# Demonstrating Effects of Management Practices on Annual Soil Loss: Using the Universal Soil Loss Equation Erosion Calculator

## Objective

By the end of this section the student/user will be able to:

• Demonstrate effects of erosion management practices on annual soil loss using the USLE erosion calculator.

Accompanying Exercise: (For students to print off, complete, and turn in for a grade)

The Universal Soil Loss Equation calculator is a tool used to estimate average annual soil loss caused by sheet and rill erosion. The equation is limited to making predictions for long-term annual soil loss only compared to making predictions on single rainfall event. In this lesson, you will use the model to evaluate the effects of various management practices on long-term annual soil loss.

The USLE Equation is: A = R * K * LS * C * P

Where,

A = predicted soil loss (tons per acre per year)

R = rainfall and runoff factor

K = soil erodibility factor

LS = slope factor (length and steepness)

C = crop and cover management factor

P = conservation practice factor

 A - the tons of soil lost per acre each year. The value 'A' is usually compared to a value 'T'. T is the amount of soil loss that is considered 'tolerable'. Each soil series has a value T listed in the soil survey. Common values range from 1 to 5 tons/acre/year. When A is less than T, soil erosion losses from that land are not considered significant. R - Rainfall and runoff factor. R is based on the total erosive power of storms during an average year and depends on local weather conditions. K - Soil erodibility factor. Depends on texture, structure, and organic matter. LS – L factor and S factor are combined into one factor. L - Length is the distance between the beginning of water runoff on the land and location of sediment deposition on the land or runoff enters a well-defined channel. The slope length factor computes the effect of slope length on erosion. Slope length longer than 1000 ft are not used in this interactive calculator because the calculation may not be reliable. S - Slope steepness. The slope steepness factor S computes the effect of slope steepness on erosion. C - Management factor. Compares cropping practices, residue management, and soil cover to the standard clean fallow plot. C-factors for different management practices are developed based on their observed deviation from the standard, which is clean-till with continuous-fallow conditions. P - Conservation practices implemented into the management system. It is the soil loss with contouring and/or strip cropping, or terracing to that with straight row cropping/planting up-and-down slope (i.e., parallel to the slope).

## Thinking Questions:

Explain how each of the six factors in the Universal Soil Loss Equation (USLE) influence the amount of soil lost by water erosion.

Which of the factors of the USLE can be controlled by the land manager?

## Instructions

The interactive USLE Calculator Program will be needed to complete the following three exercises. To download the USLE Interactive Calculator:

2. Open and print the 'HELP - for using the USLE Calculator Program'

## MODEL EXERCISE #1

A farm is located in Gage County, NE and has an average rainfall factor, R, of 163. Evaluate the effect of changing slope and slope length on an average yielding no-till corn-soybean rotation with an average of 60% residue cover. The previous year’s crop was soybean.

 Slope% (steepness) Slope Length (feet) Soil Loss (T/A) 6% 200 8% 100 10% 50 12% 30

Are there differences in the amount of soil lost? Why or why not?

Use the USLE Calculator Program.

## MODEL EXERCISE #2

A farm is located in Gage County, NE and has an average rainfall factor, R, of 163. Evaluate the effect of percent residue cover on an average yielding no-till corn-soybean rotation. The previous year’s crop was soybeans.

 Residue % Soil Loss (T/A) 90 80 70 60 50 40 30 20 10

How does an increase in the % residue cover change the rate of soil loss? Explain.

Use the USLE Calculator Program.

## MODEL EXERCISE #3

A producer in Cedar County NE has grown corn on his field for 20 years. He follows the conventional tillage practices of his father and disks his field after harvest every fall. On one 80 acre parcel of his farm, there is a slope of 6% that runs 600’ downhill to a stream. Tolerable soil loss (T) for this soil is 5 tons/acre/year (according to the NRCS soil survey).

Using the USLE calculator program, estimate the amount of soil lost annually from this parcel of his land. If he is exceeding T, make some management recommendations for his cropping system to lower his soil loss and help him meet T for this land. If you cannot meet T by altering only C factors, then try implementing some conservation practices (P factor) to help. Record all factors, recommendations and results in the table on the exercise (see pdf at top of page).

Use the USLE Calculator Program.