生物炭对林地土壤团聚体稳定性与肥料氮分布的影响

Effect of Biochar Application on Aggregate Stability and Nitrogen Fertilizer Distribution of Forestland Soil

【目的】林地土壤抗侵蚀能力、渗透性及保水性与土壤团聚体结构稳定性紧密相关,氮素的固持与分布直接影响林下植被生长与林地土壤团聚体形成。研究生物炭添加对林地土壤结构稳定性与残留氮素分配的影响,可为增强林地土壤团聚体稳定性、提高土壤氮素固持水平提供参考。【方法】利用福建省林地土壤进行盆栽试验(1年),设置4个处理:对照(CK)、化肥(F)、木炭+化肥(MC)、秸秆炭+化肥(JC),除CK外,化肥及生物炭处理均每盆施用尿素1 g、过磷酸钙2.19 g、氯化钾0.44 g,追肥^(15)N-尿素,共追施5 g,生物炭施用量为每盆140 g。测定不同处理土壤团聚体组成、团聚体稳定性指标、团聚体氮素含量与分布,结合^(15)N示踪技术分析肥料氮在土壤团聚体内的残留特点,揭示生物炭对林地土壤团聚体稳定性与氮素分配的影响。【结果】(1)与F处理相比,MC与JC处理显著提高了土壤大团聚体含量,其中>2 mm土壤团聚体增幅最大,分别增长了108.92%与119.11%;(2)施用生物炭增强了土壤团聚体稳定性,MC与JC处理平均重量直径(MWD)、几何平均直径(GMD)及>0.25 mm大团聚体含量(R>0.25 mm)较F处理均显著提升,分形维数值(D)显著下降,JC处理土壤团聚体稳定性优于MC处理;(3)施用生物炭提高了不同粒径土壤团聚体中全氮含量,MC处理土壤全氮总量高于JC处理,二者的>2 mm团聚体氮素贡献率较F处理分别显著增加了38.09%与69.10%;(4)施用生物炭使>0.25~2 mm粒级团聚体δ^(15)N富集,MC与JC处理土壤肥料氮残留量以>0.25 mm粒级最多,较F处理显著增加了2.25倍与3.89倍,土壤大团聚体中氮肥残留量与团聚体稳定性呈显著正相关。【结论】施用生物炭有利于增强林地土壤团聚体稳定性,减少土壤氮素与肥料淋失,肥料氮在大团聚体中的固持高于微团聚体,秸秆炭对土壤团聚体稳定性提升效果更显著,木炭施用更有利于土壤氮素含量增加。

【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 ^(15)N-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,moreδ^(15)N 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.