Question

Which of the following is determined using a nomograph?

• A. Rainfal runoff erosivity factor (R)
• B. Slope length factor (L)
• C. Soil erodibility factor (K)
• D. Conservation practice factor (P)

Hint:

The ______Wischmeier Soil Erodibility Nomograph______ is the standard tool used worldwide for estimating the ______K-factor______.
It is especially sensitive to the ______silt and very fine sand______ fraction, as high silt content significantly increases soil erodibility.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The Universal Soil Loss Equation (USLE) is an empirical model developed to estimate long-term average annual soil loss caused by sheet and rill erosion.
The equation is expressed as:
\[ A = R \times K \times LS \times C \times P \]
Each factor represents a specific environmental or management parameter.

Step 2: Detailed Explanation:
The soil erodibility factor ($K$) represents the inherent susceptibility of a soil to detachment and transport by rainfall and runoff.
It is determined quantitatively using a standardized mathematical relationship represented graphically as a ______nomograph______ (developed by Wischmeier, Johnson, and Cross in 1971).
The Soil Erodibility Nomograph requires five soil parameters:
1. Percentage of silt plus very fine sand ($0.002\text{--}0.1\,\text{mm}$).
2. Percentage of sand ($0.1\text{--}2.0\,\text{mm}$).
3. Percentage of organic matter.
4. Soil structure code (ranging from 1 to 4).
5. Soil permeability class (ranging from 1 to 6).
By locating these values on the respective axes of the nomograph and tracing the lines, researchers can quickly and accurately estimate the $K$ factor.
The other factors ($R$, $L$, $P$) are determined through calculations, charts, or tables, but do not rely on this specialized nomograph.

Step 3: Final Answer:
The soil erodibility factor ($K$) is determined using a nomograph, which corresponds to option (C).