Timing Initial Post-plant Irrigation Based upon Plant-Water Status
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AbstractA two year study was conducted to determine the optimum timing of the initial post plant irrigation using leaf water potential (LWP) measurements. A short - season Upland cotton (Gossvpium hirsutum L.), variety DPL 20, was planted on 19 April 1993 and 15 April 1994 at the Marana Agricultural Center on a Pima clay loam (Typic Torrifluvent) soil. Treatments, designated Tl , 72, and T3, were such that the initial post plant irrigation would be applied when the midday LWP of the uppermost, fully- developed leaf exposed to full sunlight measured -15, -19, and -23 bars, respectively. All treatments received the same irrigation regime following the initial post plant irrigation. Basic plant measurements, including plant height, mainstem node number, fruit retention, number of nodes above the uppermost white bloom, fresh bloom count within a 166 -ft1 area, and percent canopy cover, were taken weekly from each plot. Soil -water data was collected at 10 inch depth increments, to a depth of 60 in. , from access tubes located in each experimental unit. Yields were 1112, 1095, and 977 lbs lint/acre in 1993 and 1082, 1035, and 964 lbs lint /acre in 1994 for T1, 72, and T3, respectively. Yields were reduced when the midday LWP was allowed to fall below -19 bars, however, reduction was significant (P 5 0.05) only in 1993. At the time of the initial post plant irrigation for each treatment, approximately 83, 62, and 32 % of the total plant available water was present in the upper 60 in. of the soil profile for Ti, 72, and T3, respectively.