Soil N Dynamics 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 N changes in a goat-loblolly pine silvopasture system in the south-east U.S.  The study is being done at the Federation of Southern Cooperatives, Epes, Alabama. 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 rate treatments and an enhanced soil management treatment were studied in 2007 and 2008. Baseline soil analyses in 2007 showed that the soil at project site is characterized by low pH (<5) and critically deficient in major soil N. After 1yr of grazing and soil management in 2008, low soil pH nutrient deficiency are still major problems in the silvopasture system. However, NH₄-N in the 0-60 cm soil profile had increased from 10 mg kg^-1 in 2007 to 14 mg kg^-1 due to grazing. Soil management through inorganic N fertilizer application combined with grazing had increased soil NH₄-N in the 0-60 cm soil profile from a mean of 10 mg kg^-1 in 2007 to 18 mg kg^-1. NO₃^-N in the 0-60cm soil profile averaged 5 mg kg^-1 after grazing and soil management in 2008, up from about 1 mg kg^-1 in 2007. Grazing had a significant influence on available N supply through nutrient cycling. We hypothesize that grazing without inorganic fertilizer application can, in the long-term, provide adequate N to support forage and tree growth, thereby making the silvopasture system both economic and environmentally sustainable.