YIELD ENHANCEMENT IN COTTON BY FREQUENT IRRIGATIONS DURING FRUITING

Daily drip irrigation often increases yield and water-use efficiency of cotton (Gossypium hirsutum L.) compared to conventional irrigations applied at long intervals. A 2 yr experiment was designed to test whether these benefits could be achieved without using an expensive drip system. Cotton was irrigated every 10 d in the first year and every 14 d in the second year (control treatment). A supplemental irrigation was applied during either one or two long irrigation cycles coinciding with peak fruiting. The total amount of water applied was minimally changed from the control because other irrigations were reduced to compensate for the supplementation. Another treatment was drip-irrigated daily throughout most of the season. One supplement increased seedcotton yield 15% over the control, and two supplements increased it 25%, compared to a 40% yield increase with drip irrigation. These three treatments increased crop water-use efficiency (yield per unit applied water plus rainfall) by 12, 22 and 50%, respectively. Yield increases were associated with a lengthened period of profuse flowering and a delay in the onset of cutout. Both drip irrigation and mid-cycle supplements increased midday leaf water potential and apparent hydraulic conductance of the plants for an extended period during fruiting, indicating enhanced water uptake and transport capacity compared to plants on long cycles. The results show that a drip system is not necessary for substantial improvements of yield and water-use efficiency. Doubling the number of irrigations for a short period during peak fruiting achieved much of the benefits of drip irrigation.