Submitted to: Agricultural Water Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/29/2007
Publication Date: 1/1/2008
Citation: DeTar, W.R. 2008. Yield and growth characteristics for cotton under various irrigation regimes on sandy soil. Agricultural Water Management. Vol 95/1:pp 69-76. Interpretive Summary: Over-watering cotton wastes a valuable and scarce resource and under-watering can reduce yields. The goal here was to find an optimum rate of water application for two varieties of cotton. A very efficient drip irrigation system was used to apply water daily at six different rates, ranging from 33% to 144% of normal. The experiment was repeated for four seasons. There was no difference in yields for the two varieties nor was there any difference in the yields for the three wettest treatments (treatments 4, 5, and 6). Treatment 4 (95% of pan evaporation) had been considered the normal and it turned out to be a critical level. Any application less than applied with treatment 4 reduced the yield. The wettest treatment produced plants over 6.5 ft. tall, and the driest treatment had some plants as short as 2 ft. The length of season for the driest treatment was about four weeks shorter than for the wettest treatment. This information can be used to establish the proper amount of water to apply to cotton.
Technical Abstract: An irrigation experiment was set up to apply water to cotton at six different rates ranging from 33% to 144% of normal, with hopes of identifying the regime that produces maximum yield. Two cultivars, Acala Maxxa and Acala PhytoGen-72 were planted on sandy soil and irrigated daily with a highly efficient subsurface drip irrigation system for four seasons. The results showed that on the average there was no significant difference in the yields of the two cultivars, and there was no significant difference in the yields of the three wettest treatments (treatments 4, 5, and 6). Treatment 4 had been considered close to normal, and it turned out to be a critical point on the water production function curve. It represented the least amount of water applied that produced essentially maximum yield, and it produced the highest water use efficiency. This critical level of water application during mid-season was found to be, on the average, 95% of Class A pan evaporation (Kcp = 0.95); it corresponded to a total seasonal application of 654 mm of water. Any application less than this critical level decreased yields. We documented the degree to which the water application rate controlled plant height and length of season. The final plant height was closely related to the depth of water applied, with the wettest treatment producing plant heights of 2.0 m, and the driest treatment producing plant heights of 0.6 m. The length of season for the driest treatment was about four weeks shorter than for the wettest treatment for both cultivars.