Simulating Maize (Zea Mays L.) Performance Using Aquacrop Model Under Varying Irrigation Schedules and Water Depletion Levels in Bura Irrigation Scheme, Kenya

Abstract

Supplemental irrigation is an important practice in sustaining soil moisture for optimal crop yield especially in ASAL regions, where during the growing season, potential evapotranspiration exceeds precipitation and the available soil water content. To investigate this, two parallel field experiments were done during the 2015 short rain (October - December) and 2016 long rain (April - July) at Bura Irrigation Scheme, Tana River County, to model maize growth and yield, under seven irrigation treatments. Effect of four irrigation schedules of daily (Td), weekly (Tw), bi-weekly (Tbw) and tri-weekly (Ttw) and three levels of depletion of available water capacity (AWC) at 75% (T75), 50% (T50) and 25% (T25) were tested on maize (Zea mays L.) variety PH4. Percentage canopy covers, above ground biomass and grain yield were the parameters used to gauge maize performance. From the results, Tw and Tbw treatments gave 13.9 and 13.7 Tonha-1 of above ground biomass, respectively, which were significantly higher (P≤0.05) compared to Td and Ttw, which gave 7.2, and 8.8 Tonha-1 of above ground biomass, respectively. Grain yield for Tw was significantly higher (P≤0.05) at 5.9 Tonha-1 compared to Tbw at 5.7 Tonha-1. Compared to the other irrigation schedule treatments, Td and Ttw had significantly lower (P≤0.05) grain yield of 2.0 and 2.6 Tonha-1, respectively. T75and T50 treatments gave the highest above ground biomass of 15.8and 15.5 Tonha-1 and grain yield of 6.2 and 6.1 Tonha-1, respectively. This was significantly higher (P≤0.05) compared to T25, which gave 6.2 and 2.7 Tonha-1 of above ground biomass and grain yield, respectively. Irrigation scheduling treatments gave lower grain yield and water use efficiency compared to water depletion level treatments. The lowest (3.21 kgmm-1ha-1) and the highest (13.6 kgmm-1ha-1) water use efficiency were recorded under T75 and Td treatments, respectively. Treatments Tw, Tbw, T75 and T50 were found worth of consideration for testing under the soil and weather conditions of the study area. Aquacrop model was hence used to simulate and predict attainable yield in the irrigation scheme for these four treatments. There was agreement between the model‘s simulated and observed canopy cover, biomass yield and soil water content giving r2 values of between 0.90 - 1.00, 0.94 - 1.00 and 0.84 – 0.98 (P≤0.05), respectively. The model predicted higher above ground biomass and grain yield than what was attained in the field, an indication that yields in the farm can further be improved. Keywords: ASALs, Irrigation schedule, water depletion levels and WUE