Simulation of Moisture Dynamics of the Soil Profile of a Maize Crop under Deficit Irrigation Scheduling

An understanding of moisture dynamics of the soil profile of a crop under different water regimes is important in determining the optimum deficit irrigation scheduling practice for the crop in an area. Such understanding is necessary in order to know when to irrigate, what extent of deficit should be allowed, and at what growth stage of the crop should deficit irrigation be allowed. A model which can simulate the moisture dynamics of the plant root zone is a valuable tool. In this paper, the water balance unit of the crop growth cum irrigation scheduling model named Irrigation scheduling Impact Assessment Model (ISIAMod) was used to simulate the moisture dynamics of the soil profile layers of a maize crop grown under deficit irrigation scheduling in Mkoji sub-catchment in Tanzania during the 2004 irrigation season. The soil moisture contents of the different layers of a one-metre soil profile depth simulated by the model agreed fairly well with field measured data. The simulated average soil moisture contents of the effective root zone depth also agreed well with field measured data. Both the simulated and fieldmeasured moisture contents suggest that the crop extracted moisture effectively from the 0-400 mm soil depth when the crop was irrigated at 7 days interval throughout the crop growing season. However, when irrigation event is skipped after every other irrigation, the changes in soil moisture contents suggest that crop extended its moisture extracted region beyond the 400 mm depth up to the 700 mm depth. Changes in soil moisture contents were not noticed beyond the 700 mm soil profile depth, which suggest that the effective root zone depth of the crop did not exceed 700 mm depth.