Effects of Nitrogen Nutrition on Grain Yield of Upland Rice and Paddy Rice under Different Cultivation Methods

Upland rice and dry-cultivated paddy rice have been attracted more and more attention because of limited water re- sources in China. Researches on interaction between water and nitrogen supplies for crop resistance to drought stress has become the hot topic regarding regulation on nutritional physiology. However, there is little information available on effect of nitrogen (N) nutrition on grain yield and its components of upland rice and paddy rice under different cultivation methods. The objective of this study was to evaluate the difference between upland rice and paddy rice and interaction between cultivation methods and N levels. One upland rice cultivar Zhonghan 3 (japonica) and one paddy rice cultivar Yangjing 9538 (japonica) were grown under moist cultivation (MC, control) or bare dry-cultivation (DC) with three N levels, low amount of N (LN, 100 kg ha-1), normal amount of N (NN, 200 kg ha-1), and high amount of N (HN, 300 kg ha-1). The results showed that, compared with NN, the grain yield under HN was lower for both upland and paddy rice under DC and for paddy rice under MC, whereas higher for upland rice under MC. With the increase in N levels, upland rice and paddy rice showed higher productive tillers, more or fewer spikelets per panicle, lower percentage of ripened grains under two cultivation methods. However, the percentage of ripened grains was reduced more for paddy rice than for upland rice. There was no significant difference in 1 000-grain weight for upland rice among three N levels, whereas grain weight was reduced with the increase in N levels. Compared with MC, DC showed no significant difference in grain weight for upland rice, whereas a significant decrease for paddy rice. DC significantly increased the percentage of ripened grains for both upland and paddy rice, and that were more for upland rice than for paddy rice. Compared with paddy rice, upland rice showed less number of adventitious roots, lower nitrogen absorption ability and lower productive tillering ability, fewer pani- cles, fewer spikelets per panicle and lower grain yield. However, upland rice exhibited quicker increase in adventitious roots and slower declining in leaf nitrogen content from jointing to heading, and a faster declining speed in chlorophyll content (SPAD value) after flowering. Also, upland rice had less negative response to water stress and more positive response to N. The results suggest that the response to cultivation methods and N levels varies largely between upland rice and paddy rice. The approaches to in- crease the grain yield of both paddy and upland rice were discussed.