Impact of broad-based terraces on water and sediment losses in no-till (paired zero-order) catchments in southern Brazil

Abstract

Soil degradation is a widespread problem and currently one of the biggest challenges in modern-day agriculture. The partial adoption of conservation agriculture, such as no-till management, does not provide adequate erosion control, and the hydrology dynamics on hillslopes under no-till management remain poorly quantified. This study examines the hydrology of agricultural hillslopes under no-till management, with and without terraces in southern Brazil. Water and soil losses were measured in two paired, zero-order catchments (2.4 ha) under no-till cultivation, with and without broad-based retention terraces. Rainfall, surface runoff, and suspended sediment concentrations were monitored during major rainfall events. Analysis of hydrographs and sedigraphs was used to derive the peak flow, runoff duration, and sediment yield values and the hysteresis between surface runoff and the suspended sediment concentration during different seasons. The results show higher soil and water losses in the catchment without terraces. Terracing reduced peak flow rates by 79%, sediment yield from 0.44 to 0.16 t ha−1, and the total surface runoff from 3943 (126 mm) to 855 m3 (36 mm) during 31 events over 16 months. The no-till system without terraces was unable to adequately control surface runoff and soil erosion. Surface runoff and sediment yield were higher under no-till without terraces than under no-till with terraces. The difference in terms of surface runoff volume and sediment yield indicates an important difference in the hydrology and soil erosion in the catchment without terraces, which is represented by high-surface-runoff coefficient values observed during the rainfall-runoff events. The short lag time and steep rising limb of the hydrographs indicate high-surface-runoff responsivity to rainfall in no-till without terraces.