The influence of agricultural land-use practices on selected soil chemical properties: implications for fertility and sustainability in sub-humid upper Eastern Kenya

Résumé fourni par la source

Soil fertility decline associated with agricultural intensification threatens the sustainability of smallholder farming in sub-Saharan Africa. However, quantitative, depth-resolved evidence on how contrasting land-use practices influence soil chemical properties in highly weathered tropical soils remains limited. Our study offers a novel methodological approach by combining depth-resolved Nutrient Index (NI) and Principal Component Analysis (PCA) across six land-use systems. We assessed the effects of six land-use systems: agroforestry, coffee, monocropping, intercropping, Napier grass production and undisturbed vegetation on soil fertility in Nitisols. Land-use practices significantly influenced soil fertility and structural stability. We observed significant loss in soil organic carbon and nitrogen in monocropping, while agroforestry had higher content across depths. Coffee systems exhibited phosphorus enrichment, while intercropping showed enhanced potassium levels throughout the soil profile. Aggregate stability was highest under agroforestry and undisturbed systems. Soil pH was a key factor regulating nutrient and metal dynamics, with positive correlations observed with carbon, nitrogen, calcium, magnesium, and zinc, and negative correlations with phosphorus, iron, and copper. Nutrient Index showed that agroforestry and undisturbed systems maintained medium to high fertility status. The multivariate analyses revealed three components, namely PC1 (Organic Matter–Base Cation), PC2 (Phosphorus–Metal Dynamics), and PC3 (Potassium–Zinc Nutrient). Diversified, perennial-based systems, particularly agroforestry, enhance soil nutrient balance, structural stability, and resilience in highly weathered tropical soils, whereas continuous monocropping accelerates soil degradation. These findings support soil health–based land management strategies aligned with SDGs 2 and 13 and provide quantitative evidence for sustainable intensification in East African smallholder systems.

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