Abstract

Nitrogen (N) mineralization in soil depends on carbon (C) input of plant materials, site environmental conditions, and soil texture. Empirical correlates of N mineralization can be difficult to interpret, however, because of interactions among these factors. A multiple regression model relating N mineralization to C input rates, litter quality, and soil texture in Chilean temperate rain forest soils was developed. Nitrogen mineralization rates ranged from 3.0 to 5.7 mg kg-1 soil d-1 depending on C input rate and soil texture but were not influenced by litter quality. We compared C storage of both forest and long-term-cropped soils with the protective capacity (i.e., the expected maximum C pool associated with the clay and silt fractions). Soil organic C associated with the fine fraction of forest soils was significantly greater than the calculated protective capacity, with clay-rich soils averaging 141% more C than this limit and coarser soils having 56% more than predicted. In contrast, C content of cropped soils was well below the calculated protective capacity, averaging ∼32-60% less than this limit, showing the potential of these soils for sequestering C. The results were consistent with the finding that N mineralization was positively correlated with the amount of free organic matter associated with the sand-size fraction in forest soils. The study illustrates that (i) the capacity of soils to preserve soil organic C in clay- and silt-sized particles was greater than that of agricultural soils and (ii) in highly saturated soils, the N mineralization is a function of the quantity of organic-matter input, which in turn accumulates as free organic C in the sand-size fraction. Copyright © Taylor & Francis Group, LLC.