Long-Term Effects of Mineral Fertilisation on Soil Fertility and Crop Yield Trends in Northern Nigerian Farming Systems

This study analyses the long-term effects of continuous mineral fertilisation on soil fertility trajectories and crop yield trends in northern Nigerian farming systems, using data from long-term experiment plots and farmer field historical records. Long-term fertilisation experiments provide invaluable evidence on the cumulative agronomic and soil health effects of management systems that cannot be detected in short-term trials. This study uses data from the Samaru long-term fertility experiment established in 1962 at Ahmadu Bello University Zaria, alongside similar long-term plots at the International Crops Research Institute for the Semi-Arid Tropics Kano substation, spanning treatments of continuous mineral NPK, mineral NPK plus crop residues, residues alone, and unfertilised control. Soil organic carbon, total nitrogen, pH, micronutrient availability, and maize-sorghum-groundnut crop yields over 20-year periods are analysed using trend analysis, structural break tests, and mixed-effects models. Findings reveal that continuous mineral NPK without organic matter addition maintains crop yields for 15 years but subsequently shows declining yield trends and accumulating micronutrient deficiencies, particularly zinc and boron. Integrated mineral-organic management maintains positive yield trends over the full observation period. Soil acidification under continuous ammonium-based fertilisation reduces pH from 6.2 to 5.1 over 20 years without liming. The study contributes original long-term agronomic evidence for northern Nigeria and recommends integrated soil fertility management as the standard recommendation to prevent the long-term soil degradation documented under mineral-only approaches.

Keywords: long-term fertilisation, soil fertility trends, northern Nigeria, integrated soil fertility, yield decline.