Responses of Rice Yield, N Uptake, NH and NO Losses from Reclaimed Saline Soils to Varied N Inputs.

It is of agronomic importance to apply nitrogen (N), but it has high environmental risks in reclaimed saline soils. Therefore, we should apply N fertilizer at an appropriate rate to increase crop yield but decrease N losses. In this soil column experiment, rice yield, N uptake, and ammonia (NH) and nitrous oxide (NO) losses were measured in four treatments with no N application (control) and with N applications of 160, 200, and 240 kg/ha (N160, N200, and N240, respectively). The results show that grain yield, spike number, and thousand-kernel weight increased with increases in N application rate, but there was no significant difference in grain yield between N200 and N240. However, the kernels per spike increased first and then decreased with the increase in N application, of which N200 was recorded to have the highest kernels per spike value, which was 16.8 and 9.8% higher than those of N160 and N240, respectively. Total NH volatilization of the rice season increased with increasing N input, especially during the first and second supplementary fertilization stages. The NH-N concentration of overlying water was relatively lower under the N200 treatment in these two stages, and the yield-scaled NH volatilization and the emission factor were the lowest in N200, which were 26.2-27.8% and 4.0-21.0% lower than those of N160 and N240, respectively. Among the three N-applied treatments, NO losses and the emission factor as well as the yield-scaled NO emissions were the lowest under the N200 treatment, which had 34.7% and 78.9% lower NO emissions and 57.8% and 83.5% lower emission factors than those of the N160 and N240 treatments, respectively. Moreover, the gene copies of AOA and AOB , , and in cultivated layer soils all reached the minimum under the N200 treatment. According to the comprehensive effects of N fertilizer on rice grain yield and NH and NO losses, we recommend applying 200 kg/ha to reclaimed saline soil to ensure crop yield and reduce N losses.