Issue At Hand

The U.S. is embarking on an aggressive agenda to reduce dependency on fossil fuels. In response, the demand for biofuel feedstocks will continue to grow into the foreseeable future. While grain-derived ethanol will meet much of the initial need, cellulosic materials are expected to comprise at least a portion of biomass feedstocks and provide a more sustainable solution. Celluosic feedstocks show numerous potential advantages compared to grain-based systems, including reduced energy and nitrogen inputs, higher rates of energy return, utilization of more complex species mixes, greater soil carbon sequestration, reduced greenhouse gas emissions, and enhanced ecosystem services. It is unlikely, however, that a single cellulosic biomass source will suit all of these purposes. A portfolio approach to bioenergy feedstock production is needed. Potential systems to be included in the feedstock portfolio need to be developed, tested, and compared to conventional production systems before they can be recommended for implementation.

What We Hope to Accomplish

Our goal is to develop such a portfolio of biomass cropping systems, which will include systems that are productive, profitable, and mitigate the negative effects of annual crops on soil, water, and air quality. To accomplish this goal, we are developing several alternative biomass cropping systems and comparing them to a conventional continuous corn system. Alternative cropping systems were chosen because of their potential to provide: superior biomass yields (Sweet Sorghum/ Triticale), some biomass yield while mitigating some negative environmental impacts (Corn-Soybean-Triticale/Soybean and Corn-Switchgrass), or some short-term biomass yield and superior long-term yield while strongly mitigating negative environmental impacts (Trees/Triticale).

Photo courtesy of John Sellers.

As agronomic, environmental, and (to some extent) economic performance is strongly tied to site factors, we are evaluating these biomass cropping systems across a series of landscape positions. Hypothesized performance is shown in the figure to the left. Our experiment will test these hypotheses, eventually allowing for optimized bioenergy feedstock production across agricultural landscapes.

How We Go About It

We have designed and are implementing a randomized, replicated block experiment that tests and compares the five cropping systems across five landscape positions. The replicated experiment is being established at an ISU Research and Demonstration Farm (see figure at right). To meet Objective 1, we are collecting data on energy and fertilizer inputs, grain crop yield, harvest biomass on all crops except trees, and seasonal patterns of tree diameter and height growth to estimate standing biomass level. Objective 2 is being met using data from the experimental cropping systems with other agronomic, technical, and economic data to estimate costs and returns on an annual basis and as an annuity for each of the proposed treatments. Estimates will be prepared for establishment, production, harvest, and transport. For Objective 3, we are collecting seasonal soil moisture to a depth of 1m, water quality in the root zone, and seasonal ground water level.