A common question that I have received from numerous consultants over the last several days is as follows. Hey don’t hammer me, but what happens if we mistakenly burned our corn stubble after we spread fall mixed good fertilizer and lime? At the speed in which we harvest and prepare for the next planting season in the Delta it’s an easy thing to happen with labor that is stretched out. Over the last two weeks I have received calls about this subject ranging from both North and South Delta and all points in between.
The first question asked is how bad it is going to hurt me? I think most feel like, I just spent around 80 to $100/acre and threw a match on it something’s got to happen to the nutrients right? Well not necessarily. Temperatures reached from most residue burning practices will not affect the physical properties of Lime, Potash, and/or Triple Super Phosphate. The temperatures are simply not hot enough to cause loss, and unlike nitrogen and sulfur, these three fertilizer materials are not volatile.
If it makes you feel better. Think about the way fertilizer guarantees are expressed on a bag of fertilizer. For P and K we talk about P2O5 and K2O, which are the elements in the oxide form. Why do we do this? Before new technological laboratory advancements to guarantee fertilizer grade, the old method was to weigh the fertilizer after combustion. This method allowed the impurities in the fertilizer to burn off and we are left with P2O5 and K2O oxide ash. By this logic, even if the corn stubble fire gets hot enough to influence the physical properties of Potash and TSP, you still are Ok.
The greatest concern from residue burning after fertilization would be nutrient movement within and out of the field via wind erosion. Most everyone has heard me say at one time or another that when we burn stubble a portion of our nutrients contained in the stubble float off in the ash that lands on the pickup truck window. This would hold true too for any fertilizer material that may get picked up in the vortex we usually see coming off of burned corn fields. Also, depending on the fineness of lime spread, wind erosion after burning could move lime away from target areas simply because there is little to no corn stubble left to provide a wind break.
So in short is burning after fertilization a practice I would suggest? Common sense and the feel good aspect says NO and I tend to agree. However, if you find yourself in the situation where fertilizer and lime have been spread and the field is then burned, you can ease up a little knowing that you are not losing the nutrients you just spent money on spreading.
Remember you are going to lose a portion of the nutrients that were contained in the stubble and valuable organic matter, and that decision was made when we elect to burn the field. For more on this aspect go to: http://www.mississippi-crops.com/2013/09/03/burning-stalks-what-does-it-really-cost/