Improving rice population productivity by reducing nitrogen rate and increasing plant density

<div><p>In terms of tillering potential, the aboveground portions of rice are significantly influenced by the nitrogen level (NL) and transplant density (TD). To obtain a suitable combination of NL and TD, five NLs (0, 90, 180, 270 and 360 kg ha^-1) and two TDs [high density (HD), 32.5×10⁴ hills ha^-1; low density (LD), 25.5×10⁴ hills ha^-1] were used in the rice experiments during 2012 to 2014, in Jiangsu, China. The results showed the highest grain yield of rice obtained at HD and LD when N supply was 180 and 270 kg ha^-1, respectively. That’s because there are more tillers per unit area, a larger leaf biomass fraction of total aboveground biomass, a larger leaf area index (LAI) and a larger canopy photosynthesis potential (CPP) at HD. It can be concluded that, higher rice planting densities resulted in less N inputs, while more N is needed to improve single plant actual tiller ability under low density to offset the reduced planting density. When the NL was more than 180 kg ha^-1, the actual tillering ability of a single plant at LD was 20% more than that at HD. Based on these results, the supply of 1 kg N can be replaced by adding approximately 1000 planting hills per hectare. Therefore, adjusting the transplant density could be an efficient method to reduce the amount of nitrogen fertilizer and increase the nitrogen fertilizer use efficiency, which is very conducive to the sustainable development of agriculture.</p></div

Effects of N level and transplant density on nitrogen concentration in the leaf, sheath, stem, and spike (mg g^-1) of rice at different growth stages during 2012–2014.

<p>Effects of N level and transplant density on nitrogen concentration in the leaf, sheath, stem, and spike (mg g^-1) of rice at different growth stages during 2012–2014.</p

Estimation of the minimum amount of nitrogen fertilizer for the highest yield of rice at high density (red) and low density (black) separately using the model of linear plus platform in SAS software.

<p>Estimation of the minimum amount of nitrogen fertilizer for the highest yield of rice at high density (red) and low density (black) separately using the model of linear plus platform in SAS software.</p

Effects of N level and transplant density on agronomic efficiency of N (AE_N, %) and yield contribution of N (YC_N, %) of rice during 2012–2014.

<p>Effects of N level and transplant density on agronomic efficiency of N (AE_N, %) and yield contribution of N (YC_N, %) of rice during 2012–2014.</p

Grain yield, panicles, spikelets per panicle, filled grain rate and 1000-grain weight of rice under different N levels and transplant densities during 2012 to 2014.

<p>Grain yield, panicles, spikelets per panicle, filled grain rate and 1000-grain weight of rice under different N levels and transplant densities during 2012 to 2014.</p

The common coordination of the yield component parameters spike number of per unit area and kernel number of per spike of rice to different N levels and transplant densities.

<p>The common coordination of the yield component parameters spike number of per unit area and kernel number of per spike of rice to different N levels and transplant densities.</p

Effects of N level and transplant density on nitrogen accumulation in aboveground organs of rice at different growth stages.

<p>The data are the mean values ± SD.</p

The relationship between N accumulation and biomass of aboveground plant parts at five different growth stages: Max-tillering, booting, flowering, filling and harvest.

<p>The data are the mean values.</p

Effects of N level and transplant density on the leaf biomass fraction of aboveground (A), leaves area index (B), and canopy photosynthesis potential (CPP, C), at the max-tillering, booting, and flowering stages.

<p>The data are the mean value ± SD. Different small letters in each group indicate significant differences at <i>P</i>< 0.05.</p