Emeribe C.N¹, Isagba E.S^2,, Fasipe O.A³

The present study examines the possibility of determining supplementary water requirements of selected food Crops per growth stage using the climatic indices alone. Rainfall and temperature datasets on high-resolution (0.5x0.5 degree) grids resolution were assembled from the Climatic Research Unit CRU TS 3.21 of the University of East Anglia, Norwich, United Kingdom for the period 1943-2012. To ascertain the suitability of the datasets for use in the study area the Pearson Product moment correlation was undertaken with measured rainfall data from Yelwa synoptic station, Nigerian Meteorological Agency. Melon, Beans, Millet, Sorghum, Soybean and Cucumber were used for estimating seasonal supplementary irrigation water needs in the Sokoto Rima, River Basin. The observed seasonal patterns of rainfall and PET shows that soil moisture surplus in the basin sets in from June – August while April to May is the soil water recharge periods. From October, water is withdrawn from the basin, paving way for moisture deficit which last from November-March. The study shows that even during the rainy months, supplementary irrigation is needed to compensate for deficit due to increased rate of evapo-transpiration. It is also possible to carry out an all year round cultivation in the basin. For an all-year-round cultivation of crops with greater yields, full scale irrigation is needed for a second cultivation season (from October to February) when the soil moisture storage of the basin is below the basin field capacity. In absence of spatial dataset, the use of CRU proves to be an alternative in climatic response and modelling studies.

potential evapotranspiration, rainfall, crop water requirement, supplementary irrigation