The Acidity Correction of Soil Cultivated with Grass in a Medium-Term Experimental Area Under the Application of Biomass Ash

The disposal of agro-industrial by-products presents a significant environmental and economic challenge, while highly weathered tropical soils, such as Oxisols, persistently suffer from severe acidity and low fertility. To address this problem, the agricultural application of biomass ash serves as a sustainable alternative for acidity correction. However, the temporal stability and medium-term residual effects of ash on soil chemical dynamics under field conditions remain poorly understood. This study aimed to evaluate the medium-term effects of applying biomass ash to a tropical pasture area as an active conditioner for correcting soil acidity and enhancing nutrient availability. This experiment was conducted over a five-year period (2019–2023) under field conditions in an Oxisol cultivated with Urochloa brizantha. The experimental design was in randomized blocks, in a strip scheme, evaluating five doses of biomass ash (0, 8, 16, 24, and 32 t ha−1) and two application methods (incorporated and unincorporated) with four replications. Soil chemical attributes, specifically pH, calcium, and magnesium, were analyzed. The results demonstrated a substantial and persistent increase in soil pH, calcium, and magnesium over the five years, confirming the long-term potential of biomass ash as a soil acidity corrector. Unincorporated application favored immediate nutrient availability, whereas the incorporated form improved efficiency under specific seasonal conditions. In conclusion, soil acidity is effectively corrected and sustained by biomass ash, with its chemical conditioning effect lasting for at least four years.