If producers choose to burn their wheat stubble, timing is important. It’s best to burn as late as possible, close to the time of wheat planting. This minimizes the time that the field will be without residue cover and vulnerable to erosion of surface sealing. Before burning, producers should first check with the Farm Service Agency to find out if this will affect their compliance in any government farm programs.
Advantages of a late-season burn:
- Removes residue cheaply and quickly. If the producer’s drill or planter has a hard time going through wheat residue, or the amount of residue is unusually heavy, this can be an advantage.
- Can control tan spot disease. Tan spot spores oversummer on wheat residue, and burning will usually kill most of the spores.
- Can help control take-all. Take-all seems to be a bigger problem in continuous wheat on cooler, wetter soils. Burning off the residue results in a warmer, and potentially drier, seedbed. Burning late, however, can reduce the beneficial effects mid-summer burning has on take-all.
- May help control Hessian fly. This is one “advantage” that’s a little more hype than reality. Hessian fly flaxseed oversummer in wheat residue and in old wheat crowns. Some, or most, of the flaxseed is at or below ground level in the crowns. These flaxseed will not be controlled by burning. A slow, hot fire can kill flaxseed that is in residue above ground, however.
- May help control winter annual grasses, volunteer wheat, and summer annual broadleaf weeds. This is another perceived “advantage” that is only partially true. It takes a very slow, hot fire to kill cheat and volunteer seed present on the soil surface. Usually, the control is only partial. Cheat and volunteer seed that is in the soil will not be controlled by fire. Likewise, a slow, hot fire can kill summer annual broadleaf weeds that are up and growing in the field. Burning may knock back volunteer wheat if the fire is hot enough, but the growing point is below the soil at this time of the year and the volunteer may come back strong if there is good moisture and no competition from other grasses and weeds. A fast fire will be relatively ineffective in controlling weed seeds and emerged weeds and grasses.
Disadvantages of a late-season burn:
- Removes a major source of organic matter from the field. The residue and stubble are an important source of organic matter for the soil. Burning off this organic matter will gradually reduce soil organic matter levels.
- Can harden the ground. Burning can made the soil hotter and drier on the surface, creating a hard seedbed.
- Reduces water infiltration capacity. Burning can temporarily seal the soil surface to some extent.
- Loss of nutrients. Wheat straw contains many nutrients. Burning will result in the loss of some of the volatile nutrients, such as nitrogen, in the residue. Phosphorus and other minerals are not volatilized by burning and will remain on the field in the ash, unless the ash is blown away.
- Results in smoke pollution. Air quality concerns are greater now than in the past.
What about the effect of burning on wheat yields in continuous wheat, compared to tillage and no-till? Mark Claassen, former agronomist-in-charge at the Harvey County Experiment Field, conducted a long-term study of this since 1997. His results show the long term average yields are similar for all treatments, so burning neither helped nor hurt wheat yields.