Carbon, nitrogen, and phosphorus dynamics in a loblolly pine-goat silvopasture system in the Southeast USA

Agroforestry presents an opportunity to increase land productivity and improve cash flow by combining income from crop or animal production and forestry on the same land. In addition, agroforestry offers numerous environmental benefits such as increased diversity of plants and animals, nutrient recycling, erosion control, and carbon (C) sequestration. We investigated the effect of grazing and forage enhancement on total soil C (TSC), soil nitrogen (N), and phosphorus (P) dynamics in a goat (Capra aegagrus hircus)-loblolly pine (Pinus taeda L.) silvopasture system on a Kipling silt loam soil (fine, smectitic, thermic, Typic Paleudalfs) at Epes, Alabama from 2006 to 2010. In 2007, the soil in the silvopasture plots was characterized by low pH, low TSC, and was deficient in N and P. Four years after tree thinning and after 3 years of grazing in June 2010, the silvopasture plots still depicted low soil pH (< 6) and TSC levels less than 20 g kg(-1). TSC content in all the silvopasture plots in June 2010 were generally similar to levels obtained after thinning and prior to grazing in May 2007. However, soil disturbance for liming, fertilizer incorporation, and forage planting increased soil N and P levels, but resulted in lower TSC in the enhanced forage plots compared to the other treatments. Grazing increased N and P levels during the study period. Our study suggests that in the long-term, grazing without additional soil management practices can improve soil fertility through nutrient recycling and C sequestration and thereby making the goat-loblolly silvopasture system both environmentally and economically sustainable.