Legume cover crops combined with no-tillage increase extractable sulfur in a subtropical Acrisol

Abstract

Sandy soils have low sulfur (S) supply capacity and a high potential for loss of the element by leaching. Therefore, it is fundamental to adopt intensive management in the use of S aiming to increase the availability of the element in the soil. This study evaluated the long-term (34 years) impact of soil tillage (CT, conventional tillage; NT, no-tillage) combined with three cropping systems (O/M, oat/maize; V/M, vetch/maize; O+V/M+C, oat+vetch/maize+cowpea), with (180 kg ha–1) or without nitrogen (N) fertilization for the maize crop, on the soil extractable S in a sandy clay loam Acrisol from Southern Brazil. Soil samples were taken from the 0–5, 5–10, 10–20, 20–30, and 30–40 cm layers, and the extractable S was estimated by extraction with 500 mg L–1 of P. The largest soil extractable S in NT occurred with vetch, higher than the oat/maize system to 30 cm depth (11.1 and 7.3 mg dm–3, respectively). The extractable S in the surface layer (0–5 cm) in NT showed a strong relationship (R2 = 0.83) with SOC, increasing 0.85 mg dm–3 for each increment of 1 g kg–1 of SOC. In the absence of N, systems with legume cover crops cycled 1.7 and 2.0 times more S (17 and 22 kg ha–1 yr–1) than in the oat/maize (10 kg ha–1 yr–1). Nitrogen fertilization tripled S removal in grains (73 kg ha–1 O/M-0 to 236 kg ha–1 V/M-180) but did not negatively affect soil extractable S. The S input via formulated fertilization and atmospheric deposition (12.5 and 3.3 kg ha–1 yr–1, respectively) was enough to supply the S removal by maize. However, only in the most intensive and diverse systems was it possible to maintain S availability above the critical level. In sandy soils that naturally have low S supply capacity, it is possible to maintain adequate levels of extractable S when combining NT and legume cover crops that intensify the cycling of S and prevent the loss of nutrient by leaching.