Combine Harvest Losses

Pre-harvest is the time to maintain, adjust, and set the combine for harvest. Regardless of field conditions, take the time to check for field losses and make appropriate combine adjustments.

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Field losses from the combine should be one bushel per acre or less under normal conditions. A one bushel loss is equivalent to two corn kernels or four soybeans on the ground per square foot of area. One dropped ear represents hundreds of kernels. One 3/4 lb ear in 1/100th acre (436 sq ft) is equivalent to one bushel per acre loss.

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Header ear loss can result from harvest speed being too fast or slow, driving off the row, or harvesting with the header too high. Proper adjustments can hold losses to one percent from an average loss of three to four percent.1 Header kernel loss occurs when kernels are lost in the snapping mechanism. Reducing average loss from 0.6 percent to 0.4 percent should be a goal.1 Cylinder loss occurs when kernels remain on the cob. Proper concave adjustments and cylinder speed should limit cylinder loss to 0.3 percent.1 Separation loss occurs when individual kernels pass over the sieves and are blown out the rear of the machine. Separation loss should be held to 0.1 percent.1

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Combine settings and adjustments. Always refer to the manufacturer’s manual before performing any maintenance. Rotor/cylinder speed should be set at the lower end of acceptable range, then increase speed as required to keep threshing losses acceptable.2 Concave clearance should start near the wider end of the range and be narrowed for acceptable threshing and material flow.2 In the cleaning shoe, begin with suggested sieve settings and the fan speed near the higher end of the acceptable range.2 Fan speed should be lowered to avoid grain loss. If corn has lighter test weight, fan speed should be reduced to avoid blowing grain out of the combine.

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Of the total machine losses in soybean, 85-90% tend to be at the head and 80% of those losses occur at the cutter bar. Check the cutter bar for wear, flex, and height-control adjustments to help ensure more soybeans are harvested. Check the cleaning shoe for bent or broken sieves. Keep knives sharp and knife guards tight and in good condition.

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Harvest guidelines. Operate at 2.8 to 3.0 miles per hour. Stripper plates or snapping bars should be adjusted to prevent ears from passing through. Chain flights over the stripper plates should be adjusted to extend beyond the plate edges about 1/4 inch. Ears should be snapped near the upper third of snapping roll. Snouts should float on the ground with chains just above the ground.