Fuel Use per Unit Area

Fuel is metered per hour and budgeted per hectare, and the bridge between the two is field capacity. A tractor burning 28 L/h is meaningless on its own — it might be covering four hectares in that hour or one — and the same tractor moved onto a heavier operation can burn the same fuel for a quarter of the ground. Dividing by capacity is what makes the figure comparable to anything.

The dominant term is the operation, not the machine. Primary tillage is where the diesel goes: mouldboard ploughing runs roughly 20–30 L/ha and deep ripping more, because both are moving a large mass of soil against its own strength. Secondary tillage falls to 5–10, seeding is typically 8–15 depending on the opener and the depth, combining runs 12–20, and spraying is 1–3 because a sprayer is doing almost no work on the soil at all. A season's fuel budget is therefore mostly a decision about the tillage system, which is one of the quieter arguments for reduced tillage — the fuel saving is real and it is the easiest part of the case to verify.

Two mistakes recur. The first is comparing fuel per hour between machines: a bigger tractor burns more per hour and usually less per hectare, because it covers ground faster than it burns extra fuel, and the per-hour figure inverts the ranking. The second is ignoring load factor. A diesel engine is most efficient near its rated load, and a tractor loafing at 40% of capacity burns far more fuel per unit of work done than the same tractor properly matched to its implement. An oversized tractor on a light job is expensive in exactly the way the per-hour figure conceals.

Worth knowing for a cross-check: a well-loaded agricultural diesel delivers roughly 3.5 to 4 kWh of drawbar work per litre of fuel. Multiply the drawbar power by the hours and divide by the capacity, and the answer should land near the figure this calculation gives. When the two disagree badly, the usual culprit is a field capacity estimate that assumed an efficiency the operation never achieved.