弃耕行为对亚热带农田土壤有机质时空变化作用机理研究

为明晰弃耕行为对耕地质量关键性指标——土壤有机质时空变化的作用机理，以粤东粮食主产区海丰、陆丰和陆河3个县（市）农田为研究对象，2015─2018年连续4年对205个典型亚热带农田样点进行跟踪监测，综合野外调查采样、农户调查走访及室内检测分析，采用统计分析与地理探测器相结合的方法，构建了研究区典型弃耕行为模式，分析了不同地理情境下弃耕行为对农田土壤有机质含量变化的作用机理。结果表明：研究区农田弃耕行为主要表现为季节弃耕、调整弃耕、年轮弃耕、长期弃耕4种模式，在总体监测样点中具有弃耕行为的农田样点173个，占总数的84.39%，其中年轮弃耕和长期弃耕综合占比达59.03%。各种弃耕行为模式农田土壤有机质均呈增长趋势，而长期耕作则导致整体下降，监测样点4年间土壤有机质平均增加量表现为：季节弃耕（1.55 g·kg^-1） > 调整弃耕（1.43 g·kg^-1） > 年轮弃耕（0.27 g·kg^-1） > 长期弃耕（0.24 g·kg^-1） > 长期耕作（-0.42 g·kg^-1）。在不同地理情景下，随着海拔高度增加，弃耕农田的土壤有机质整体下降；田间含水量过大或较少，会导致弃耕行为对农田土壤有机质影响显著；相对于滨海沙土，容重较大的赤红壤和红壤农田土壤有机质对弃耕行为的响应更强，应重点防范台地、水浇地及容重较大的土壤类型农田因弃耕行为导致的耕地质量下降。研究表明，农田弃耕行为在我国部分地区表现异常严重，且弃耕类型在不同地理情景下对土壤有机质含量影响不同，亟需通过制定相关政策制度将无序弃耕规范为有序休耕。

Study on the spatiotemporal variation of soil organic matter induced by abandoned tillage behavior

With the acceleration of non-agricultural processes in China, the marginal cost of agricultural production is increasing, leading to the increasingly serious phenomenon of disordered abandonment and its adverse impact on national food security. Therefore, it is necessary to analyze the mechanism of abandoned behavior on the quality of cultivated land, especially the key index of farmland soil organic matter. In this study, the farmland of Haifeng, Lufeng, and Luhe, the main grain-producing areas in east Guangdong, was used as target areas. From 2015 to 2018, 205 typical subtropical farmland samples were tracked and monitored. Field survey and sampling, household surveys, and indoor laboratory analysis were used in combination with statistical analysis and a geodetector method to construct the typical abandonment behavior pattern in the study area and analyze the mechanism of the effects of abandonment on soil organic matter content in farmland under different geographical conditions. Results showed that there were four patterns of farmland abandonment in the study area:seasonal abandonment, adjustment abandonment, annual ring abandonment, and long-term abandonment. Among the total monitoring sites, 173 farmland samples were abandoned, accounting for 84.39% of the total, of which annual ring abandonment and longterm abandonment accounted for 59.03% of the total. Soil organic matter increased under all kinds of abandoned tillage patterns but decreased under long-term tillage. Results showed that the average increase during the four years was as follows:season abandonment (1.55 g kg^-1) > adjustments abandonment(1.43 g·kg^-1) > annual ring abandonment(0.27 g·kg^-1) > long-term abandonment(0.24 g·kg^-1) > long-term cultivation(-0.42 g kg^-1). For different geographical situations, as the altitude increased, the of abandoned farmland in the soil organic matter decreased. If the water content in the field was too high or too low, the abandonment behavior would significantly affect soil organic matter. Compared with coastal sandy soil, the response of soil organic matter in lateritic red soil and red soil with higher bulk density was stronger than that in coastal sandy soil. Therefore, it is necessary to focus on the prevention of farmland quality degradation caused by abandoned tillage in the mesa area, in irrigated land, and in areas containing soil type with high bulk density. The behavior of farmland abandonment is very serious in some areas of China. Moreover, the effects of different types of abandoned land on soil organic matter content are different under different geographical situations. Therefore, it is necessary to formulate relevant policies and regulations to convert disordered abandonment into orderly abandonment.