Masters Theses

Date of Award

6-1981

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

M. E. Springer

Committee Members

David Lietzke, Frank Bell

Abstract

Milan Field Station, Ames Plantation, and Knoxville Plant and Soil Science Farm were chosen for comparison of different methods of predicting the effect of length and steepness of slope on soil erosion. Methods used to predict soil loss from a sample two segment slope were: old, addition, average LS, average slope. Fort Worth, substitute, and Wischmeier method. Predicted soil losses differed among methods because of the way length and steepness of slope were considered. The Wischmeier method is probably the most accurate because of the way it handles complex slopes. The substitute method is next best. Average slope, average LS and Fort Worth methods seem to predict close to Wischmeier method only on some situations. The old and addition method exaggerate the amount of soil loss. Necessary cropping management systems and support practices (NOP) to keep soil loss within tolerance were used to estimate susceptibility of each piece of land to erosion. A set of NCP values of >0.32, 0.16-0.32, 0.08-0.16, 0.08-0.4, 0.02-0.04, and <0.02 were chosen as breaks between isoerodent classes. On slopes of average length, these values compared favorably with land subclasses I, IIe, Ille, IVe. VIe and VIIe respectively. Isoerodent maps by the old, average LS, and Wischmeier methods were drawn on a sample portion of Milan Field Station. Points of equal NCP were joined together to form isoerodent lines as a means of estimating erosion hazard. High NCP values suggest lower soil loss and low NCP values predict higher soil loss. Results showed that the old method predicted higher soil loss and average LS predicted lower soil loss than the Wlschmeler method. For the first segment of the slope, all methods gave identical results. Differences occurred because of the way the second segment of the slope was handled. Nomographs were developed for each location. The function of these nomographs was to quickly determine NCP for a given length of slope, and also to find length of a simple slope for a given NCP. Thus they duplicate one function of a slide rule calculator. For comparison with land capability subclasses e map (LCCe), the Wischmeier method was chosen to draw isoerodent maps for the three areas. These isoerodent maps are useful, because on complex slopes they predict erosion more accurately than either the LCCe map or the slide rule calculator. Both isoerodent maps and slide rule calculator predict erosion more accurately than ICC2. maps except on simple slopes of average length. Since the maps are based on NCP, they are useful for designing conservation plans. The Wischmeier method of predicting soil erosion on complex slopes and NCP isoerodent maps based on this method certainly are useful tools for planning soil conservation. For complex slopes the predictions are more precise than either LCCe maps or the various methods which use the slide rule calculator.

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