The multi-faceted relationship between nitrogen mineralization and soil texture

Soil texture can affect soil temperature, soil moisture, the protection of organic material against microbial degradation, and other soil properties. All these factors potentially influence net nitrogen (N) mineralization. The objective of this analysis is to investigate the relationship between soil texture and net N mineralization using different approaches, including a 10-week laboratory incubation of undisturbed soil cores from 47 sites in California, modeling, and a meta-regression analysis of 461 datasets from 20 studies. In the laboratory incubation as well as in the meta-analysis, total soil N increased significantly with increasing clay content. Net N mineralization expressed in mg kg-1 soil did not change significantly with increasing clay content, but significantly decreased when expressed as a proportion of total soil N. These results are most likely explained by physical and chemical protection of organic molecules by clay minerals. Protection in turn led to the observed increase in total soil N over time. Based on the incubation and measured bulk densities, net N mineralization in the top 15 cm of the soil profile was 30% higher in a sandy loam compared to a clay soil. Model simulations indicated that texture-related differences in soil temperature and moisture have only a small effect on net N mineralization in irrigated agricultural fields under Mediterranean conditions. Total soil N increased with increasing clay content. The proportion of total soil N mineralized decreased with increasing clay content. Clay minerals protect organic molecules physically and chemically. Texture-related differences in soil moisture and temperature had a minor effect on N mineralization.