Nitrogen Mineralization in Humid Tropical Forest Soils: Mineralogy, Texture, and Measured Nitrogen Fractions

Abstract

AbstractChemical and physical stabilization of soil organic matter by the interaction of organic compounds with soil clay minerals may affect N mineralization in tropical forest soils. Nitrogen mineralization rates during long‐term incubation were determined on soils of several mineralogies collected from native forests in Costa Rica, Colombia, Peru, and Brazil. Amounts of N mineralization were related to soil mineralogy, texture, and N fractions in order to determine the effects of these soil components on N mineralization and to evaluate measurements of these components for their use as potential N availability indices. Allophanic soils produced higher cumulative levels of mineralized N and had higher initial levels of several N fractions than soils with smectitic, oxidic, and kaolinitic mineralogies. This mineralogical effect was attributed to greater initial N stabilization in allophanic soils followed by greater N release after the addition of nutrient solution during incubation. Total soil N had the strongest correlation with N mineralization among the N measurements considered in this study. The active N pool, as calculated by a two‐pool regression model of cumulative mineralized N, had the highest positive relationships with NH+4‐N evolved in a 1‐wk anaerobic incubation and soluble N. The stable N pool had the strongest correlations with total N and light‐fraction N. The relationships between soluble N or NH+4‐N evolved after a 1‐wk anaerobic incubation and N mineralization were affected by soil mineralogy, which suggests the need for further evaluation of potential N availability indices for the effects of soil mineralogy.