Where:

• \( D \) is the unit draft of the implement, in Newtons per square centimeter (N/cm²).
• \( S \) is the implement speed, in kilometers per hour (kph).

Formulas for different soil types:

• Silty Clay: \( D = 7.0 + 0.049 S^2 \)
• Clay Loam: \( D = 6.0 + 0.053 S^2 \)
• Loam: \( D = 3.0 + 0.021 S^2 \)
• Sandy Silt: \( D = 3.0 + 0.056 S^2 \)
• Sandy Loam: \( D = 2.8 + 0.013 S^2 \)
• Sand: \( D = 2.0 + 0.013 S^2 \)