Comparative Impact of Organic vs. Inorganic Fertilizers on Wheat Yield

Thesis Abstract

This study investigates the comparative effects of organic and inorganic fertilizers on wheat yield under temperate agricultural conditions, addressing the persistent challenge of optimizing yield while maintaining soil health and environmental sustainability. The aim is to quantify the yield response, soil fertility changes, and environmental trade-offs associated with each fertilizer type across diverse farming systems. Specific objectives include (1) comparing grain yield, above-ground biomass, and ear density under organic, inorganic, and integrated nutrient management regimes; (2) evaluating soil chemical and biological properties (organic matter, pH, available phosphorus, microbial biomass carbon, and enzymatic activity) before and after two growing seasons; (3) assessing input cost efficiency and net returns; (4) identifying farmer-perceived constraints and adoption factors through stakeholder insights; and (5) developing a predictive model linking fertilizer regime variables to yield outcomes. Methodologically, the study employs a multi-site, randomized complete block design with a factorial arrangement implemented over two wheat growing seasons. The population comprises commercial wheat fields in three agroecological zones with distinct rainfall patterns and soil textures. A total of 180 plots (15 plots per site per treatment across four treatments organic, inorganic, integrated, and control) will be established to ensure adequate power for detecting medium effect sizes (power = 0.80, alpha = 0.05). Organic treatments utilize well-composted poultry manure and green manures applied at agronomically relevant rates, while inorganic treatments use standard NPK blends aligned with regional extension recommendations. Integrated management combines organic inputs with reduced-rate inorganic fertilizer. Data collection instruments include calibrated yield monitors, grain moisture meters, soil test kits, and standardized farmer survey questionnaires. Temporal sampling occurs at key phenological stages tillering, booting, and harvest. Analytical techniques comprise analysis of variance (ANOVA) for yield and soil parameters, post hoc Tukey tests for mean separation, multivariate regression to quantify factors driving yield, and a structural equation model to elucidate causal pathways among soil health, nutrient availability, and yield. Descriptive statistics and diagnostic checks (normality, homoscedasticity) accompany model validation. Economic analysis employs standard gross margin and benefit-cost ratio calculations, incorporating input costs, labor, and market grain prices. Expected findings anticipate that organic and integrated regimes will achieve yields comparable to inorganic inputs under favorable rainfall, with organic inputs improving soil organic matter and microbial activity; inorganic inputs are expected to yield higher short-term outputs in high-input systems but with lower soil health indicators over time. The integrated regime is hypothesized to provide a balanced outcome with substantial yield gains and improvements in soil properties relative to exclusive organic management. The regression and structural equation models are anticipated to reveal that soil organic matter, micronutrient availability, and biological indices mediate the relationship between fertilizer type and yield, with environmental indicators such as nitrate leaching showing reduced risk under organic and integrated practices. The study will also identify cost-efficient strategies and adoption barriers, highlighting the potential for policy-driven incentivization of integrated nutrient management. Contributions to knowledge include (1) empirical evidence on long-term yield trajectories under organic versus inorganic fertilization in temperate wheat systems; (2) a comprehensive assessment of soil health dynamics as mediators of fertilizer effects; (3) a robust economic framework comparing profitability and risk across fertilizer regimes; and (4) a practical, regionally transferable model to guide recommendations for sustainable wheat production. The study concludes that while inorganic fertilizers may deliver higher immediate yields, organic and integrated approaches offer superior soil health and longer-term productivity, with favorable economic performance when accounting for environmental costs. Recommendations emphasize adopting integrated nutrient management tailored to site-specific soil properties and rainfall, investing in soil organic matter enhancement, and promoting farmer education on balanced nutrient strategies to safeguard both yield and environmental integrity.