Document Type



Soil Quality, SOM, Erosion


The Clear Creek, IA Experimental Watershed (CCEW), which drains to the Iowa River, experiences severe surface erosion due to a combination of high slopes, erodible soils, and extensive agriculture. Concurrent with soil loss is the removal of Soil Organic Matter (SOM). High values of SOM have been related to soil quality; therefore, excessive SOM loss corresponds to degrading soil health. Soil quality assessments are important tools for evaluating management practices in agricultural systems; however, it is difficult to measure soil quality directly at the watershed scale because it varies with a number of site-specific soil characteristics. The coupling of soil surveys with GIS and Non-Point Source computer simulation models will effectively forecast the impacts of ever-changing management practices on soil quality at the watershed scale in less time. NPS models can be extended to evaluate the movement of additional particle-bound constituents like SOM, by incorporating erosion rates and enrichment ratios. The ANNualized AGricultural Non-Point Source pollution modeling system (AnnAGNPS) was used to evaluate upland erosion, enrichment ratios, and SOM loss at the watershed scale in the headwaters of the CCEW using current crop rotations. Gross erosion rates averaged 7.73 MT/ha/yr for individual cells within the watershed. In addition, enrichment ratios, which were determined using gross and net erosion values from AnnAGNPS, were coupled with an organic matter coverage map of the watershed to determine an SOM loss of0.41 MT/ha/yr, which was similar to the loss rates determined by AnnAGNPS (0.29 MT/ ha/yr). To understand the state of soil health in this watershed, the NRCS Soil Conditioning Index (SCI) was determined for the watershed. The average SCI for the watershed was 0.38, which suggests improving soil health conditions. This improvement is most probably due to conservation practices like reduced tillage.

Publication Date

January-December 2009

Journal Title

Journal of the Iowa Academy of Science





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