Technical Abstract: In 2003, the Leon River basin was selected as a Benchmark watershed for the USDA Conservation Effects Project (CEAP) to complement the historical USDA-ARS experimental watersheds near Riesel, TX. In both watersheds the major water quality concerns are excessive nutrient and bacteria concentrations contributed by agricultural, urban, and natural sources. Thus, CEAP research focuses on modeling and field evaluation of hydrologic impact, water quality, and soil quality response to tillage and nutrient management conservation practices. Water quality data collection is ongoing in 15 Leon River watersheds ranging from 0.3 ha (0.75 ac) to 6070 km**2 (2340 mi**2) and in 13 Riesel watersheds from 1.2 ha (3.0 ac) to 70.4 ha (174 ac). Hydrologic and nutrient modeling research in these watersheds improved P transformation and transport routines and incorporated field- and farm-scale model output into basin-scale models for national assessment. Field research has facilitated Soil and Water Assessment Tool (SWAT) calibration and validation for small watersheds and large river basins, developed improved erosion control methods on military lands, quantified C sequestration for various agricultural land uses, and determined the environmental and economic impacts of organic fertilizer management.