Contributions of Microorganisms to Soil Fertility in Adjacent Forest, Fallow and Cultivated Land Use Types in Nsukka, Nigeria

Abstract

Soil chemical properties and microbial populations were determined in this study in order to compare the contributions of microorganisms to soil fertility in three land use types in an Ultisol of southeastern Nigeria. A total of 27 samples were collected from 0-20 cm depth as follows: 21 samples from a fallow land (3 replicates from 7 plots) that has been under 10-year fallow, three samples from an adjacent forestland and finally, three samples from an adjacent cultivated land owned by a farmer. These samples were air dried, passed through a 2-mm sieve before soil properties were determined following standard methods. Fresh soil samples were used to determine the number of soil microorganisms via the dilution spread plate technique using the nutrient agar for bacteria and potato dextrose agar for fungi. Results showed that the forest and fallow lands had significantly (P < 0.05) lower mean pH value, available P, exchangeable K and Na, but significantly higher exchangeable H and bacteria population than the cultivated land. The mean exchangeable Ca was significantly (p < 0.05) higher in the cultivated land than in the fallow land but similar to that from the forestland. The fungi population was significantly (p < 0.05) higher in the forestland than in others which are similar statistically. The mean soil organic matter, total N, exchangeable Mg, exchangeable Al and CEC were statistically similar in all the land use types. Contributions of microorganisms to soil fertility were generally more in the uncultivated lands, an indication that tillage operations may have affected the microbial populations. Significant correlations (p < 0.05) obtained between some soil chemical properties and microbial densities signify important roles microorganism play in soil nutrient build up.