Effect of N rates on growth, development and N utilization of mechanical sowing wheat in rice-wheat cropping system in Sichuan Basin

The effects of different N application rates on the growth, development and N utilization of mechanical sowing wheat in rice-wheat cropping system were studied from 2010 to 2012 in Guanghan City, Sichuan Province. Four N rates were designed: 0, 105, 150 and 195 kg/ha in the experiments. The results show that the increase of N rate is good for increasing the tillering ability, the numbers of effective spike, spikelet and grain per spike, but a bit of unfavorate to the grain filling. The highest yield were achieved when the N rate was 150 kg/ha in the two growing seasons and all the experimental sites with different soils textures., When the N application rate were higher than 150 kg/ha, the yield increase less or even start to decline. Although the N accumulation and N content in the plants are continuing increase, the corresponding N agricultural use efficiency, N productivity efficiency, N uptake efficiency and N utilization efficiency are all declined, and the N harvest index and apparent N recovery efficiency have no significantly changes from 105 kg/ha to 195 kg/ha. Therefore, applying 150 kg/ha is recommended for higher yield and highest profit in the current production levels of Sichuan Basin.