Soil physical and mechanical attributes in response to successive harvests under sugarcane cultivation in Northeastern Brazil

Abstract

Soil degradation due to agricultural field traffic is a serious issue affecting soil functions in modern agriculture. With sugarcane cultivation, the number of harvests through successive ratoons has become a challenge for the maintenance of soil quality in the topsoil and subsoil. The objective of this study was to evaluate physical and mechanical responses of soil to successive harvests under sugarcane cultivation in an Ultisol of coastal tablelands in Northeastern Brazil. Disturbed and undisturbed soil samples were collected from five sites at depths of 0–0.20 m (topsoil) and 0.20–0.40 m (subsoil), in which one, two, three or four harvests had taken place. In addition, one site had been kept without cultivation for one year after a sugarcane crop. Organic carbon (OC), maximum soil bulk density (BDmax), critical water content (wc), degree of compaction (DC), precompression stress (σp), compression index (CI) and the angle of internal friction (φ) were measured and subjected to multivariate analyses for the different sugarcane ratoons. Soil compaction indicators and OC in the topsoil were sensitive to the number of harvests, where compaction and OC increased with each ratoon sugarcane crop. The increase in OC with successive harvests resulted in a decrease in the BDmax and an increase in the wc, which suggest that optimum water content for compaction is moved to wetter zone due organic matter effects. The DC increased considerably after the third harvest, and it was at a maximum level before the sugarcane renovation (i.e. at the harvest immediately before the new seeding). In the subsoil, immediately below the plough layers, where plough pan formation typically occurs in conventional tillage, considerable changes in the soil physical and mechanical indicators are unlikely to occur due to the persistence of compacted layers. The increase in the organic carbon content results in better soil physical condition in the soil surface, but the degree of compaction may slightly increase due to frequency of traffic caused by the increase in the number of harvests, becoming compaction more severe close to the sugarcane renovation.