The inherent ‘safety-net’ of an Acrisol: measuring and modelling retarded leaching of mineral nitrogen
The inherent features of Acrisols with their increasing clay content with depth are conducive to reducing nutrient losses by nutrient adsorption on the matrix soil surfaces. Ammonium (NH4+) and nitrate (NO3) adsorption by a Plinthic Acrisol from Lampung, Indonesia was studied in column experiments. The peak of the H218O breakthrough occurred at 1 pore volume, whereas the median pore volumes for NH4+ and NO3 ranged from 6.4 to 6.9 and 1.1 to 1.6, respectively. The adsorption coefficients (Ka in cm3 g–1) measured were 1.81, 1.51, 1.64 and 1.47 for NH4+ and 0.03, 0.09, 0.10 and 0.17 for NO3, respectively, in the 0–0.2, 0.2–0.4, 0.4–0.6 and 0.6–0.8 m soil depth layers. The NH4+ and NO3 adsorption coefficients derived from this study were put in to the Water, Nutrient and Light Capture in Agroforestry Systems (WaNuLCAS) model to evaluate their effect on leaching in the context of several cropping systems in the humid tropics. The resulting simulations indicate that the inherent ‘safety-net’ (retardation mechanism) of a shallow (0.8–1 m) Plinthic Acrisol can reduce the leaching of mineral N by between 5 and 33% (or up to 2.1 g m2), mainly due to the NH4+ retardation factor, and that the effectiveness in reducing N leaching increases with increasing depth. However, the inherent ‘safety-net’ is useful only if deep-rooted plants can recover the N subsequently.
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Publication year
2022
