林下养鸡年限对杨树人工林土壤磷素形态和生物有效性的影响

林下养殖是一种经济有效的林地空间利用方式, 但长期高负载的林下养殖对林地土壤性状究竟产生何种影响, 目前尚无定论。以不同林下养鸡年限(0年、1年、3年和5年)的美洲黑杨(Populus deltoides)人工林为对象, 采用Hedley磷素分级法, 分析其林地土壤的磷素组成和形态变化, 探讨林下养鸡年限对土壤磷库特征及其生物有效性的影响。结果表明, 0-5 cm土层土壤的全磷、碳酸氢钠提取态无机磷和有机磷(NaHCO3-Pi和NaHCO3-Po)以及氢氧化钠提取态无机磷和有机磷(NaOH-Pi和NaOH-Po)含量均随养鸡年限延长显著上升, 放养5年后达对照林分的1.4-2.4倍, 而5-10 cm土层4种磷素形态含量没有显著变化。0-10 cm土层土壤的稀盐酸提取态无机磷(D.HCl-Pi)和浓盐酸提取态无机磷(conc.HCl-Pi)含量在养鸡1年时显著下降, 之后随养鸡年限延长逐渐回升; 浓盐酸提取态有机磷(conc.HCl-Po)和残留态磷(Residual-P)两种磷素形态含量在各养鸡年限间差异不显著。0-10 cm土层土壤的总无机磷含量在养鸡1年后显著下降, 之后开始上升; 而总有机磷含量随养鸡年限延长显著上升, 受养鸡年限的影响较大。表层土壤的有效磷和活性磷含量随养鸡年限延长均有所上升, 且均与NaOH-Pi和NaOH-Po的含量呈极显著正相关, 表明NaOH-P, 尤其NaOH-Po是林地土壤中可供转化为有效养分的最主要潜在磷源。总体而言, 土壤中较易被分解利用的磷素形态含量随养鸡年限延长明显积累, 难分解的磷素形态含量则变化不显著, 同时林地表层土壤有效磷或活性磷的供应水平随养鸡年限延长得到明显改善, 土壤磷的生物有效性不断提高。

Effects of in-forest chicken-raising duration on soil phosphorus fractions and bio-availability in poplar plantations

In-forest raising is a cost-effective way to improve the comprehensive utilization of forest land.However,it is currently unclear what impact of long-term and high-load in-forest raising has on soil properties.In order to reveal the effects of chicken-raising duration on soil phosphorus pool and its bioavailability,this study used plantations of Populus deltoides under different in-forest chicken-raising duration(0,1,3,and 5 years)to analyze the changes in soil phosphorus fractions by Hedley phosphorus fractionation method.The results show that the contents of soil total phosphorus and the fractions of NaHCO₃-extracted inorganic and organic P(NaHCO₃-Pi and NaHCO₃-Po)and NaOH-extracted inorganic and organic P(NaOH-Pi and NaOH-Po)in 0-5 cm soil layer increased significantly with the extension of in-forest chicken-raising duration,even showing a 1.4-to-2.4-time increase in the plantations with 5-year in-forest chicken-raising than in the control plantation.However,no obvious changes of the four fractions were found in 5-10 cm soil layer.The contents of diluted HCl-extracted inorganic P(D.HCl-Pi)and concentrated HCl-extracted inorganic P(conc.HCl-Pi)in 0-10 cm soil layer decreased significantly after 1-year of chicken raising,and then increased with the extension of in-forest chicken-raising duration.The contents of concentrated HCl-extracted organic P(conc.HCl-Po)and the more chemically stable P(Residual-P)showed similar trends as D.HCl-Pi and conc.HCl-Pi,but no significant differences were found among different in-forest chicken-raising duration.The contents of soil total inorganic phosphorus in 0-10 cm soil layer decreased significantly after 1-year of chicken raising,and then increased with the extension of in-forest chicken-raising duration,while the contents of soil total organic phosphorus significantly increased.The contents of bio-available P(available P and labile P)in the topsoil increased with the extension of in-forest chicken-raising duration,and both were significantly aand positively correlated with the contents of NaOH-Pi and NaOH-Po,showing that the fractions of NaOH-P,especially NaOH-Po,was the most important potential source that could be transformed into bio-available fractions.Overall,the contents of phosphorus that are more easily decomposed and utilized in the soil obviously accumulate with the extension of in-forest chicken-raising duration,and the contents of phosphorus that are difficult to decompose do not change significantly.The supply level of available phosphorus or labile phosphorus in the topsoil of forest land is improved obviously with the extension of in-forest chicken-raising duration,and the bioavailability of soil phosphorus has continued to increase.