Professor Wilson and coinvestigator Neilsen will analyze soil and crop yield information to develop an improved version of the soil productivity index developed by Larson and associates at the University of Minnesota. The index will also be modified so it can be applied to cereal grain crops. The investigators will use data on Montana's climates, soils, and cropping systems to further modify the index so that it can be used to compare productivity index values across geographic regions. They will test the accuracy of the resulting model in two small drainage basins for which they will obtain detailed erosion and productivity measurements. Relationships between soil erosion and productivity are complicated. They are of worldwide concern because of the great losses of productivity that can result from severe erosion. Developing a productivity index that could be applied across regions would be of considerable theoretical interest. Such an index would also be helpful in developing policies and programs to reduce erosion associated with cropping.