Low Energy Precision Application Irrigation Research Articles

Low-Energy Precision Application (LEPA) Irrigation: A Forty-Year Review

Abstract. The low-energy precision application (LEPA) irrigation concept was developed 40 years ago (ca. 1978) to address the depletion of irrigation water from the Ogallala Aquifer and the sharp increase in pumping costs caused by the 1970s fuel crisis occurring at that time in the Texas High Plains. The LEPA method applies water to the soil surface at low pressure using a tower-truss irrigation system that continually moves through the field. This method brought changes in irrigation equipment and management that resulted in improvements in water productivity, particularly in semi-arid locations with diminishing water supplies. A review of published information pertaining to LEPA history, evaluation, and usage was performed. On landscapes of less than 1% slope, negative crop yield effects caused by irrigation runoff and start-stop system alignment were overcome with appropriately spaced basins, or furrow checks, and multiple irrigations over the course of the growing season. No consistent yield advantage at any level of irrigation was documented by placing water in every furrow (1 m spacing) compared to alternate furrows (2 m spacing). In irrigation treatments having =50% of the estimated full irrigation quantity, LEPA resulted in a 16% yield increase over sprinkler methods, although subsurface drip irrigation (SDI) resulted in a 14% yield increase over LEPA. At irrigation levels >50% of full irrigation, crop yields of sprinkler treatments were only slightly less than those of LEPA, and SDI yields were 7% greater than LEPA. The LEPA irrigation method was the catalyst for innovations in chemigation, no-till planting, and site-specific irrigation. As irrigation water becomes more limited, use and proper management of optimum irrigation methods will be critical. Keywords: Basin tillage, Chemigation, Evapotranspiration, Irrigation methods, LEPA, Low-energy precision application, Runoff, Spray irrigation, Sprinkler irrigation, Uniformity, Water use efficiency.

Comparative research on water and energy-saving irrigation systems in the GAP and Aegean regions of Turkey

This research was carried out to determine the effects of furrow, sprinkler, drip, mobile nozzle, mobile drip and LEPA (Low Energy Precision Application) irrigation methods on the yields and Water Use Efficiency of cotton in the South Eastern Anatolian Project (GAP) Area and in the Aegean Region. According to the results obtained, the highest yield was produced from the drip irrigation method. The drip, sprinkler and mobile nozzle forms of irrigation require 31, 28 and 26% less irrigation water respectively than furrow irrigation when related to the optimum yields and the feasible irrigation water quantities in the GAP Area. The drip irrigation method has utilised the irrigation water more efficiently than the other methods. LEPA and mobile drip did not show any significant difference in the effective use of irrigation water compared to furrow irrigation. Similar results were obtained in the Aegean Region of Turkey.

Comparative research on water and energy-saving irrigation systems in the GAP and Aegean regions of Turkey

This research was carried out to determine the effects of furrow, sprinkler, drip, mobile nozzle, mobile drip and LEPA (Low Energy Precision Application) irrigation methods on the yields and Water Use Efficiency of cotton in the South Eastern Anatolian Project (GAP) Area and in the Aegean Region. According to the results obtained, the highest yield was produced from the drip irrigation method. The drip, sprinkler and mobile nozzle forms of irrigation require 31, 28 and 26% less irrigation water respectively than furrow irrigation when related to the optimum yields and the feasible irrigation water quantities in the GAP Area. The drip irrigation method has utilised the irrigation water more efficiently than the other methods. LEPA and mobile drip did not show any significant difference in the effective use of irrigation water compared to furrow irrigation. Similar results were obtained in the Aegean Region of Turkey.

LEPA and trickle irrigation of cotton in the Southeast Anatolia Project (GAP) area in Turkey

This study was designed to evaluate the yield response of low-energy precision application (LEPA) and trickle-irrigated cotton grown on a clay-textured soil under the arid Southeast Anatolia Project (GAP) area conditions during the 1999 growing season at Koruklu in Turkey. The effects of four different irrigation levels (100, 75, 50, and 25% of cumulative Class-A pan evaporation on a 6-day basis) for LEPA, and two irrigation intervals (3-day and 6-day) and three different levels (100, 67, and 33% of cumulative Class-A pan evaporation on a 3-day and 6-day basis) for the trickle system on yield were investigated. Water was applied to alternate furrows through the double-ended Fangmeier drag-socks in the LEPA system. Trickle irrigation laterals were laid out on the soil surface at a spacing of 1.40 m. A total of 814 mm of water was applied to the full-irrigation treatments (100%) for both irrigation systems. Seasonal water use ranged from 383 to 854 mm in LEPA treatments; and 456 to 868 mm in trickle treatments. Highest average cotton yield of 5850 kg/ha was obtained from the full-irrigation treatment (100%) in trickle-irrigated plots with 6-day intervals. The highest yield in LEPA plots was obtained in LEPA-100% treatment with an average value of 4750 kg/ha. Seed cotton yields varied from 2660 to 5040 kg/ha and 2310 to 5850 kg/ha in trickle irrigation plots with 3-day and 6-day intervals, respectively, and from 2590 to 4750 kg/ha in LEPA plots. Irrigation levels both in LEPA and trickle-irrigated plots significantly increased yield. However, there was no significant yield difference between 100 and 67% irrigation levels in trickle-irrigated plots. Maximum irrigation water use efficiency (IWUE) and water use efficiency (WUE) were found as 0.813 and 0.741 kg/m 3 in trickle-irrigated treatment of 67% with 6-day interval. Both IWUE and WUE values varied with irrigation quantity and frequency. The research results revealed that both the trickle and LEPA irrigation systems could be used successfully for irrigating cotton crop under the arid climatic conditions of the GAP area in Turkey.

EFFICIENCY AND UNIFORMITY OF THE LEPAAND SPRAY SPRINKLER METHODS: A REVIEW

Application efficiencies and uniformity coefficients reported for the low energy precision application (LEPA)and spray sprinkler irrigation methods are reviewed and summarized. The relative sizes of the water loss pathways forthe two sprinkler methods are also summarized. With negligible runoff and deep percolation, reported applicationefficiencies for LEPA are typically in the 95 to 98% range. Measurements such as chemical tracers, weighing lysimetercatches, and energy balance modeling are believed to be more accurate than small collector measurements forestimating spray application efficiency. Spray application efficiencies based on these other measurements exceed 90%when runoff and deep percolation are negligible. Because of the start and stop nature of mechanical move irrigationsystems, uniformity coefficients for LEPA and spray are measured both along the irrigation system mainline and in thedirection of travel. Along the mainline, reported uniformity coefficients are generally in the 0.94 to 0.97 range for LEPAand in the 0.75 to 0.85 range for spray. In the direction of travel, the uniformity coefficients are generally in the 0.75 to0.85 range for LEPA with furrow diking and in the 0.75 to 0.90 range for spray. On start and stop sprinkler systems,basin tillage on a 2 to 4 m spacing is critical for uniform LEPA irrigation because the basins prevent runoff and averagethe applications during several unequal start and stop times. Runoff is the largest potential water loss pathway for bothLEPA and spray irrigation. For the spray method, runoff can exceed either droplet evaporation and drift or nonbeneficialcanopy evaporation.

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.

LEPA Irrigation of Grain Sorghum with Varying Water Supplies

Research was conducted on the Texas Southern High Plains to determine optimum water management practices for low energy precision application (LEPA) irrigation of grain sorghum. Irrigation quantity treatments ranged from 0.4, 0.7, 1.0, and 1.3 BI (BI = ET rain) and were applied both alternate and every furrow at intervals of 3.5, 7, 10.5 and 14 days during the growing season from 1992 through 1994. The experiment was conducted at Halfway, Texas on an Olton loam soil with moderately slow permeability. Highest average grain sorghum yields were obtained with the 3.5-day irrigation intervals (7.57 Mg ha1) which was significantly different (P = 0.05) from 7, 10.5, and 14-day intervals when averaged across all years and quantities. These treatments yielded 7.37, 7.33, and 7.33 Mg ha1 respectively. Grain yield was significantly different between preplant only, 0.4 BI and 0.7 BI water quantities. However, there were no yield differences between 0.7, 1.0, and 1.3 BI water quantity treatments (7.51, 7.62, and 7.55 Mg ha1, respectively) which resulted in seasonal irrigation water use efficiency (IWUE) for the 0.7 BI treatment of almost double that of the 1.3 BI treatment (1.16 kg m3 vs. 0.63 kg m3). Total seasonal water use efficiency [WUE = yield/(irrigation + rainfall + soil water depletion)] varied with irrigation quantity and frequency. Values were 1.69, 1.56, 1.36, and 1.19 kg m3 for the 0.4, 0.7, 1.0, and 1.3 BI treatments respectively. WUE for preplant only irrigation was 1.52 and was equal to the 0.7 BI irrigation treatment. The three year average 3.5-day irrigation interval resulted in a significantly higher WUE than the 14-day interval (1.47 vs. 1.43 kg m3, respectively). There were no significant responses in yield, IWUE or WUE due to applicator location (alternate vs. every furrow). Tests show that deficit seasonal LEPA irrigation (approximately 0.7 BI) of medium maturity grain sorghum varieties on the Southern High Plains can be employed without significant yield loss if adequate preplant soil water is available. Frequent irrigation intervals added only slightly to yield but are desirable in order to decrease surface relocation of water from high intensity LEPA application.

Effect of LEPA Irrigation on Storage in Implanted Reservoirs

Successful irrigation with a Low Energy Precision Application (LEPA) package on a center pivot depends on storing some water on the soil surface until it can infiltrate. Storage can be increased with basin or implanted reservoir tillage; however, persistence of storage throughout the irrigation season may be limiting. We developed a method to measure the cross-sectional profiles and the volume of storage in implanted reservoirs. We used these methods to measure the change of storage during the irrigation season on a silt loam soil (0.2% slope). We evaluated three configurations of the implement used to create the reservoirs and five water discharge rates with the LEPA devices.

Role of transpiration suppression by evaporation of intercepted water in improving irrigation efficiency

Sprinkler irrigation efficiency declines when applied water intercepted by the crop foliage, or gross interception (Igross), as well as airborne droplets and ponded water at the soil surface evaporate before use by the crop. However, evaporation of applied water can also supply some of the atmospheric demands usually met by plant transpiration. Any suppression of crop transpiration from the irrigated area as compared to a non-irrigated area can be subtracted from Igross irrigation application losses for a reduced, or net, interception (Inet) loss. This study was conducted to determine the extent in which transpiration suppression due to microclimatic modification resulting from evaporation of plant-intercepted water and/or of applied water can reduce total sprinkler irrigation application losses of impact sprinkler and low energy precision application (LEPA) irrigation systems. Fully irrigated corn (Zea Mays L.) was grown on 0.75 m wide east-west rows in 1990 at Bushland, TX in two contiguous 5-ha fields, each containing a weighing lysimeter and micrometeorological instrumentation. Transpiration (Tr) was measured using heat balance sap flow gauges. During and following an impact sprinkler irrigation, within-canopy vapor pressure deficit and canopy temperature declined sharply due to canopyintercepted water and microclimatic modification from evaporation. For an average day time impact irrigation application of 21 mm, estimated average Igross loss was 10.7%, but the resulting suppression of measured Tr by 50% or more during the irrigation reduced Igross loss by 3.9%. On days of high solar radiation, continued transpiration suppression following the irrigation reduced Igross loss an additional 1.2%. Further 4–6% reductions in Igross losses were predicted when aerodynamic and canopy resistances were considered. Irrigation water applied only at the soil surface by LEPA irrigation had little effect on the microclimate within the canopy and consequently on Tr or ET, or irrigation application efficiency.

Yield and Water Use Efficiency of Corn in Response to LEPA Irrigation

Center-pivot sprinklers are rapidly expanding on the Southern High Plains, and LEPA (low energy precision application) application methods are widely used in this region to reduce water application losses, to use the relatively low well yields, and to reduce energy requirements for pressurization. This study was conducted to evaluate LEPA irrigation response of corn (Zea mays L.) on slowly permeable Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll). The effects of irrigation amount were investigated in a field study during the 1992 and 1993 cropping seasons at Bushland, Texas. In 1992, a wetter than normal season, grain yields varied from 0.6 to 1.2 kg/m2 while in 1993, which was a season with slightly less than normal rain, grain yields varied from 0.4 to over 1.5 kg/m2 as irrigations increased from no-post plant irrigations to fully meeting the crop water use. Irrigation amounts for the full irrigation varied from only 279 mm for the wet year to over 640 mm for the more normal year. A significant relationship was found between grain yield and water use for the two years described as GY (kg/m2) = 0.00169 [WU (mm) 147] with an r2 of 0.882 and a Sy/x of 0.10 kg/m2. Deficit irrigation of corn, even with LEPA, reduced yields by affecting both seed mass and kernels per ear. Generally, the grain yield was in proportion to dry matter yield. LEPA irrigation was shown to be efficient in terms of partitioning the applied water into crop water use. Irrigation amounts should not exceed 25 mm for alternate furrows (0.76-m rows) LEPA on the Pullman-type soils with furrow dike basins.

Lepa Corn Irrigation with Limited Water Supplies

Declining water tables on the Southern High Plains may reduce irrigated corn area in the region and/or cause a shift to deficit irrigated production. This research was conducted to determine optimum water management practices for low energy precision application (LEPA) irrigation of corn with limited water supplies and to evaluate the prospects for deficit irrigation based on yield response. Irrigation quantities ranged from deficit to excess irrigation [0.4, 0.7, 1.0, and 1.3 BI (BI = ET rainfall)] and were applied both alternate and every furrow at intervals of 3, 6, 9, and 12 days from 1989 through 1991. The study was conducted at Halfway, Texas, on a moderately permeable (2.5 mm h1) Olton loam soil. Seasonal irrigations (1.0 BI) ranged from 299 mm in 1991 to 453 mm in 1990. Highest corn grain yields were obtained with three-day and six-day irrigation intervals (11.1 Mg ha1 each). Significant yield declines occurred for the 9-day (10.6 Mg ha1) and 12-day (10.2 Mg ha1) intervals. Grain yield increased with water quantity and ranged from 8.3 Mg ha1 for the 0.4 BI treatment (147 mm average seasonal irrigation) to 12.4 Mg ha1 for the 1.3 BI treatment (428 mm average irrigation). Applicator location (alternate vs. every furrow) had no effect on yield except for the 0.7 BI quantity treatment where alternate was greater than every furrow (P = 0.05). Water use efficiency responded significantly to water quantity (P = 0.05) with the highest occurring also at 0.7 BI (1.90 kg m3). This research showed that irrigation quantities applied at infrequent intervals typical of furrow irrigation (9 to 12 days) can be reduced as much as 30% by lowering the irrigation interval to six days or less without corn grain yield reduction. It was concluded that substantial water savings can be achieved by adopting a high frequency LEPA irrigation schedule and a moderate deficit irrigation management program (0.7 to 0.8 BI) without experiencing significant yield decline, but rather, resulting potentially in increased net returns.

Impact of Reservoir Tillage on Runoff Quality and Quantity

The effects of reservoir tillage on runoff and water quality were studied under two levels of soil compaction in the production of cotton. A wide frame tractive vehicle was used during plot establishment and during all farm operations to provide the desired soil compactions. LEPA (Low Energy Precision Application) irrigation was used to apply supplemental water as required. Runoff quantity was monitored with flumes and runoff samples were taken using Coshocton-type runoff samplers. Thirteen runoff events were monitored and analyzed over a two-year period for the replicated, four-treatment study. Reservoir tillage decreased runoff and total discharges of organic nitrogen and phosphate. Differences in concentrations of water quality parameters (total solids, ammonium, total kjeldahl nitrogen, nitrate, phosphate, and COD) were not statistically significant. Although not statistically different, total runoff and total discharge of water quality parameters (except phosphate) were lower for the low compacted treatments compared to the high compacted treatments.

Importance of Soil and Cropping Systems in the Development of Regional Water Quality Policies

AbstractTargeting certain soils and cropping systems may be necessary in consideration of regional water quality protection policies. However, little information is available relating soils and cropping practices to regional water quality problems. This study evaluates crop yield and NO3‐N movement to surface and groundwater on four soils and nine principal cropping systems in the High Plains region of Oklahoma. The cropping systems involve wheat (Triticum aestivum L.), grain sorghum [Sorghum bicolor (L.) Moench], and corn (Zea mays L.), and are part of a regional data base also containing soils and chemical management information. For each combination of crop, soil, cropping system, and chemical alternative, a 20‐yr simulation was made. The simulation was based on a modeling system that includes EPIC‐PST (crop growth/chemical movement model) interfaced with a Geographic Information System (GIS), Earthone. Results of each simulation included crop yield and NO3‐N movement in runoff and percolation. Results show wide variations in NO3‐N losses for different soils, irrigation systems, and cropping systems. When compared with continuous irrigated wheat and grain sorghum cropping systems, double‐cropped wheat‐grain sorghum resulted in greater NO3‐N loss in percolation. Compared with sprinkler and LEPA (low energy precision application) irrigation systems, furrow irrigation resulted in high NO3‐N loss on both fine‐textured and coarse‐textured soils, with significantly greater loss on the coarser‐textured soils. The modeling framework can be used to compare alternative water quality policies. Broad policies such as a restriction on the amount of N that can be applied per hectare can be compared with targeted policies, such as limiting N applications or irrigation water use on coarser soils or under furrow irrigation.

Uniformity of Infiltrated Water Under a Low Energy Precision Application (LEPA) Irrigation System

ABSTRACT UNIFORMITY of infiltrated water of LEPA irrigation systems is not only affected by hydraulic losses, but also by the machine movement, the furrow check spacing, and the variability of soil infiltration rates, since water is ponded between dikes or checks along a furrow. We assessed the impact of these sources of nonuniformity using both machine movement characteristics measured during a field evaluation of a linear-move machine and soil infiltration measurements made over consecutive 1-m intervals during an unrelated project. Results showed that while the reported uniformity of the nozzle discharges may be 95%, the uniformity of infiltrated water may be between 80% to 85%. For small check spacings, uniformity was primarily affected by the machine movement, while for larger spacings, variability in the soil infiltration rate was the controlling factor. Results show need to consider all sources of nonuniformity of infiltrated water.

Lepa irrigation system evaluation

ABSTRACT THE LEPA (Low Energy Precision Application) irrigation concept has been extensively tested for two years and compared with sprinkler and furrow methods. The evaluation included application efficiency, distribution efficiency, water use efficiency and energy savings potential. The LEPA system was superior in all categories. Soybeans were used as a test crop and the yield data support the irrigation efficiency results and indicate an economic justification for conversions to LEPA irrigation.