Assessing the Impact of Organic Amendments on Soil Microbial Diversity and Fertility

Thesis Abstract

Soil fertility and microbial diversity are critical components of sustainable agriculture, yet these parameters are increasingly threatened by intensive farming practices and declining organic matter content. This study investigates the effects of organic amendments—specifically composted animal manure and plant-based residues—on soil microbial diversity and fertility within maize-growing fields in the Central Plains. The primary aim is to quantify how different organic amendments influence soil microbial communities and nutrient status, thereby informing sustainable soil management practices. The specific objectives include (i) evaluating changes in microbial biomass and diversity indices following organic amendment application; (ii) assessing alterations in key soil fertility parameters such as organic carbon, nitrogen, phosphorus, and pH; (iii) determining the relationships between microbial diversity and soil nutrient levels; and (iv) comparing the efficacy of manure-based versus plant-based amendments in enhancing soil health. The research adopts a factorial randomized complete block design (RCBD) across four farm zones, with three treatment levels—control (no organic amendment), composted manure, and plant residues—each replicated five times, totaling 45 experimental plots. The population comprises agricultural fields actively used for maize production, with a total sample size of 45 plots. Soil samples are collected at baseline and six months post-treatment, with microbial biomass and diversity assessed using phospholipid fatty acid (PLFA) analysis and high-throughput 16S rRNA gene sequencing. Soil fertility parameters are measured via standard laboratory protocols, including dichromate oxidation for organic carbon, Kjeldahl method for nitrogen, and Olsen's method for phosphorus. Data analysis employs analysis of variance (ANOVA) to determine treatment effects, followed by Tukey's post-hoc tests for multiple comparisons. Regression analysis is used to explore relationships between microbial diversity indices and soil nutrients, while multivariate techniques such as principal component analysis (PCA) elucidate shifts in microbial community composition. Expected findings suggest that organic amendments significantly increase soil microbial biomass and diversity, with manure-based amendments showing a greater effect compared to plant residues. Improvements in soil fertility parameters—particularly organic carbon and nitrogen—are anticipated to correspond with increases in microbial diversity, supporting the hypothesis that enhanced microbial activity promotes nutrient cycling. These results are expected to demonstrate that organic amendments lead to more resilient and fertile soils, thereby validating the role of organic inputs in sustainable soil management. The study contributes to existing knowledge by providing empirical evidence on the comparative efficacy of different organic amendment types in promoting soil biological health and fertility, filling previous gaps related to microbial community dynamics under diverse organic inputs. In conclusion, the findings emphasize the importance of organic amendments in improving soil health through enhanced microbial activities and nutrient availability, encouraging farmers to adopt organic-based soil management strategies. Recommendations center on integrating specific organic amendments into conventional farming systems to optimize microbial functioning and fertility, with suggestions for further research into long-term impacts and the mechanisms underlying microbial responses to organic inputs. Overall, this study advances the understanding of soil microbiome dynamics in response to organic amendments, providing a scientific basis for policy and practice aimed at sustainable soil management in maize production systems.