When it comes to increasing soil health, we most often focus on increasing organic matter.
Practices that build organic matter include reducing tillage, planting more high-residue crops such as corn and wheat, rotating to sod grass crops that produce a lot of root biomass with stable carbon, planting and managing grass cover crops so they produce stable carbon, applying compost and manures and other organic wastes, and controlling erosion.
Organic matter is composed of the remains of plants and animals that live in the soil or lie on the surface. Everything that we consider organic matter starts as raw organic materials that decompose into complex insoluble carbon chains, short soluble carbon chains, soluble nitrogen, other mineralized nutrients and humus. Humus is the natural organic matter in soil. It’s high in passive carbon and resistant to further breakdown, and decomposes very slowly.
Organic matter has doubled during the last 15 years on our Nebraska family farm, where we adopted a 100% no-till system and a two-thirds corn to one-third soybean rotation, as well as planted cereal rye as a cover crop. Our soil tests routinely measure 3% organic matter.
In our three-year rotation, we also apply 6 tons of compost that adds 3 tons of carbon to soil. Without the compost, doubling organic matter in a decade probably wasn’t achievable. I also suspect that cereal rye, while it has many great attributes, mainly stimulated soil biology but breaks down too fast to build organic matter.
Soil contains an almost unbelievable amount of organic matter. An acre slice of soil 6 inches deep weighs 2 million pounds. At 3% organic matter, that slice contains 60,000 pounds of organic matter that includes more than 50,000 pounds passive carbon, 4,000 pounds organic nitrogen, 2,000 pounds organic phosphorus, 1,000 pounds microbial biomass or active carbon, and more than 1.9 million pounds of soil minerals. For each 1% increase in organic matter, you are adding more carbon, nitrogen and phosphorus, and other nutrients.
It takes 10 pounds of organic material to produce 1 pound of stable humus material. Microbes will consume the other 9 pounds during the process. Increasing organic matter 1% requires adding 200,000 pounds of organic material per acre to end up with only 20,000 pounds of stable carbon in the soil. A 200-bushel corn crop generates about 10,000 pounds above-ground and 10,000 pounds below-ground residue per acre. That is 20,000 pounds per acre per season that produces only 2,000 pounds of organic matter per year, a 0.1% increase.
Soil health and building organic matter takes commitment and strategy, but we are showing it can be done.
The information provided is general only and should not be taken as a professional recommendation.
If you have a question, e-mail Dr. Daniel Davidson at AskDr.Dan@dtn.com