Christopher O. Akinbile
Rice is a staple food cultivated and consumed in Nigeria. Several research efforts on the crop had centered on the agronomic, soil and disease behavioural pattern with little work on its water use pattern. The study was aimed at estimating irrigation water requirements and establishing crop water use with its attendant effect on the rice crop. A two-year dry season experiment was conducted at the research farm of International Institute of Tropical Agriculture, IITA Ibadan, Nigeria. Two upland rice varieties (NERICA 2 and NERICA 4) were planted on a 5m X 5m plot in a randomized complete block design (RCBD). Four treatments based on different water distribution levels were adopted. Daily meteorological data were used to determine reference evapotranspiration (ET) and other supporting information relating to crop water use were also obtained. The results were subjected to statistical analysis. Total irrigation water applied were 3047mm, 2656mm, 2223mm and 1789mm while reference ET were 236.5mm, 260.6mm, 283.9mm 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 for NERICA 4. The total average weekly crop ET used were 31.6mm, 36.8mm, 39.9mm and 42.9mm in all the four treatments while the highest weekly crop water use was observed during ripening stage at 8 WAP in all the treatments; 3.18mm/day (A), 3.66mm/day (B), 3.94mm/day (C) and 4.24mm/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 behaviour 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. Increasing irrigation water application does not imply increased but decreased crop water use.
