Impact of conservation agriculture on soil health: lessons from the university of fort hare trial.

Abstract Conservation Agriculture (CA) promotes soil health, but issues to do with soil health are poorly researched in the Eastern Cape, South Africa. This study reports on findings from a field trial done on the effects of tillage, crop rotations composed of maize (Zea mays L.), wheat (Triticum aestivum L.) and soybean (Glycine max L.) and residue management on a number of soil health parameters such as carbon (C)-sequestration, CO2 fluxes, enzyme activities, earthworm biomass and the Soil Management Assessment Framework soil quality index (SMAF-SQI). The field trial was done in a semi-arid region of the Eastern Cape Province, South Africa, over five cropping seasons (2012-2015). It was laid out as a split-split plot with tillage [conventional tillage (CT) and no-till (NT)] as main plot treatment. Sub-treatments were crop rotations: maize-fallow-maize (MFM), maize-fallow-soybean (MFS); maize-wheat-maize (MWM) and maize-wheat-soybean (MWS). Residue management: removal (R-) and retention (R+) were in the sub-sub-plots. Particulate organic matter (POM), soil organic carbon (SOC), microbial biomass carbon (MBC) and enzyme activities were significantly (p < 0.05) improved by residue retention and legume rotation compared to residue removal and cereal-only rotations. Also, carbon dioxide (CO2) fluxes under CT were higher compared to NT. The calculated soil quality index (SQI) was greatly improved by NT and residue retention. MWM and MWS rotations, in conjunction with residue retention under NT, offered the greatest potential for building soil health. Residue retention and inclusion of soybean in crop rotations are recommended for improving soil health under CA systems in the semi-arid regions of South Africa.