The impact of karst landform types and land uses on the leaching of nitrogen and phosphorus in soil solution

Abstract

To analyze the impact of karst landform types and land use patterns on the movement of nitrogen and phosphorus in soil solution, we utilized soil solution nitrogen and phosphorus monitoring data from the Huixian Wetland Experimental Area in the Li River Basin from March to December 2021. The study area was divided into three categories based on karst landform types, namely, non-karst landforms, peak-cluster depressions, and peak-forest plains. Additionally, two categories were considered based on land use patterns, namely, paddy fields and uplands. Single-factor variance analysis and Pearson correlation analysis were employed to examine the transportation of soil solution nitrogen and phosphorus at different soil depths during the irrigation and non-irrigation seasons. The results indicate that (1) the concentrations of NO3--N in the soil solution at depths of 30 cm, 60 cm, and 100 cm exhibited significant differences between the irrigation and non-irrigation seasons. The total nitrogen (TN) concentration at a depth of 30 cm also displayed significant differences between the two seasons. Pearson correlation analysis of nitrogen and phosphorus concentrations in the soil solution revealed a significant positive correlation between NO3--N and TN, with a correlation coefficient of 0.666 (p<0.01). (2) The downward migration distance of NO3--N varied among different karst landform types, following the sequence of peak-forest plains > peak-cluster depressions > non-karst landforms. The NH4+-N migration distance followed the order of peak-cluster depressions > peak-forest plains > non-karst landforms. (3) The NO3--N concentration in irrigated paddy fields generally remained at a high level at a depth of 100 cm during the irrigation season. In upland areas, the NO3--N concentration followed a consistent pattern of 30 cm > 60 cm > 100 cm. However, during periods of heavy rainfall, anomalous increases or decreases in concentration were observed at depths of 60 cm and 100 cm.