It is not an uncommon sight in the fall or spring to see columns of smoke on the horizon in the Blue Mountain region. Longtime residents of the area familiar with farming practices know all the reasons for field burning but folks new to the area may not understand that there are a number of agronomic reasons for using fire as a tool.
Fire may be used for disease or insect control although these instances are rare. In grain production for example, some soil-borne diseases such as straw-breaker foot-rot may be made worse with field burning of stubble while other diseases such as stripe rust may be reduced slightly due to fire.
Using fire for weed control (and achieving satisfactory results) is very rare. There are instances, however, when burning is the only answer, such as when the wind fills a farmed draw 10-15 feet deep with weeds like Russian thistle or kochia. Burning for control of grassy weeds only works if the burn occurs before the seed heads have shattered. Fire temperatures at the soil surface are not sufficient to kill the viability of the seed reserve in the soil. However, once most of the residue is removed, tillage tools can handle sprouting grass and other weeds. The downside is the potential for high erosion rates on unprotected soils.
Farmers in the business of growing seed often rely on fire. In our local alfalfa seed industry, alfalfa is chemically defoliated prior to harvest. After harvest, the remaining materials are then unsuitable for feed so this material is burned. Burning also stimulates the plant for higher yields.
Economics is probably the driving force for most field burning in the region because it lowers seedbed preparation costs. Handling crop residue (straw) is the biggest problem grain producers face in seedbed preparation, especially in the higher rainfall zones where yields commonly exceed 80 bushels per acre.
So a farmer has some decisions to make. What was the previous crop yield and how much straw must be reduced?
What tillage tools are available and how much material can they handle satisfactorily?
What is the time frame -- will the next crop be fall seeded or spring seeded and is it grain or a rotational crop like peas or garbanzo beans?
How much material can be seeded into with existing drills and satisfactory seed/soil contact achieved? What are the alternatives to tillage for residue reduction (burning, baling, or multiple tillage trips)?
Each method has a cost and resulting environmental impacts.
Multiple tillage trips are costly and time-consuming, taking far more fossil fuel energy (diesel). It can result in pulverized soil conditions and high levels of erosion.
Baling also has some energy costs. Grain farmers rarely own baling equipment and must hire others to bail and haul the straw. Some of the value of the nutrients in the straw may be recouped through the sale of the straw. The farmer can then more successfully plant the next crop using a one-pass or two-pass direct seed system.
Burning field straw is the alternative that results in the smoke plumes we commonly see. This practice is not free and because burning affects air quality, field burning is rigidly controlled in this state.
Producers pay a burn fee of $3 per acre. The Department of Ecology controls the burning and will only authorize a certain number of acres to be burned on any given day, basing their decision on meteorological conditions that allow for smoke dissipation.
A burn day will not be authorized if wind velocities are too high or there is poor ventilation. After a burn, the field is perfect for direct seeding the next crop.
There are some hidden costs with field burning. Fires can get away leaving the burner liable for damages. Nutrients in the straw are gasified and must be replaced.
If the recommended one-pass or two-pass direct seed methods of planting are not followed, accelerated water/wind erosion can result.
From an agronomic standpoint, field burning is an alternative the agricultural industry needs to keep in its toolbox. While not a perfect solution to dealing with too much or unusable crop residues, we have a system in place that works well most of the time.
What folks need to remember is that not all of the smoke that shows up in the Walla Walla Valley comes from local fires. Washington has no control of what happens to the south of us. Much of the smoke in the valley this fall came from fires in another state hundreds of miles downwind.
Larry Hooker is agricultural projects coordinator for the Walla Walla County Conservation District.