Effect of alternate soil moisture regimes on rice nutritional and grain quality

Variations in watering regimes and intermittent wetting and drying of rice fields, significantly (P<0.05) alter the nutritional profiles of rice (Oryza sativa L.) grain quality. The object of this study was to investigate the effect of alterations of soil moisture regimes on rice grain nutritional quality under Uganda conditions. The structure of the water regime included alternate wetting (at two weeks of full watering) and drying (one week of no watering (AWD). The nutritional properties of different rice varieties were the parameters determined. Results showed that accumulation of biomass was variety dependent, though was not significantly affected (P>0.05) by the manipulation of the soil water regimes. Carbohydrates and crude fiber, which form the largest percentage of biomass for rice, showed significant variation (P<0.05) among the different treatments. Watering or flood treatments did not significantly affect (P>0.05) accumulation of metabolites, except for the amount of protein, with means ranging from 5.24 to 6.5 g 100 g-1. Substantial amounts of crude fiber were observed in three varieties (WDR 73, PR-107 and WITA 9), compared to ARIZE. AWD treatment registered higher amounts of crude fiber in all varieties, compared to the continuous flooding (CF) treatments. On the other hand, variety specific differences were observed for total carbohydrates, with more carbohydrate mass observed in the CF treatment compared to AWD. There was a negative relationships between the amount of amylose and protein (r = -0.218.), carbohydrates and protein (-0.177); and therefore, protein accumulation was dependent on carbohydrate mass accumulation. Protein accumulation was positively correlated with secondary metabolites, such as anti-oxidants (r=0.126) and phenolic (r= 0.267), suggesting roles of proteins in secondary plant metabolism. The results were indicative of the minimal effect of differing watering regimes on the composition of the rice grain, hence its nutritional quality.