Hay is more Carbon (C) by dry weight than anything else. When we feed hay we are also adding carbon to the soil in addition to the Nitrogen (N) and Phosphorous (P) discussed in the earlier posts in this series. Adding carbon increases the water and nutrient holding capacity of the soil through increase in soil organic matter.
How much carbon do we add to the soil with hay feeding?
Let’s do the math.
Hay is typically between 40-50% Carbon depending on plant maturity at harvest time. Some of this C is in cells as soluble sugar or other easily digested materials. The bulk of the C is in plant fiber that varies in degree of digestibility.
What’s left behind after feeding is a combination of unconsumed plant material and dung and urine. Both are important contributors to soil health.
Unconsumed hay is intact plant material that helps provide the ‘armor’ on the soil. During the growing season we refer to litter cover on the soil surface. Hay residue provides the same benefits to the water cycle as plant litter.
The consumed part of hay that is not digested comes out as manure. We have already discussed the N & P values of manure and urine following hay feeding. Whereas we can add too much N or P to the soil through excessive hay feeding, it is almost impossible to add too much C.
The digestible part of the hay is utilized by ruminant livestock as their primary energy source. Maintenance quality cow hay may be as low as 50% digestibility while high quality ‘calf hay’ may be close to 70% digestible. The C from digested material is incorporated into body tissue or expelled as CO2.
It is the non-digested plant material that contributes to building soil organic matter through dung returned to the soil. Manure on the ground does not contribute a lot to ‘soil armor’, but it contributes to feeding soil life.
The rate of manure breakdown is largely driven by digestibility of the residual fiber. If rumen microbes could not quickly digest it, soil microbes aren’t much faster. Manure breaks down much more quickly in warm-wet environments compared to cold-dry environments.
Hay residue left on the ground will ultimately contribute to soil organic matter. Many people have the bad habit of wanting to burn residue piles in the Spring. Please, do not!
These piles become enriched soil organic matter sites and can be above average production areas for years to come. Burning piles sends most of the valuable C into the atmosphere.
While in the first year following feeding there may be some weeds grow up on these piles, most of those weeds are making a contribution to soil development or get grazed by the livestock during the growing season.
The bottom line is, each ton of hay fed will contribute about 400 to 600 lbs of C to the soil as either hay residue or manure.
That is a valuable addition to your land. Make the most of it!
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