SOIL 153 | Nebraska

USLE - Universal Soil Loss Equation Nebraska Edition - Agricultural Land

Topographic map The USLE can alert soil managers to potential erosion hazards, identify factors responsible for excessive erosion, and aid in selecting of appropriate conservation practices. Each factor affecting erosion can be changed individually to illustrate its impact. This version of the USLE is applicable for Nebraska. Note: Factors other than those considered in this equation can affect actual erosion loss.

Introduction

The Universal Soil Loss Equation predicts soil loss from sheet and rill types of water erosion based on site characters and management inputs. The USLE predicts if erosion will exceed a "tolerable" rate. Conservation hints and explanations of equation factors help users understand soil erosion processes and their control.

examples of rill erosion and inter-rill erosion

USLE Equation, Factors, and T-Value

The Universal Soil Loss Equation is: A = RxKxLSxCxP

where:
A - Predicted soil loss (tons per acre per year)
R - Rainfall and runoff factor
K - Soil erodibility factor
LS - Topographic factor
C - Crop and cover management factor
P - Conservation practice factor
Soil loss in tons/acre/year, and is the product of multiplying each factor’s numerical value. By changing one factor at a time each factor’s influence on the total erosion can be shown.
In this application the amount of soil loss for the selected management and conservation practices is computed and compared to the tolerable soil loss (tons/ acre/year) for a selected soil type. This value is commonly referred to as "T"

Determine Soil Factor

The first step in the process of calculating soil erosion is to select a soil type. Use the color coded map of Nebraska below to identify the soil type of the location you are interested in. The colors represent major soil associations dominant in an area. Use the number in the center of the colored area to select the soil type for the area of interest from the list.

Color coded map showing soil type in Nebraska map of counties in Nebraska

Select Number for the area of interest from the drop down below

Associated Soil Type

R Factor – Rainfall and Runoff

The R factor (rain and runoff) is based on the erosive power of the rainfall events common to the area. Sometimes called the "erosive index" R values for each region have been set using weather records of rainfall energy and maximum rainfall intensity. Extrapolate an R value for your site from the region averages shown in the picture.

color coded map of average R values in Nebraska

Extrapolate an R value for your site from the region averages shown in the picture

Please enter a value between 40 and 55

K Factor - Erodibility

The soil erodibility factor, K, indicates the inherent susceptibility of soil to erode. Two soil properties: infiltration capacity and structural stability exert the grates influence on erosion.

Soil Type Selected :---
K Factor :---
T Value :--- Tons/Acre
R Factor :---

LS Factor - Topography

The effect of slope length and steepness on water erosion appears in LS or Topography factor. Erosion increases when the length of slope increases, the seepness of slope increases or both.

Step 1: Enter a slope length < 1000 feet
feet

Step 2: Enter a slope steepness < 25%

LS Factor is : ------

C Factor – Crop and Cover Management

Both the growing crop and the residue from the crops affect erosion control. The C factor compares erosion from sites with different crops and residue covers to that of a bare, un-cropped site. Thus, management decisions about crop rotations and tillage system determine the value of C. Undisturbed grassland and forests have very little erosion and the lowest C value, typically below 0.2. Soils with no plant or residue cover are more susceptible to erosion and have the highest possible C factor (1.0).

Current Crop and Cover Managment choices	Adjustment
Cropping System : --for-% cover	--
Tillage Effect:--	--
Expected Yield : --	--
Previous crop : --

Make a selection from each of the live lists.

Select a cropping sequence
What tillage has been used on the site?
Percentage of soil surface covered by residue
Expected yield:
Previous crop?
Adjusted C Factor	---

A = R x K x LS x C x P A Value when:

Soil Type : --	R : --
Slope Length : --	K : --
Slope Steepness : --	LS : --
Crop : --	C : --
Cover : --%	P : --
Practice : --
Predicted Soil Loss A =
Tolerable Soil Loss T = tons/acre

P Factor – Erosion Control Practice

Management practices that reduce the erosivity of water moving across slopes will reduce soil erosion. Contouring, strip-cropping, terraces, and grassed waterways are all examples of erosion control practices used to establish the P factor. Contouring is tilling and planting across the slope rather than with it. Strip-cropping uses alternate bands of cover and row crops across the slope. Terraces are soil embankments that reshape slopes into a series of short slopes that slow water flow and reduce its erosivity. Terrace that open to grassed waterways further limit erosion.

Current erosion control practice	Adjustment
Unadjusted P-Factor	1

Terraces for
Adjusted P-Factor

Make a selection from each of the live lists.

Which conservation practice is used	Strip cropping reduces erosion more than contouring
Which terrace if any is used?	Closed terraces reduce erosion more than open terraces
Terrace Interval (Omit if terrace is not used)	Short intervals between terraces reduce erosion more than wide