Lulu

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

Summary

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 A_p horizon was sampled four times during one growth period and soil basal respiration, microbial biomass C (C_mic) and N (N_mic), soil organic C (C_org), total soil carbohydrates monoculture (ehy) , soil pH and N were determined. Alley cropping increased C_org, C_mic, basal respiration, qC0₂, the C_mic :C_hy ratio, and soil N, while under monoculture C_mic:N_mic and soil C:N ratios were increased. A single-time application of 5 and 10t ha^-1 Sesbania prunings resulted in an increase of C_org contents still detectable after 7 years. C_org 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 C_mic and C_mic:N_mic 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.