Some producers express concern that SOM levels are not necessarily increasing as they had hoped, despite minor changes in production practices that help build their SOM levels.

Why the concern? Because, SOM takes time to build - contrary to some false beliefs that it is a quick process, and SOM is known to be the single most important soil property in agriculture. Ideally, farmers should strive to build their SOM levels to at least 3.5%. To maintain a good SOM level, use:

• No-till or conservation tillage practices
• Proper crop rotations that include small grains and broadleaf crops
• Manure or compost
• Adequate fertilizer to ensure high yields, better root proliferation and abundant residue

Cover crops also enhance SOM. They enhance microbial diversity and population, which convert soil organic material to SOM. You can find more on cover crops on the NDSU plant sciences website: https://www.ag.ndsu.edu/plantsciences/research/forages/cover-crops or the NDSU Livestock Extension website: https://www.ag.ndsu.edu/livestockextension/grazing-management-folder/cover-crops.

Farmers should not be overly concerned about small fluctuations in SOM content if their soil test results are just a few percentage points less (typically < 0.4%) than the previous year or two. Annual climatic changes, and changes in crops grown often cause changes in SOM content.

Figure 1 shows four-year average SOM content, averaged across three types of four-year crop rotations and N rates on no-till and conventional till cropping systems study by Ezra Aberle (Cropping Systems research specialist, NDSU Carrington REC). SOM was always greater for NT than conventional till. Differences in SOM content on the graph every 4-years is common.  

You can find more on soil organic matter from Naeem Kalwar, soil health Extension specialist at the NDSU Langdon REC here: https://www.ag.ndsu.edu/langdonrec/soil-health/soil-organic-matter-and-its-benefits/view and on the Soil Health Nexus blog here: https://soilhealthnexus.org/soil-organic-matter-and-its-benefits/

Jasper M. Teboh, Ph. D.
Jasper.Teboh@ndsu.edu
Research Soil Scientist