Relationship Between Labile Soil Organic Matter Fractions and Plant Productivity.

Measures of labile (aka active) soil organic matter (SOM) that predict nutrient supply and trends in carbon sequestration are highly desirable. Permanganate oxidizable C (POXC) has been described as a rapid and less expensive procedure and that POXC reflects a relatively smaller-sized (53–250 µm), heavier (>1.7 g cm^–3) fraction of particulate organic C (POC) that is sensitive to management. Here, we extend the analysis to assess the relationship of POXC and other measures of soil C with plant productivity (“plant productivity” being defined as grain yield, non-grain aboveground biomass, and total N uptake). More than 1000 soil samples from >50 sites spanning a broad spectrum of soils and management histories and distributed across the United States were used in this comparative analysis. Results obtained so far indicate significant positive relationships between POXC and soil organic C (SOC), soil microbial biomass C (SMBC), and mineralizable C. The strength of the relationship between POXC and these labile SOM fractions greatly improved with the use of site and sampling depth as covariates. In general, our analysis also showed significant linear relationships between these labile SOM fractions and plant productivity. This study demonstrates that POXC, along with other measures of labile SOM reported here, are useful indicator of available soil nutrients and crop performance.