Effects of best management practices on nitrogen load reduction in tea fields with different slope gradients using the SWAT model

Abstract

Increasing fertilizer inputs in tea (Camellia sinensis L.) fields, especially in hilly areas, poses serious potential risks of surface water contamination. Best management practices (BMPs) have been extensively implemented to control nutrient loads from non-point sources. However, little research has been conducted to evaluate the effects of dynamic BMPs on nitrogen (N) load reductions in tea fields with different slope gradients. This study is conducted in subtropical tea fields in the Machuan River watershed, which adjoins Huangshan Mountain of Anhui Province in China. Three BMP scenarios, viz., avoiding fertilizing before rain, contour planting and applying slow-release fertilizers, are simulated to model the N load reduction using the Soil and Water Assessment Tool (SWAT). The objectives of this study are as follows: (1) to build a calibrated SWAT model for the Machuan River watershed, (2) to evaluate and compare the effects of three BMPs on N load reduction in tea fields with different slope gradients, and (3) to identify critical slope gradients and BMPs for effective N load control. The results indicate that three BMP scenarios significantly impact N losses reduction in tea fields and that their effects vary among different slopes and months. Compared with the baseline condition, the N losses rate could be reduced by approximately 24%, 28%, and 66% for three scenarios, respectively. Generally, tea planted on steep-sloping land leads to great losses of N, and tea fields on slopes exceeding 15° should be prioritized for BMP implementation as tea fields planted here tend to have the highest N losses. This will offer sound information for the development of better pollution-control strategies for tea fields in the Machuan River watershed.