Agriculture relies on the widespread application of nitrogen fertilisers to improve crop yields and meet the demands of a growing population. However, the excessive use of these fertilisers has led to significant water quality challenges, posing risks to aquatic life, ecosystems, and human health. This study examines the relationship between synthetic nitrogen fertiliser usage and water pollution while identifying gaps in existing research to guide future studies. A systematic search across databases (Scopus, Web of Science, and Greenfile) identified 18 studies with quantitative data, synthesised using a single-group meta-analysis of means. As the data were continuous, the mean was used as the effect measure, and a random-effects model was applied due to varied study populations, with missing data estimated through statistical assumptions. The meta-analysis found an average nitrate concentration of 34.283 mg/L (95% confidence interval: 29.290–39.276), demonstrating the significant impact of nitrogen fertilisers on water quality. While this average remains marginally below the thresholds set by the World Health Organization (50 mg/L NO₃⁻) and EU Nitrate Directive, it exceeds the United States Environmental Protection Agency limit (44.3 mg/L NO₃⁻), signalling potential health risks, especially in vulnerable or unregulated regions. The high observed heterogeneity (I² = 100%) suggests that factors such as soil type, agricultural practices, application rate, and environmental conditions influence nitrate levels. While agriculture is a key contributor, other anthropogenic activities may also affect nitrate concentrations. Future research should comprehensively assess all influencing factors to determine the precise impact of nitrogen fertilisers on water quality.

Unsafe disposal of pesticide waste remains a critical environmental and public health issue in developing agricultural systems. This study examined cocoa farmers’ disposal behaviours and their determinants across Nigeria’s major cocoa-producing regions using an explanatory sequential mixed-methods design. Quantitative data were collected from 391 farmers, followed by 23 in-depth interviews to contextualise behavioural drivers. Results showed that knowledge of pesticide risks and availability of disposal facilities significantly predicted safer disposal practices (R² = 0.469, p < 0.05), whereas age had a negative influence. Qualitative findings revealed that negative attitudes, social norms, and limited infrastructure reinforced unsafe behaviours, while membership in farmers’ associations promoted safer practices through peer learning. A joint display demonstrated convergence between structural enablers (collection cages, extension support) and behavioural factors (knowledge, attitudes, norms). The study identifies a dual challenge of systemic shortcomings and behavioural inertia, suggesting that regulatory action alone is insufficient without farmer engagement and education. Policy and extension programmes should prioritise collection infrastructure, association-based training, and Integrated Pest Management to promote sustainable pesticide waste management. These insights advance understanding of pesticide disposal behaviour and offer actionable guidance for environmental governance in low- and middle-income agricultural contexts.