Steve Hague, Alphonse Coco and Donald J. Boquet

Profitable cotton yields can be produced on Louisiana’s alluvial soils when limiting factors are overcome. These include insect, nematode and weed pests and water. Too much or too little water within the soil profile retards cotton root development and nutrient uptake efficiency. Irrigation, properly applied, can increase yields, but improper management of irrigation can limit yields. Although 40 percent of Louisiana cotton is irrigated, the optimal criteria for when to initiate, apply and terminate irrigation are lacking for Louisiana’s unsettled weather patterns.

The most important reason farmers irrigate cotton on Louisiana’s alluvial soils is to avoid catastrophic yield losses from severe drought. This is crucial considering the costs of equipment, labor, seed technology, fertilizer and pest control in the early part of the growing season. The most effective cotton irrigation schemes probably will take several years to provide a return on investment. Economic benefits from irrigation systems may be increased if producers rotate cotton with other crops such as soybean, corn or rice, which have a higher water-use demand. If producers choose to irrigate cotton on alluvial soils, timing is critical.

LSU AgCenter research focuses on low-input programs that offer the best opportunity for producers to realize a return on investment. Furrow irrigation tests were conducted on both Sharkey clay and Commerce silt loam on large commercial fields owned by the Panola Corp. and on Sharkey clay at the Northeast Research Station near St. Joseph, La. These tests compared the effectiveness of several scheduling techniques.

One of the systems included the Arkansas Irrigation Scheduler (AIS), a computer program developed at the University of Arkansas. The program recommends irrigation when soil moisture reaches a water-budget deficit designated by the user. Irrigation treatments included a 2-inch (AIS 2.0) and 3-inch (AIS 3.0) deficit as well as a non-irrigated control. An AIS treatment (AIS 4.0) was tested in 2000, which allowed the soil moisture deficit to reach 4 inches before irrigation and then maintained a 2-inch deficit for the rest of the growing season.

A water-budgeting system developed at the LSU AgCenter was included in the trials. This system assumes daily 0.22-inch water use and recommends irrigation when the water budget deficit reaches 1.5 inches (1.5 WB). U.S. Department of Agriculture cotton loan schedules were used to calculate gross revenue from lint per acre based on yield and fiber properties from each treatment.

In 2000, less than 7 inches of rain fell in June, July and August, resulting in high irrigation demand. Responses to irrigation were observed (Figures 1 and 2) at Panola Corp. on both soil types. Performance of all irrigation schedules exceeded non-irrigated control treatments. Schedules that required the most frequent irrigation applications were slightly advantageous in terms of yield and fiber quality; however, high gross returns were realized from regimes with fewer applications.

In 2001 and 2002, timely rainfall occurred during the growing season. Damaging precipitation just before harvest caused severe yield and quality losses in both years. At the Panola Corp. in 2001, AIS 2.0 performed well on both soil types and cotton responded better to 1.5 WB on Sharkey clay than on Commerce silt loam. The on-station tests showed little to no economic benefit from irrigation in 2001 and 2002 (Figure 3). In fact, plants suffered from mild waterlogging because of irrigation in 2002.Research findings suggest small yield advantages and no economic benefit from irrigating cotton on alluvial soils in years with normal to above-average rainfall. In a drought year, such as 2000, positive yield responses and economic benefits can be expected from irrigation.

Scheduling methods affect the yearly number of irrigation applications and can influence yield significantly. While AIS 2.0 most often maximized gross returns, other schedules performed well and conserved more water. AIS may be a viable option for scheduling irrigation, but other options are needed for Louisiana that will account for local conditions and needs of growers. Efforts are being directed toward developing an irrigation scheduling system for Louisiana cotton producers that is user friendly, optimizes yield and fiber quality, conserves water and maximizes profit. Studies are under way to determine the correct time to initiate and terminate irrigation using crop growth monitoring and also to determine the interactions of irrigation with various management practices.

(This article appeared in the spring 2003 issue of Louisiana Agriculture.)