Nutrient Loss In Straw Burning

Burning fields for residue management is a practice that is done much more sparingly these days than in past decades. If you are choosing this method for residue management, especially in high residue crops such as grain corn, it is interesting to know what is being lost when the straw is burnt vs incorporated and if there is any value the ash provides to the field in nutrient content.

Table 1: MASC provides a Straw Cost Calculator with estimates on the amount of nutrients per ton of different straw types:

These numbers can vary based on growing conditions, some management practices, and whether there has been a rain on the straw that has leached some nutrients out – for example: potassium is susceptible to leaching from straw.

              Research done in the early 2001 by John Heard and team analyzed 3 straw types: wheat, oats, and flax. When looking at the last column that shows the % of nutrients that is lost during the burning process, all three crops showed similar numbers.

Generally, you will lose 90-97% of your carbon that would have contributed to soil organic carbon and soil organic matter. And nearly all nitrogen will be lost during the burning process.

Some nutrients are retained in the ash better than others such as phosphorus, potassium, and some other micronutrients.
Table 2: Nutrient content in pounds per tonne of straw and resulting ash (Heard et al, 2001)

~Katie Meggison