National Comparison of the Total and Sequestered Organic Matter Contents of Conventional and Organic Farm Soils

Abstract

Abstract Intensive agriculture has been linked to declining soil fertility and is a known source of greenhouse gas emissions. Decline in soil organic matter (SOM) is of particular concern due to its key role in maintaining soil health. Previous research supports the view that fertility management practices utilized in organic agriculture can maintain and even grow the SOM pool, but fewer studies examine what proportion of SOM is sequestered over long periods of time. Using data from the National Soil Project SOM sequestration between soils from organically and conventionally managed farms from across the United States is compared. Total %SOM ranged from 0.63 to 46.1 for conventional farm samples (mean 7.37) and 0.5 to 88.9 for the organic samples (mean 8.33). %FA ranged from 0.08 to 2.20 (mean 0.26) for conventional and 0.04 to 14.8 (mean 0.65) organic farm soils. %HA ranged from 0.17 to 23.0 (mean 2.85) for conventional and 0.25 to 48.9 (mean 4.1) for organic samples. Mean %humification (i.e., sequestration) was 45.6 for conventional soils and 57.3 for organic. Results presented here support previous assertions that FA are the precursors of HA. With the exception of water retention, comparisons of SOM, FA, HA, and humification suggest that organic farming practices support healthy soils and build and/or or maintain SOM more effectively than conventional farming practices. The data from this study can serve as benchmarks for other soils, and the spectroscopic analytical approaches employed should be useful in tracking the effects of changes in farm soil management practices over space and time.