Managing Crop Residues in the Midsouth--The Future
Residue management has become a hot topic because removing aboveground biomass for energy production (as cellulosic ethanol) is receiving increased attention. In fact, it is anticipated that production of cellulosic ethanol will surge in 2013 as the first high-volume refineries go into production.
In 2009, the USDA-ERS published a Report entitled “Ethanol and a changing agricultural landscape“, which provides an analysis of the projected effects on agriculture where crop residues serve as the primary cellulosic feedstock.
Even though most of this interest is centered in the Midwest, dedicated energy crops such as switchgrass have drawn considerable attention in the Southeastern US. Also, corn stover and wheat straw are now being viewed as feedstock for cellulosic ethanol production. In fact, two of the above-mentioned plants (located in Nebraska and Kansas) will use wheat straw as the feedstock.
It is an accepted fact that returning crop residues to the soil environment is an agronomically sound practice. The positive effects are many and well-documented, and include providing ground cover to reduce erosion potential, recycling nutrients removed by a growing crop, and maintaining or increasing soil organic carbon (SOC) to provide a substrate for soil microorganisms and to increase the organic component of soil. Removal of aboveground biomass changes this dynamic.
Furthermore, an Auburn University publication provides estimates that the value of nutrients lost when wheat straw from a 60 bu/acre crop is baled and removed from the production site is $62/acre.
Even though the MSSOY website is mainly devoted to soybean issues, and even though soybean residue is not a topic of general conversation when discussing bioenergy production from cellulose feedstocks, soybean production systems will involve residue management when corn and wheat are grown in rotation. Thus, the subject of this article will address residue management as an ancillary component of soybean production systems.
Doublecropping soybeans with wheat is a common production system in the Midsouth. In this system, wheat residue is often burned following harvest to create optimum planting conditions for the following soybean crop and to reduce nutrient tie-up from decomposing residues.
In a Nov. 2012 article in Crop Management, Dr. Kristofor Brye of the University of Arkansas reports the results from a 7-year study that was conducted to measure the effects of this practice on soil properties.
The major finding was that burning wheat residue reduced the amount of carbon recycled to the soil by an average of about 2000 lb/acre/year. Both annual aboveground residue production and wheat grain yields were unaffected by burning the residue across the years of the study. Thus, the only measurable (but very significant) negative effect from burning wheat residue in this study was the large reduction in potential SOC available for recycling to the soil.
From Dr. Brye’s results, it goes without saying that the current practice of burning wheat straw in the Midsouth appears to be a non-sustainable practice for maintaining or improving soil health. Also, it can be surmised from his burning experiment that removal of wheat straw by any method and for any reason will be detrimental.
Since the long-term sustainability of any agronomic system is closely linked to maintaining an adequate SOC content, it is critical that new agricultural practices–e.g., annual removal of plant residues for bioenergy production–that have the potential to decrease the SOC pool be carefully evaluated before they are arbitrarily adopted.
In a previous blog on this website, I presented and/or linked to Midwestern US sources that discuss how the removal of corn residue can be managed without jeopardizing soil properties. Research into this subject has not been conducted in the Midsouth. In my opinion, the findings from the Midwest indicate that Midsouth research that explores a production system that utilizes corn should include assessing the effects of stover removal on soil properties since the stover removal issue will likely be debated if cellulosic ethanol production moves into the Midsouth.
As stated above, residue management in soybean production is not a hot topic. However, this article is meant to provide a preface to how the management of residues from crops rotated with soybeans in the humid subtropical environment of the Midsouth should be carefully considered when options other than maintenance of soil health are available. Hopefully, the rotation projects that are being funded by the MSPB and the MSSB will provide data that will shed more light on this subject for Midsouth producers.
Composed by Larry G. Heatherly, Apr. 2013, larryheatherly@bellsouth.net
