The impact of rubber monoculture and agroforestry on soil nutrient dynamics: a comparative analysis

Abstract

The expansion of rubber monoculture (RM) in tropical regions has led to significant land-use changes, contributing to soil acidification and nutrient depletion. This study evaluates soil nutrient status under three rubber-based land use types (RLUTs) in south-western Karnataka: rubber monoculture (RM), rubber agroforestry (R+AF) and rubber with natural vegetation (R+NV). Results indicated that RM exhibited significantly lower pH, SOC (38 and 71% lower than R+AF and R+NV, respectively) and base cations, but increased soil acidification and exchangeable Al³⁺ and H⁺ concentrations (p <0.05). RM exhibited significantly lower available nutrients compared with R+AF and R+NV (p <0.05), with reductions of 48 and 34% for N, 340 and 30% for P, 26 and 243% for Ca, 73 and 142% for Mg, 67 and 208% for Zn, and 57 and 74% for B, respectively. Available P, Zn and B were found deficient in soils, while iron (Fe) and manganese (Mn) were in near toxic concentrations. Soil pH, exchangeable acidity and organic carbon (SOC) are critical in maintaining nutrient availability. SOC was positively correlated with available nutrients, namely N, K, Ca, Fe, Mn, Cu, Zn and B, while soil acidity was negatively correlated with available Ca and Mg content. The study recommends avoiding RM or selecting rubber-based agroforestry systems or naturally managed rubber plantations incorporating legumes, cover crops or medicinal plants to improve nutrient availability.