2007 Annual Report 1a.Objectives (from AD-416) The objective of this cooperative research project is to identify all changes in the quantity and biochemical nature of soil organic matter that occur under continuous intensive rice cropping in the Mekong Delta and to establish any effects of these changes on rice grain yield and on the cycling of soil nitrogen into plant-available forms. 1b.Approach (from AD-416) Soil will be sampled from experimental plots in farmers’ fields in the Mekong Delta. Soils will be extracted for specific humic fractions, and these will be analyzed for their biochemical nature. The results will be compared to crop uptake of nitrogen and grain yield in order to establish any relationships. Crop management options for improving the chemical nature of soil organic matter and nitrogen availability will be evaluated in a pot study. Soil from the pots will be analyzed similarly as for the field study. 3.Progress Report This report documents research conducted under a Non-Funded Cooperative Agreement between Agricultural Research Service (ARS) and Can Tho University of Can Tho, Vietnam. Additional details of research can be found in the report for the parent CRIS 3625-11120-003-00D, Biogeochemical processes influencing formation and stabilization of soil organic matter and soil structure. ARS staff is providing guidance to the Vietnamese collaborators for their field, greenhouse, and laboratory studies on soil nitrogen cycling under continuous rice cropping in the Mekong Delta. The Vietnamese staff invited ARS staff to visit for two weeks. During this time, ARS staff developed outlines for three potential publications and two conference abstracts, contributed to the research plan for a new M.S. student of the Vietnamese collaborators, and gave three presentations (one being part of a half-day symposium). Monitoring activities during the visit included reviewing new research data and the quality of current laboratory activities of the Vietnamese collaborators, as well as setting up a new laboratory analysis for phenols analysis.