Abstract
N fertilizer is usually supplied via multiple applications in rice production in China. Due to the high N-recovery efficiency (NRE) of panicle fertilizer, applying large amounts of fertilizer at the booting stage is considered to be an effective measure of increasing yields, although it has adverse effects on eating quality. In this study, using six inbred and four hybrid japonica varieties, we postponed topdressing-N to increase the ratio of panicle N from 20% to 40% by correspondingly reducing the N amount applied only at the tillering stage. We also analyzed the effects of postponing the topdressing-N on grain yield and dry matter accumulation in both high- and low-fertility blue clayey paddy fields in 2016 and 2017. The effects of postponing topdressing-N applications on japonica rice were related to variety, meteorological conditions, and soil fertility. With respect to the inbred varieties, regardless of whether panicle N was applied as a single or split application, increasing the ratio of panicle N had no effect on the yield components or dry matter accumulation of plants grown in either high- and low-fertility soils. Regarding the hybrid varieties grown in the high-fertility soil, although postponing the topdressing-N application had no effect on yield under good weather conditions (no low-temperature stress during grain-filling), a single application of 40% of the total N at the panicle initiation stage significantly decreased both the dry matter accumulation after heading and the seed-setting rate of varieties that presented long growth periods under low-temperature conditions. With respect to hybrid varieties grown in low-fertility soil, postponing the application of topdressing-N had an adverse effect on the number of effective panicles. Our results suggested that the proportion of panicle N applied to japonica rice should not exceed 30% in clayey paddy fields and that fertilizer management with respect to rice production should be adjusted according to soil type, soil fertility, and variety.
Highlights
Due to the cultivation of high-yield varieties and the development of high-yield cultivation techniques, rice yields in China have increased
We previously found that the N-recovery efficiency (NRE) of N applied both before transplanting and at tillering was significantly lower than the NRE applied at panicle initiation (PI) when fertilizer-N uptake only in plants was considered; when the distribution of fertilizer-N in both the plants and soil was compared, 70% of the basal-15 N, 29% of the tillering-15 N, and 46% of the panicle-15 N was recovered in the plants and soil [7,19]
When inbred japonica rice were grown in high-fertility soil, the grain yield of the inbred japonica varieties under different N treatments in 2016 ranged from 6675 to 9409 kgha−1, which was significantly greater than the yield in 2017 (5889–7563 kgha−1 )
Summary
Due to the cultivation of high-yield varieties and the development of high-yield cultivation techniques, rice yields in China have increased. In 2017, rice production in China reached 221.76 million tons, accounting for 32.1% of total grain output. N is essential for rice production and has an important effect on rice growth and yield formation [1]. Excessive N fertilizer application and improper fertilization methods increase production costs, which restrict the production potential of rice and negatively affect the environment by leaching, runoff, and volatilization [2,3]. Optimizing the application of N fertilizer to synchronize the supply of N with crop demand is of great significance for high-yield and high-efficiency rice production.
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