Cotton irrigation scheduling improvements using wetting front detectors in Uzbekistan

Previous research established growth-stage-specific irrigation scheduling for upland cotton (Gossypium hirsutum L.) in Uzbekistan. We report further investigation of irrigation scheduling for two cotton varieties and its effect on seed-lint yield and irrigation crop water productivity with and without use of a wetting front detector (WFD) to trigger irrigation cessation. A WFD is a device buried in the soil to sense when the wetting front from irrigation reaches a certain depth. The depth may be adjusted upon installation of the WFD. Field trials were conducted in silt loam soil near Tashkent, Uzbekistan, in 2016, 2017, and 2018. The growth stages of germination to flowering, flowering to boll formation, and maturation were considered for the development of irrigation scheduling regimes with respect to field capacity water content (Fc). The best growth, development and seed-lint yield for the Sultan cotton variety were achieved with irrigations scheduled at soil water content levels of 70%, 75%, and 65% of Fc during the aforementioned three growth stages, respectively, and were achieved for variety UzPITI-103 with irrigations scheduled at 70%, 70%, and 60% of Fc during the aforementioned plant growth stages, respectively. There were appreciable varietal differences in water requirement with the early maturing Sultan variety having a larger water requirement. In contrast, irrigation scheduling with larger Fc values did not result in increasing the yield for the UzPITI-103 cotton variety. In comparison with irrigation without WFD, the use of the WFD decreased irrigation duration by 2.0–3.5 h, net irrigation amount by 7–90 m3ha−1, irrigation run off by 69–134 m3ha−1, and deep percolation below the root zone by 10–17 m3ha−1, while increasing irrigation crop water productivity by 0.08–0.10 kg m−3 and seed-lint yield by 0.04–0.10 Mgha−1. Irrigation scheduling regimes based on percentages of Fc and irrigation with WFD should be considered applicable practices for upland cotton varieties on silt loam soils of the central zone of Uzbekistan and for similar soil-climatic conditions of Central Asian countries.