Low Elevation Spray Application Research Articles

Evaluation of three irrigation application systems for watermelon production in the Texas High Plains

AbstractAbout 90% of the Texas High Plains area depends on the water supply from the Ogallala aquifer. The decline of the Ogallala water table raises a concern for the sustainability of producing the traditional irrigated field crops due to their high water demand. Thus, diversifying cropping systems may be a solution. However, about 70% of the irrigated cropland uses center pivots that may negatively impact specialty crop quality. Thus, a 3‐year experiment was conducted to assess the potential of using mobile drip irrigation (MDI) to produce fresh watermelon compared to center pivot sprinkler irrigation using low‐elevation spray application (LESA), and surface drip irrigation with plastic mulch (DI). The study evaluated the effects of irrigation systems on crop yield, fruit quality, physiological responses, water use efficiency (WUE), and irrigation use efficiency (IUE). On average, plants under MDI had higher yields (106 Mg ha−1) than those under DI (70 Mg ha−1) and LESA (68 Mg ha−1). Plants under MDI and DI also had more fruits per plant (1.9) than those under LESA (1.4). The higher yield was associated with higher biomass and photosynthetic function. In general, fruit quality was not affected by irrigation system. In addition, plants under MDI system showed a higher WUE and IUE, and less water stress than those under LESA and DI systems. Results of this study suggest that irrigating under an MDI system is a good alternative for growers in the Texas High Plains that aim to diversify their cropping system with high‐value vegetable crops such as watermelon (Citrullus lanatus).

Measuring Evapotranspiration Suppression from the Wind Drift and Spray Water Losses for LESA and MESA Sprinklers in a Center Pivot Irrigation System

Wind drift and evaporation loss (WDEL) of mid-elevation spray application (MESA) and low-elevation spray application (LESA) sprinklers on a center pivot and linear-move irrigation machines are measured and reported to be about 20% and 3%, respectively. It is important to estimate the fraction of WDEL that cools and humidifies the microclimate causing evapotranspiration (ET) suppression, mitigating the measured irrigation system losses. An experiment was conducted in 2018 and 2019 in a commercial spearmint field near Toppenish, Washington. The field was irrigated with an 8-span center pivot equipped with MESA but had three spans that were converted to LESA. All-in-one weather sensors (ATMOS-41) were installed just above the crop canopy in the middle of each MESA and LESA span and nearby but outside of the pivot field (control) to record meteorological parameters on 1 min intervals. The ASCE Penman–Monteith (ASCE-PM) standardized reference equations were used to calculate grass reference evapotranspiration (ETo) from this data on a one-minute basis. A comparison was made for the three phases of before, during, and after the irrigation system passed the in-field ATMOS-41 sensors. In addition, a small unmanned aerial system (UAS) was used to capture 5-band multispectral (ground sampling distance [GSD]: 7 cm/pixel) and thermal infrared images (GSD: 13 cm/pixel) while the center pivot irrigation system was irrigating the field. This imagery data was used to estimate crop evapotranspiration (ETc) using a UAS-METRIC energy balance model. The UAS-METRIC model showed that the estimated ETc under MESA was suppressed by 0.16 mm/day compared to the LESA. Calculating the ETo by the ASCE-PM method showed that the instantaneous ETo rate under the MESA was suppressed between 8% and 18% compared to the LESA. However, as the time of the ET suppression was short, the total amount of the estimated suppressed ET of the MESA was less than 0.5% of the total applied water. Overall, the total reduction in the ET due to the microclimate modifications from wind drift and evaporation losses were small compared to the reported 17% average differences in the irrigation application efficiency between the MESA and the LESA. Therefore, the irrigation application efficiency differences between these two technologies were very large even if the ET suppression by wind drift and evaporation losses was accounted for.

Characterizing Evaporative Losses From Sprinkler Irrigation Using Large Weighing Lysimeters

Highlights Losses for MESA and LESA were comparable on the day of irrigation and oftentimes greater for the subsequent day. Losses were greater due to incomplete canopy conditions for both MESA and LESA on both days. Evaporative losses from irrigation extended to at least the subsequent day following irrigation in most cases. Losses over two days accounted for as much as 39.5% and 28.0% of irrigation depth for MESA and LESA, respectively. Abstract. Effective irrigation systems that increase crop water productivity by minimizing evaporative losses are paramount for extending the longevity of finite groundwater resources in the semi-arid U.S. Southern High Plains (SHP). Although subsurface drip irrigation (SDI) acreage has increased in recent years, center-pivot sprinkler systems still account for greater than 85% of the irrigated area in the SHP. Modern sprinkler configurations are typically classified according to application height as either mid-elevation spray application (MESA) or low-elevation spray application (LESA). While application drift and evaporative losses are easily measured under fallow conditions, quantifying evaporative losses under cropped conditions is difficult. Lysimeter-derived daily evapotranspiration (ET) values for SDI-irrigated and sprinkler-irrigated fields planted to corn in 2016 (MESA) and 2018 (LESA) near Bushland, TX, were compared for days when sprinkler irrigation events occurred and for subsequent days, when possible. Differences (extra ET) were attributed to evaporative losses associated with MESA and LESA irrigation. Average daily extra ET values for both sprinkler irrigation methods were similar on the day of irrigation, although MESA was slightly larger than LESA at 1.4 and 1.2 mm, respectively. The average daily extra ET values for incomplete canopy conditions were 2.2 mm for MESA and 1.9 mm for LESA, while values were identical for both methods at 0.6 mm for full canopy conditions. Average daily extra ET values were also expressed as a percentage of daily standardized grass reference ET (ETos) values. Average values for MESA and LESA were 20.1% and 13.5%, respectively, for the season, with similar findings of 29.3% and 19.4% for incomplete canopy conditions. Average extra ET/ETos values for incomplete canopy conditions were similar at 7.5% and 7.7% for MESA and LESA, respectively. Evaporative irrigation losses, calculated as the percentage of extra ET to irrigation depth, were slightly larger overall for the day of irrigation for MESA (5.4%) than LESA (5.2%). Losses of 7.9% and 7.0% were observed for incomplete canopy conditions for MESA and LESA, respectively. Average losses for LESA (3.5%) under full canopy conditions were greater than those for MESA (1.9%). A comparison of extra ET values for days following irrigation revealed that evaporative losses from irrigation events extended beyond the day of irrigation. MESA extra ET values for the day following irrigations increased by 57.1% (2.2 mm) overall, 13.6% (2.5 mm) for incomplete canopy conditions, and 150.0% (1.5 mm) for full canopy conditions. The same was true for LESA, with increases of 125.0% (2.7 mm) overall, 78.9% (3.4 mm) for incomplete, and 216.7% (1.9 mm) for full canopy conditions. Summing of extra ET values for the day of irrigation and the subsequent day yielded average values more than double those for the day of irrigation only, at 3.9 and 4.3 mm for MESA and LESA, respectively. Similarly, values for extra ET as a percentage of irrigation depth were also more than double those for the day of irrigation only, with the greatest loss values of 39.5% for MESA and 28.0% for LESA. These findings suggest that although LESA appears to mitigate evaporative losses marginally more in corn than MESA on the day of irrigation, considerably more evaporative losses occurred for both methods during the subsequent day, with slightly increased losses for LESA, resulting in little difference between overall losses over the two days. This may in part be explained by the temporary cooling effect of the irrigation inside the canopy on the day of irrigation, which is diminished by the second day. A greater discrepancy between evaporative losses for MESA and LESA is likely to be observed for crops having shorter stature or lower leaf density, such as cotton, although more study is needed to corroborate this claim. Knowledge of these findings provides useful information for both producers and water managers when considering irrigation management and water planning strategies. Keywords: Evaporation, Evapotranspiration, LESA, MESA, Semi-arid, Sprinkler Irrigation, Subsurface Drip Irrigation, Transpiration, Weighing Lysimeters.

The synergy between water conservation and economic profitability of adopting alternative irrigation systems for cotton production in the Texas High Plains

Declining water levels of the Ogallala Aquifer challenge economic availability of the groundwater and necessitate adoption of advanced irrigation systems with efficient irrigation strategies. Irrigation methods and application levels affect water productivity and farm profitability. This study evaluated the synergy between water conservation through a deficit irrigation strategy and economic profitability of agricultural production. The economic feasibility of cotton production was compared using field data for mid- and low-elevation spray application (MESA and LESA, respectively), low-energy precision application (LEPA), and subsurface drip irrigation (SDI) systems in the Texas High Plains (THP) region. Treatments included irrigated cotton with water application at 25%, 50%, 75%, and 100% evapotranspiration (ET) replacement levels and near-dryland cotton production. Both field-level data and well-calibrated model simulation data were used to assess cotton profitability at varying risk attitudes of producers. Results showed that more irrigation water consistently increased average net return of cotton production for all irrigation systems, except for SDI, which produced a similar net return at both 75% and 100% ET replacement levels. A larger chance of getting a net return greater than $380 ha−1 was observed for MESA, LESA and LEPA systems with the full irrigation at the 100% ET replacement level as well as for SDI with 75% ET replacement. Economic risk analysis showed that LEPA had a higher net return than other systems at each of the four irrigation levels and it would be preferred by risk-neutral, somewhat risk-averse, and rather risk-averse cotton producers. For each irrigation system, full irrigation was most preferred by risk-neutral producers and only minor differences were observed in the expected returns between 75% and 100% ET replacements as the producers became somewhat or more risk-averse. Groundwater conservation can be achieved with SDI without compromising crop yield or farm income, while government policies and financial incentives can help motivate producers to save irrigation water and maintain a high farm profit under spray and LEPA systems.

Evaluating Soil Water Redistribution under Mobile Drip Irrigation, Low-Elevation Spray Application, and Low-Energy Precision Application Using HYDRUS

AbstractA study to assess soil water redistribution under mobile drip irrigation (MDI), low-energy precision application (LEPA), and low-elevation spray application (LESA) was conducted under a cen...

Using stable water isotopes to assess the influence of irrigation structural configurations on evaporation losses in semiarid agricultural systems

The arid areas east of the Cascade Mountains in the Pacific Northwest have high irrigation water use and changing the elevation of sprinkler nozzles in these systems has been proposed as a strategy to reduce evaporative losses in order to diminish the total irrigation water demand. Validation of any structural modifications requires techniques able to identify water losses from these systems that were non-productive, particularly soil evaporation. In this study, we quantified evaporation losses from soils under Mid Elevation Spray Application (MESA) and Low Elevation Spray Application (LESA) irrigation systems by using stable isotope tracers to estimate the fraction of non-productive water losses (i.e. the ratio of soil water evaporation to irrigation water applied, E/I). During mid-summer 2017 in eastern Oregon and southeast Washington, we collected soil samples at multiple positions and depths around the central irrigation tower from four different agricultural fields, each with both LESA and MESA configurations. We measured the hydrogen and oxygen stable isotope ratio of soil water at MESA and LESA field locations using H2O liquid – H2O vapor equilibration laser spectroscopy. Though soil moisture contents were similar, the average isotope ratio of soil water under LESA irrigation (δD = −114.5‰, δ18O = −14.5‰) had lower values than under MESA irrigation (δD = −108.2‰, δ18O = −13.1‰). Calculated E/I values demonstrated higher sprinkler and soil water evaporation occurring at the MESA irrigated locations (E/I = 16.1%) compared to the LESA irrigated locations (E/I = 9.0%). We find that LESA systems have lower non-productive water losses than MESA systems and are thereby more efficient users of applied water. Our results suggest that stable water isotopes provide a technique for improving the management of water resources through the assessment of irrigation efficiency.

Economic feasibility of conversion to mobile drip irrigation in the Central Ogallala region

As groundwater levels continue to decline in the Ogallala Aquifer, stakeholders, policymakers, and producers encourage the adoption of new irrigation technology in an effort to conserve groundwater, extend the economic life of the aquifer, and enhance profitability. One such technology currently receiving attention in the Central Ogallala region is the mobile drip irrigation (MDI) application system. This study compares MDI to low elevation spray application irrigation by evaluating the changes in variable cost per hectare to calculate the payback period for a MDI system under three levels of investment cost for grain and fiber crops representing three levels of water use while holding yield constant. Using a 3% discount rate, under the medium level of investment cost ($371 per hectare), a discounted payback period of 4.9, 9.0, and 6.3 years is required for corn, cotton, and sorghum/wheat, respectively. As the cost per hectare to convert an existing center pivot drops to $185 per hectare, the payback period also drops to 2.3, 4.2, and 3.0 years, respectively. Thus, producers growing higher water use crops are able to recover the costs of the conversion to MDI through increased water use efficiency quicker than producers growing medium and lower water use crops.

Evaluation of dynamic uniformity and application efficiency of mobile drip irrigation

Irrigation uniformity, application efficiency and seasonal irrigation uniformity of mobile drip irrigation (MDI) were compared to those of low elevation spray application (LESA) and low energy precision application (LEPA). A center pivot fitted with two sets of MDI (with dripper flow rates of 3.8 L/h and 7.6 L/h), LESA and LEPA was used in this study. Irrigation uniformity tests were conducted in accordance with the American Society of Agricultural Engineers’ standards. Application efficiency was computed as the ratio of depth of water retained in the root zone to that applied. Potential differences in season-long irrigation uniformity were evaluated by analysis of periodically acquired aerial vegetative index data. The coefficient of uniformity of the 3.8 L/h and 7.6 L/h MDI was 93.8% and 93.7%, respectively, and 95.1% for LEPA, and 83.8% for LESA. Application efficiencies for the 3.8 L/h and 7.6 L/h MDI, LEPA and LESA were 76.1, 96.8, 98.4 and 51.2%, respectively. There were no significant differences (p value = 0.5749) in the amount of water stored in the soil profile between MDI, LESA and LEPA, 72 h after irrigation. For three irrigation capacities of 6.2, 3.1 and 1.6 mm/day, there were no significant differences in mean seasonal Advanced Difference Vegetative Index (ADVI) between MDI, LESA and LEPA, with p value = 0.987, 0.999 and 0.999, respectively. A similar observation was made for Normalized Difference Vegetative Index, with p value = 0.998, 0.999 and 0.999, for MDI, LESA and LEPA, respectively. Higher coefficient of uniformity and higher application efficiency for MDI and LEPA indicate that they were more efficient than LESA. These results show that MDI can adapt the high efficiency of traditional drip irrigation to center pivot systems.

Assessing suitability of modified center pivot irrigation systems in corn production using low altitude aerial imaging techniques

This study evaluated corn (Zea mays var. indentata) canopy vigor and temperature variations using small unmanned aerial system (UAS) based spatiotemporal imagery data. The key objective was to develop understanding on site-specific suitability of the Mid Elevation Spray Application (MESA) and Low Elevation Spray Application (LESA) sprinkler systems in irrigating corn crop and potential water as well as energy savings. Aerial data was collected through small UAS flights at 100 m height above ground level and on 49, 59, 65, 77, 105, 114, 134 days after planting (DAP). Small UAS had 5-band multispectral and radiometric thermal imager on-board the platform. Custom image processing algorithms were developed to extract various vegetation indices (Normalized difference vegetation index [NDVI], Green NDVI [GNDVI] and Normalized difference red edge [NDRE]) and canopy temperature maps from the imagery data. Two sample T-test was performed on extracted data to understand significant difference, at 5% level, within the LESA and MESA treatments. For both the irrigation techniques, the crop vigor increased in the early growth stage (49, 65 DAP), peaked in the mid growth stage (77, 105, 114 DAP) and then decreased in the late growth stage (134 DAP). The MESA irrigated sections had higher vigor (NDVI, GNDVI, NDRE), but not significant, compared to LESA throughout the season. Similarly, the MESA irrigated areas had significantly (0.61–2.07 °C) cooler canopies than LESA. Such results were anticipated, in part due to the issues with the sprinkler heads used in LESA. The heads were being pulled off in the corn field, causing the weighted hose to damage the crop. A different kind of sprinkler head was used after this incident. However, some strips of corn had already been damaged. Overall, this study results confirm suitability of aerial imagery data in evaluating pertinent irrigation treatments. Additional season’s data would be needed to clearly understand which technique (LESA or MESA) is more suitable for irrigating corn crop in the central part of state of Washington.

Evaluation of maize production under mobile drip irrigation

Declining water levels in the Ogallala aquifer of the U.S. High Plains necessitate more efficient irrigation technology to sustain agricultural production. A study to evaluate the performance of Mobile Drip Irrigation (MDI) for maize production, in comparison to common center-pivot nozzles (Low Elevation Spray Application (LESA) and Low Energy Precision Application (LEPA)) was conducted. A center-pivot was retrofitted with MDI, LEPA and LESA. Irrigation capacities of 6.3, 3.1, and 1.6 mm/d were considered. Grain yield, water use efficiency, above ground biomass, leaf area index (LAI), and soil water content was compared. Differences in grain yield between irrigation application devices were not significant (p = 0.085), but there were differences between irrigation capacities (p < 0.0001) at 5% significance level. There were no significant differences in monthly biomass yield between the application devices but there were significant differences in biomass yield between irrigation capacities. There were no significant differences in LAI between both the application devices and irrigation capacities. There were no significant differences in water use efficiency between the application technologies (p = 0.2352), at 5% significance level, however, differences between irrigation capacities were significant (p = 0.050). Generally, crop biophysical measurements under MDI were not significantly different from those under LEPA and LESA. Any marginal benefits of MDI were likely masked by rainfall, thus further evaluation of MDI is recommended under conditions of less applied water than LEPA or LESA accompanied by low rainfall. The other benefits of MDI were found in reduction of wheel-track rutting and ease of carrying out fertigation.

Economical thermal-RGB imaging system for monitoring agricultural crops

In this study, a low-cost thermal-RGB imager was developed for use in agricultural crop monitoring applications. It is weatherproof, and has a geo-referencing capability along with a power management panel that allows unattended field deployment of the systems for crop monitoring over extended period of time. The imager is made up of single-board Linux-based computer integrated with RGB and thermal imaging modules. The imager can be configured as FTP server to allow data transfer to/from a client computer. Developed was also the custom image-processing algorithm which overlays, aligns thermal and RGB images, and mask for the thermal image to remove the soil background and shaded leaves. The algorithm outputs are the average temperature of sunlit leaves and canopy coverage. Prior to field validation, the performance of ten thermal modules and four fully assembled RGB-thermal imagers were assessed under laboratory conditions. In the spring of 2017, two imagers were mounted on a center pivot retrofitted with Medium Elevation Spray Application (MESA) and Low Elevation Spray Application (LESA) systems in a mint field near Toppenish, WA. The thermal modules showed an accuracy of ±2.4 °C on average over a range of 0–50 °C of a blackbody target. Although accurate for larger canopies, the imperfect alignment of RGB and thermal images introduced significant errors in the calculations of sunlit leaves surface temperature in images with small canopy coverage. Further investigations revealed that the first peak of thermal image relative frequency histogram could be a more accurate representative of sunlit leaf surface temperature. Overall, the amended image-processing algorithm was able to successfully extract canopy surface temperature and percent canopy cover from a wide range of images captured during the crop growing season. The current design of imager allows for creating a network of imaging units in the field to obtain real-time surface temperature data from plant canopies. The system has the potential to be used for creating evapotranspiration and prescription maps in real-time, and irrigation scheduling.

Performance of Precision Mobile Drip Irrigation in the Texas High Plains Region

Mobile drip irrigation (MDI) technology adapts driplines to the drop hoses of moving sprinkler systems to apply water as the drip lines are pulled across the field. There is interest in this technology among farmers in the Texas High Plains region to help sustain irrigated agriculture. However, information on the performance of this system and its benefits relative to common sprinkler application technologies in the region are limited. A two-year study was conducted in 2015 and 2016 to compare grain yields, crop water use (ETc) and water use efficiency (WUE) of corn (Zea Mays L.) irrigated with MDI, low elevation spray application (LESA) and low energy precision application (LEPA) methods. Irrigation amounts for each application method were based on weekly neutron probe readings. In both years, grain yield and yield components were similar among application treatment methods. Although WUE was similar for the MDI treatment plots compared with LEPA and LESA during the wet growing season (2015), MDI demonstrated improved WUE during the drier year of 2016. Additional studies using crops with less than full canopy cover at maturity (sorghum and cotton) are needed to document the performance of MDI in the Texas High Plains region.

Hydraulic Performance Assessment of Lesa at low Pressure

AbstractTo assist with the selection of appropriate low elevation spray application (LESA) technology, hydraulic performance tests at low pressure were conducted. The main structural parameters in this study were the aboveground height (A), spacing between the sprinklers (B), travel speed (C), and sprinkler nozzle diameter (D). An orthogonal array with four factors and three levels was selected, and the direct analysis technique was used to analyze the test data. Results show that the influencing factors in decreasing order of importance were as follows: CDBA for application depth; BACD for irrigation uniformity (CU); ACBD for application efficiency; CDBA for surface runoff; and CDBA for soil water content. The highest application efficiency obtained during the experiments was 95.1%, and the highest uniformity coefficient obtained was 96.4%. The application efficiency was high when the sprinkler height was low. CU was high when the spacing between the sprinklers was small. The surface runoff amount was low when the travel speed was high. The application depth and surface runoff were higher when the sprinkler nozzle diameter was larger. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Emitter Uniformity and Application Efficiency for Centre‐ Pivot Irrigation Systems

AbstractA significant portion of the intensively cultivated agricultural areas in the Southern Great Plains of the USA is located in the Texas High Plains. Agriculture in this region mainly depends on water from the vast underground Ogallala Aquifer. Due to excess withdrawal and a slow recharge process, groundwater levels are declining in many areas of the aquifer. Recently, regulations have been enacted in the Texas High Plains for restricting the amount of water pumped from the Ogallala Aquifer. In addition to pumping restrictions, conserving water by promoting irrigation systems with high application efficiency is also a priority. We investigated the emitted uniformity and application efficiency of 14 centre‐pivot irrigation systems in the Texas High Plains. Application efficiencies were in the range of 60–70% for mid‐elevation spray application (MESA) systems, 70–80% for low‐elevation spray application (LESA) systems, and greater than 90% for low‐energy precision application (LEPA) systems. Correction of the small number of defective emitters per system would not realize significant water savings. However, water savings could be realized by switching from MESA or LESA to LEPA, assuming the choice of crop allowed it. Copyright © 2015 John Wiley &amp; Sons, Ltd.

LEPA and Spray Irrigation for Grain Crops

Two low energy precision application (LEPA) sprinkler methods (double-ended socks and bubblers) and two spray sprinkler methods (low-elevation spray application and overhead spray) were used to irrigate corn, grain sorghum, and winter wheat in the Southern High Plains. For full or 100% irrigation, sufficient 25-mm applications were applied to maintain soil water at non-yield-limiting levels determined in earlier research with the three crops. Deficit-irrigated treatments were irrigated on the same days as the control treatment in 25 or 33% increments of the fully irrigated amount. Irrigation water was applied to or above alternate furrows with a three-span lateral move irrigation system. Corn and sorghum were grown on beds and furrows with all furrows diked, and wheat was flat-planted without basin tillage. Grain yields increased significantly with irrigation amount (p ≤ 0.05) for all crops during all years. With full irrigation, grain yields varied little among the sprinkler methods, and yields averaged 13.5, 8.9, and 4.6 Mg/ha for corn, sorghum, and wheat, respectively. With the 25 and 50% deficit irrigation amounts, sorghum yields with LEPA irrigation were 1.1 Mg/ha larger than with the two spray methods. For 75% irrigation of sorghum and for deficit irrigation of the other two crops, there was little yield difference between the LEPA and spray sprinkler methods. Grain yields were significantly correlated with seasonal water use with regression coefficients of 2.89, 1.84, and 0.915 kg/m3 for corn, sorghum, and wheat, respectively.

EVALUATION OF LESA TECHNOLOGY IN A SASKATCHEWAN ENVIRONMENT

The need for high energy input is one of the primary limitations to developing the sustainability of centre pivot irrigation. The purpose of the project described in this paper was to evaluate Saskatchewan performance data for Low Elevation Spray Application (LESA) irrigation technology. A centre pivot irrigation system equipped with standard impact nozzles was modified by the addition of drop tubes and Low Drift Nozzles (LDN). The application efficiency for the impact and LDN nozzles showed that both had a decreasing trend with increasing wind speeds, but the low drift nozzles had a better efficiency at all wind speeds. The application efficiency for the high pressure nozzles ranged from 69%–86% and the low drift nozzles from 74%–98%: an 8% difference in application efficiency for the LESA technology. The energy consumed by the two systems indicated that both systems had increased energy consumption with increased wind speed, but the low pressure LESA system used on average one half the energy required by the medium pressure impact system to deliver the same amount of water (0.107 kWh/m3 as compared to 0.057 kWh/m3).