Effects of rainfall characteristics on bromide leaching in a typical tobacco field in China's Yunnan Province

Knowledge about water and solute transport in the vadose zone is critical for agrochemical management, especially for the tobacco cultivation characterized by extensive fertilizer and pesticide applications. Under the field conditions, however, natural soil heterogeneity complicates and limits the analysis of water and solute transport. Applying the scale-dependent treatment distribution in a rainfall simulation experiment, the objective was to evaluate the impact of rainfall characteristics on bromide (Br-) leaching in a typical tobacco field in China's Yunnan Province. On a transect established with 24 plots, rainfall amount, intensity, and time delay relative to solute application were arranged in cyclic patterns at different spatial scales. Soil samples in 10-cm increments down to 50 cm depth were collected for Br- determination after the simulated rainfall. The results display a significantly decreasing trend of Br- concentration with depth, suggesting the predominance of matrix diffusion over preferential flow at the scale of investigation in the intensively cultivated tobacco field. The Pearson correlation analysis only detected significant associations of Br- with rainfall intensity at the 0-10 cm depth and with rainfall amount at the 20-30 cm. With the aid of frequency-domain analysis, by comparison, strong spatial correlations were revealed with rainfall characteristics at each depth, even with the presence of a plow pan at the depth of 30-40 cm due to deep tillage. Although the dominant control of Br- distribution varied with depth, these findings demonstrate the profound effects of rainfall characteristics on solute leaching and the usefulness of scale-dependent treatment distribution in field-scale investigations of solute transport as well as other hydrological processes.