The Effects of Conservation Agriculture on Soil Organic Matter Content and Water Infiltration of Contrasting Soils in Zimbabwe and Zambia.

Multi-location on-farm trials were initiated in 2004 on two contrasting soil types in Zimbabwe, one on very sandy soils (90-94% sand) content and one on loamy clay soils, representing two of the major agricultural soils in the country, to evaluate the effects of conservation agriculture (CA) technologies under smallholder farming conditions. CA, comprising the principles of minimal soil movement and permanent residue cover, has been established using animal traction implements adapted to farmer circumstances, and, where feasible, crop rotation has been included. At the same time two researcher-managed trials have been established, one in southern Zambia and one in north-eastern Zimbabwe, including a wider range of conservation agriculture technological options. After three seasons of continuous conservation agriculture, crop yields have increased in the CA plots relative to plots representing farmers’ conventional tillage practices, but using the same crop varieties and fertilizer levels as the CA plots.  Both soil organic matter and water infiltration rates are now higher in the CA plots than with the farmers’ practice, and we believe that these increases, due to retention of crop residues and increased biological activity on the CA plots, largely explain the observed yield increases.