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

The differences between upland and paddy rice (Oryza sativa L.) as well as the interaction between cultivation methods and nitrogen (N) levels were evaluated. The upland rice cultivar Zhonghan 3 (japonica) and the paddy rice cultivar Yangjing 9538 (japonica) were field grown under moist cultivation (MC, control) and bare dry-cultivation (DC). Each cultivar had 3 N-treatments under either MC or DC, that is, low N supply (LN, 100 kg ha−1), normal N supply (NN, 200 kg ha−1), and high N supply (HN, 300 kg ha−1). Compared with NN, HN reduced grain yield for both upland and paddy rice cultivars under DC and for the paddy rice cultivar under MC, whereas, it increased the yield of upland rice under MC. With an increase in N level, both upland and paddy rice showed higher productive tillers, more or fewer spikelets per panicle, and lower percentage of ripened grains under MC and DC. However, the seed-setting rate reduced to a greater extent in paddy rice than in upland rice. There was no significant difference in 1000-grain weight for the upland rice among the 3 N levels, whereas, the 1000-grain weight reduced with the increase in N level in the paddy rice. Compared with MC, DC had no significant influence to grain weight of upland rice, however, a significantly negative effect was observed in paddy rice. DC increased the seed-setting rate in both cultivars, with more increase in upland rice than in paddy rice. The upland rice had less number of adventitious roots, lower N absorption ability, lower productive tillering ability, fewer panicles, fewer spikelets per panicle, and lower grain yield than paddy rice. However, upland rice showed more rapid increase in adventitious roots and a slower decline in leaf N content from jointing to heading, and a faster decline in chlorophyll content (SPAD value) after anthesis. In addition, upland rice had a weak negative response to water stress and a strong positive response to the N level. The responses to cultivation methods and N level varied largely between upland and paddy rice.