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Document Type

Thesis - University Access Only

Award Date

2010

Degree Name

Master of Science (MS)

Department

Agricultural and Biosystems Engineering

First Advisor

Todd P. Trooien

Abstract

A survey of South Dakota Conservation Reserve Program (CRP) contract holders, conducted in 2007, indicated that large areas of land in the CRP could be returned to grain production in the next four years. Conversion of these acres from CRP back to row crop production without regard to environmental quality could have huge impacts on water quality in the state. The objective of this study was to calibrate an erosion prediction model and use it to estimate increased soil erosion due to this land use change. The Water Erosion Prediction Project (WEPP), a process based erosion prediction model developed by USDA, was utilized in this study for this purpose. Runoff and sediment yield data from a continuous com field in Brookings, South Dakota were used to calibrate the model. Data collection took place during frost free season of 2009. To determine hillslope and channel networks in the watershed GeoWEPP and ArcMap were utilized. Input DEM and ASCII files were generated from GPS data of watershed and soil map was obtained from Geospatial Datagateway, NRCS, USDA website. A WEPP management file for continuous com was adjusted to simulate actual field conditions. Initial soil moisture values were also adjusted to simulate actual field conditions at the time of each runoff event for single storm simulation. Initially, for single storm simulation, WEPP predicted the sediment yield quite satisfactory but it heavily under predicted the runoff. To evaluate the model performance Nash-Sutcliffe efficiency (NSE), root mean square error (RMSE) -observation standard deviation ratio (RSR) and percent bias (PBIAS) were calculated. For runoff prediction WEPP performance was considered "unsatisfactory" (NSE =-0.32 and RSR =1.15) and for sediment yield prediction WEPP performance was considered "very good" (NSE =0.95 and RSR = 0.23). Because of very good sediment yield prediction, WEPP calibration was not performed. This uncalibrated model was then used to predict annual soil loss for different management practices including CRP across four different locations in South Dakota. Unalibrated WEPP indicated that when changing the land use from CRP to other management annual soil erosion was increased by various amounts depending upon the management practice, watershed slope, soil type and location. The least increase was indicated when adopting no-till option and highest increase was indicated for soybean spring chisel and fall MB plow. For Brookings watershed, having existing soils and slope, sediment yield increased by 4.9 to 5.5 tons/ha per year while switching the land use from CRP to continuous com spring chisel plow or com-soybean spring chisel plow. Also if the slope is higher than 4% at Brookings location, for- existing soil and slope conditions, these two management practices have soil loss higher than soil loss tolerance limit (T ~ 11 ton/ha), indicating unsustainable land use. For Brookings site least increase of 0.4 to 0.9 ton/ha per year was indicated for no till practices (Com no till and com soybean no till).

Library of Congress Subject Headings

soil erosion prediction
soil erosion computer simulation

Description

Includes bibliographical references (56-59)

Format

application/pdf

Number of Pages

76

Publisher

South Dakota State University

Rights

Copyright © 2010 Rajendra P. Sishodia. All rights reserved

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