One-stop cropping
Matt Liebman, Rob Anex and Andy Heggenstaller.
An Innovative Grant from the Plant Sciences Institute helped launch a project for the sustainable production of lignocellulosic feedstocks. These feedstocks will play a large role if the United States is to succeed in producing the 36 billion gallons of domestic biofuel by 2022, mandated by the Energy Independence Security Act of 2007.
To this end, bioenergy double-cropping systems that include winter biomass cover crops offer a viable alternative to the single row crop systems currently dominating Iowa’s landscape. Their advantage is the ability to produce more biomass by capitalizing upon the entire growing season.
A three-year study initiated in 2005, led by then Ph.D. student Andy Heggenstaller; Matt Liebman, Wallace Endowed Chair for Sustainable Agriculture and professor in the Department of Agronomy; and Rob Anex, Bioeconomy Institute associate director for research and associate professor in the Department of Agricultural and Biosystems Engineering, put the double-cropping theory to the test.
In addition to a conventionally managed single crop of corn, “our double-cropping systems included winter triticale, which was planted in the fall after soybeans and harvested in spring the following year. Depending on the cropping system, triticale was followed directly by corn, sorghum-sudangrass or the tropical legume, sunn hemp,” explains Heggenstaller.
The researchers measured total biomass yield, potential ethanol yield, nutrient capture, and nutrient export. Comparing results, the team discovered total biomass yields were twenty-five percent higher with two of the three double-cropping strategies—triticale/corn and triticale/sorghum-sudangrass. In addition, the estimated ethanol production capacity for the triticale/corn system outperformed the next best candidate — sole-cropped corn.
Another benefit confirmed by the study was successful nitrogen sequestration in crops, particularly “during periods of the year when it is most susceptible to loss from the soil,” says Heggenstaller.
One downside to the double-cropping systems tested was that biomass harvest resulted in the removal of significant amounts of nutrients — including nitrogen — from the soil. These nutrients would need to be returned to the soil in some fashion to maintain superior biomass yields. Heggenstaller and his colleagues are now addressing several sustainable approaches to achieve this, including recycling residual materials from biorefineries back to fields used for crop production.
The results of this three-year effort appear in the November-December 2008 issue of Agronomy Journal.
