Climate and soil management factors control spatio-temporal variation of soil nutrients and soil organic matter in the farmland of Jiangxi Province in South China

PurposeThis study aims to explore the spatio-temporal variation of soil nutrients as well as soil organic matter (SOM), and clarify the role of environmental and soil management factors in determining soil nutrients and SOM in farmland over Jiangxi Province of Southern China.Materials and methodsBetween 2005 and 2012, we collected 16,504 surface soil samples (0-20 cm) from farmland across Jiangxi Province. Based on this soil dataset, we summarized the changes in SOM, alkali-hydrolyzable nitrogen (available N), available phosphorus (P), available potassium (K), pH, and cation exchange capacity. Then, we used the geostatistical method to explore and map the spatio-temporal variability of SOM, and available N, P, and K. Finally, the random forest algorithm was used to identify the main factors controlling the variation of SOM and available N, P, and K.Results and discussionOur results revealed a clear right-skewed trend for the histogram of available P and K, pH, and cation exchange capacity in farmland soil of Jiangxi Province. From 2005 to 2012, the average concentrations of SOM and available P showed an insignificant decreasing temporal trend in the farmland of Jiangxi Province. The average concentrations of available N and available K showed a significant increasing trend between 2005 and 2012. In general, most of the soil samples had SOM, available N and P content at or above the level of Class 3 (high grade), and available K at or below the level of class 4 (moderate grade). The apparent lack of K fertility was detected. Regarding the spatio-temporal variation pattern, noticeable changes in the concentrations of SOM and available N, P, and K were detected in most of the region in 2012 when compared with 2005.ConclusionFarmland soils in Jiangxi Province had good fertility, and soil nutrients and SOM in farmland showed strong spatial variability. Overall, the climate (e.g., mean annual precipitation and mean annual temperature) and soil management (e.g., straw return and chemical fertilizer application) had dominant effects on soil nutrients and SOM, while other factors such as relief and soil properties had slight effect. The straw return is a sustainable way to improve soil fertility. Moreover, soil pH has a slight impact on soil nutrients and SOM. Great efforts are needed to prevent farmland soils from further acidification.