Subtopic: Cost analysis of implements and tractors
Question Statement:
The total width between the two extreme furrow openers in a tractor-drawn 9-row wheat seed drill is 1.6 m. The average mass of wheat seeds dropped per meter of row length in each furrow opener is 2.15 g. Seed rate obtained with the seed drill in kg ha⁻¹ (rounded to 1 decimal) is ______.
Official Answer Key:
107.4 to 107.8
Step-by-Step Solution & Explanation
The 1.6 m span covers the (9−1) = 8 gaps between 9 openers; the effective working width (each row 'owns' one full row-spacing strip) is therefore W_eff = (1.6/8) × 9 = 1.8 m.
Seed dropped per metre of travel (all 9 rows together) = 2.15 g/m × 9 = 19.35 g per metre of forward travel.
This is distributed over a strip 1.8 m wide × 1 m long = 1.8 m² of field.
Seed rate = 19.35 g / 1.8 m² = 10.75 g/m². Converting g/m² → kg/ha (1 ha = 10,000 m², so multiply by 10,000 and divide by 1000, i.e. ×10):
Seed rate = 10.75 × 10 = 107.5 kg/ha. (A common error is to use the raw 1.6 m as the effective width, which gives 120.9 kg/ha — outside the accepted range.) Answer: within 107.4–107.8.
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