Agricultural Production and Processing Systems
System boundaries first
Nearly every production or processing item is a material balance wrapped around a machine-management or unit-operation question. Start by defining the system boundary, then list inputs, outputs, and losses. In crop systems that means seeded population, emergence, harvest loss, and shrink; in livestock systems it means feed, water, animals, manure, and ventilation air; in processing it means feed rate, product yield, byproduct, and waste streams.
Machinery management
Know the difference between theoretical and effective field capacity. Theoretical capacity ignores turning, loading, and adjustment time; effective capacity applies a field efficiency factor (roughly 70-85% for tillage and row crop, lower for irregular fields and harvesting). Timeliness costs and machinery selection (power, width, speed trade-offs) are common variations.
Traps
- Mixing bushels (volume) with pounds (weight); use standard test weights (corn 56 lb/bu, wheat and soybeans 60).
- Reporting moisture on the wrong basis. Wet basis = water / total mass; dry basis = water / dry matter. Drying calculations must conserve dry matter.
- Using theoretical capacity when the question supplies field efficiency.
- Forgetting that field efficiency falls with small, odd-shaped, or distant fields.
Worked example
A 30 ft implement at 5 mph: theoretical capacity = (30 x 5) / 8.25 = 18.2 ac/h. At 80% field efficiency, effective capacity = 14.5 ac/h. For a 200 ac field, operating time = 200 / 14.5 = about 13.8 h, before adding travel and refueling.
Rule of thumb
Metric: ha/h is approximately width (m) x speed (km/h) / 10 at 100% efficiency; multiply by field efficiency.