Researchers at the USDA-ARS have concluded that the corn stover needed to maintain soil organic carbon, and thus productivity, are a greater constraint to environmentally sustainable cellulosic feedstock harvest than that the use of stover to control water and wind erosion.
Wally Wilhelm, USDA-ARS scientist with the Agroecosystems Management Research Unit, Lincoln, NE, and his team compared the amount of stover needed to replenish soil organic matter and control water and wind erosion under a limited number of production conditions—continuous corn and corn produced in rotation with soybean with moldboard plow or conservation tillage practices.
The amount of stover needed to replenish soil organic matter was greater than that required to control either water or wind erosion in the ten counties (in nine of the top eleven corn production states in the US) investigated. This outcome emphasizes the need to further evaluate the validity of widely circulated estimates of US cropland capacity to sustainably supply feedstock for the emerging cellulosic ethanol industry. The study in published in the Agronomy Journal.
Corn stover, the above-ground material left in fields after corn grain harvest, has been identified as a primary feedstock for the production of cellulosic ethanol. Stover and other crop biomass or residue is frequently referred to as trash or a waste, implying it has minimal value. However, when returned to the land, this carbon-rich material helps control erosion, replenishes soil organic matter, and improves soil quality.
Organic matter in the soil retains and recycles nutrients and improves soil structure, aeration, and water exchange characteristics. In addition, organic matter is the energy source for the soil ecosystem.
Most estimates of the amount of crop residue that can be sustainably harvested consider only erosion as a constraining factor, without considering the need to maintain soil organic matter. Recently Jane Johnson and her coworkers at the USDA-ARS North Central Soil Conservation Research Laboratory at Morris, MN, reported estimates of the minimum biomass input needed to maintain soil organic matter (5.25–12.50 Mg ha–1).
The authors conclude that there is a critical need to gather additional high-quality replicated field data from multiple locations to confirm their calculations and to expand the computations to a broader range of cropping systems before major decisions are made about the percent of stover that can designated for biomass energy production. In addition, they state that an extensive effort is needed to expand development of existing crops, discover and develop unconventional crops, and create and deploy advanced cropping systems that exploit the potential of all crops so that biomass production can be greatly expand to provide a sustainable supply of cellulosic feedstock without reducing soil organic matter, thus undermining the productive capacity of the soil.
The article is available for 30 days free access at the Agronomy Journal website. Agronomy Journal is a peer-reviewed, international journal of agronomy published six times a year by the American Society of Agronomy.
W. W. Wilhelma, Jane M. F. Johnson, Douglas L. Karlen and David T. Lightle. Corn Stover to Sustain Soil Organic Carbon Further Constrains Biomass Supply, Agron J 99:1665-1667 (2007) DOI: 10.2134/agronj2007.0150