基于模糊c-均值聚类的亚热带丘陵区土壤肥力空间分异与管理分区

The spatial variability and management zoning of soil fertility in subtropical hilly region based on fuzzy c-means algorithm

[目的]亚热带丘陵区地形复杂,土壤肥力空间变异大,科学地将土壤按照相似地力进行分区,是实现丘陵区土壤精确管理,优化土壤培肥技术的理论基础。[方法]研究对象位于亚热带丘陵区的典型小流域-湖南省长沙县金井镇,2009年在全镇范围内(112 km~2)密集布置946个样点采集土壤样品,以测定的土壤肥力指标为数据源,包括土壤有机碳(SOC)、全氮(TN)、全磷(TP)、速效氮(AN)、有效磷(AP)和pH,采用地统计学和模糊c-均值聚类算法,分析流域土壤肥力的空间异质性;采用主成分分析法进行土壤肥力分区,并根据数据的差异显著性和变异系数对分区结果进行验证。[结果]除pH外,流域内土壤有机碳、全氮、全磷、速效氮和有效磷均存在中等至强的空间变异,变异系数(CV)介于36%~125%。基于主成分分析和模糊c-均值聚类可将研究区划分为3个肥力管理分区:MZ1、MZ2和MZ3,分区后各土壤肥力指标的变异系数(CV)不同程度地降低,以pH变异系数降幅最小(6%),AP变异系数降幅最大(96%)。同一分区内主要土壤肥力指标趋于同质化,分区间则异质化显著(P<0.01)。分区间水稻产量差异明显,MZ1区晚稻产量和早晚稻总产量显著高于MZ2和MZ3 (P<0.01)。MZ1、MZ2和MZ3区土壤pH值分别为4.12、4.04和4.00,均属于极酸水平;SOC分别为15.15、14.38和12.24 g/kg,均处于高水平;TN也为高水平(1.56、1.48和1.34 g/kg);TP为高至很高水平(0.86、0.69和0.60 g/kg);AN则处于很低至低水平(41.08、35.33和26.16 mg/kg);AP为中低水平(8.63、4.46和3.39 mg/kg)。[结论]亚热带丘陵区地形地貌复杂,是土壤肥力空间变异较大的主要影响因素。通过土壤肥力管理分区,可有效降低区域内肥力指标的变异程度,优化复杂丘陵区耕地管理措施。本研究区域中MZ1、MZ2和MZ3区均应着重改良土壤酸化现象,提高肥料氮素利用率,避免过量施用化学氮肥;MZ1区可适当减施磷肥,避免关键生育期过量施用磷肥;MZ2和MZ3区可以考虑适量施用生物酶活化磷肥或增施有机肥,以提高作物对磷素的利用效率。

[Objectives]Our study focused on understanding the spatial variation of soil fertility in subtropical hilly region with complex terrain,and aimed to approach an effective way for regional nutrient management in hilly regions.[Methods]A case study was carried out in a typical watershed,Jinjing Town,Changsha County,Hunan Province,which belongs to subtropical hilly region.A total of 946 soil samples were collected within the study area of 112 km²in 2009.The tested soil fertility indicators included soil organic carbon(SOC),total nitrogen(TN),total phosphorus(TP),available nitrogen(AN),available phosphorus(AP),and pH.Geographical statistics and fuzzy c-means clustering algorithm were used to analyze the spatial heterogeneity of soil fertility.Principal component analysis was employed to divide the watershed into different fertility zones.The results were validated using significance test of difference and coefficient of variation.[Results]Except for soil pH,SOC,TN,TP,AN and AP exhibited moderate to strong degree of spatial variations,with the coefficient of variation(CV)ranging from 36%to 125%.The study area was then divided into three soil fertility zones(MZ1,MZ2 and MZ3)based on principal component analysis and fuzzy c-means clustering algorithm.The CV values of soil fertility indices after zoning were distinctively reduced,the lowest and highest reduction were in the CV of pH and AP,with the zoning CV reduction of 6%and 96%,respectively.Soil fertility indices tended to be homogeneous within a zone,but more heterogeneous among zones(P<0.01).The late rice yields and total yields of early and late rice were significantly higher in zone MZ1 than in MZ2 and MZ3.In the three zones,soil pH was 4.12,4.04 and 4.00,respectively,all of which were at acidic levels.SOC contents were at a high level(15.15,14.38,and 12.24 g/kg).TN contents were at a high level(1.56,1.48,and 1.34 g/kg).TP contents were at high to very high level(0.86,0.69,and 0.60 g/kg).AN contents were at a low level(41.08,35.33,and 26.16 mg/kg).AP contents were at a middle or low level(8.63,4.46,and 3.39 mg/kg).[Conclusions]Soil fertility exhibites significantly spatial variations in the subtropical hilly region due to the complex topography.Zoning based on the soil fertility is an effective way to eliminate the heterogeneity and propose regional nutrient management strategies.The watershed of the case study is divided into three fertility zones,the MZ1,MZ2,and MZ3 zones should focus on ameliorating soil acidification,enhancing the utilization efficiency of fertilizer nitrogen,and avoiding the over-application of chemical nitrogen fertilizers.For zone MZ1,a moderate reduction in the application of inorganic phosphorus fertilizers was recommended,with particular attention to preventing excessive phosphorus fertilization during critical growth stages.MZ2 and MZ3 zones should consider appropriate application of biological enzyme-activated phosphate fertilizer or increasing application of organic fertilizers to enhance the utilization efficiency of phosphorus by crops.