Soil Organic Matter and Its Active Pools as Affected by Legume/cereal Cropping Systems Under Some Agronomic Practices in the Derived Savannah Zone of Nigeria

Introduction of grain legumes facilitates farmers’ acceptance in adopting legume cropping system. This study evaluated effect of four cropping systems on soil organic carbon (SOC), total vesicular arbuscular mycorrhiza (VAM) spore count, soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN) and soil microbial biomass phosphorus (SMBP) within two locations (Nsukka and Moniya) of the derived savannah zone of Nigeria. The experiment was set up in a 4 x 2 x 2 factorial in randomized complete block design (RCBD), representing 4 cropping systems, 2 fertilizer application rates (0 and 60 kg N ha-1) and 2 residue management methods (incorporated and not-incorporated). This set-up was replicated three times and the experiment was repeated the following year (2008 and 2009). At the end of the experiment, soil samples for laboratory analyses were collected from 0 – 20 cm soil depth using auger. The result showed that SOC was not significantly (p≤0.05) affected by all factors and their interaction at both locations. In Nsukka, cropping systems and their interaction with residue management significantly (p≤0.05) affected SMBP and total VAM spore count. Continuous maize had the highest total VAM spore count (280), which was statistically the same with cowpea/maize rotation (277). Soybean/maize cropping system had the least value (259). Velvet bean/maize cropping system had the highest SMBP (0.0007 mg g-1). In Moniya, SMBC, SMBN and SMBP were significantly (p≤0.05) affected by the cropping systems with velvet bean/maize plots having highest values (0.053, 0.006, 0.0007 mg g-1). Residue incorporation and fertilizer application (60 kg ha-1) significantly (p≤0.05) increased SMBC and SMBN at Moniya. Interaction between cropping systems and residue managements at this location also significantly affected SMBC, SMBP and SMBC. In this study, SMBP distinguished the effect of the factors on soil quality better than the other measured parameters. Velvet bean-based cropping system improved soil microbial properties better than other cropping systems.