The effect of crop rotation and tillage practice on residue decomposition and wheat performance in the Western Cape, South Africa

Conservation agriculture relies on residue retention, crop rotation and reduced tillage. Crop rotation determines residue type, while tillage affects residue load and distribution. Although crop residue retention is often beneficial, residues can create challenges, including obstruction of planters during establishment and stubble-borne diseases. This study determined the effects of crop rotation and tillage on the residue decomposition and response of wheat (Triticum aestivum L.) in the Western Cape Province, South Africa. Wheat response was investigated to determine relationships between residue decomposition and its agronomic performance. Crop rotations in long-term trials in areas of the Swartland and southern Cape consisted of the following: wheat-medics, lupin-wheat-canola-wheat, canola-wheat-lupin-wheat, and a wheat monoculture. Crops were established with four tillage practices: conventional tillage (CT: chisel plough followed by soil inversion/ploughing, tine planter establishment), minimum tillage (MT: chisel plough, tine planter establishment), no-tillage (NT: direct drilling with tine planter) and zero tillage (ZT: direct drilling with double disc planter). Crop rotation had no effect on residue decomposition but increased wheat leaf area and grain yield when rotated with medics, lupin and canola when compared with monoculture wheat. ZT increased residue load and improved seedling establishment. ZT (50.9%) and NT (51.1%) increased residue decomposition compared with CT (34%). Faster residue decomposition could be achieved with less soil disturbance.