Biochar addition to control nitrogen pollution in riparian forests

Objective This paper explores the effects of different biochar additions on soil chemical properties, soil enzyme activity and microbial community composition of riparian forest, and understands the removal mechanism of nitrogen pollution reduction in riparian forest by biochar addition, so as to provide scientific basis for the prevention and control of non-point source pollution in watershed and ecological restoration technology.

Method Using one-way ANOVA and correlation analysis, the effects of different biochar levels (0, 3, 6 t/ha) on nitrogen pollution control were analyzed in Populus tomentosa along Qingshui River in Baoding, Hebei Province of northern China.

Result (1) There were significant differences in soil chemical properties of forest with different biochar levels (P < 0.05). Compared with control group, total nitrogen, ammonium nitrogen, nitrate nitrogen, organic matter and organic carbon in 3 t/ha biochar addition group increased by 10.39%, 46.15%, 8.57%, 38.03% and 51.23%, respectively. In the 6 t/ha biochar addition group, total nitrogen, ammonium nitrogen, nitrate nitrogen, organic matter and organic carbon increased by 26.62%, 92.31%, 65.00%, 78.05% and 135.47%, respectively. (2) There were significant differences in soil enzyme activities of forest with different biochar levels (P < 0.05). Compared with control group, the activities of urease, nitrate reductase and nitrite reductase in 3 t/ha biochar addition group were increased by 35.00%, 69.41% and 85.71%, respectively. The activities of urease, nitrate reductase and nitrite reductase in 6 t/ha biochar addition group increased by 63.33%, 104.31% and 77.92%, respectively. (3) The results of high-throughput sequencing showed that the addition of biochar increased the relative abundance of Proteobacteria, unclassified bacteria and Bacteroidota, while decreased the relative abundance of Actinobacteriota. (4) The correlation analysis of soil chemical properties, enzyme activities and bacterial dominant phyla showed that organic matter, organic carbon, nitrate reductase and nitrite reductase were the main factors affecting the level of soil microbial community.

Conclusion Biochar addition could improve nitrogen retention and enzyme activities related to soil nitrogen cycle, improve soil microbial community structure, and further affect the transformation and removal of nitrogen in soil. Among different treatment groups, the application rate of 6 t/ha showed the most significant effect.