Effects of Reduced Tillage on Crop Yield, Plant Available Nutrients and Soil Organic Matter in a 12-Year Long-Term Trial under Organic Management

Abstract

A field experiment was performed in Southwest Germany to examine the effects of long-term reduced tillage (2000–2012). Tillage treatments were deep moldboard plow: DP, 25 cm; double-layer plow; DLP, 15 + 10 cm, shallow moldboard plow: SP, 15 cm and chisel plow: CP, 15 cm, each of them with or without preceding stubble tillage. The mean yields of a typical eight-year crop rotation were 22% lower with CP compared to DP, and 3% lower with SP and DLP. Stubble tillage increased yields by 11% across all treatments. Soil nutrients were high with all tillage strategies and amounted for 34–57 mg kg⁻¹ P and 48–113 mg kg⁻¹ K (0–60 cm soil depth). Humus budgets showed a high carbon input via crops but this was not reflected in the actual C_org content of the soil. C_org decreased as soil depth increased from 13.7 g kg⁻¹ (0–20 cm) to 4.3 g kg⁻¹ (40–60 cm) across all treatments. After 12 years of experiment, SP and CP resulted in significantly higher C_org content in 0–20 cm soil depth, compared to DP and DLP. Stubble tillage had no significant effect on C_org. Stubble tillage combined with reduced primary tillage can sustain yield levels without compromising beneficial effects from reduced tillage on C_org and available nutrient content.