Question

Consider the following statements
A. Effective operating time per hectare is less than the theoretical time per hectare if less than the full rated width is utilized
B. Disc blades sharpened from the concave side penetrate more readily than disk blades sharpened from convex side
C. Scouring occurs as long as the frictional resistance at the soil tool interface is less than resistance at soil-soil interface
D. Small diameter discs penetrate more readily than large discs
Choose the correct answer from the options given below:

• A. A, B and C only
• B. B, C and D only
• C. A, C and D only
• D. A, B and D only

Hint:

To remember the scouring condition:
Scouring occurs when: \[ \text{Friction (Soil-Tool)} < \text{Shear Strength (Soil-Soil)} \] If this inequality is reversed, the soil shears within itself and sticks to the plow.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
This question covers fundamental mechanics of tillage tools, focusing on disc plows, soil-tool interactions, and field operating capacities.
Detailed Explanation:
Let us evaluate each statement individually:
- Statement A:
Theoretical operating time per hectare is the absolute minimum time required to cover a hectare under ideal conditions (using full rated width and maximum speed).
If less than the full rated width of the machine is utilized, the effective field capacity decreases, which means it will take more time to cover a hectare.
Thus, the effective operating time per hectare will be greater than the theoretical time.
Therefore, Statement A is false.
- Statement B:
Sharpening disc blades from the concave side creates an acute cutting angle at the point of soil contact.
This shape helps the disc slice through soil and crop residue, improving its penetration ability compared to convex-sharpened blades.
Therefore, Statement B is true.
- Statement C:
Scouring is the sliding of soil along the tool surface without sticking.
For scouring to occur, the friction force between the soil and the tool steel must be less than the internal shear strength of the soil (soil-soil resistance).
If the soil-tool friction is greater, the soil will stick to the tool, causing clogging.
Therefore, Statement C is true.
- Statement D:
For a given implement weight, smaller diameter discs have a smaller contact area with the soil.
This smaller area results in higher contact pressure at the cutting edge, which helps the disc penetrate the soil more easily than a larger disc.
Therefore, Statement D is true.

Step 2: Final Answer:
Since statements B, C, and D are correct, and statement A is incorrect, the correct option is B, C and D only.