Straw Burning: Gains and Losses

Straw removal by burning improves seedbed preparation and seedling establishment. Burning also helps to reduce nitrogen (N) tie-up, as microbes decompose the straw residue, and it results in nutrient release from the combusting straw. However, burning can result in loss of most of the N and sulfur (S) contained in the residue and it can create concerns regarding environmental quality.

Recent changes relating to small-grain production will likely reshape the way many farmers manage straw. Conservation tillage equipment improves stand establishment in heavy residue. Straw is now recognized for its market value as a soil protector and as landscape mulch. Also, straw incorporated into certain soils tends to improve soil structure, water infiltration and soil carbon levels.

With the present value of crop nutrients, the loss of N, S and possibly other nutrients can no longer be ignored. Manitoba scientists, Mr. J. Heard, Mr. C. Cavers and Mr. G. Adrian, have reassessed nutrient loss caused by the burning of wheat, oats and flax straw.¹  They reported the following:

• Burning spring wheat, oat and flax straw resulted in 98 percent to 100 percent loss of N, 70 percent to 90 percent loss of S, and 20 percent to 40 percent loss of phosphorus (P) and potassium (K.)

• Nutrient content of each ton of wheat straw before burning was 826 pounds carbon (C), 22 pounds N, 6.2 pounds phosphorus pentoxide (P₂O₅), 3.5 pounds potassium oxide (K₂O) and 2.2 pounds S. After burning, the ash from a ton of wheat straw contained 77 lbs. C, 0.4 pounds N, 5.5 pounds P₂O₅, 2.9 pounds K₂O and 0.7 pounds S. Some of the P and K loss was contained in smoke and particulate matter drifting away from the field.

• Growers should avoid soil test sampling from heavy straw burn areas.

• Straw nutrient content is largely influenced by growers’ fertilizer management.

¹Better Crops, Vol. 90, 2006, No. 3.

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