Soil type and structure, water quality and capacity and type of system play important roles in efficient peanut irrigation.
Different systems may work best at different times during the growing season or under different local conditions, says Dana Porter, Texas Cooperative Extension engineer at Lubbock, Texas.
Low Energy Precision Application (LEPA) and Low Elevation Spray Application (LESA) offer better moisture management opportunities than Subsurface Drip Irrigation (SDI) season-long,” Porter said in response to a recent peanut production seminar audience in Seminole, Texas.
“LEPA generally provides good moisture for germination but in coarse soils may not distribute water laterally near the soil surface to support pegging and pod development as well as LESA.”
Most LEPA systems distribute moisture on every other row, relying on the soil's hydraulic conductivity to distribute the water laterally across the root zone. In particularly coarse soils, this lateral water distribution may not be sufficient. LESA systems use low-hanging nozzles to spray inside the canopy, wetting part of the plant and the soil surface.
“With LEPA, farmers have less evaporation loss. With LESA, it’s easier to manage near surface soil moisture,” Porter said. “Management is the key for either system.”
She doesn’t recommend subsurface drip irrigation (SDI) alone for peanuts. “Germination may be a problem without a timely planting rain,” she said. “I’m a little nervous with drip irrigation for peanuts. However, a combination of drip and an overhead system would probably work well. Growers can assure adequate moisture for germination and keep the soil surface wet at pegging time with the overhead system, and take advantage of the efficiency of subsurface drip irrigation during the vegetative growth stage.”
“Early in the season most crops develop roots and grow in moist soil.” She said even with a long drought, growers still find some moisture a few inches deep in much of the West Texas peanut area.
Porter said peanut moisture use differs from cotton. “The effective root zone of a peanut is three feet, shallower than for most other crops. And peanuts need near-surface moisture during pegging.” Peanut rooting depth ranges from 1.6 feet to 3.3 feet.
Hard pans and caliche layers may restrict root penetration, she said.
Peanut plants require more water, at 20 inches to 30 inches per season, than does cotton at 13 inches to 27 inches. Sorghum also needs 13 inches to 27 inches, but corn demand ranges from 28 inches to 32 inches.
“We assume about one-fourth inch of moisture a day for peanuts,” Porter said. “They may use one-third inch or more on hot, dry days. And peanut soils typically do not have good water-holding capacity.
“Too much water, however, especially late in the season, may result in increased pod rot.”
She said peanut plants have two functions: pod support and plant support. “The water use curve is generally downward after the peak but growers want to keep moisture available a little longer than they would for cotton.”
“Available moisture is limited in the sandy soils typical for peanut production, but over-watering may result in moisture leaching out the bottom. Watering heavier, clay soils too much results in runoff. “We may often face a trade-off between efficient water use and timely application with a limited water capacity.”
Porter said proper irrigation system maintenance also improves water use efficiency. “Checking nozzles and water pressure will help growers achieve optimum performance,” she said.
Water quality is another factor. In West Texas, there are some localized problems with salinity in irrigation water. “Farmers may see a salt crust on the soil surface or may notice some leaf burn,” she said. “They have to manage salty water carefully in peanuts. SDI or LEPA irrigation are good options for managing saline waters.
“Evaporation pulls the water out of the soil and leaves a crusty salt deposit,” Porter said. “The plant takes up some salt. More irrigation water may be necessary to flush the salt out of the soil.”
Porter said a new Web site, txhighplainset.tamu.edu, takes farmers to the evapo-transpiration network database where they can evaluate in-season plant moisture needs.