Nutrient transport in surface runoff and sediment yield on macroplots and zero-order catchments under no-tillage

Abstract

No-till farming is widely used in grain production in Brazil. However, the lack of runoff control and the low phytomass input are major causes of soil degradation. In addition, surface runoff transports chemical elements, including carbon and nutrients, in dissolved and particulate forms impacting water quality. Given this scenario, this study sought to evaluate the influence of phytomass amount, chiseling, and terracing on nutrient loss (NH4+, NO3− + NO2−, total N, P, K, Ca, Mg, Cu, and Zn) associated with surface runoff, suspended sediments, and to quantify their presence in sediment deposits at the end of the monitoring unit. This study was based on hydrological monitoring in four macroplots and two paired zero-order catchments during rainfall events. The macroplots reproduce use or absence of chiseling with lower or higher phytomass input, and the catchments, presence or absence of terraces. Nutrient concentrations were determined in surface runoff and sediment. In surface runoff, the highest median values of NH4+, NO3− + NO2−, total N, P, K, Ca, Mg, Cu and Zn concentrations in the catchments were 0.9,1.0, 1.5, 0.1, 3.1, 3.9, 1.1, 0.0, and 0.01 mg/L, and in the macroplots 1.0, 1.2, 2.1, 0.2, 3.4, 5.3, 1.7, 0.0, and 0.02 mg/L. In the suspended sediments, the highest median values of P, K, Ca, and Mg concentrations in suspended sediment in the catchments were 0.6, 6.7, 3.4, and 0.8 g kg−1 and in the macroplots 0.6, 6.1, 1.9 and 0.7 g kg−1. Our findings revealed a wide variation in nutrient concentrations in runoff and sediments regardless of the management practices. Nevertheless, the dissolved fraction of surface runoff controls the loss of nutrients during high-magnitude rainfall events. The effects of the increased phytomass and the presence of terraces, affect nutrient losses due to runoff control.