Crop Water Use Responses of Upland Rice to Differential Water Distribution under Sprinkler Irrigation System

A two-year dry season experiment was conducted at the research farm of the International Institute of Tropical Agriculture, IITA Ibadan, Nigeria to estimate irrigation water requirements and establish crop water use. Two upland rice varieties (NERICA 2 and NERICA 4) were planted in a randomized complete block design (RCBD). Four treatments based on different water distribution levels were adopted. Total irrigation water applied were 3047 mm, 2656 mm, 2223 mm, and 1789 mm while reference ET were 236.5 mm, 260.6 mm, 283.9 mm, and 310.9mm in treatments A, B, C, and D, respectively, for NERICA 2. There were no significant differences in these parameters for NERICA 4 variety. Total irrigation water applied were 3054 mm, 2649 mm, 2220 mm, and 1792 mm while total reference ET were 238.6 mm, 258.8 mm, 285.9 mm, and 308.8 mm in A, B, C, and D, respectively. The total average weekly crop ET used were 31.6 mm, 36.8 mm, 39.9 mm, and 42.9 mm in all the four treatments while the highest weekly crop water use was observed during ripening stage at 8 weeks after planting (WAP) in all the treatments; 3.18 mm/day (A), 3.66 mm/day (B), 3.94 mm/day (C), and 4.24 mm/day (D). The minimum consumptive water use of 1.16mm/day was observed in 13 WAP in A. The water use efficiency (WUE) decreased in line with water distribution pattern in all the treatments. In NERICA 2, it decreased from 0.0165 t/ha/mm (A), to 0.0152 t/ha/mm (B), to 0.0099 t/ha/mm (C), and 0.0044 t/ha/mm (D). Similar pattern were observed in NERICA 4 variety. 0.0175 t/ha/mm (A), 0.0154 t/ha/mm (B), 0.0110 t/ha/mm (C), and 0.0087 t/ha/mm (D). The behavior of rice crop in extracting water varied with the phenological stages with the highest quantity of water extraction taking place at the mid season/ripening stage during which increased metabolic activities lead to grain formation. (