by Helen Lammers-Helps

Putting a value on crop residue

WITH ESCALATING CONCERNS about global warming and greenhouse gases, industry is looking to biomass-based fuels such as wheat straw and corn stover to replace fossil fuels. But if we sell the crop residues off farm fields year after year, what impact will this have on the productivity of farmland?

There has been very little research into this question, says Ian McDonald, Applied Research Coordinator at Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). “There is very little data to indicate the amounts of nutrients, organic matter and other variables that could be lost from the landscape with residue removal,” he explains.

To help answer this question, McDonald and others have launched a two-year project sampling crop residues from corn, soybean and wheat fields across Ontario. Starting in 2009, whole plant samples will be taken by hand from 30 fields of each crop. One half of the samples will be analyzed immediately. The other half will be placed into mesh bags and left outdoors to determine the effects of “weathering.” Soybean and wheat straw will be left for about a month post-harvest and corn stover through the winter. “With corn stover, this over-wintering option is probable since it is unlikely that fall harvest of corn stover can occur at moisture contents that enable storage,” explains McDonald.

The weathering period also allows some water soluble nutrients such as chloride and potassium to be leached from the crop residue allowing these nutrients to be retained in the soil for future crops, says McDonald. High nutrient levels in the biomass can also cause problems for combustion and other technologies.

Grain weight, cob weight, stover weight and moisture content will be measured for each sample. The Harvest Index (the above-ground dry weight partitioned between grain and foliage) will be calculated and for corn and the cob:grain index will be also determined. This is the ratio of cob weight versus grain weight. “Those cultivars that have the best grain yield and higher cob index would be preferred if the farmer wanted to maximize the potential to sell grain and cobs off-farm since they will be paid by tonnage in either case,” explains McDonald.

For each sample location, a corresponding soil sample will be taken and analyzed for nutrients, organic matter, pH and soil texture to enable the correlation of biomass nutrient content to soil nutrient levels.

Crop rotation, tillage system and routine nutrient additions will also be documented for each site. This will allow the researchers to determine the variation in nutrient content according to soil test, soil type and management.

Sampling will be repeated in 2010 with the release of the final report planned for 2011.

According to McDonald, this project will help put a value on crop residue. Those outside of agriculture perceive crop residue as a waste so they figure it should be cheap, or even free. “We have to change that mind set. It’s not waste–it has value as fertilizer, as a soil erosion reducer and as organic matter,” he points out. “We need to start talking about it as a resource.”

“The results of this project are important from both an environmental and biomass quality standpoint for end uses,” continues McDonald. “To maintain productive soils, we need to understand how much can be sustainably removed and the costs associated with removing that biomass from the landscape,” he explains. “As the dynamics change, we must understand the impact of residue removal so that the correct decisions about land use and biomass supply can be made.”

While the results of this study will help put a value on the fertilizer replacement cost of removing corn, soybean and wheat crop residues, McDonald points out that the study doesn’t take into consideration the value of organic compounds, micro-nutrients, and other chemical components contained in the residue. To determine the full value of the crop residue will require longer term research, says McDonald. “It will be tougher to put a dollar value on the value of crop residue for soil structural stability and erosion control,” agrees Greg Stewart, OMAFRA Corn Specialist who is also involved in the project along with Bill Deen, University of Guelph, and Peter Johnson and Horst Bohner, OMAFRA.

Funding for the project comes from OMAFRA via the Environmental Sustainability Directed Research Program with further funding/partnering being sought from OSCIA, OCPA and Agri-Food Labs.