[Characteristics of Biochar-mediated N₂O Emissions from Soils of Different Surface Conditions]

It was aimed to investigate the response to biochar addition on N₂O gas production and emission in different surface conditions. To study the dynamic changes of soil N₂O release, soil nitrate(NO₃^--N) and ammonium(NH₄⁺-N), a field trials experiment was conducted from 2014 to 2015 in wheat and corn season, which contained three treatments[the blank control group (CK), biochar applied at 5 t·(hm²·a)^-1(BC5) and 45 t·(hm²·a)^-1(BC45), respectively] under crop cultivation(+) and non-cultivation(-) condition. The results indicated that:1 During the season of wheat growth, the soil N₂O emissions of CK+, BC5+, BC45+ were 21.70-88.91, 21.42-130.09, 64.44-179.58 μg·(m²·h)^-1 respectively, and that of BC45+ possessed a higher value than those of the other treatments(P<0.05). Compared with wheat winter period, the soil N₂O emissions of the three treatments decreased evidently in wheat peak stage(returning green and jointing stage, booting and heading stage) (P<0.05), and the amplification of BC45+ reduced by 18.43% and 14.62% in comparison with CK+ and BC5+ in wheat booting and heading stages. In the early stage of maize growth, the soil N₂O emissions of BC45+ were significantly increased compared with CK+ and BC5+(P<0.05). However, there were no significant differences among treatments of maize heading stage and mature stage. It showed that the biochar-mediated promotion effect of soil N₂O emissions was effectively inhibited by crop growth and the increase of surface mulch. Besides, the result of soil N₂O release in the same treatment had also confirmed this conclusion in bare land. 2 Under the conditions of wheat cultivation and homochronous non-cultivation, the soil NO₃^--N and NH₄⁺-N contents of BC5+ and BC45+ treatments were raised with respect to CK+, but the values dropped significantly in wheat peak stage, especially for BC45+ treatment, with 96.44% and 69.40% decrease respectively. The soil inorganic nitrogen content of maize growth season had a similar trend in wheat season. Parallel to this result of the apparently falling soil NO₃^--N and NH₄⁺-N concentrations, the soil N₂O emissions of BC45+ also declined remarkably in peak stage. The decline in respiratory substrate caused by the increase of nitrogen uptake by crop growth, may be one of the reasons for the decrease of N₂O emission. 3 In wheat growth season, the soil pH values of the biochar treatments were improved from 4.62 to 5.18. In maize season, the soil pH values ranged from 4.42 to 5.02. When the soil pH value was relatively low, the soil N₂O emission was high, and vice versa. The soil N₂O emission was partly influenced by the soil pH value.