Greenhouse gas emissions in an agroforestry system in the southeastern USA

Authors: Franzluebbers, Alan; CHAPPELL, JANET - North Carolina State University; SHI, WEI - North Carolina State University; CUBBAGE, FREDERICK - North Carolina State University

Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2016
Publication Date: 5/1/2017
Citation: Franzluebbers, A.J., Chappell, J., Shi, W., Cubbage, F. 2017. Greenhouse gas emissions in an agroforestry system in the southeastern USA. Nutrient Cycling in Agroecosystems. 108:85-100.

Interpretive Summary: Agroforestry systems combine management of trees with various agricultural operations, whether crop based or animal based. Such systems offer income diversity and ecological benefits to make them more resilient to potential changes from extreme weather. An ARS scientist in the Plant Science Research Unit in Raleigh NC collaborated with investigators from North Carolina State University to determine greenhouse gas emissions from soil under the diversity of conditions in a young agroforestry system. Greenhouse gas emissions were carbon dioxide and nitrous oxide (300 times more potent than carbon dioxide). Soil under trees had lower greenhouse gas emissions, partly due to lack of fertilizer application to these areas directly under trees, but also due to lower temperature and lower soil water content. These results will contribute to a better scientific understanding of how agroforestry systems can be developed and managed in the southeastern USA to overcome weather extremes. Farmers and ranchers will also be able to use results from this study to understand the ecological and economic benefits of mixing pastures and trees.

Technical Abstract: Agroforestry systems may provide diverse ecosystem services and economic benefits that conventional agriculture cannot, e.g. potentially mitigating greenhouse gas emissions by enhancing nutrient cycling, since tree roots can capture nutrients not taken up by crops. However, greenhouse gas emission data from agroforestry systems are not available in the southeastern USA, thus limiting our ability to optimize agroforestry management strategies for the region. We hypothesized that tree-crop interactions could prevent excess N from being released to the atmosphere as nitrous oxide (N2O). We determined N2O and carbon dioxide (CO2) emissions and soil temperature and water content in an 8-year-old agroforestry site at the Center for Environmental Farming Systems in Goldsboro, North Carolina, USA. The experimental design was a factorial arrangement of soil texture (loamy sand, sandy loam, and clay loam) and position / canopy cover (cropped alley, margin between crops and trees, and under Pinus palustris, Pinus taeda, and Quercus pagoda) with three replications. Sampling occurred 42 times within a year using static, vented chambers exposed to the soil for 1-hr periods. Soil N2O emission was lower under tree canopies than in cropped alleys, and margin areas were intermediate. Soil texture and soil water content were key determinants of the magnitude of N2O emission. Soil CO2 emission was controlled by temperature and water content as expected, but surprisingly not by their interaction. Soil temperature was 1.8 °C lower and soil water content was 0.043 m3/m3 lower under tree canopy than in cropped alleys, which helped to reduce CO2 emission under trees relative to that in cropped alleys. Our results provide a foundation for reducing greenhouse gas emissions in complex agricultural landscapes with varying soil texture by introducing timber production without abandoning agricultural operations.