Short-term amelioration of acidic subsoil using dairy farm effluent compost and humic acid: a laboratory incubation study

Amelioration of acidic subsoil using organic amendments

Abstract

Acidic subsoils pose a significant challenge to sustainable agriculture production due to poor nutrient availability and limited productivity, particularly in regions like Malaysia with tropical climates. This incubation study explored the potential of dairy farm effluent compost (DFEC) and humic acid (HA) as organic amendments to ameliorate acidic subsoil, focusing on improving soil chemical properties while reducing fertilizer use. The experiment evaluated five treatments with varying combinations of DFEC, HA, and reduced fertilizer rates (50% and 75%) under controlled laboratory conditions. Soil samples were analysed for pH, organic matter (OM), macronutrient (N, P, K, Ca, Mg) and other selected elements (Al, Fe, Na, Cu, and Zn) concentrations across a 90-day period. The results revealed that while soil pH showed insignificant changes, treatments with DFEC and HA significantly enhanced soil OM and macronutrient levels, particularly N, P, K, and Ca. Treatment 4 (DFEC + HA with 50% fertilizer reduction) was identified as the better combination, demonstrating the best improvements in subsoil nutrient content. Sodium (Na) levels initially increased in DFEC-treated soils but declined over time, possibly driven by decomposition and adsorption processes. Micronutrient dynamics varied, with Al and Fe exhibiting fluctuating trends influenced by soil pH and redox reactions. Trace metals such as Cu and Zn were minimally affected, with Cu concentrations declined possibly due to immobilization processes. In general, study suggest possible long-term benefits of DFEC and HA in promoting nutrient retention, and organic matter enrichment. It provides insights into soil amendment strategies for subsoil rejuvenation, contributing to sustainable agricultural practices in tropical regions. Further research, including pot and field trials, is needed to evaluate the long-term effects and mechanisms in the presence of crops.