Seedling vigour influences nitrogen utilization and yield of early rice under different nitrogen-saving conditions

Objectives Vigorous seedlings and topdressing of tillering fertilizer are required for promoting early development of rice. However, tillering fertilizers tend to cause nitrogen loss and ineffective tillering, resulting in low harvest index of rice. The efficacy of nitrogen savings through cultivation of vigorous seedlings was investigated.

Methods The experiment was conducted from 2014 to 2015, using a super early rice cultivar Ganxin203. The vigour treatment consisted of the vigorous and normal rice seedlings. The experiment included no-nitrogen control and conventional fertilization using normal seedlings (NS+0N and NS+100%N), in which the N rate, 180 kg/hm² was divided into basal application (72 kg/hm²) and top-dressing of 54 kg/hm² each at tillering and jointing stages; and four vigorous seedling treatments with N input reduced by 0, 10%, 20% and 30% (VS+100%N, VS–10%N, VS–20%N and VS–30%N). All fertilizer reduction was carried out at tillering stage. The SPAD, chlorophyll content, photosynthetic rate, nitrate reductase activity and nitrogen content of the jointing, heading and maturing stage; grain yield and its components were determined. Then the total nitrogen accumulation, nitrogen transport, apparent nitrogen transport rate and nitrogen recovery efficiency were calculated.

Results Compared to the NS+100%N, the leaf SPAD values and photosynthetic rates of the VS–10%N, VS–20%N and VS–30%N treatments were not significantly influenced. During the middle and late growth stages, vigorous seedling offset the negative effect of reduced nitrogen fertilizer on dry matter accumulation of the tillering stage by promoting tillering growth and effective panicle number. The VS–10%N and VS–20%N treatments increased dry matter accumulation at the mature stage than NS+100%N and consequently improved rice yield by 8.5% and 1.5%, respectively. However, dry matter accumulation and yield of VS–30%N treatment were significantly lower. Meanwhile, vigorous seedling had higher leaf nitrate reductase activity, nitrogen content and nitrogen accumulation in leaves, stems–sheaths and panicles. Compared to NS+100%N, the total N accumulation in VS+100%N significantly increased by 6.9% while that of VS–30%N decreased by 9.7%. The N recovery efficiency and N agronomic efficiency of the vigorous seedling treatments were 12.1%–22.4% and 9.9%–24.7% higher than those of NS+100%N in the early rice (P < 0.05).

Conclusions The slow early growth of rice caused by low N input at the tillering stage can be averted by cultivating vigorous seedlings which not only produces more tillers but also exhibits higher dry matter accumulation and nitrogen translocation at the latter stage of the plant development. By cultivation of vigorous seedlings and application of 20%-less N input, the yield of early rice will not decrease, and the nitrogen saving, high yield and cost saving cultivation of rice are realized, which is beneficial to improving the nitrogen utilization efficiency and reducing the environmental pollution caused by nitrogen loss.