Effect of Biochar Application on Aggregate Stability and Nitrogen Fertilizer Distribution of Forestland Soil
[Objective]Effects of biochar addition on the soil aggregates were analyzed for controlling erosion,maintaining permeability,and retaining water and nitrogen fertilizer on forestland.[Method]In a one-year pot experiment,soil sample from a forestland in Fujian was used in treatments applying either no extra materials as control(CK),a chemical fertilizer(F),wood biochar along with a chemical fertilizer(MC),or straw biochar with a chemical fertilizer(JC).The chemical fertilizer contained 1 g of urea,2.19 g of superphosphate,and 0.44 g potassium chloride.Biochar was added at 140 g per pot.Nitrogen fertilizer distribution in soil was visualized by analytical data,and a topdressing of 5 g 15N-urea included to trace nitrogen movements.Soil aggregation and aggregate stability were monitored.[Results](1)The content of macroaggregates in soil was significantly raised by MC or JC over F with the greatest effect on the aggregates larger than 2 mm—a 108.92%increase by MC and 119.11%by JC.(2)In comparison to F,the presence of biochar under MC and JC stabilized the aggregation structure with significantly higher indexes on MWD,GMD,and R＞0.25 mm and lower D.Between the MC and JC treatments,the latter was superior to the former.(3)The biochar addition also heightened the total nitrogen content in soil aggregates of different sizes.The MC-treated soil had a higher content than the JC counterpart.The nitrogen contribution rate by larger-than-2 mm aggregates was significantly 38.09%more under MC and 69.10%under JC than F.(4)When biochar was added,more δ15N was detected in the＞0.25-2 mm aggregates.MC resulted in 2.25-fold,and JC 3.89-fold,of that of F.The nitrogen retention in large aggregates significantly correlated with the aggregate stability of soil.[Conclusion]Application of biochar not only enhanced the stability of aggregates but also reduced nitrogen loss in soil at forestland.Nitrogen fertilizer was retained more effectively in macro-than micro-aggregates in soil.The straw biochar appeared to improve more on aggregate stability,while wood biochar more so on nitrogen retention.
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