Nitrogen-Fixing Trees in Small-Scale Agriculture of Mountainous Southeast Guatemala: Effects on Soil Quality and Erosion Control Christina M. Jensen Augustine Kristiina A. Vogt Robert B. Harrison Heather M. Hunsaker ABSTRACT. Intensive, subsistence agriculture on hillsides of southeast Guatemala has caused extensive soil degradation. This retrospective study evaluated the success of an agroforestry treatment in improving the sustainability of mountainous agricultural systems in terms of soil nutrient status and erosion control. Three years after maize (Zea mays) and pasture fields were alley-cropped with N-fixing Gliricidia sepium trees, soil nutri- ent levels were examined and compared to nonalley-cropped controls. Agroforestry treatment showed significantly higher soil organic matter (SOM) over paired plots with no alley-cropping (mean 4.3% vs. 3.2% C, p  0.05). Mean total N was also higher, with 0.12% in the nonagro- forestry control plots compared to 0.16% under the agroforestry treatment Christina M. Jensen Augustine, Kristiina A. Vogt, and Robert B. Harrison are affiliated with the College of Forest Resources, University of Washington, Seattle, WA. Heather M. Hunsaker is affiliated with the Department of Crop and Soil Sciences, Brigham Young University, Provo, UT. Address correspondence to: Christina M. Jensen Augustine, 999 South 1200 East, Salt Lake City, UT 84105. The authors would like to thank the participating farmers, Carmelo Villagran Acevedo, Héctor Villeda and Pedro Acevedo; Rubén Villagran and Dany Arbisú for fieldwork assistance and Dongsen Xue for analytical work. Partial funding for this project came from the Benson Agriculture and Food Institute. Journal of Sustainable Forestry, Vol. 23(4) 2006 Available online at http://jsf.haworthpress.com  2006 by The Haworth Press, Inc. All rights reserved. doi:10.1300/J091v23n04_04 61