Tree pruning, zone and fertiliser interactions determine maize productivity in the Faidherbia albida (Delile) A. Chev parkland agroforestry system of Ethiopia

Faidherbia albida is an important tree species in the parkland agroforestry system of the Rift Valley region, central and south-eastern Ethiopia. Positive effects of F. albida on crop production are widely recognised. However, the effects of tree pruning, zone and fertiliser interactions on crop growth have not been addressed in earlier studies. A field experiment containing three levels of tree pruning (100% pruned, 50% pruned, and unpruned) as main plots, and application of recommended rates of N and P fertilisers as sub-plots, was conducted during the 2015 and 2016 growing seasons. Maize grain yield and biomass, light intensity, and soil nutrients and moisture were measured at different positions from each F. albida tree trunk (0–2, 2–4 and 4–6 m) and in crop-only plots. Biomass and yield of maize were significantly greater under tree canopies compared to crop-only plots in both the 2015 and 2016 growing seasons, regardless of pruning levels. Fertilisation significantly increased yields under tree canopies compared to crop-only plots in both years. Light intensity increased with distance from trees and with greater pruning levels. Soil carbon and nutrient concentrations and moisture content decreased with increasing distance from tree and with soil depth. These results suggest that maize production and profitability could be maintained or improved through only partial pruning of F. albida rather than pollarding, and by preferentially applying fertilisers in normal and wet years. Recommendations need to be evaluated in a total system context including other rotational crops, fuel, livestock and socio-economic factors.