Abstract
Hydrochar (HC) incorporation affects soil nitrogen (N) transformation, which could further affect the N leaching loss. We conducted a soil lysimeter experiment to evaluate the responses in terms of N leaching and rice yield to HC applied at a low (0.5%) or high (1.5%) rate, while considering three N inputs, i.e., 240, 192, and 144 kg/ha (named N240, N192, and N144, respectively). The results showed that the rice grain yield was highest (124.3 g/pot) for N192, while being significantly reduced to the minimum yield achieved in the study (110.3 g/pot) for N144. Interestingly, for the N input 144 kg/ha, HC application increased the rice grain yield by 6.9-8.0%, which was equivalent to that of N240. NH(4)(+)-N leaching occurred mainly during the first 4 weeks of the rice season, and HC did not influence NH(4)(+)-N leaching for both the N inputs, 192 and 240 kg/ha. However, compared to N144, N144 + HC1.5% recorded a significantly higher NH(4)(+)-N leaching loss of 34.6%. This suggests that the application of a high amount of HC increases the NH(4)(+)-N leaching risk when the N input is low. HC application resulted in 10.2-45.3% more NO(3)(-)-N leaching loss when the three N inputs were applied, the effect of which was significant in regard to the applications involving a 20 and 40% N reduction, but this occurred only with the applied treatments involving 1.5% HC. Moreover, we found that organic N was the main form of leachate N (>80%). More specifically, N144 + HC recorded 7.8-8.3% lower organic N leaching than N192. Based on the effects of HC on the rice grain yield and N leaching, we recommend applications involving a 40% N reduction (N144) with a lower amount of HC (HC 0.5%) to ensure high crop production and to protect the water environment.