Die Bodenkultur - Journal for Land Management, Food and Environment

B. Lulu and H. Insam:

Effects of cropping systems and manuring on soil microbial and C status of a vertisol in Ethiopia


The effect of monoculture and Sesbania alley cropping systems (with constant removing of the prunings) and single time residue input from alley crops or green manure on wheat yield was studied in a Vertisol of cool-humid tropical Africa. Seven years after the start of the experiment the Ap horizon was sampled four times during one growth period and soil basal respiration, microbial biomass C (Cmic) and N (Nmic), soil organic C (Corg), total soil carbohydrates monoculture (ehy) , soil pH and N were determined.

Alley cropping increased Corg, Cmic, basal respiration, qC02, the Cmic :Chy ratio, and soil N, while under monoculture Cmic:Nmic and soil C:N ratios were increased. A single-time application of 5 and 10t ha-1 Sesbania prunings resulted in an increase of Corg contents still detectable after 7 years. Corg contents of the green manured and fallowed wheat fields were higher than those of continuous wheat. In no case, however, did the microbial parameters exhibit any significant changes as a result of a single time organic residue application. The Cmic and Cmic:Nmic ratio exhibited seasonality, but for the former seasonality was observed only in alley plots. The results show positive effects of alley cropping on soil organic matter status, microbial biomass and activity even when prunings are removed, thus making alley cropping even more favourable in regions with scarce nutrient supply. This is further substantiated by the positive effects of single-time manuring and fallowing on soil C content.

Key words:  Monoculture, Alley cropping, Vertisol, Microbial biomass, Soil carbohydrates.