Effects of nitrogen deficiency on dry matter and grain productions of six rice {Oryza sativa L. cultivars

Effects of limited nitrogen (N) supply on dry matter and grain productions were investigated in the pot-grown six rice cultivare, Kasalath (a traditional indica), IR36 (an improved indica), Shirobeniya (a conventional japonica), Nipponbare (an improved japonica), BSI429 (an improved tropical japonica, a new plant type line) and Akenohoshi (an improved japonica-indica cross). At maturity, N limitation caused significant decreases in aboveground dry weight (DW), DW increased during heading to maturity (ΔDW), grain weight, panicle number per plant, fertility % and sink size in the six cultivars, and there were significant "cultivar x N" interactions; the magnitudes of these decreases caused by limited N supply were smallest in Akenohoshi. There were significant positive correlations between grain weight and aboveground DW at maturity under both standard-N (SN) and low-N (LN) conditions, whereas there was a significant positive correlation between grain weight and ΔDW under the LN condition but not under the SN condition. Grain weight was more closely correlated with sink size under both N conditions. Among the cultivars examined, Akenohoshi showed the highest ΔDW, fertility % and sink size under the LN condition, leading the highest grain weight. It is suggested that Akenohoshi is a breeding material useful for the improvement of adaptability to LN environment.