1a.Objectives (from AD-416):
Problems to be addressed through this agreement include the following four areas: 1. Improving our understanding of the aggregate effects of conservation practices at the watershed scale; 2. Improving our ability to select and place conservation practices on the landscape for maximum effectiveness; 3. Improving conservation practices to better protect water resources; and 4. Maintaining the effectiveness of conservation practices under changing climate and land use.
1b.Approach (from AD-416):
We will employ hydrologic and water quality data from field studies in the Mahantango Creek watershed to calibrate key fate-and-transport models (VSA-SWAT, APEX). Output from these models will be used to evaluate components of the P Index as part of a national NRCS-backed initiative to validate and, where necessary, revise the P Index.
Approximately 200 soil samples were collected from across the WE-38 sub-watershed of the Mahantango Creek watershed, representing fields for which long-term field management data are available. Soils were analyzed for general fertility characteristics, with the intent of focusing upon differences in phosphorus and carbon. Both 2 inch and 6 inch samples were collected to provide insight in to surface soil phosphorus stratification, a particular concern of no-till soils where manure has been historically applied. Hillslope runoff studies were continued, as was monitoring of flow and water quality across the WE-38 watershed. Using existing land management data, generalized descriptions of typical crop, tillage and nutrient management practices were developed. These generalizations will serve as the basis for modeling activities to evaluate the effects of alternative nutrient management approaches. Two versions of SWAT were initialized and tested within the watershed. Results point to significant improvements in the representation of hydrology and phosphorus cycling with the new routines. Specifically, hydrologic processes are better represented through an initialization routine that considers topographic and soil factors. In addition, phosphorus cycling is better represented by accounting for residual phosphorus in surface applied manures and fertilizer. This phosphorus can be directly accessed by runoff water, resulting in acute transfers of phosphorus to streams after soils have been amended.