Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/1996
Publication Date: N/A
Interpretive Summary: The quality of our nation's soil resource must be maintained or enhanced for sustained agricultural production. Water erosion moves the very best part of the soil, called the topsoil, off fields and into streams, rivers, and reservoirs degrading the aquatic habitat and increasing drinking water treatment costs. The amount of erosion leaving a field depends on many factors, including rainfall characteristics, soil properties, slope steepness and length, crop type, and degree of soil and residue disturbance by tillage equipment. The accurate prediction of erosion using equations or mathematical models to account for these many factors is necessary for good soil conservation planning. In 1985, the Water Erosion Prediction Project (WEPP) was initiated to develop new-generation erosion prediction technology to replace the Universal Soil Loss Equation, which has been used by the USDA-Soil Conservation Service since 1965 for predicting mean annual lsoil loss from cropland. Our research focused on comparing runoff and soi loss predictions from the WEPP model to measured data collected over an 11 year period (1983-1993) from 28 natural rainfall erosion plots farmed with seven different cropping and tillage treatments. In general, our results showed that mean annual runoff and soil loss values predicted by the WEPP model agreed well with measured values. However, the WEPP model significantly overestimated annual runoff and soil loss for years with low measured values. Our results indicate that the WEPP model is a good tool for predicting runoff and soil loss values for the climatic, soil, and cropping and management conditions found in the southern Cornbelt. Use of this erosion model will result in the development of better and more cost-effective soil conservation plans for agricultural lands.
Technical Abstract: Runoff and soil loss predictions from the Water Erosion Prediction Project (WEPP) Hillslope model were compared to measured losses from continuous cultivated fallow and continuous corn and soybean cropping systems using conventional, chisel, and no-till tillage methods. Runoff and soil loss data were collected over an 11-yr period (1983-1993) from 28 plots located on a claypan soil (Udollic Ochraqualf). The experimental design was a randomized complete block, with four blocks. For all treatments, the model predicted runoff and soil loss reasonably well for wet years with annual runoff > 200 mm. However, the model greatly underpredicted for dry years with annual runoff < 100 mm. For rainfall occurring after dry periods, the model generally predicted runoff when little or no runoff was measured. When averaged by tillage treatment, mean annual runoff predictions for continuous corn and continuous soybean were within 15% of those measured. The model overpredicted mean annual soil losses from continuous corn and continuous soybean by 22 and 87%, respectively. When averaged over crop, the model slightly overpredicted mean annual runoff for the conventional, chisel, and no-till systems. Predicted mean annual soil losses for conventional, chisel, and no-till tillage systems were 50, 67, and 29% higher than those measured, respectively. Runoff and soil loss data were also analyzed by cropstage period by dividing a year into rough fallow (F), seedbed (SB), rapid growth (P12), reproduction and maturation (P3), and residue (P4) periods. Runoff predictions for the F and SB periods were reasonable. The model overpredicted runoff for the P12 and P3 periods and underpredicted for period P4. The model overpredicted soil loss from all periods except period F.