Ammonium Adsorption Characteristics of Jasaan Clay Soils under Conservation Agriculture and Conventional Plow-based Production Systems

Abstract

Knowledge of nutrient adsorption characteristics of soils is important for analyzing nutrient retention for plant uptake and potential losses due to leaching in agricultural crop production systems. This study aimed to characterize and compare the ammonium adsorption behavior of Jasaan clay soils under conservation agriculture production systems (CAPS) and under conventional plow-based (PB) production systems. Soil samples were collected from plots laid in a randomized complete block design for selected treatments T2 (Maize + Stylosanthes – Stylosanthes – fallow) and T5 (Cassava + Stylosanthes – Cassava + Stylosanthes) and a PB system, T6 (Maize-Maize), at the SANREM Research site in Claveria, Misamis, Oriental. Batch adsorption experiments were performed for desorbed soil samples using ammonium solution of various initial concentrations to determine equilibrium concentrations. The adsorption isotherm models such as linear, Freundlich and Langmuir models were then fitted to the experimental data through linear regression analysis. Results showed that the Freundlich and Langmuir adsorption isotherm models best fitted the experimental data for all treatments, with the coefficient of determination R2 ranging from 0.84 to 0.98 for the Freundlich model and from 0.64 to 0.95 for the Langmuir model. Results also showed that the mean distribution coefficient Kd and the maximum adsorptive capacity of the soils under CAPS were significantly higher (α=5%) than those under PB system. The mean Kd values for treatments T2, T5 and T6 obtained in this study were 1.421, 1.585 and 0.691 L/kg, respectively. On the other hand, the maximum adsorptive capacity values were found to be 2,210.1, 2,441.6 and 1,077.3 mg/kg for treatments T2, T5 and T6, respectively. The results of this study suggest that soils under CAPS have better ammonium adsorption for plant uptake and lower leaching losses than soils under PB systems. Consequently, higher ammonium-nitrogen fertilizer application efficiency can be expected under CAPS than under PB systems.