Irrigation schedule improves productivity SCHEDULING IRRIGATION to meet crop needs while taking advantage of available soil moisture and rainfall will reduce costs, maintain yields and prevent water waste.

"The goal of irrigation in the Southern High Plains of Texas is to supplement rainfall, not provide all the water a crop needs from beginning to end," said Scott Orr, district director, High Plains Underground Water District.

Orr told farmers attending the recent Western Agricultural Chemical Institute annual conference at Lubbock that improving irrigation efficiency would preserve limited water resources and maintain profit potential.

"Declining well yield in this area poses a serious threat to irrigation," Orr said. "We have two challenges: maintain groundwater quantity by adjusting management to reduce water use and application losses, and maximize yields while reducing the amount of water we apply."

He said in areas of serious well yield decline, farmers must reduce water use. "And we must find ways to make equal or greater yields with the same or less water. Fortunately, we have systems available to help reach that goal."

Orr said irrigation scheduling will be critical. "We have to schedule applications to supplement rainfall with just enough water to maintain yields."

He said system type affects irrigation efficiency. "Most center pivots operate at 80 percent efficiency," he said. "Low Energy Precision Application (LEPA) systems operate at near 95 percent efficiency, and subsurface systems come close to 100 percent efficiency."

Excess irrigation costs include more than wasted water, Orr said. "With excess irrigation, farmers increase operating costs. They lose nitrogen from the soil and either replace it for added costs or risk yield loss. Extra energy required to pump unnecessary water means from $2 to $4 per acre additional expenses.

"We have a lot of inefficient pumps in operation. Repairing those is part of a the process to improve irrigation efficiency."

Orr said irrigation timing plays a critical role in irrigation scheduling. "Accurate timing is essential to maximum yields," he said. "And under drought conditions, proper timing helps make every drop count."

Orr said irrigating too close to a significant rainfall wastes water and risks nutrient and yield losses. "Soil type, crop rotation, and current-crop water use play important roles in preventing moisture stress or excessive irrigation," he said.

He cited five factors farmers should consider in irrigation scheduling. Farmers should determine:

Soil type.

Crop type and rooting depth.

Available water capacity.

Crop wilting point.

An estimate of the beginning soil moisture level. "The beginning point will affect the rest of the year."

He said farmers should schedule irrigation by:

- Determining effective rainfall.

- Determining net irrigation needs.

- Determining crop water use.

- Calculating current soil/water balance. "A soil probe, gypsum block or other soil moisture monitoring device will help."

- Estimating the next irrigation date and the amount needed. (Models of daily crop water needs are available.)

Orr said farmers should use the Potential Evapotranspiration (PET) coefficient to determine crop moisture needs. He said computer programs are available to help calculate irrigation schedules. "Growers can supply information on crop, field history, etc., to get a pretty good road map of where to go with irrigation scheduling," he said.

Orr said keeping up with optimum crop moisture needs in drought conditions like the one that has gripped the Texas High Plains since late June may not always be possible, but he said proper scheduling makes limited water resources go farther.

"The system does work to maintain groundwater quantity. Increasing irrigation application efficiency and reducing water loss will help farmers achieve maximum productivity," he said.

"Our goal is to make irrigation sustainable for the future."