耕作方式对紫色水稻土微团聚体分形特征影响的研究

土壤结构会影响土壤的水、肥、气、热状况，从而影响土壤肥力，而耕作方式会通过影响土壤团聚体状况来影响土壤结构，因此，为研究不同耕作制度对土壤团聚体的影响及土壤质量、结构的定量化描述，以位于西南大学农业部重庆紫色土生态环境重点野外科学观测试验站于1990年设立的长期免耕试验田为研究对象，应用微团聚体粒径分布的分形维数来探讨冬水田平作(DP)、水旱轮作(SH)、垄作免耕(LM)、厢作免耕(XM)和垄作翻耕(LF)等耕作方式对紫色水稻土土壤结构的影响。结果表明，LM、XM、LF和SH耕作方式下各土层的微团聚体含量随粒径的减小而降低，而DP处理下各土层的微团聚体含量随粒径的减小呈先降低后升高的趋势；相关分析表明，2~0.25 mm粒级团聚体含量与土壤中的有机碳、全氮、碱解氮、全磷等土壤养分含量都呈极显著正相关关系，而0.05~0.01 mm和0.01~0.005 mm粒级微团聚体含量都与这几种土壤养分呈显著或者极显著负相关，说明土壤养分主要富含在2~0.25 mm粒级团聚体中；土壤微团聚体分形维数与其各粒级含量极显著相关，微团聚体分形维数以及(< 0.005 mm)/(> 0.005 mm)粒级微团聚体含量比值都可以定量地表征紫色水稻土的结构性状；在0~70 cm土壤深度，LM、XM和LF处理下土壤微团聚体分形维数均极显著低于DP处理，表明垄作或免耕均可以改善土壤结构。

Effect of Tillage Systems on the Fractal Features of Soil Micro-aggregate Structure in a Purple Paddy Soil

Soil structure affects the water,fertilizer,gas and heat situation of soil,and soil micro-aggregate is the most important material basis.Many factors can affect the status of micro-aggregate,so as tillage system.Fractal dimension offers a new method to quantitatively investigate the soil structure.By using fractal model of soil micro-aggregate,soil structure based on a long-term（19 years） experiment with various tillage systems were studied in a purple paddy soil at the farm of Southwest University,Chongqing,China.The experimental plots included five tillage treatments：conventional tillage with rice only system（DP）,conventional tillage with rotation of rice and rape system（SH）,no-till and ridge culture with rotation of rice and rape system（LM）,no-till and plain culture with rotation of rice and rape system（XM）,and tillage and ridge culture with rotation of rice and rape system（LF）.Soil samples were collected at depths of 0-10 cm,10-20 cm,20-30 cm,30-40 cm,40-50 cm,50-60 cm and 60-70 cm.The results showed that the contents of soil micro-aggregate in each soil depth decreased with the decrease of particle size under LM,XM,LF and SH,while showed the trend of increase firstly and then decreased under DP treatment.There were highly significant positive correlation between the contents of 2-0.25 mm soil aggregate and soil organic carbon,total nitrogen,available nitrogen,total phosphorus and other nutrients,while the contents of 0.05-0.01 mm and 0.01-0.005 mm soil micro-aggregates with these types of nutrients were significantly or highly significant negative correlation,indicating that these nutrients are mainly rich in 2-0.25 mm soil aggregate.The fractal dimension and the content of grain size of soil micro-aggregates were highly significantly correlated.Fractal dimension,and（ 0.005 mm）/（0.005 mm） grain size ratio of micro-aggregate content both can quantitatively characterize the structure of purple paddy soil.In 0-70 cm soil layers,the fractal dimensions under LM,XM and LF treatments were highly significantly lower than DP treatment,showing that the ridge or no-tillage could improve soil structure.