High nitrogen input reduces yield loss from low temperature during the seedling stage in early-season rice

Abstract

Early transplanting of the first crop is often attempted by farmers to increase rice yields in double-season rice cropping systems in central China. The risk of yield loss from low temperature is high with early transplanting; heavy application of nitrogen (N) fertilizer is commonly practiced to minimize this risk. However, whether the negative effects of low temperature on rice growth and yield can be mitigated by applying more N fertilizer is unclear. To address this question, we conducted field experiments on early-season rice in Wuxue county, Hubei province, China with two transplanting dates (early and normal) and two N rates (low and high) in 2016 and 2017. Transplanting was advanced by 9 days in the early compared with that in the normal transplanting date, and the high N treatment received 70 kg ha−1 more basal N than did the low N treatment. Early transplanting reduced the grain yield of early-season rice by 20.1% in 2016 and by 7.0% in 2017 at the low N rate, but there was no difference in grain yield between transplanting dates at the high N rate in both years. The high N rate increased the grain yield of early transplanting by 21.9%, averaged across the two years. Both the reduction in grain yield due to early transplanting and the increase in grain yield due to the high N rate under early transplanting were explained by the number of spikelets m-2 and dry weight production. The high N rate promoted N uptake, tillering, and leaf area development under low temperature. Thus, we conclude that the negative effects of low temperature on early-season rice can be mitigated by applying more basal N fertilizer. Environmental concerns about the practices of early transplanting and heavy basal N application for early-season rice are discussed.