Applying organic materials to fields improves soil fertility. It is important to consider the carbon to nitrogen (C:N) ratio when applying organic materials for the maximum impact on soil fertility. You also want to use the C:N ratio when considering cover crops and crop rotation decisions.
We rely on crop residue decomposition and organic materials to rebuild soil fertility. Effectiveness of both are dependent on the C:N ratio. Soil microorganisms are responsible for maintaining soil function and your soil will only be as healthy as these microorganisms. Ideally the C:N ratio should be 24:1 to feed soil microorganisms.
Crops with a higher C:N, such as wheat at 80:1, leave soil microorganisms looking for additional nitrogen. They use nitrogen from the soil instead, and it is no longer available to crops. Nitrogen deficient crops grow slower, and lack green coloring. Mineralization, or extra nitrogen in the soil occurs when the C:N ratio is lower and soil microorganisms leave the nitrogen.
Soil covered by crop residues serve multiple purposes, including shade, minimizing damage from raindrops, and insect habitat. There must be a balance between soil cover, and crop residue decomposition for soil fertility and crop growth.
The decomposition process improves soil fertility by rebuilding organic material and providing nutrients for the next crop. Balancing crops with a faster decomposition rate, such as hairy vetch or cattle manure with crops that have a slower decomposition, such as corn Stover or wheat leads to the best results for soil fertility.
Using cover crops builds soil organic matter. Cover crops either supply nitrogen to the next crop, or remove extra nitrogen from the soil. Knowing and understanding your C:N ratio and the needs of cash crops will help decide which cover crop to use. For example, soybeans with their lower C:N ratio can follow planting corn as a cash crop. The soybeans help break down the residues from the corn stover and improve soil health. Or, corn could follow planting soybeans. Corn’s high C:N ratio offers soil protection as a cover crop after harvesting the soybean cash crop.
Growing crops with high C:N ratios too frequently depletes nitrogen and hurts future crop growth. The crop needs additional nitrogen, at an extra expense. Soil fertility is vital to the health of your crops and your operation. Balancing the C:N ratio improves soil fertility while having a positive impact on growth and yield. Adding organic materials, including cover crops, to the field is one of the best ways to balance the C:N ratio.