Submitted to: Irrigation Association Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/28/2005
Publication Date: 11/6/2005
Citation: Colaizzi, P.D., Evett, S.R., Howell, T.A. 2005. Cotton production with SDI, LEPA, and spray irrigation in a thermally-limited climate. In: Irrigation Association Conference Proceedings, November 6-8, 2005, Phoenix, Arizona. 2005 CDROM. Interpretive Summary: Cotton has long been an important crop in West Texas, and the region centered around Lubbock is one of the largest cotton producing areas in the U.S. The northernmost extent of this production has traditionally been just south of Amarillo, TX. Further north, the climate is not warm enough for cotton to be a reliable crop, and so corn is produced instead. The problem with corn is that it requires much more water than other crops such as cotton, and must be irrigated in semi-arid regions. In the Great Plains, practically all water for irrigation must be pumped from the Ogallala aquifer, a finite and declining freshwater resource. Producers in traditional corn-producing regions are therefore considering cotton as an alternative crop, which has the same revenue potential but requires less than half the irrigation water as corn. Although the cooler climate imposes some risk for cotton production, this risk can be reduced somewhat by shorter season varieties. In order to stretch irrigation water resources, many producers are also considering subsurface drip irrigation (SDI), which is a highly efficient irrigation technology and possible alternative to center pivot sprinkler systems. Center pivot sprinklers are very efficient, but they loose a small amount of water to evaporation (either from water droplets passing through the air or from water on the soil surface). With SDI, water is delivered directly to the plant root zone by plastic tubing beneath the soil surface, so the evaporative loss is eliminated, making SDI (in theory) slightly more efficient than sprinklers. The lack of soil surface evaporation with SDI is also thought to reduce evaporative cooling that would otherwise happen with sprinklers, which may lead to earlier maturity for SDI-irrigated cotton. Some producers to our south claim that they can harvest cotton a week or two earlier under SDI than under center pivot sprinklers. This consideration becomes increasingly critical as cotton moves northward. We tested the hypothesis that SDI induces earlier maturity in cotton by establishing a field experiment, where cotton is irrigated with several common sprinkler configurations and SDI. In the first two years of this study (2003 and 2004), cotton maturity was more related to irrigation rate than irrigation method, with dryland and minimal irrigation rates reaching maturity earliest. However, fiber quality was usually better with SDI, and fiber quality has become increasingly important for U.S. cotton in order to compete successfully in the global market. Lint yield was greatest with SDI at low irrigation capacities in 2003 and greatest with SDI regardless of irrigation capacity (except for dryland) in 2004.
Technical Abstract: Producers in the Northern Texas Panhandle and Southwestern Kansas are considering cotton as an alternative crop to corn because cotton has a similar profit potential for about one-half the irrigation requirement. However, limited growing degree days pose some risk for cotton production. We hypothesized that cotton under subsurface drip irrigation (SDI) would undergo less evaporative cooling following an irrigation event compared with low energy precision applicators (LEPA) or spray irrigation and, therefore, would increase growing degree day accumulation and lead to earlier maturation. Cotton maturity was more related to irrigation rate than irrigation method, with dryland and minimal irrigation rates reaching maturity earliest. However, fiber quality, as indicated by total discount, was usually better with SDI. Lint yield and water use efficiency were greatest with SDI at low irrigation rates in 2003, and lint yield and gross returns were greatest with SDI regardless of irrigation rate in 2004.