Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/30/2004
Publication Date: 12/1/2004
Citation: Colaizzi, P.D., Evett, S.R., Howell, T.A. 2004. Irrigation methods and capacities for cotton in the Northern High Plains. In: Rainwater, K.A. Editor. 2004 High Plains Groundwater Groundwater Resources: Challenges and Opportunities, Soil and Water Conservation Society, December 7-9, 2004, Lubbock, Texas. p. 154-163. 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: The Texas Panhandle has a significant concentration of corn under center pivot irrigation with various application methods (e.g., low energy precision applicator, or LEPA, mid- or low-elevation spray, etc.). Producers in this area, however, are showing interest in cotton, which has a similar revenue potential with much less irrigation. Although this area is adjacent to one of the largest cotton producing areas in the United States (centered around Lubbock), the limited growing season (length and lower cumulative growing degree days) and undeveloped industry infrastructure (gins, custom harvesters, etc.) have limited the northward expansion of cotton. We hypothesized that subsurface drip irrigation (SDI), which has been successfully adopted by cotton producers elsewhere, would result in less evaporative cooling following an irrigation event compared with sprinkler methods. This would increase heat unit accumulation and promote earlier maturity. We evaluated lint yield, water use efficiency, and fiber quality for several irrigation methods (SDI, LEPA, and spray) and several irrigation capacities (dryland, 25%, 50%, 75%, and full irrigation) during the 2003 season. We did not observe any clear differences in growth and maturity rates among irrigation methods. However, final lint yield and water use efficiency was greater with SDI under low irrigation capacities (25% and 50% of full irrigation), and 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.