Effects of long-term grazed crop and pasture systems under no-till on organic matter fractions and selected quality parameters of soil in the Overberg, South Africa

Abstract

There is limited soil research on semi-arid, grazed no-till crop and pasture systems. The long-term (10 years) effect of three grazed no-till dryland crop and pasture rotation systems, and perennial lucerne pasture were assessed on soil carbon (C) and nitrogen (N) stocks, soil organic matter functional pools and selected soil quality parameters in the Overberg, South Africa. The largest soil C and N stocks (0–30 cm) were found in crop–pasture systems containing wheat and medic/clover (70.2–74.9 Mg C ha⁻¹ and 8.3–8.4 Mg N ha⁻¹), compared with perennial lucerne pasture (63.4 Mg C ha⁻¹ and 7.7 Mg N ha⁻¹) or cropping-only systems (54.7–58.9 Mg C ha⁻¹ and 6.3–6.7 Mg N ha⁻¹). Significantly higher labile C and N (free particulate organic matter fraction) contents were observed in crop–pasture systems (1.37–1.74 g C kg⁻¹ and 0.107–0.110 g N kg⁻¹) than in continuous cropping systems (0.9–1.0 g C kg⁻¹ and 0.042–0.045 g N kg⁻¹), attributed to higher annual C and N inputs and lower extent of soil disturbance. Significant positive correlations were found between soil C and N functional pools and soil quality parameters (soil respiration, effective cation exchange capacity and aggregate stability) and wheat yields. The results show the importance of the medic/clover pasture and wheat rotations in enhancing soil quality in the Overberg region.