Topographic Factor LS

The topographic factor is a measure of the expected soil loss for the field compared to the arbitrary field with a slope length of 72.6 ft and a slope of 9%. It is a combination of the slope length and the percent of slope. An estimate for LS can be found in Figure 18.1.

TABLE 18.1. Soil erodibility factor (K) (ton/ac).

Organic matter content %

Organic matter content %

TABLE 18.1. Soil erodibility factor (K) (ton/ac).

Textural class

0.5

2.0

4.0

Fine sand

0.16

0.14

0.10

Very fine sand

0.42

0.36

0.28

Loamy sand

0.12

0.10

0.08

Loamy very fine sand

0.44

0.38

0.30

Sandy loam

0.27

0.24

0.19

Very fine sandy loam

0.47

0.41

0.33

Silt loam

0.48

0.42

0.33

Clay loam

0.28

0.25

0.21

Silty clay loam

0.37

0.32

0.26

Silty clay

0.25

0.23

0.19

Slope length (ft)

FIGURE 18.1. Typical topographic factors (LS) for slopes of 3-20% and slope lengths of 10-600 ft.

Table 18.2. Typical cropping and management factors (CP).

Cropping practices

Table 18.2. Typical cropping and management factors (CP).

Cropping practices

Management

Up and down

Terraces and

On the

factors

the slope

field boundary

contour

Continuous small grain MRU (6/20)

0.29

0.21

0.15

Continuous small grain HRU (6/20)

0.22

0.16

0.11

Continuous small grain MRU (8/1)

0.22

0.16

0.11

Continuous small grain HRU (8/1)

0.18

0.13

0.09

Continuous small grain ROS

0.12

0.09

0.06

Continuous cotton MF no WC

0.59

0.42

0.30

RC Continuous grain sorghum (25-30 bu)

0.48

0.34

0.24

RC Continuous grain sorghum (35-45 bu)

0.42

0.30

0.21

Continuous peanuts with WC

0.43

0.30

0.22

Continuous peanuts no WC

0.54

0.38

0.27

Alfalfa 5 yr/small grain 2 yr

0.05

0.05

0.05

MRU = Moderate Residue Turned Under; HRU = Heavy Residue Turned Under; RC = Row Crop; ROS = Residue on Surface at Seeding Time; MF = Moderate Fertilizer; WC = Winter Cover.

MRU = Moderate Residue Turned Under; HRU = Heavy Residue Turned Under; RC = Row Crop; ROS = Residue on Surface at Seeding Time; MF = Moderate Fertilizer; WC = Winter Cover.

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