Crop Residues - Your Future Cash Crop?

There is lots of talk about new opportunities in the biomass, fossil fuel replacement "Green Economy". However, there needs to be some consideration as to where all the biomass is going to come from to meet the diverse needs.

Some big players are lining up to use different forms of biomass as an energy source in an effort to reduce costs, secure supply, increase efficiency and reduce their environmental footprint. LaFarge at Bath, Ontario, is testing biomass as an energy source for cement production. Ontario Power Generation (OPG) is exploring opportunities to use biomass to fire electricity generation as a coal replacement strategy. OPG has put out a call for 2 million tonnes of biomass per year. Greenfield Ethanol is trying to overcome the technical hurdles of making ethanol from cellulosic materials. The auto industry is working closely with the University of Guelph and others to explore opportunities to make car parts out of bio-based feedstock. There are also a multitude of smaller players exploring opportunities for utilizing biomass.

In the long term, the agricultural feedstock to supply these markets is likely to come from perennial grasses, such as switchgrass, miscanthus, big blue stem, reed canarygrass and prairie cord grass. Annuals, such as hemp, pearl millet, sorghum and others are being evaluated. In the near future, the feedstock is likely to be crop residues, such as corn stover, soybean and cereal straw and forages. There are ready supplies of these over significant acreages across the province.

Crop Residue Volumes

How much of these crop residues are out there? How much can practically be removed? How much should sustainably be removed? The question of gross volume is relatively simple to calculate. Table 1.has been calculated from 2008 Ontario crop yield statistics, harvest index and moisture values. Considering all the Ontario acreages of corn, soybean, wheat and forages, there is approximately 15 million tonnes of material available each year. This assumes that all of the above ground crop residue is available, with the exception of soybean leaves that drop prior to harvest. It also assumes the total use of forages, which is not going to happen based on the ruminant livestock industry in Ontario.

How Much Can We Practically Harvest?

A more difficult question to answer is "how much of the available biomass can be practically harvested?" (Table 2) For cereal residue, we have a defined harvest system. The combine leaves the crop residue in a compact windrow that is easily harvested with a baler or forage harvester. There are some losses such as awns, heads and other plant parts that might fall through the windrow. Soybeans are similar to cereals, in that we put the whole plant (minus the leaves) through the combine and could leave a windrow of straw behind the combine for later harvest. Combine modifications are being investigated that would collect the residue directly from the combine (Figure 1).

Figure 1. Modified Combine for Crop Residue Capture


Iowa State University Research

Corn is more problematic because much of the foliage never goes through the combine. Only the ears are popped off the stalks and enter the combine. The remaining residue is pulled down through the corn header and left in the field. It is run over by the combine and grain buggy, and much of it is not dislodged from the ground. In this case there would be a need for mowing and windrowing the field prior to baling or chopping the corn stover. This would take time and has significant costs. We are often up against impending winter weather and lack of drying conditions to harvest high quality corn stover. It is unlikely that we would normally have the luxury of slowing down the grain harvest to also accommodate stover removal. However, there may be custom capacity in big square balers or forage harvesters to take some of this role. Many options need to be considered and explored.

On-farm storage of the bio-mass and associated costs will also need to be considered. The end users are not going to have the capacity to receive it all at harvest

How Much Can We Harvest and Still Be Sustainable?

What is the level of crop residue removal that can be accommodated without negative sustainability impacts? Traditionally, cereal straw has been harvested while soybean and corn residues have been left in the field. This residue contributes to nutrient return and cycling, soil organic matter building, erosion control, water infiltration, soil health and a multitude of other positive impacts. We do not have research experience to determine how much removal of soybean and corn residue is sustainable, or how long it would take for impacts to be felt. Research needs to be done that considers changes in the production system that could offset negative impacts of residue removal. For example, if no-till systems were adopted for all the land supplying biomass, would it stabilize soil properties and increase productivity as a result of better crop emergence and growth in a residue free environment? Many fundamental questions need to be researched.

There appears to be potential to utilize some of the vast supplies of crop residues as bio-mass. Practical considerations, such as timing, logistics, nutrient replacement, harvest technology, potentially negative soil impacts, and many other questions need to be addressed. Let's get to work.