Water deficits and nitrogen uptake as affected by water table depth in rice (Oryza sativa L.)

Summary

Nitrogen responsiveness of modern rice cultivars was a key factor in their success in irrigated fields. However, these cultivars and the associated high level of nitrogen fertilization have generally not been adopted in poorly irrigated and rainfed rice sectors. Rice crops grown with inadequate water show less nitrogen uptake although contradictory results are to be found in the literature. In the current study, varying degrees of inadequate irrigation decreased both nitrogen uptake and grain yield in the modern semidwarf rice cultivar IR36. Although there was a linear relationship between nitrogen uptake and grain yield across the two experimental locations, the response functions of nitrogen uptake and grain yield regressed on nitrogen rate and irrigation treatment varied greatly between the two sites. The most significant difference in the locations was the depth to the water table during the crop season. Although the soil surface dried and cracked in both locations because of inadequate surface irrigation, the lower profile must have been affected by water table depth. These findings illustrate the importance of understanding the role of subsurface water depth in soil nitrogen management of partially irrigated and rainfed rice. In addition they provide an explanation for past contradictory reports on the interaction of nitrogen fertilization and irrigation inadequacy on rice crop yield.