Christian Thierfelder, Stephanie Cheesman and Leonard Rusinamhodzi
Increasing soil degradation in southern Africa and the potentially negative effects of climate change demand “greener” solutions to reverse this trend. Conservation agriculture (CA) has been proposed as one of those solutions and field level data show marked benefits of this new cropping system. Nevertheless, the use of rotations and/or associations in CA systems is challenging at both the farm and community level. Intercropped maize (Zea mays L.) with grain legumes, cowpea and pigeonpea (Cajanus cajan L. (Millsp.)), as well as maize rotated with cowpea (Vigna unguiculata L. (Walp)) and sunnhemp (Crotalaria ochroleuca L.) was studied for up to eight seasons under CA and conventional agriculture in Zimbabwe. The objective of this study, carried out on-farm and on-station, was to highlight the effects of CA systems on some soil quality indicators and crop productivity. Where possible the specific effects of rotation and intercropping was separated and compared with monocropping. The on-station and on-farm results show: an increase of up to 331% in water infiltration, a 31% greater soil carbon in the top 60 cm than on adjacent conventionally ploughed fields, a 6% lower bulk density in the top 10 cm and 32.5–36 t ha−1 less cumulative soil erosion in CA fields after seven cropping seasons compared with the conventional control treatment. The comparative productivity analysis between continuous maize, maize intercropped with cowpea or pigeonpea and maize in rotation with cowpea or sunnhemp, shows marked benefits of rotation especially in CA systems. The benefits of CA especially when rotated with leguminous crops, increase over time, suggesting that there are improvements in soil structure and fertility. However, field level benefits will not increase the overall adoption of rotations and intercropping in CA systems, unless the socio-economic constraints at the farm and community level are addressed.
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