Effects of Irrigation Timing and Rate on Cotton Boll Production in West Texas.

Because most of the upland cotton (Gossypium hirsutum L.) growing regions in the US require supplemental irrigation for maximum yields, there is always a risk of yield loss due to temporary decreases in water availability. This risk is particularly high in semi-arid regions of the cotton belt, including California, Arizona, and Texas. Research was conducted at the Texas A&M Agrilife Research Center in Halfway, Texas.  Irrigation treatments were conducted over three defined time periods, based on growing degree day (GDD_15.6) accumulation from crop emergence. The first irrigation period was focused on plants prior to flowering (< 525 GDD), the second occurred during primary reproductive development (525-750 GDD), and the third focused on the period of fruit maturation (>750 GDD). Three irrigation levels were tested during each of three irrigation timings. At each timing, the irrigation level targets were 0 mm d^-1 (low); 3.2 mm d^-1 (medium); and 6.4 mm d^-1 (high). Actual irrigation levels were similar to these amounts, but were adjusted based on rainfall totals using the method described by described by Bordovsky and Lyle (1996). The combination of three irrigation levels at each of three growth periods resulted in 27 individual combinations of irrigation level and timing. Low irrigation during middle the middle of the season (flowering) had the greatest effect on boll distribution, especially with boll production towards the top of the plant. High irrigation early on to middle of the growing season did not necessarily equate to more bolls higher on the plant. Because of the numerous treatments many findings about boll distribution were produced from this study.