长期施肥对旱地红壤团聚体磷素固持与释放能力的影响

在中国科学院红壤生态试验站26年的旱地红壤长期肥料定位试验中,选取无机肥试验区的NPK、NK处理,有机无机肥配施试验区的对照(CK)、CK+稻秆(RS)、CK+花生秸秆还田(PS)、CK+绿肥(FR)及CK+猪厩肥(PM)等7个肥料处理土壤,采用湿筛法逐级提取并得到粒级依次为2 mm、2~1 mm、1~0.25 mm与0.25~0.053 mm的团聚体土壤样品;通过室内分析获得了土壤及各粒级团聚体的全磷(TP)、有效磷(Available P)、水溶性磷(CaCl_2-P)、土壤磷素吸持指数(PSI)及土壤磷素饱和度(DPS)等指标值,并探讨了上述测定指标间的相关关系。结果表明:长期施用磷肥可有效保持旱地红壤的供磷水平,配施猪厩肥可显著增加旱地红壤及大小团聚体的TP、有效磷及CaCl_2-P含量、降低土壤PSI并显著增大旱地红壤DPS,加大了旱地红壤磷素的流失风险;随着土壤中1 mm粒级团聚体数量的增多,旱地红壤磷素储量显著增加,磷素固持能力显著下降,土壤磷释放潜能随之增大。由DPS、有效磷及CaCl_2-P的分段线性拟合方程可以推断得出,当旱地红壤中有效磷为168~260 mg kg~(-1)时或DPS28%,土壤磷素具有潜在流失风险;当有效磷≥260 mg kg~(-1)或DPS≥28%,土壤磷素具有极高的流失风险,应立即停止施用磷肥尤其是有机磷肥,并重新调整施肥方案,以避免土壤磷素流失及其对水体环境的污染。

Effects of Long-term Fertilization on Phosphorus Retention and Release of Soil Aggregates in Upland Red Soils

Objective]Soil aggregates in the soil are important media capable of storing,transforming and activating soil phosphorus(P),and distribution and stability of soil aggregates is influenced by long-term fertilization. However,little has been reported on release pattern and adsorption capacity of P across various soil aggregates and their relationships in red soils as affected by long-term fertilization,which are essential to sustainable management of P sources in agricultural fields. The objectives of this study are to:(i)investigate changes in TP,available P,CaCl2-P,PSI and DPS,in soil aggregates of different particle-size fractions in a red soil under long-term fertilization;(ii)to explore relationships between CaCl2-P, available P,DPS;and(iii)to study how DPS andAvailable P affect P loss potential.Method]A long-term fertilization experiment was established in 1988 and soil samples were collected from the 7 fertilization treatments,designed in the experiment as follows:NPK,NK,Control(CK),CK + peanut straw (PS),CK + rice straw(RS),CK + fresh radish(FR)and CK + pig manure(PM). The soil samples were fractionated,using the wet sieving method,into aggregates of different particle sizes(> 2.0 mm, 2.0~1.0 mm,1.0~0.25 mm and 0.25~0.053 mm). Then the various fractions of aggregateswere analyzed for total P(TP),available P,CaCl2-P,P sorption index(PSI)and degree of P saturation(DPS)and relationships between the parameters.Result]Results show that Treatment NK was the lowest in TP,and DPS but the highest in PSI in all the aggregates,regardless of particle size fraction in the red soil. Compared with Treatment CK,TreatmentsPS,RS and FR were quite similar in effect on soil TP,PSI,Available P and DPS;but Treatment PM significantlydecreased soil P retention capacity with the highest TP and lowest PSI, and increased P release or loss potential in all the fractions of aggregates with the highest DPS,Available P and CaCl2-P. All the fertilization treatments,irrespective of their pattern,significantly increased P content in the > 2.0 mm fraction of aggregates with PEC(P enrichment coefficient)>1,but in Treatment NPK +PM soil P was more easily enriched in macro-aggregates(> 0.25 mm). Conclusion]Correlation analysis indicates that the P accumulated in the soil may be subject to potential loss to the safety of water quality when available P was range in 168~260 mg kg-1 or DPS < 28% in the red soil;otherwise P loss would be significant. Therefore,new strategies of using both commercial fertilizers and animal manures must be established and implemented to prevent P build up in the soil and to minimize P loss to water bodies in the red soil region.