With the depletion of some underground water sources, many growers are seeking greater irrigation efficiency without loss of yields. Researchers in Texas may have the answer in socks.

They're growing 70- to 80-bu/acre soybeans using LEPA irrigation that provides up to a 98% water-use efficiency.

Using LEPA (low-energy precision application) double-ended socks, Arland Schneider, USDA-ARS ag engineer, is getting yields comparable to those produced from LESA (low-elevation spray application) and traditional above-canopy center-pivot watering systems. But he's saving water at the same time.

Schneider has been with ARS at Bushland, TX, over 30 years. Until recently, soybeans have not been part of regional corn-wheat, corn-sorghum or cotton rotations. Bean acres are higher now. And for growers seeing their irrigation water sources dwindle, beans could be a more attractive crop.

"With a sound LEPA or LESA irrigation program, we can grow 70- to 80-bu soybeans in this area," he says. "But what is just as important is the grower's ability to get the most out of his water. Both LEPA and LESA do a good job, but LEPA provides for lower evaporation rates. And with runoff controlled, LEPA's water-use efficiency is usually higher."

Traditional LEPA systems feature drop lines fitted with socks that drag along the furrow and distribute water directly to the surface. There is no chance for drift. The evaporation rate is 6-10% less than spraying above the crop canopy with LESA, which features low-pressure nozzles situated 1-2' above the surface.

In Bushland studies last year, Schneider and his associates planted 30"-row beans and had 60" spacings of both LEPA socks and LESA nozzles, spacings common among pivot irrigators using 30"-row cropping systems. They also included mid-elevation nozzles situated 5' above the surface.

About 14" of water were applied in each system. Above-normal spring and early summer rains helped reduce irrigation needs. Total water use was about 32". All three systems yielded close to 80 bu, but water-use efficiency was greatest for the LEPA beans.

Schneider says that for most effective results, fields must be furrow-diked to provide surface-water storage capacity. "LEPA applications should not exceed the size of water storage capacity. Furrow dikes can hold up to 1" of water from either irrigation or rainfall and prevent runoff."

He also suggests deep tillage to enhance infiltration, or leaving the previous crop's residue in the field to hold more water.

In Southern areas, Schneider sees soybeans under LEPA as a good rotational crop with cotton. "Cotton still gives the highest return per unit of water applied. Soybeans can fit well into such a program."

He advises growers not to skimp on water with soybeans if possible. "Don't use deficit irrigation with beans," he says. "You need to go for the high yields."