ABSTRACT
High-frequency low-volume irrigation (drip irrigation) often increases yields in Arizona. Previous studies revealed that daily drip irrigation preserves the capacity of cotton (Gossypium hirsutum L.) roots to absorb water during heavy fruiting, when more protracted irrigation cycles allow the roots to senesce. Here we report that increased irrigation frequency during a portion of the boll-loading period has a similar effect. 'Deltapine 90' cotton was grown in two years in central Arizona either with a long irrigation cycle (10 to 14 days) throughout the season or with the July irrigation cycles modified to include twice as many irrigations as normal. Water applied was decreased on each occasion so that the total applied during the cycle was little changed. All treatments were compared to drip-irrigated plots in a randomized complete-block design. In the first year, modification of the July irrigations increased seedcotton yields by 45% over the check, from 3880 to 5610 kg/ha. Season-long drip irrigation increased yields to 6310 kg/ha. Modified irrigation cycles in July delayed cutout by two weeks compared to the check. In the second year, yields followed the same pattern but the differences were smaller and were not significant (95% probability level). Again, modification July irrigation cycles produced about two-thirds of the yield increase associated with drip irrigation. The results indicate that modified irrigation practices during one or two cycles may "recapture" most of the increased yield and improved water-use efficiency associated with drip irrigation.
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