ABSTRACT

The impact of organic and inorganic fertilizers namely cow dung, poultry manure, NPK (15:15:15) and urea on soil microbial population and enzyme activities were analysed. The field experiment was laid out on an agricultural site in National Root Crops Research Institute (NRCRI), Umudike and soil samples collected at two weeks intervals for the period of twelve (12) weeks. The samples were analysed for chemical properties (pH, total nitrogen, available phosphorus, organic carbon and exchangeable potassium), microbial population (bacteria, fungi and actinomycetes) and soil enzymes (urease, phosphatase, cellulase and dehydrogenase activities). The experiment was laid in a Randomized Complete Block Design (RCBD) with each treatment replicated three times to give total of 15 plots. Chemical and microbial properties (pH, total nitrogen, available phosphorus, exchangeable potassium, organic carbon, bacterial and fungal counts) of the study site and organic fertilizers used in the experiment were analysed prior to treatments application using standard methods. The study site was moderately acidic (5.63), low in organic carbon (0.49%) and moderate in nitrogen, potassium and phosphorus content (0.16%, 0.22cmol/kg and 13.51mg/kg respectively). From the results, pH of the treated plots ranged from acidic to moderately acidic (5.22-6.01). The treated plots were high in nitrogen (0.23-0.74%). Organic carbon content ranged from low to moderate (1.43-2.94%). The plots were moderate in available phosphorus (12.92-15.98mg/kg) and high in exchangeable potassium (0.58-1.06cmol/kg). The fertilizers applied to the soil were also observed to have significant effects on the enzyme activities. Soil acid and alkaline phosphatase, urease, cellulase and dehydrogenase activities ranged between 48.23 and 132.77mg/p-nitrophenol/g, 27.53 and 87.33mg/p-nitrophenol/g, 24.07 and 56.30µgN-h^-1g^-1, 46.23 and 79.94µgG-g^-1h^-1, 37.70 and 83.91µgTPFg^-1h^-1 respectively. The mean total bacterial, fungal and actinomycetes counts ranged from 3.42 to 6.43cfu/g, 1.81 to 6.55cfu/g and 1.13 to 5.33cfu/g respectively. The results suggest the use of fertilizers in enhancing soil chemical and biological properties as revealed by the recorded values from the organic and inorganic treated plots when compared to the control. However, the use of organic over inorganic fertilizers is recommended due to their compositions and higher positive effects on the soil fertility parameters.