Carbon and Nitrogen Cycling in a Goat-Loblolly Pine Silvopasture System in the South-East U.S.

Agroforestry presents an opportunity to increase land productivity and improve cash flow by combining income from agriculture, forestry, and animal production on the same piece of land. In addition, agroforestry offers numerous environmental benefits such as nutrient recycling, erosion control, increasing the diversity of plants and animals, and carbon sequestration. This paper presents data on soil C and N dynamics in a goat-loblolly pine silvopasture system. The study is being done at the Federation of Southern Cooperatives, Epes, Alabama in the south-east U.S.  A seven year old loblolly pine plantation was thinned from 600 to 150 trees per acre in 2006. Paddocks were fenced out and treatments consisting of 0, 4, and 8 goats per acre stocking rates and an enhanced soil management treatment were studied in 2007 and 2008. Baseline soil analyses showed that the soil in the paddocks were characterized by low pH (<5) and critically deficient in soil C and N.  Preliminary results two years after tree thinning and one year of grazing and soil management treatments in 2008 showed no significant changes in soil pH and soil C in the silvopasture system. However, there was an increase in soil NH₄-N from 10 mg kg^-1 to 14 mg kg^-1 due to grazing. A combination of grazing and enhanced soil management practices increased soil NH₄-N in the 0-60 cm soil profile from 10 mg kg^-1 in 2007 to 18 mg kg^-1, while soil NO₃^--N was increased from a mean of 1 mg kg^-1 to 5 mg kg^-1. These results were attributed to nutrient cycling in the form of forage biomass production and animal manure. We hypothesize that grazing without inorganic fertilizer application will, in the long-term, improve soil quality and support forage and tree production, thereby making the silvopasture system economic and environmentally sustainable.