Submitted to: Irrigation Association Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: September 15, 2004
Publication Date: November 17, 2004
Citation: Colaizzi, P.D., Evett, S.R., Howell, T.A. 2004. Comparison of SDI, LEPA, and spray irrigation performance for cotton in the North Texas High Plains. In: Irrigation Association Conference Proceedings. 25th Annual International Irrigation Show, November 14-16. 2004, Tampa, Florida. p. 459-474. 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 is 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. Our first year of data did not support this hypothesis, but we did find that SDI was more efficient than the sprinkler systems for limited irrigation (a.k.a. deficit irrigation, where plant water needs are only partially met, which is typical in our region due to limited irrigation well capacities), but sprinklers were more efficient than SDI for full irrigation (where plant water needs are fully met). Also, cotton fiber quality was slightly better under SDI. We are continuing this experiment for several more seasons, and we plan to modify the experiment beginning in 2005 to simulate a more "real-world" use of SDI.
Technical Abstract: Producers in the North Texas High Plains (Amarillo and north) are considering cotton as an alternative crop to corn because cotton has a similar profit potential for about half the irrigation requirement. However, limited heat units 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 to low energy precision applicators (LEPA) or spray irrigation and therefore increase heat unit accumulation and lead to earlier maturation. In the 2003 season, lint yield and water use efficiency were greater with SDI under low irrigation capacities (25% and 50% of full irrigation), but were greater with LEPA and spray under full irrigation. Fiber quality, as indicated by total discount, was greater with SDI for all capacities except full irrigation. We are continuing this experiment for two more seasons.