Impact of Effective Rainfall on Crop and Irrigation Water Require-ments of FARO-59 Rice in Edo State, Nigeria

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Efficient planning of irrigation systems, especially in rainfed rice cultivation, depends on accurate estimates of effective rainfall and crop water requirements. This study evaluated the effective rainfall, crop water requirements, and irrigation requirements of FARO-59 rice cultivated on two contrasting soils—loamy sand (Auchi) and silty loam (Agbede) in Edo State—using four CROPWAT estimation methods for effective rainfall (fixed percentage, empirical formula, United States Department of Agriculture, and Food and Agriculture Organization of the United Nations) implemented in CROPWAT 8.0. The characterisation of soil samples revealed significant differences between the reference locations, with higher total available moisture (153 mm/m), lower infiltration rate (17 mm/day), and deeper rooting depth (24.3cm) recorded for silt loam soil at Agbede compared with loamy sand soil at Auchi. The effective rainfall varied significantly among the methods, with FP and EF (488.30 mm and 482.70 mm, respectively) the highest, while USDA estimated the lowest (383.40 mm). Across all methods and locations, the crop water requirements were similar, ranging from 316.30 to 317.30 mm, indicating that the seasonal rainfall distribution adequately supported the crop water demand of FARO-59 rice. A minimal or zero irrigation water requirement was estimated for most methods, except for a slight increase in supplemental irrigation need (12.20 mm) estimated by FAO. This study revealed that the choice of method significantly affects the estimation of effective rainfall with little or no influence on the crop water requirements of FARO-59 rice under intense rainfall conditions in Edo State, Nigeria. The results of this study provide a helpful baseline for optimising FARO-59 water-use efficiency and a valuable guide for informed irrigation scheduling in similar agroecological zones.

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