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.