|DALZELL, BRENT - University Of Minnesota|
|TALLAKSEN, JOEL - University Of Minnesota|
|ALLAN, DEBORAH - University Of Minnesota|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2013
Publication Date: 7/1/2013
Citation: Dalzell, B.J., Johnson, J.M., Tallaksen, J., Allan, D.L., Barbour, N.W. 2013. Simulated impacts of crop residue removal and tillage on soil organic matter maintenance. Soil Science Society of America Journal. 77(4):1349-1356.
Interpretive Summary: Stover or residue is the leaves, husks, cobs and stems remaining after corn grain harvest. This material can be sold as bioenergy feedstock. Harvesting residue exposes soil making it more vulnerable to wind and water erosion. Soil organic matter imparts many characteristics that make soil productive. Thus, it is important to maintain or increase its amount in soil. Every year a fraction crop residue decomposes and a portion of it becomes soil organic matter. Soil organic matter formation relies on the annual crops residue input. Whether, soil organic matter increases, decreases or stay the same over time varies based on tillage, amount and type of residue returned, soil and environmental factors. Measurable changes in soil organic matter happen slowly. Therefore, we used a model called CQESTR for predicting changes in soil organic matter under different tillage and residue harvest scenarios in West Central Minnesota. The model predicted changes for both the top 12 inches and the top 24 inches. The study found that found that tilling with a moldboard plow or a chisel plow even returning all crop residues to the field was not enough to maintain soil organic matter. Returning more residues is needed to maintain soil organic matter in the top 24 inches of soil. The model predicted a loss in soil organic matter in the top 24 inches even when it was maintained in the top 12 inches unless the field was managed without tillage and with continuous corn. The model predicted 3 ton per acre or more dry residue be returned annually or else soil organic matter in the top 24 inches would decline. The 2005-2011 average corn yield for Stevens County, which is in West Central Minnesota, was only 160 bushels per acre. In addition almost all row crops are tilled. Thus, routine harvest of corn stover is not compatible with increasing soil organic matter. To achieve an increase in soil organic matter in the top 24 inches, we advise producing high residue crops like corn coupled with no tillage. This information provides guidance to the bioenergy industry, producers and the general public including policy-makers of the benefits and risks associated with plant-based energy. The study results suggest corn yields routinely exceed 175 bushels per acre in a corn-soybean rotation with no-till before it is advisable to harvest corn stover.
Technical Abstract: Cellulosic biofuel production may generate new markets and additional revenue for farmers. However, residue removal may cause other environmental problems such as soil erosion and loss of soil organic matter (SOM). The objective of this study was to determine the amounts of residue necessary for SOM maintenance under different tillage and removal scenarios for corn-soybean (Z. mays - G. max, respectively) and continuous corn rotations for a site in west-central Minnesota. We employed a process-based model (CQESTR) to evaluate current management practices and quantify SOM changes over time. Results showed that conventional tillage resulted in SOM loss, regardless of the amount of residue returned. Under no-till, the amount of residue was important in determining SOM accumulation or depletion. For the upper 30 cm of soil, average annual rates of 3,650 and 2,250 kg crop residue ha-1 yr-1 were sufficient to maintain SOM for corn-soybean and continuous corn rotations, respectively. Soil OM in soil layers below 30 cm was predicted to decrease in all scenarios as a result of low root inputs. When considered over the upper 60 cm (maximum soil depth sampled), only continuous corn with no-till was sufficient to maintain SOM. Results from this work are important because they show that, for the scenarios tested here, no-till management is necessary for SOM maintenance and that determining whether SOM is accumulating or depleting depends upon the soil depth considered. At current yields observed in this study area, only continuous corn with no-till may generate enough residue to maintain or increase SOM. [REAP publication].