organic soil

Soybean Business: Soil Organic Health

This story first appeared in the October-November 2015 issue of Soybean Business, the magazine of the Minnesota Soybean Growers Association. Click here to read more articles from Soybean Business

Health of farm land provides benefits

Farmers know the value of their soil. And soil organic matter is a key piece of a soil profile that farmers are working to protect. But when different industries, researchers, organizations and agencies differ in their opinions about what elements should be included in soil organic matter (SOM), it can be a daunting element to focus on.

But all parties can agree that SOM is very complex, deserves attention and is one of the least understood component of soils. Researchers point out that it has been directly and positively related to soil fertility and agricultural potential.

The Soil Science Society of America defines SOM as the organic fraction of soil after removing undecomposed plant and animal residues. In most agricultural soils, organic matter is increased by leaving residue on the soil surface, rotating crops with pasture or perennials, incorporating cover crops into the cropping rotation, or by adding soil organic residues such as animal manure.

Jodi DeJong-Hughes, Extension educator out of the Mid-Central Research & Outreach Center in Willmar, has dedicated a lot of time and effort in researching and educating on soils. As DeJong Hughes points out when speaking with farmers, SOM is a complicated puzzle.

“Soil organic matter improves the structure of the soil, which ultimately aids in water infiltration, water retention, bulk density of soil, defense against compaction damage and reduces the potential for erosion by wind or water.”

DeJong-Hughes said there are a lot of things going on in the soil that cannot be seen or measured. “Out of sight is not out of mind.” Organic matter is also known to maintain nutrients in the soil longer so they don’t leach through the soil profile. Three agricultural practices DeJong-Hughes points out that have a big impact on SOM include tillage, cropping rotations and fertilization.

“Building soil health is so important, and probably every farmer could improve the health of their soil,” DeJong-Hughes said. “Lots of farmers are really up on equipment technology or corn and soybean hybrids, but soil is still fairly unknown to us. We’re just hitting the tip of the iceberg in what the soil does and can do for us.”

DeJong-Hughes has also worked closely with Dr. Abbey Wick, North Dakota State University Extension Assistant Professor of Soil Health. Wick has been a big proponent of cover cropping utilized in crop rotations. She points out that using a cover crop mix can increase organic matter through root turnover in the soil. This can ultimately lead to taking inorganic forms of nutrients that can leach and turning them back into an organic form that can be retained for the following year.

“The Conservation Technology Information Center with funding from Sustainable Agriculture Research and Education has done several cover crop surveys the past couple years. They are finding that soybean yields can be increased by an average of 2.19 bushels per acre, or 4.2 percent, following a cover crop,” Wick said. “But reasons for utilizing cover crops on one’s farm are different for every farmer.”

Wick said that even with this data, most farmers are using cover crops for other reasons besides boosting yields, like erosion control for example. And while cover crops do have their benefits, it would be naïve to say there are not any disadvantages she said. Time for establishment needed, herbicide residual and the learning curve to figure out cover crops and how to incorporate them are a few she sees with farmers.

“Other than those, I have not seen a whole lot of disadvantages to using cover crops,” Wick said. “The inadvertent inclusion of a third crop in rotation to use cover crops is such a good thing that I don’t see that as a disadvantage.”

Farmers know that how they farm has an effect on their soil and how much soil organic matter is available to their crops. That’s why the Minnesota Research & Promotion Council has funded research and efforts to learn more about soil health and management, and knows a focus on healthy soil means cleaner water, a better use of nutrients and ultimately a healthier and more profitable soybean crop.

Tips to Improve Your Soil Organic Matter & Health

  1. Use reduce-tillage techniques including no-till, strip-till or ridge-tillLeave as much residue as possible on the soil surface and prevent extreme losses of SOM through mineralization of carbon due to breakdown of soil aggregates & changes in temperature and moisture regimes.
  2. Apply livestock manure or incorporate cover crops, adding organic residue to the soil surface can restock needed carbon to the soil.
  3. Include perennial or companion crops into rotation. Will increase organic matter content over time, reduce pest and disease pressure, reduce fertilizer inputs and help control erosion. Crop rotations can include perennial grasses and legumes.
  4. Carefully manage fertilization and soil nutrients. Will directly and indirectly affect soil microbial community, ultimately affecting increased production of plant biomass to serve as microbial food source. There is still no clear answer to how fertilization does effect SOM levels since vegetation, soil type, climate and present types of SOM are also factors that must be considered.

Benefits of Improving Soil Organic Matter

1. Get into field sooner after rainfall
2. Less plant stress during the dry months
3. Break up pest cycles
4. Potential for higher nitrogen mineralization
5. Less compaction
6. Less erosion
7. Less fuel, labor and parts cost
8. Soil and nutrients stay in field with less leaching or erosion

Remember: Soil health is specific to soil type and geography.

Resources for Regional Soil & Management Information

  • NRCS Soil & Water Conservation Districts
  • University of Minnesota Extension
  • North Dakota State University Extension
  • Minnesota Soybean Research & Promotion Council
  • North Central Soybean Research Program
  • Local Events such as the Conservation Tillage Conference, Dec. 15-16, Best Western Plus, Willmar, Minn