Nature is desperate to keep soils covered with living plants for two important reasons. Firstly, for temperature moderation from intense heat (and cold) and moisture retention and absorption. Secondly, for “sugars” plants photosynthesize from sunlight and carbon dioxide and then push out through the roots system to feed bacteria and other critical soil biology.
Just like diets for cows, the most basic feed ingredients are energy and protein. For soil life, those diet ingredients are carbon and nitrogen. In agronomy, we talk about healthy soils striking a balance of carbon and nitrogen of 11 parts carbon to 1 part nitrogen, or a C:N ratio of 11:1. Many farm fields, where dairy manure is applied and crops are harvested for feed, test very low in carbon. Many dairy fields have C:N ratios of 3:1 or 4:1. These soils are tight, have poor water holding capacity and have no resilience to swings in weather.
Soil Health
High-carbon soils are soils that have a C:N ratio closer to 11:1 than 4:1. Their soils are friable, dark colored and mellow and retain more moisture. High-carbon soils make excellent use of manure and produce forages higher in nutrient density.
We lose soil carbon with tillage, with forage harvesting and from applications of manure after forage harvesting. Dairy manure can range from high nitrogen, liquid manure with C:N of 10:1 to bed pack and dry lot manure with a C:N of 40:1. Soil biology prefers a plant residue C:N ratio of 25:1. Liquid dairy manure is not going to build soil organic matter or soil carbon. Bed pack and dry lot manure can rebuild carbon because they combine high carbon with a source of nitrogen.
Winter Absorption
Work from the University of Wisconsin and Penn State demonstrates how grasses can absorb and hold manure nutrients over winter. Winter hardy cover crops planted behind the chopper and allowed to grow to a reasonable biomass are excellent conditions to apply manure into either in fall or in spring. Later, when the covers are terminated at corn planting time, they begin to break down and those valuable nutrients are returned to the cash crop. With this strategy, we can manage manure nutrient release with the timing of plant breakdown and feed our crop for months and build soil carbon at the same time!
Adding a few pounds of grass into alfalfa stands can dramatically improve the absorption rates of summer manure applications. A sound rule of thumb is to always apply manure to a green cover. So much of the value of manure applied to the bare ground is lost. Luckily now, we are starting to see better ways to use manure and build carbon if we can extend out the growing season with green covers.
Bill Powel-Smith is the owner of LandCares within GPS Dairy Consulting, an innovative soil health and dairy forage consulting business serving customers throughout the Midwest.
Nature is desperate to keep soils covered with living plants for two important reasons. Firstly, for temperature moderation from intense heat (and cold) and moisture retention and absorption. Secondly, for “sugars” plants photosynthesize from sunlight and carbon dioxide and then push out through the roots system to feed bacteria and other critical soil biology.
Just like diets for cows, the most basic feed ingredients are energy and protein. For soil life, those diet ingredients are carbon and nitrogen. In agronomy, we talk about healthy soils striking a balance of carbon and nitrogen of 11 parts carbon to 1 part nitrogen, or a C:N ratio of 11:1. Many farm fields, where dairy manure is applied and crops are harvested for feed, test very low in carbon. Many dairy fields have C:N ratios of 3:1 or 4:1. These soils are tight, have poor water holding capacity and have no resilience to swings in weather.
Soil Health
High-carbon soils are soils that have a C:N ratio closer to 11:1 than 4:1. Their soils are friable, dark colored and mellow and retain more moisture. High-carbon soils make excellent use of manure and produce forages higher in nutrient density.
We lose soil carbon with tillage, with forage harvesting and from applications of manure after forage harvesting. Dairy manure can range from high nitrogen, liquid manure with C:N of 10:1 to bed pack and dry lot manure with a C:N of 40:1. Soil biology prefers a plant residue C:N ratio of 25:1. Liquid dairy manure is not going to build soil organic matter or soil carbon. Bed pack and dry lot manure can rebuild carbon because they combine high carbon with a source of nitrogen.
Winter Absorption
Work from the University of Wisconsin and Penn State demonstrates how grasses can absorb and hold manure nutrients over winter. Winter hardy cover crops planted behind the chopper and allowed to grow to a reasonable biomass are excellent conditions to apply manure into either in fall or in spring. Later, when the covers are terminated at corn planting time, they begin to break down and those valuable nutrients are returned to the cash crop. With this strategy, we can manage manure nutrient release with the timing of plant breakdown and feed our crop for months and build soil carbon at the same time!
Adding a few pounds of grass into alfalfa stands can dramatically improve the absorption rates of summer manure applications. A sound rule of thumb is to always apply manure to a green cover. So much of the value of manure applied to the bare ground is lost. Luckily now, we are starting to see better ways to use manure and build carbon if we can extend out the growing season with green covers.
For more on sustainability, read:
- New Efficiencies Bring Sustainability Benefits to Clearview Dairy
- Bar 20 Dairy Named 2023 Innovative Dairy Farmer of the Year
- Is Technology the Answer to Dairy’s Sustainability Triple Threats?
Bill Powel-Smith is the owner of LandCares within GPS Dairy Consulting, an innovative soil health and dairy forage consulting business serving customers throughout the Midwest.
