Universal Soil Loss Equation Questions and Answers

Answer: C

The plot is 22 m long on a 9% slope.

In the universal soil loss equation the erodibility factor K is defined as the soil loss per unit of rainfall erosion index measured on the standard unit plot: 72.6 ft (22.1 m) long on a uniform 9% slope, kept in continuous clean-tilled fallow with tillage up and down the slope. The slope length and steepness factors L and S equal 1 for exactly this plot, which is why the other dimensions are adjusted relative to it.

The other length and slope pairs (19 m and 12%, 21 m and 11%, 23 m and 8%) are not the standard plot, so a K measured on them would have to be corrected through L and S before use.

Answer: C

With no conservation practice, the factor P is 1.0.

In the Universal Soil Loss Equation, A = R K L S C P, the support practice factor P is the ratio of soil loss with a practice such as contouring, strip cropping or terracing to the soil loss with straight up-and-down slope farming. With no practice, the two are the same, so P = 1. Practices reduce P below 1, for example to about 0.5 for contouring on moderate slopes.

P = 0 would mean no soil loss at all, which no practice achieves. 0.5 is a typical value with contouring, and 1.5 is impossible, since P never exceeds 1.