In the first seven years here on our farm, we have sequestered over 325,500 lbs of Soil Organic Carbon on 35 acres. We have sequestered as much carbon as the yearly CO2 output from approximately 146 cars. That was accomplished by increasing the soil organic matter on most of the farmland by almost one percentage point. That is without spreading organic matter or fertilizers other than lime. The only manure was the droppings from chickens when they are on the pasture and from the sheep and cows while they are grazing.
The method that we used to sequester the carbon was letting the grass grow a foot or more tall and then grazing or mowing the grass and letting it decompose into the soil. This is a method that we discovered as we mowed the grass in the American chestnut orchard located here on the farm and observed the significant increased growth of the grass and the increased growth, vigor, health, and blight resistance of the American chestnut trees. Grasses have approximately the same amount of root mass and depth as the mass and height of grass above the ground. When the grass is mowed from a height of 24″ down to 4″, the roots slough off from a depth of 24″ to approximately 4″. As these roots decompose, they build organic matter in the soil to the depth the roots had been. It is not just organic matter on the surface of the ground from the mowed grass.
The soil tests that we took are just of the top 6″ of soil and do not represent any increase in organic matter below 6″. It would be interesting to test the soil at a greater depth. The soil test from A&L Eastern Labs tested at the end of 2013 shows that the front pasture closest to the road had an organic matter percentage of 4.6%. A soil test from the small parcel of ungrazed fallow grassland adjacent to the road was used as a control to compare with the front pasture soil test since we do not have soil tests before we started managing the farmland. That small parcel of fallow grassland in years past had been part of the front pasture. That area had soil organic matter of 3.8%. 3% organic matter is considered good soil and 1% is not uncommon on cropland. The soil tests show an increase of .8% organic matter in the front pasture.
Our goal is to build enough organic matter in the soil to try to “drought proof” the pastures and to make the soil like a sponge so that there is very little water runoff when there is a heavy rain. Carbon acts like a sponge and holds moisture and other nutrients such as nitrogen and phosphorous and keeps them from being leached out of the soil into the Bay. The carbon then releases the water and nutrients to the plants as needed.
One method that we have experimented with to increase the carbon content of the grasses was to spray the grass with a mist of a mixture that consisted of water, raw milk from our cows, a little honey, and some eggs. The milk, honey and egg mixture increases the photosynthesis of the leaves and increases the brix/sugar (which is high carbon) content of the grasses about three percentage points. The sugar is transported from the leaves to the roots. In theory, if we can increase the sugar/carbon production in the leaves of the pasture grasses we should be able to increase the amount of carbon that we can sequester in the soil. We want to experiment with this some more. Last year we did not have enough milk.