Effects of Tillage and Reduced Irrigation on Cotton Yield in Southern Texas: A Five-Year Experiment.

In semi-arid regions, shortage of water is the primary factor limiting crop growth and production. Water savings through improved irrigation management has significant economic impact in areas with large crop acreage. Limited tillage has been shown to enhance soil productivity by improving various physical, chemical and biological properties of the soil, leading to potential soil water conservation and crop yield. However, the extent to which this benefit can be realized at the farm scale depends on various environmental and management factors. We report a five-year study on the interactions of irrigation and tillage management on cotton lint production in southwest Texas. We hypothesized that (a) regulated deficit irrigation can maintain crop yield while saving irrigation water and (b) limited tillage can conserve soil water and improve crop yield. The experiment was conducted in a quarter (about 6 ha) of a center-pivot irrigated field at the Uvalde Research and Extension Center. The pivot quarter was divided into three sections radially for three irrigation treatments (100% irrigation based on potential evapotranspiration and crop coefficient; 70% reduced irrigation during early crop stage; and 70% of full irrigation throughout the crop season). The early reduced irrigation was applied during the early growth stage (prior to flowering). We call this ‘primed acclimation (PA)’ for stress resistance. The whole pivot field was divided into eight concentric belts of conventional tillage (replicated four times) and strip tillage (also with four replications). The cotton plants (variety DP 935) were grown during the period from mid-April to mid- to late August from 2009 to 2013 in a rotational fashion in different quarters of the pivot field. The soil types of the pivot field are clay and silty clay loam. Standard practices were adopted in order to control weeds and diseases. The experiment was considered as a split-split plot design and analyzed using ANOVA. Across the five years, irrigation had significant effect on cotton yield (p=0.027), with production from the 70% deficit irrigation treatment being lower than the full irrigation and the PA treatment (2277 ± 106 kg/ha, 2895 ± 110 kg/ha and 2957 ± 93 kg/ha). The effect of tillage was not significant (p=0.27), although the yield from the strip-tilled plots was numerically higher than that from the conventional tillage (2789 ±90 kg/ha vs. 2631 ± 95 kg/ha).  Despite the influence of other factors (such as soil type), the lowest yield was observed in the driest year 2011 (2267 ± 102 kg/ha), with an averaged March-August Palmer Drought Severity Index of -3.3. The measured stomatal density collected on leaf samples in mid-July of 2011 showed no significant effects of irrigation and tillage treatments (average = 151 ± 5 stomata/mm²). The overall results reinforced the earlier finding that a 10% reduction in early irrigation water use (in PA treatment) resulted in similar (and even numerically higher) yields when compared with the full irrigation treatment. This demonstrated the value of regulated deficit irrigation in crop management. Although results from this study did not show a statistically significant effect of limited tillage on cotton production, further measurements on crop water use and root growth are needed to clarify the subtle effects of conservation tillage on crop growth and production in this region.