南方典型丘陵区耕地土壤全氮、有机碳和碳氮比空间变异特征及其影响因素

  【目的】  了解土壤全氮、有机碳和碳氮比空间变异及其影响因素是进行土壤碳氮调控的前提和基础。  【方法】  以江西省丰城市为案例区，通过实地采样获取2018年139个表层土壤数据，运用地统计学、普通克里格插值等方法对南方丘陵区县域尺度下耕地土壤全氮、有机碳和碳氮比的空间变异特征及其影响因素进行系统的分析。  【结果】  研究区土壤全氮 (TN) 含量介于0.74～3.80 g/kg、土壤有机碳 (SOC) 含量介于8.14～36.67 g/kg、土壤碳氮比 (C/N) 介于6.31 ～15.15，均值分别为2.24 g/kg、22.52 g/kg和10.15，变异系数分别为25.45%、26.24%、14.38%，均呈中等程度的空间变异。半方差分析结果显示，TN、SOC、C/N的块金效应分别为44.44%、56.97%、19.57%，这表明TN、SOC和C/N的空间分布受结构性因素和随机性因素共同影响。普通克里格插值结果显示，在空间分布上，研究区土壤TN和SOC具有相似性，总体表现出由中部向南北递减的趋势；土壤C/N空间分布与TN和SOC有所不同，总体呈现出西高东低的趋势。逐步回归分析结果显示，成土母质、土壤类型、土壤pH、氮肥施用量和土壤质地对土壤全氮，成土母质、土壤类型、土壤pH对土壤有机碳，土壤类型对土壤碳氮比影响极显著 (P<0.01)。  【结论】  成土母质对土壤TN和SOC的独立解释能力最高，分别为28.1%和23.2%；土壤类型对研究区土壤C/N的独立解释能力达到了13.2%。因此，成土母质是引起研究区土壤全氮、有机碳空间变异的主要因素，土壤类型则是引起研究区土壤碳氮比空间变异的主要因素。

Spatial variation characteristics of total nitrogen,organic carbon and ratio of carbon to nitrogen of cultivated land in typical hilly areas in south China and its influencing factors

  【Objectives】  Understanding the spatial variation of soil total nitrogen, organic carbon and ratio of carbon to nitrogen and their influencing factors is the premise and foundation of soil carbon and nitrogen regulation.  【Methods】  This study took a case of Fengcheng City, where 139 surface soil data were obtained in 2018 through field sampling. We used Geostatistics, Ordinary Kriging interpolation and other methods systematically to analyze the spatial variation characteristics and influencing factors of total nitrogen, organic carbon and ratio of carbon to nitrogen of cultivated land in typical hilly areas in south China.  【Results】  Soil total nitrogen (TN) in the study area ranged from 0.74 g/kg to 3.80 g/kg, soil organic carbon (SOC) ranged from 8.14 g/kg to 36.67 g/kg, and soil carbon to nitrogen ratio (C/N) ranged from 6.31 to 15.15, with mean values of 2.24 g/kg, 22.52 g/kg and 10.15, respectively. The coefficients of variation of TN, SOC and C/N were 25.45%, 26.24% and 14.38% respectively, showing moderate spatial variation. The results of semi-variance analysis showed that the Nugget effect of TN, SOC and C/N was 44.44%, 56.97% and 19.57%, respectively, indicating that the spatial distribution of TN, SOC and C/N was affected by both structural factors and random factors. The results of Ordinary Kriging interpolation showed that soil TN and SOC in spatial distribution were similar in the study area, and generally showed a trend of decreasing from the middle to the north and south. The spatial distribution of soil C/N was different from that of TN and SOC, with the general trend of higher in the west and lower in the east. Stepwise regression analysis showed that soil parent material, soil type, soil pH, nitrogen fertilizer application amount and soil texture had significant effects on soil TN, soil parent material, soil type and soil pH had significant effects on SOC, and soil type had significant effects on soil C/N (P<0.01).  【Conclusions】  The independent interpretation of soil TN and SOC by parent materials is the highest which are 28.1% and 23.2%, respectively. The independent interpretation ability of soil type to soil C/N in the study area could reach 13.2%. Therefore, the soil parent material is the main factor causing the spatial variation of total nitrogen and organic carbon in the study area, while the soil type is the main factor causing the spatial variation of ratio of carbon to nitrogen in the soil of this study area.