of 0.63E. Therefore, for winter wheat in the NCP the recommended amount of irrigation to apply for each event is the total 0.63E that occurred after the previous irrigation provided total E is in a range of 30-40 mm.     

基于作物耗水特性的夹砂地膜下滴灌模式优选

在2个灌水水平下（I1：高水，I2：低水）以不同滴灌带间距（A1：1m，A2：0.5m）与覆膜方式（M1：全膜覆盖，M2：半膜覆盖）进行2a田间试验，结合作物产量、作物水分利用效率（WUE）以及产投比筛选适宜的膜下滴灌模式，并利用产量水分敏感系数（ky）确定最优的膜下滴灌模式。结果表明：在低频灌溉模式下，部分覆膜处理的蒸腾（ET）高于全覆膜处理，而产量和WUE低于全覆膜处理。尽管滴灌带间距对ET的影响不明显，然而在高水处理下，“一管单行”作物的产量与WUE高于“一管双行”。高频灌溉模式下，作物产量及WUE对灌溉量、覆膜方式、滴灌带间距的响应呈现耦合性。低频灌溉条件下，ky对灌溉量及滴灌带间距的响应均不显著，而部分覆盖处理WUE低，ky高，对水分胁迫的响应敏感。高频灌溉条件下，覆膜方式、灌溉量以及滴灌带间距均对ky 产生影响。高频灌溉条件下，ky能对经WUE筛选出的膜下滴灌处理进行进一步的优选。基于ky的结果，结合产量、水分利用效率与产投比，建议在高频灌溉条件下采取“全膜低水+一管双行”模式或“半膜高水+一管单行”模式，在低频灌溉条件下采取全膜高水模式。     

Corn crop response under managing different irrigation and salinity levels

Non-uniformity of water distribution under irrigation system creates both deficit and surplus irrigation areas. Water salinity can be hazard on crop production; however, there is little information on the interaction of irrigation and salinity conditions on corn (Zea Mays) growth and production. This study evaluated the effect of salinity and irrigation levels on growth and yield of corn grown in the arid area of Egypt. A field experiment was conducted using corn grown in northern Egypt at Quesina, Menofia in 2009 summer season to evaluate amount of water applied, salinity hazard and their interactions. Three salinity levels and five irrigation treatments were arranged in a randomized split-plot design with salinity treatments as main plots and irrigation rates within salinity treatments. Salinity treatments were to apply fresh water (0.89 dS m⁻¹), saline water (4.73 dS m⁻¹), or mixing fresh plus saline water (2.81 dS m⁻¹). Irrigation treatments were a ratio of crop evapotranspiration (ET) as: 0.6ET, 0.8ET, 1.0ET, 1.2ET, and 1.4ET. In well-watered conditions (1.0ET), seasonal water usable by corn was 453, 423, and 380 mm for 0.89EC, 2.81EC and 4.73EC over the 122-day growing season, respectively. Soil salt accumulation was significantly increased by either irrigation salinity increase or amount decrease. But, soil infiltration was significantly decreased by either salinity level or its interaction with irrigation amount. Leaf temperature, transpiration rate, and stomata resistance were significantly affected by both irrigation and salinity levels with interaction. Leaf area index, harvest index, and yield were the greatest when fresh and adequate irrigation was applied. Grain yield was significantly affected in a linear relationship (r² ≥ 0.95) by either irrigation or salinity conditions with no interaction. An optimal irrigation scheduling was statistically developed based on crop response for a given salinity level to extrapolate data from the small experiment (uniform condition) to big field (non-uniformity condition) under the experiment constraints.