Impact of Organic Amendments on Soil Fertility and Microbial Diversity in Agroecosystems

Thesis Abstract

Recent concerns over soil degradation and declining fertility in agroecosystems have heightened interest in sustainable land management practices, particularly the use of organic amendments. This study investigates the impact of various organic amendments—specifically composted manure, crop residues, and biochar—on soil fertility parameters and microbial diversity within maize-cultivated fields across a representative agricultural region. The primary aim is to quantify the extent to which organic amendments influence key soil chemical characteristics and microbial community structure, thereby informing sustainable soil management strategies. The specific objectives include 1) assessing changes in soil chemical properties (pH, organic carbon, nitrogen, phosphorus, and cation exchange capacity) following organic amendment application; 2) characterizing shifts in soil microbial community composition and diversity using high-throughput sequencing techniques; and 3) elucidating relationships between soil chemical parameters and microbial diversity indices through multivariate statistical analysis. Employing a mixed-methods research design, the study integrated field experiments with laboratory analyses. A total of 60 experimental plots, established in a randomized complete block design with five treatments (including control, composted manure, crop residues, biochar, and combined organic amendments), were monitored over two full growing seasons. Soil samples were collected quarterly from each plot and analyzed for chemical properties using standard laboratory procedures adhering to Valuation of Sustainable Agriculture Protocols. Microbial community composition was characterized via 16S rRNA gene sequencing for bacteria and ITS sequencing for fungi, utilizing Illumina MiSeq platforms. Data were analyzed through a combination of descriptive statistics, analysis of variance (ANOVA) to determine treatment effects, and multivariate regression to examine relationships between soil chemical factors and microbial diversity metrics. Additionally, diversity indices such as Shannon, Simpson, and operational taxonomic units (OTUs) were computed to quantify microbial richness and evenness. Expected findings suggest that organic amendments will significantly enhance soil fertility parameters, notably increasing organic carbon, nitrogen levels, and cation exchange capacity compared to control plots. It is anticipated that microbial diversity will be positively correlated with the degree of improvement in soil chemical attributes, with biochar and combined amendments producing the greatest microbial richness and diversity. The study is projected to reveal shifts in microbial community composition, favoring beneficial microbial taxa such as nitrogen-fixing bacteria and organic matter decomposers, which contribute to soil resilience and productivity. These findings will contribute to a better understanding of the microbiological mechanisms underpinning soil health and productivity in response to organic inputs. Furthermore, this research advances knowledge by integrating chemical soil analytics with microbial ecology in the context of organic amendment strategies, grounded in the theoretical framework of the Soil Food Web Theory and Ecosystem Services Theory. The study’s results will provide evidence-based guidance for farmers and policymakers aiming to optimize organic inputs for sustainable agriculture. The main conclusion will emphasize that organic amendments considerably improve soil chemical fertility and promote microbial diversity, thereby enhancing soil resilience and crop productivity. Recommendations will include adopting integrated organic amendment practices, particularly biochar combined with composted manure, for long-term soil health maintenance. The study will also highlight the need for further research into the long-term impacts of organic amendments under varying climatic and soil conditions, and suggest avenues for developing tailored organic soil management protocols.