Evaluation of FAO-56 crop coefficient procedures for deficit irrigation management of cotton in a humid climate

Abstract

The main goal of this research was to measure cotton water use, and to determine irrigation water scheduling parameters associated with optimal seed-lint yield and irrigation water use efficiency, which are poorly understood in the Central Asian Republic of Uzbekistan. A cotton (Gossypium hirsutum L.) field experiment with drip irrigation in comparison to furrow (conventional) irrigation was conducted on a deep silt loam soil (Calcic Xerosol) at the Central Experiment Station of the Uzbekistan National Cotton Growing Research Institute at Tashkent in 2003, 2004 and 2005. To investigate irrigation scheduling, the field capacity (Fc) index was adopted, which was 0.30 m(3) m(-3) in this soil. Irrigations were scheduled when soil water in the root zone was depleted to specific fractions of Fc, e.g., 70% of Fc, for each of three main plant growth periods (germination-squaring; squaring-flowering; beginning of maturation-maturation). Crop water use, which we here define as the sum of transpiration and evaporation, was established using the soil water balance approach on a weekly basis. Soil profile water content was determined using a neutron moisture meter (NMM), which was calibrated in polyvinyl chloride (PVC) access tubes for each differing soil layer. Under drip irrigation and the optimal mode (70-70-60% of Fc) of irrigation scheduling, 18-42% of the irrigation water was saved in comparison with furrow irrigated cotton grown under the same condition; and irrigation water use efficiency increased by 35-103% compared with that of furrow irrigation. Seed-lint cotton yield was increased 10-19% relative to that for furrow irrigated cotton. The irrigation scheduling rule developed here should be considered an improved practice for drip irrigated cotton that is applicable to irrigated Calcic Xerosols of Uzbekistan. (C) 2007 Elsevier B.V. All rights reserved

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