9. Soil Microbial Biomass Carbon, Nitrogen and Phosphorus Dynamics under Different Amendments and Cropping Systems in the Semi – deciduous Forest Zone of Ghana

Abstract

A field experiment to monitor the dynamics of microbial biomass carbon, nitrogen and phosphorus under amendments and cropping systems were conducted in 2006 and 2007 at the Central Agricultural Station, Kwadaso Kumasi, Ghana. The field experiment was a split plot with three replications. Three different amendments (poultry manure, poultry manure + chemical fertilizer, chemical fertilizer) and a control (no amendment) constituted the sub-plots whereas cropping systems (continuous maize, maize/soybean intercrop
and maize/cowpea rotation) were assigned to the main plots. Soil samples under each amendment and cropping system were taken at 3 weeks interval within each cropping season and analysed. The results of the study revealed a general buildup of microbial biomass over the seasons. Microbial biomass carbon ranged from 25 to 248 mg/kg soil in 2006 (major season) to 87 to 713 and 546 to 770 mg/kg soil in 2006 (minor) and 2007 (major seasons), respectively. Biomass carbon showed positive correlations with soil organic carbon with r values of 0.71, 0.40 and 0.64 in 2006 (major) 2006 (minor) and 2007 (major seasons), respectively. Biomass nitrogen showed more temporal fluctuations than biomass carbon. Negative values (-47.7 to -7.40 mg/kg soil) for microbial biomass phosphorus were observed at 42 and 63 days after amendments application (DAAA), signifying immobilization of phosphorus at the peak of crop growth. The immobilized phosphorus was, however, released 84 DAAA, thus, adding to the available phosphorus content of the soil. The study has shown that microbial biomass could be influenced positively by amendments and cropping systems overtime, and that phosphorus could be immobilized at the peak of crop growth; its release not concurring with peak nutrient demands of crops, hence, the need for synchronization.