From Fred Vocasek, senior lab agronomist:
Occasionally, the question of just how much fertilizer value is lost due to burning the stubble comes up. It often is an issue when a fire gets out of control and someone wants to include nutrient loss as part of an insurance claim.
Here is a Crop File that can be a useful reference in these situations: Burning crop residue nutrient losses.
From the file:
Crop residue can be burned off either accidentally or deliberately as part of a controlled burn program. In
some cases, burning can replace the cost of a tillage operation when residue is extra heavy. Corn residue
is probably most susceptible to accidental burning, but wheat and soybean residues are also vulnerable.
Crop residue contains nutrients which can be recycled to replace part of the nutrients removed by grain
harvest. Nutrient loss from the burned residue is a major concern for damage assessments. After the
fire, a common question is “What went up in smoke”?
Initial amount of residue
The first step to assess nutrient loss is estimating the amount of residue that would have been present
before the fire. A yield of one to two bushels of grain typically results in about a pound of residue,
depending on the crop and weather conditions. Table 1 provides a quick way to estimate the
predicted residue weight. Multiply the yield as bushels per acre (bu/ac) by the index value.
For example, the grain sorghum index value is “60″. If the the crop yield was 70 bu/ac, the estimated residue
weight would be about 4200 pounds per acre (70 bu/ac x 60 = 4200 lb/ac). Dividing this result by
“2000″ yields the residue weight in “tons per acre (ton/ac)”.