Upland cotton growth and yield response to timing the initial postplant irrigation

Cotton (Gossypium spp.) production in arid and semiarid regions depends on well-managed irrigation systems for optimum yield and production efficiency. Water deficit stress early in the growing season can affect the subsequent growth and development of short-season cotton. A 2-yr field study was conducted in southern Arizona to determine the optimum timing of the initial postplant irrigation for a short-season upland cotton variety based on midday leaf water potential (LWP) measurements, and to evaluate the season-long effects of delayed irrigation on subsequent plant growth patterns. In both years, the short-season upland variety, DPL 20, was planted into a Pima clay loam soil [fine-silty, mixed (calcareous), thermic Typic Torrifluvent] that had received a preplant irrigation of 152 (1993) or 254 mm (1994) approximately 3 wk prior 10 planting. Treatments, designated T1, T2, and T3, received the initial postplant irrigation when the average midday LWP of the uppermost, fully expanded leaf measured - 1.5, -1.9, and -2.3 MPa, respectively. Daily midday LWP measurements were taken using the pressure chamber technique. Soil water was measured at 25-cm depth increments using neutron attenuation. Plant height, number of mainstem nodes, nodes above white flower (NAWF), and canopy closure were measured at weekly intervals. All treatments reached maturity, as measured by NAWF ≤ 5, at approximately the same time during the growing season. Complete canopy closure was delayed in the T3 plots resulting in reduced interception and utilization of available solar radiation early in the growing season. When treatments were initiated, approximately 84% (T1), 62% (T2), and 32% (T3) of the total plant-available water (field capacity less permanent wilting point) was present in the upper 1.5 m of the soil profile. Yields were 1263, 1244, and 1110 kg lint ha^-1 in 1993 and 1229, 1176, and 1095 kg lint ha^-1 in 1994 for T1, T2, and T3, respectively. Lint yields were significantly different in 1993 (P = 0.001), indicating that timing the initial postplant irrigation affected plant growth and lint yield potential.