Nitrogen use efficiency and optimal N application rate of rice in Chaohu Lake region
A field experiment with six N rate treatments,i.e.0, 60, 120, 180, 240 and 300 kg/hm2 was conducted to study effects of N application rate on crop yield, uptake, accumulation, and use efficiency of N by rice cultivar Wandao 52 and Ningjing 3. The result showed the rice yield response to added N was very low when the N application rate exceeded 180 kg·hm-2, and the rice production began to decline when the N application rate was more than 240 kg·hm-2. When N application rate increased from 60 up to 300 kg·hm-2, the nitrogen apparent recovery efficiency(REN) declined from 75.1% to 49.4% for Wandao 52, and from 62.1% to 50.2% for Ningjing 3, and the corresponding nitrogen agronomy efficiency(AEN) was 17.3-7.33 kg·kg-1 and 16.8-8.64 kg·kg-1 for Wandao 52 and Ningjing 3, respectively. The experiment results suggest that the optimal N application rate is 178 and 190 kg·hm-2for Wandao 52 and Ningjing 3, respectively, to maintain a better grain yield and a better nitrogen use efficiency.