Effects of grazing, rotation, and tillage on surface runoff in a heavy textured Uruguayan soil

Abstract

Adopting no-till (NT) after conventional tillage (CT) could affect surface runoff, but this effect may also depend on the rotation type, such as continuous grain crop (CC) or crop–pasture rotation (CP). The objective of this study was to assess the effects of soil-tillage practices and rotation type on runoff in a long-term field (LTF) trial established in 1993 on a Mollisol. This experiment was carried from 2012 to 2017 and included three tillage rotations (NT–CP, NT–CC, and CT–CP) and a natural pasture (NP) as a control, with three replications. Runoff was monitored under natural rainfall in microplots. The pasture of the CP treatment was rotationally grazed with dairy cows at high stocking rates before this experiment. We hypothesized that soil compaction by animal trampling during grazing would increase surface runoff regardless of tillage type. We measured the number of events and runoff depth in all treatments, grain yield, soil bulk density (BD), and infiltration rate (IR) in NT–CP and NT–CC. The results showed a statistically significant increase in average runoff (107 mm yr–1) for all rotations relative to NP (68 mm yr–1) and a significant difference for the mean of both CP rotations (119 mm yr–1) compared with NT–CC (83 mm yr–1). During the crop phase (excluding the pasture), the two NT rotations showed a similar trend, but with higher BD (1.23 g cm–3) and lower IR (27.2 mm h–1) for NT–CP. We concluded that animal trampling increased surface runoff regardless of tillage, but this effect would need to be confirmed at other sites.