Drip Irrigation Project Yields Promising Results

Dr. John Sij, AgriLife Research agronomist, said his cotton trials suffered through hail and drought, but he was able to produce more cotton with less water using subsurface drip irrigation.

"We started out with good stands and then a hail storm in June knocked out 25 percent of the plants," Sij said. "But under drip, the plants came roaring back, and we still made two-and-a-half to three-bale cotton, so that is really kind of amazing."

The other result he saw in this past year's trials is that 100 percent replacement of water lost by evapotranspiration not only didn't help the cotton, but in some cases set it back by delaying boll opening and thus harvesting. Evapotranspiration is the loss of water from the soil both by evaporation and by transpiration from the plants growing there.

Sij stressed this is the first year of results in a three-year study, but the boll numbers did not increase beyond 66 percent of evapotranspiration replacement.

"We only put on 7 ½ inches of water with the 100 percent irrigation treatment, along with a rainfall total of about 17 inches, for a total water application of 24.65 inches to the crop for the season," he said.

The study is designed to develop conservation tillage and water management strategies that enhance crop-stand establishment, water-use efficiency and yield in subsurface drip-irrigated cotton production in the Rolling Plains.

Sij is looking at different tillage systems, including conventionally tilled bedded rows, reduced-tillage flat-planted rows; no-till flat-planted rows and no-till rows planted into a terminated wheat cover crop.

The cotton was irrigated from June 4 to Aug. 14, after a May 15 planting date. The irrigation rates of 0 percent, 33 percent, 66 percent, 100 percent and 133 percent evapotranspiration replacement were tested.

Some of Sij's other findings this first year included: no significant difference among tillage treatments for plant height and no significant differences among tillage systems for lint yield within an irrigation treatment.

He found there was a significant increase in plant height with increased evapotranspiration replacement, and the economics of the drip irrigation favored a no-till flat planting at the 66 percent to 100 percent replacement rate. The station has 13 acres partitioned into 72 small plots and another 18 acres divided into larger, commercial-sized production fields under subsurface drip irrigation.

"We worked up some economics from a cropping system study, and we figured we grossed over $800 an acre, and netted more than $500 an acre," Sij said. "Our yield monitor on our commercial harvester showed areas of production that hit four bales per acre. I think we would have had higher yields in places if we hadn't had the hail and the lost heat units."

"In production-sized fields, we compared a 100 percent ET (evapotranspiration) treatment with a furrow-irrigated field," he said. "The drip field yielded 2.5 bales per acre and the furrow field yielded 1.6 bales per acre. That's about $250 per acre difference in gross income.

"The difference is due in part to being able to put more water on the field with the drip, and the efficiency with which we can supply water directly to the roots of the plants." He said because a low-pressure pump was used, electricity cost $1.69 per acre inch of water with a low-pressure pump on the drip irrigation system. They also realized another unexpected savings due to the quality of the water pumped on the crop.

The water from the well used was is high in nitrates, so the crop essentially received 35 pounds of free nitrogen that was put out with the irrigation water, or about $1 per pound savings last summer, Sij said.

"In our area, that is a positive. Producers should check out the nitrate levels of the irrigation water," he said. "While we know we have to have other nutrients met by other fertilization requirements, these nitrates coming through the drip irrigation system directly feed the roots of the plants, so it is nearly 100 percent efficient."

Sij said samples of the cotton have been submitted for fiber quality testing, but he expects to have good quality cotton.