CROP YIELD STUDIES


LEPA & close drop spacing A historical look at how & why this technology was developed


By Guy Fipps, PhD, PE


Close drop spacing is not a new concept but actually dates back to the 1970s. It’s hard to imagine what things were like back then in many ways, including the science of irrigation. Center pivot water application was dominated by high-pressure impacts located on top of the pivot mainline, which were inefficient and had high energy requirements. “Lower” pressure impacts began to be used in the late 1970s, which reduced operating pressures from 60 – 100 psi to 30 – 45 psi. Also in the 1970s, the United States experienced several energy shocks, including an oil embargo by OPEC, leading to gasoline shortages, long lines at gas stations and even-odd day rationing based on license plate number — even in oil rich Texas.


Growers who relied on groundwater were being squeezed hard by energy costs for pumping, including those on the High Plains of Texas. Two agricultural engineers at the Texas A&M AgriLife Research Center at Halfway (Bill Lyle, PE, and Jim Bordovsky) developed a simple idea to address the high energy use of pivots. While simple in concept, this idea resulted in a revolutionary center pivot water application technology and farming system, referred to as LEPA [low energy precision application]. LEPA is one of the best examples of a “disruptive” technology, in that after its introduction, center pivot irrigation was never the same again.


To lower energy requirements and improve water application efficiency, goosenecks and drops were developed. The drops were positioned close together, and water was discharged at or near the soil surface. Close drop spacing greatly improved the distribution efficiency or uniformity of water application. Positioning


14 Irrigation TODAY | October 2017


the applicator close to the ground eliminated spray evaporative losses and took advantage of the elevation change from the main line to the applicator to reduce pressure requirements. With LEPA, operating pressures for pivots on level ground could be reduced to as low as 6 psi, with greatly improved efficiencies.


The first LEPA applicators were fabricated from a variety of materials on hand, including a plastic soft drink bottle. Originally, they positioned a drop in every row with furrow diking, which necessitated planting in a circle. During that time, furrow diking was rapidly catching on in the Texas High Plains as a method to maximize the


An early LEPA applicator


fabricated from a plastic soft drink bottle


capture of rainfall and reduce runoff during irrigation. Some of the first research that Lyle and Bordovsky conducted was to determine if LEPA drops could be placed in every other row with equal effectiveness. The table illustrates some of their results with little difference in yield compared to every row. As a result, drops with spacing in every other row became established.


The other name synonymous with close drop spacing and LEPA is Leon New,


Comparison of crop yields from five multiyear experiments using applicators of given spacings, Texas A&M AgriLife Research, Halfway, Texas


Yield {lb/acre} Crop (location)


Corn grain (Halfway)


Sorghum grain (Halfway)


Soybean grain (Halfway)


Cotton lint (Halfway)


Cotton lint (Lamesa)


% of base irrigation


40 70


100 130


40 70


100 130


100 50 100


50 75


100


LEPA: 40" applicator spacing


7,410 a 9,110 b 10,400 a 11,100 a


6,290 a 6,790 a 6,800 a 6,630 a


2,460


700 a 990 a


770 a 980 a 1,030 a


570 b 910 a


610 b 825 b 970 a


* Yield means in same row followed by common letter are not significantly different (p < 0.05, Duncan).


LEPA: 80" applicator spacing


7,410 a* 9,820 a 10,360 a 11,160 a


6,020 a 6,620 a 6,800 a 6,850 a


2,110


LESA: 80" applicator spacing


Overhead spray: 240" applicator spacing


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