A regional synthesis of seven-year maize yield responses to conservation agriculture technologies in Eastern and Southern Africa

In an effort to address the challenges of low crop productivity and food insecurity among Africa's smallholder farmers, Conservation Agriculture (CA) is considered a promising strategy. This study synthesized and analyzed the maize yield merits of CA systems relative to conventional farmer practices and the contribution of agro-ecological zones, seasonal rainfall regimes and soil characteristics in five Eastern and Southern African (ESA) countries, namely Ethiopia, Kenya, Malawi, Mozambique and Tanzania, over a seven-year period. Agronomic data generated from 287 smallholder on-farm trials testing the productivity of CA cropping systems with a total of 4976 observations, were compiled and collated. Across the five countries, the factors country, cropping system, rainfall regime, agro-ecological zones and soil texture, accounted for 51, 20, 16, 10 and 3% of the yield variation, respectively. Furthermore, CA reduced yield variability by 11% (from 67% under conventional tillage to 56%). Across all the ESA environments and relative to conventional tillage with a mean of 2401 kg ha(-1), CA-rotation had the highest maize yield increase (35%) compared with CA-sole (29%) and CA-intercrops (15 %) systems and thus offered the best opportunity for improved maize productivity compared with intercrops, CAsole or conventional filled systems. Furthermore, the highest returns (90-95%) to CA investments by smallholder farmers were realized under low rainfall conditions (< 700 mm), thereby providing clear evidence of the climate smartness of CA systems under soil moisture stressed conditions. These CA yields relative to conventional fill however were subdued to 26, 19 and 15% in medium-wet (700 -1300 mm) and depressed even further to + 1, -18 and + 9% in wet (> 1300 mm) environments, for CA-rotations, CA-sole and CA-intercrops, respectively. The study also showed that the most beneficial effects of CA occurred under loam textured soils. In addition, CA systems responded best (16%) on well drained soils yet depressed yields by 33% on poorly drained soils. We conclude that the prime conditions for CA performance relative to conventional tillage, involve use of CA-rotations, low rainfall (< 700 mm) conditions, medium textured loam and well drained soils.