Microbial indicators of soil quality under integrated soil fertility management practice effects in Madeya, Siaya County, Kenya
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Date
2024-07
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Kenyatta University
Abstract
Decline in soil and crop productivity, following soil infertility and poor soil health and agronomic practices, has threatened food availability amidst the growing world human population. Integrated soil fertility management (ISFM) practices can greatly avert these problems by enriching soil health, fertility and increasing crop production. However, despite these benefits, there is scanty knowledge on the potential impacts of different ISFM practices on soil microbial community structure, abundance, enzyme activities and of greenhouse gas emissions in western Kenya. This study investigated the effects of different long-term ISFM practices on soil bacterial community composition; extracellular soil enzyme activities, nutrient mineralization, maize performance and greenhouse gas emissions in western Kenya. The five objectives of this study were to determine the effects of farmyard manure, inorganic fertilizers and residue application on: (i) soil microbial biomass and bacterial abundance; (ii) the potential activities of extracellular phosphomonoesterase, β-glucosidase, and β-glucosaminidase enzymes in soil; (iii) soil bacterial phoC and phoD genes abundance; (iv) greenhouse gas emissions; and (v) soil organic carbon (SOC) and chemical parameters, nitrogen (N) and phosphorus (P) nutrient mineralization and their monetary values and maize performance. The study was carried out under maize-tephrosia rotation and continuous maize systems in an existing long-term trial. The experiment was set up in randomized complete block design. Twelve treatments were selected, replicated thrice. Soil samples were taken at 0-15 cm depth. Three closed chambers, installed per plot, in three treatments (0N+45P; 90N+45P and 0N+45P+FYM), were used to assess the effects of phosphorus, nitrogen and farmyard manure, respectively on greenhouse gas (CO2 and N2O) emissions. Gas sampling was done once per week, with four gas samples taken at 15-minutes sampling intervals per plot, and later analyzed using Gas Chromatography. Samples for objectives (i), (ii) and (iii), respectively, were analysed using Illumina Miseq sequencing, high-throughput colorimetric assays and standard laboratory procedures. Normality test was conducted on all the data using Shapiro-Wilk test before any data analysis was done. Analysis on objective (i) for bacterial species data involved Shannon wiener diversity measure, Canonical correspondence analysis, non-metric dimensional scaling (NMDs) and one-way analysis of variation (ANOVA). Data on objectives ii, iii, iv and v were analyzed using one-way ANOVA and Pearson correlation tests. Tukey Honest Significant Difference (HSD) was used to separate the significantly different means at P≤ 0.05. Application of FYM increased bacterial abundance and diversity. Microbial biomass carbon (C) and phoD gene abundance were not significantly affected by treatments, but sole application of residue significantly reduced bacterial phoC gene abundance. Application of FYM, in combination with other inputs, increased soil extracellular enzymatic activities. Application of FYM significantly increased CO2 and N2O fluxes. Additionally, FYM increased the quantities of P mineralised and its equivalent monetary value, but reduced N mineralised and its monetary equivalent. Nitrogen fertilization reduced the quantity of N mineralized and its monetary equivalent. FYM addition significantly increased maize performance and grain prices. Thus, FYM addition, either alone or in combination with other inputs, can enhance soil quality and nutrient availability, microbial diversity and functions as well as overall maize performance.
Description
A research thesis submitted in fulfilment of the requirements for the degree of doctor of philosophy in environmental studies (agroforestry and rural development) in the School of Agriculture and Environmental Sciences of Kenyatta University, Nairobi (Kenya), July 2024
Supervisors:
Prof. Monicah W. Mucheru-Muna
Dr. Job Kihara