Effects of biochar addition on different forms of nitrogen in facility agricultural soils under various fertilization regimes

Biochar application in facility agriculture soil has a significant impact on the forms of soil nitrogen. Clarifying the effects of different fertilization treatments with the addition of biochar on various forms of nitrogen in the soil of facility agriculture can provide a scientific basis for emission reduction through the application of biochar in facility agriculture. The dissolved organic nitrogen (DON) and inorganic nitrogen (N_min) in soil were measured in greenhouse vegetable soil (brown fluvio-aquic soil) after biochar application under different fertilization regimes (no fertilizer (CK), manure (M), chemical fertilizer (F), chemical fertilizer plus manure (M+F), using indoor constant temperature aerobic cultivation and gas chromatography. Incubation was carried out to investigate N₂O release and the contents of DON, N_min after 2% (biochar/dry soil) and 4% biochar application under the different fertilization regimes. The influence of biochar addition on soil N₂O releases was studied, and the correlation between the changes in DON and N_min contents and soil N₂O releases was analyzed. The research indicated that the application of biochar had different effects on the release rate and cumulative release of soil N₂O under different conditions. Under CK and M patterns, biochar application significantly increased the rate and amount of soil N₂O release in the early period (0-1.5 d). During 2-60 d, biochar application had no significant effect on the rate and amount of soil N₂O release in CK pattern. Biochar application had no significant effect on the soil N₂O release rate, but 4% biochar at the end of the incubation significantly increased the cumulative soil N₂O release in M pattern. In F and M+F treatments, biochar application reduced the soil N₂O release rate in the early period (0-2 d), with an increasingly apparent effect as the amount of biochar applied increased. In F and M+F treatments, biochar application significantly increased the soil N₂O release rate during 2-25 and 3-14 d, respectively, but the effect on the rate was not significant in the subsequent stages. After cultivation, the cumulative soil N₂O release in F and M+F treatments with 2% and 4% biochar application were significantly increased by 78% and 90%, 80% and 67%, respectively. The correlation analysis results showed that there was an obvious positive correlation between DON and N_min contents and N₂O emission with biochar application. The addition of biochar had a direct impact on N₂O release by adjusting the contents of DON and N_min in the soil. The release rate and cumulative release of N₂O from different fertilized soils showed different trends when biochar was added. However, due to the diversity of biochar properties, the variation in types of chemical and organic fertilizers, and differences in fertilization methods and timing, a reasonable analysis was required based on the specific conditions of the study when assessing the impact of biochar addition on soil N₂O cumulative release.