Erosion and hydrological response in no-tillage subjected to crop rotation intensification in southern Brazil

Abstract

No-tillage (NT) is a practice that has been used for >30 years and is used as the main soil conservation strategy in South America. However, recent studies have demonstrated soil erosion problems in agricultural fields in southern Brazil related to soybean monoculture, low phytomass production by crops and an absence of runoff control. This study describes the erosion and hydrological response of chisel ploughing and crop rotation intensification in a NT traditionally managed without crop rotation on a Nitisol on an agricultural hillslope in southern Brazil. The water and soil losses were monitored in natural hillslope (Macroplots) approximately 90 m in length and 6000 m2 in area and with a rectilinear plane curvature and a slope of 9%. The treatments tested were as follows: i) NT without crop rotation (NTnocr), ii) chisel ploughing in NT without crop rotation (CH + NTnocr), iii) NT with crop rotation (NTcr), and iv) chisel ploughing in NT with crop rotation (CH + NTcr). Monitoring was performed in the period from July 2015 to June 2016, during which 9 significant rainfall events occurred at different intensities and accumulated volumes. The monitoring results indicated that NTnocr is insufficient to control soil erosion, even during low-intensity events. The crop rotation intensification in NT with increased phytomass production by crops reduced runoff only by 18% and soil losses by up to 84%. Care in relation to chisel ploughing was evidenced by a 2.4-fold increase in NTcr soil losses associated with soil mobilization due to chiseling and high-intensity events. In conclusion, the results revealed that the isolated adoption of NT is insufficient to control runoff, even under crop rotation intensification. This result clearly indicates that complementary conservation practices are necessary to control runoff and all its associated processes, from soil erosion and nutrient and pesticide mobilization to water resources, to improve the definition of conservation agriculture.