土壤分散性与分形维数对坡耕地转变为藤椒林地的响应

Response of soil dispersion and fractal dimension to conversion from slope farmland to Zanthoxylum armatum plantation

为了解坡耕地转变为藤椒林地后土壤分散性、分形维数和肥力特征,探讨土壤分形维数与肥力的相互关系,为坡地退耕种植藤椒和土壤管理提供参考,以川东丘陵区坡耕地退耕后种植形成的3 a(TJ-3)和5 a(TJ-5)藤椒林及对照农耕地(CK)为对象,采集0~20 cm土层样品,测定土壤微团聚体组成、颗粒组成、养分含量、酶活性和微生物数量,运用隶属函数法综合评价藤椒种植对土壤分散性和肥力的影响。结果表明:坡耕地转变为藤椒林地后,土壤微团聚体组成中2~0. 02 mm粒级颗粒含量增加,<0. 02 mm粒级颗粒含量降低。土壤结构性颗粒指数、团聚状况、团聚度、物理稳定性指数,有机质、全氮、碱解氮、有效磷和速效钾含量,细菌、真菌、放线菌和总微生物数量,蔗糖酶、脲酶、磷酸酶和过氧化氢酶活性,颗粒分形维数和肥力综合值均随种植年限延长而增加;相反,土壤分散率、侵蚀系数、分散性综合值和微团聚体分形维数随种植年限延长而降低。土壤分散性综合值和微团聚体分形维数与土壤养分含量、微生物数量和酶活性及土壤肥力综合值均呈显著相关性(P <0. 05)。说明种植藤椒促进土壤较小粒级的微团聚体向较大粒级微团聚体聚合,改善土壤微团聚体组成,增加土壤结构稳定性。土壤分散性综合值和微团聚体分形维数可以作为坡地退耕后土壤肥力变化的综合性评价指标。

The objective of the study was to evaluate the effect of conversion from slope farmland to Zanthoxylum armatum plantation on soil dispersion,fractal dimension and soil fertility characteristics,to understand the relationship between fractal dimension of soil particles and soil fertility,and to provide references for further cultivation and soil management of Z.armatum.The experiment included three treatments:(1)slope farmland(CK);(2)three-year-old Z.armatum plantation(TJ-3);(3)five-year-old Z.armatum plantation(TJ-5).Soil samples of 0-20 cm layers in the hilly area of eastern Sichuan were collected for determination of soil micro-aggregate composition,soil particle composition,nutrients contents,enzymes activities and microbe number.Membership function was used for the comprehensive evaluation of soil dispersion,fractal dimension and soil fertility.It was shown that large particle(2-0.02 mm)content increased yet small particle(<0.02 mm)content decreased in soil micro-aggregate determination after conversion from slope farmland to Z.armatum plantation.Soil structural particle index,aggregation status,aggregation degree and physical stability index,contents of organic matter,total N,hydrolysis N,available P and available K,number of bacteria,fungi,actinomycetes and total microorganisms,activities of invertase,phosphatase,urease and catalase,particle fractal dimension,and soil fertility(CVSF)of Z.armatum plantations were higher than those of CK,and the values of these indexes increased with plantation age.Soil dispersion rate,erosion coefficient,comprehensive value of soil dispersion(CVSD),and micro-aggregate fractal dimension(D)of Z.armatum were lower than that of CK and decreased with plantation age.The CVSD and D were significantly correlated to soil nutrients contents,microbes number,enzyme activities and CVSF(P<0.05).Conversion from slop farmland to Z.armatum plantation promoted transform of smaller soil micro-aggregate to larger ones,soil micro-aggregate composition and stability were improved.The indexes of CVSD and D could be used to evaluate soil fertility under land use conversion.