基于增强回归树的鄱阳湖平原区耕地土壤钾素空间变异影响因素研究

  【目的】  研究区域土壤钾素空间变异特征及其影响因素，为土壤钾素涵养及合理利用提供依据。  【方法】  本研究以鄱阳湖平原区2016年测土配方施肥项目采集的6316个耕层 (0—20 cm) 土壤样本数据为基础，运用普通克里格法、相关性分析和增强回归树(BRT)等方法，分析了区域土壤全钾与速效钾的空间分布特征以及区位、环境、土壤和人为4个方面的因素对二者空间变异影响的边际效应。  【结果】  鄱阳湖平原区耕地土壤全钾含量在1.70～23.40 g/kg，平均值为11.82 g/kg，变异系数为40.02%；速效钾含量在21.00～237.00 mg/kg，平均值为91.76 mg/kg，变异系数为45.27%，二者均呈中等程度变异。全钾与速效钾空间分布的块金效应分别为27.19%和50.00%，变程分别为74.10 和41.10 km，二者均主要受随机因素的影响，但速效钾受随机因素的影响更为明显。普通克里格插值结果显示，全钾与速效钾在空间分布上存在明显差异。增强回归树结果表明包含土壤地理环境信息的区位因素可作为解释土壤全钾与速效钾空间变异的有力因素，年降雨量是土壤全钾空间变异最为明显的影响因素，土壤有机质和交换性阳离子含量的综合作用是土壤速效钾空间变异的主要影响因素，钾肥施用会明显干扰耕地表层土壤钾素的平衡状况。  【结论】  鄱阳湖平原区土壤钾素呈中等程度变异，但全钾空间分布的聚集性强于速效钾，速效钾受外界因素特别是人类活动的干扰更加明显。

Study on the factors influencing the spatial variability of soil potassium in cultivated land in Poyang Lake Plain based on boosted regression tree

  【Objectives】  Understanding the regional spatial variability of potassium (K) in soils and the influencing factors will provide a basis for soil K conservation and rational utilization.  【Methods】  During the conduction of the project “Soil Testing and Formula Fertilization in Poyang Lake Plain” in 2016, 6316 surface soil samples were collected, and the soil total potassium and readily available potassium contents were measured. Based on these data, the spatial distribution characteristics of soil total K and readily available K, and the marginal effect of location, environment, soil and human factors were analyzed used the Ordinary Kriging, the correlation analysis and the Boosted Regression Tree (BRT) methods.  【Results】  Soil total K concentration of cultivated land in the Poyang Lake Plain was ranged between 1.70 and 23.40 g/kg, with an average of 11.82 g/kg and cofficient of variation (CV) of 40.02%. The soil readily available K concentration was ranged between 21.00 to 237.00 mg/kg, with the mean value of 91.76 mg/kg and CV of 45.27%. Both total K and available K concentrations had moderate variation. The nugget effects of spatial distribution of total K and readily available K were 27.19% and 50.00%, respectively, and the variation ranges were 74.10 and 41.10 km, respectively. Both the total K and readily available K were mainly influenced by random factors, and the influence of random factors on readily available K was more obvious. The results of Ordinary Kriging interpolation showed significant differences in spatial distribution between total K and readily available K. The results of Boosted Regression Tree showed that location factors could be a powerful factor to explain spatial variability of total K and readily available K in soil. The annual rainfall had the most significant effect on total K spatial variability, while the comprehensive effect of soil organic matter and cation exchange capacity (CEC) was the main factor affecting spatial variability of soil available K. The application of K fertilizer disturb the balance of K in the surface soil of cultivated land significantly.  【Conclusions】  Soil K contents in the Poyang Lake Plain vary moderately. The spatial distribution of total K clusters more than that of readily available K. Readily available K is more obviously disturbed by external factors, especially human activities.