Impact of tobacco management practices on soil, water and nutrients losses in steeplands with shallow soil

Abstract

Tobacco is produced in Brazil mainly by small farmholders, on shallow soils on steeplands or on sandy soils, usually under intense soil tillage and lacking soil conservation measures, which can result in large losses of water, soil and nutrients such as P and K. We studied soil management systems for tobacco cropped using animal traction, on shallow soil on steeplands. On a Leptosol, we evaluated conventional tillage (CT), minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage without ridge (NT), no-tillage with ridge (NTr) and no-tillage with consolidated ridge (NTrc), in a completely randomized blocks design with three replicates. Runoff plots of 1.2 m2 were used to determine water and soil loss by runoff, and total and soluble P and K losses in eight rainfall events during the tobacco crop cycle. Oat cultivation prior to tobacco provided higher dry-mass mulch production and the lowest proportion of exposed soil and rocks in NTr, NTrc and NT systems. The losses of water and of P and K in the soluble forms during the storm rainfall events evaluated were lower for NT management compared to the other treatments. Total soil loss for the monitored rainfall-events was 15 and 16 Mg ha−1 for CT and MTf management, and it was reduced about five times for MTo, NTrc and NTr treatments. However, the lowest soil loss was observed for NT (0.2 Mg ha−1). This same trend was observed for total losses of P and K, where NT reduced about 97 and 57 times the losses of these nutrients compared to CT. Therefore, these results show that conservation managements such as no-tillage or minimum tillage associated with winter cover crops without grounding of tobacco seedlings may be effective to reduce soil losses along with P and K adsorbed in the soil. However, reduction of losses of water, soluble and total P and K was only effective combining no-tillage with no ridge construction and winter cover crop.