Microbial population dynamics, enzyme activity and quantification of nutrient release in soil amended with composed with varying degree of maturity

Abstract

The activity and functional diversity of micro-organisms contribute to the stability and productivity of agro-ecosystems. Soil micro-organisms and enzyme activities have been suggested as potential indicators of soil quality. Hence, management practices that can enhance microbial diversity and enzyme activities are essential for improving soil health and soil fertility status. The aim of the study was to assess the effects of compost maturity age on the change in bio-quality indicators of compost and compost amended soil. Cattle manure-rich compost was prepared through thermophilic windrow composting using cattle manure and wood chips mixed at a proportion of 4:1 (w/w) to achieve a C:N ratio of 30:1. This compost was sampled at regular intervals of 30 days after the initiation of the composting process until 150 days when it was finally cured. Compost samples of varying degrees of maturity age were air-dried, pulverised and mixed with 1.2 kg surface soil at an equivalent rate of 100 kg P ha-1. Each compost amended soil was transferred into well labelled plastic pots for incubation. Sampling of incubated amended soils was performed at 7 days interval until 42 days; and the samples were used for microbial count, enzyme activity, and mineralisation assessments. Data generated were analysed as factorial experiment using SYSTAT package. Treatment and interaction effects were evaluated using Fisher protected least significant difference at probability level of 5%. Results of the chemical composition of the different composts are similar and comparable. Variation in compost maturity date, incubation time and their interaction exerted significant effects on the measured microbial counts and enzyme activities as bio-quality indicators. The content of bacteriameasured was consistently highest at each sampling date followed by the actinomycetes while fungi population count remained persistently lowest. Bacteria and β-glucosidase represent the dominant microbe and enzyme, respectively in all compost samples taken at different maturity age.The highest count of actinomycetes (6.18 CFU g-1), bacterial (6.73 CFU g-1) and fungi (3.06 CFU g-1) were obtained during the 42-day incubation period.Of all the enzyme activities studied, β-glucosidase content was consistently highest in all compost samples across the sampling dates. Similarly, the highest concentration of ß-glucosidase (3076 mg kg-1 hr-1), phosphatase (1480 mg kg-1 hr-1), dehydrogenase iv (120.07 μg INF g-1 2hr-1) and urease (26.15 mg kg-1 2hr-1) were obtained during the 42-day incubation period. The highest microbial counts and enzyme activities were reached beyond 19 days after incubation. Maximum Bray P1 (20.10 mg kg-1), ammonium N (108 mg kg-1) and nitrate N (189 mg kg-1) were obtained at 42, 14 and 42 days after incubation, respectively. The measured temporal change in the concentrations of bio-quality parameters in the compost-amended soils were highest in compost sampled at 90 days, except for phosphatase, indicating the peak of the thermophilic process. The bio-quality parameters of these composts and the compost amended soil were influenced by compost maturity and incubation time. The uses of mature compost with desirable level of bio-quality indicators are crucial for fertility management and improved soil health. Keywords: Compost maturity, enzyme activities, microbial count, nutrient release, soil fertility