Top of the crops

USDA scientist: Some crop residues may be too valuable for biofuels

Posted by Ron Steenblik (Guest Contributor) at 6:55 AM on 17 Jul 2008

Read more about: agriculture | biofuels | ethanol | scientific research

Converting crop residues into cellulosic ethanol sounds to many people like a good idea -- certainly better than using food crops themselves. Yet according to respected USDA soil scientist Ann Kennedy, the stems and leaves left over after crops are harvested may have more value if they are left on the ground, especially in areas receiving less than 25 inches of precipitation annually.

That includes most of the United States (click on link to see map) west of the 100th meridian, which runs roughly from Bismark, S.D. through Laredo, Texas.

To regular readers of Gristmill, this probably does not sound like news, but to others it may.

According to Kennedy (the full story can be found at ScienceDaily), a USDA Agricultural Research Service soil scientist and adjunct professor of crop and soil sciences at Washington State University:

"With cultivation, organic matter tends to decline in most places around the world. In the more than 100 years that we have been cultivating soils in the Palouse [the wheat-growing region of Eastern Washington, Northern Idaho and Northeast Oregon] we have lost about half of the original organic matter.

In terms of organic matter content, "according to Kennedy, soils in the Palouse should contain about 3.5 percent organic matter. In most farm fields in the region, however, it is now closer to 2 percent."

As explained in the article, organic matter provides crop nutrients, improves the water-retention capacity of soil, and contributes to the formation of soil clods that help prevent wind erosion. Generally speaking, more moisture encourages more vegetation, which is the feedstock for the microbes that break down residue into organic matter.

Kennedy again:

A lot of people think residue is part of organic matter. But that is not correct. Organic matter is well-decomposed plant material and microbes. It is black and rich and gives soil its dark color.

The tillage system used to prepare the soil for planting is crucial to the conversion of residue to soil organic matter. As explained by Kennedy, "in no-till (direct seed) or one-pass tillage systems ... at least a ton of residue per acre per year is needed to build soil organic matter over time." In minimum tillage systems, decomposing roots, as well as the residues left over after harvesting, add to the soil's organic-matter content. In no-till research plots at the Palouse Conservation Field Station, Kennedy found that the percentage of organic matter "increased from 1.9 percent to 3.6 percent over the course of 20 years."

Kennedy thinks than one of the problems of multiple tillage is that it mixes the soil and residues too well -- essentially, over-feeding the microbes. The microbes as a result consume the incorporated residue too quickly, releasing most of its carbon it into the air as CO2. Or, as Kennedy puts it, cultivated soil is like a "pig out" for microbes, who, in a very real sense, develop indigestion.

Thus, for the long-term health of the soil, leaving residue on the soil surface works best.

"It will tend to stay around longer, and the microbes will slowly invade it and convert it into organic matter with less lost as carbon dioxide," said Kennedy.

As for proposals to harvest crop residues for the production of biofuels, Kennedy notes that

"You could remove the extra residue, but it still provides surface cover and will eventually become organic matter; this residue layer is especially important if you rotate with low-residue crops legumes and canola."

Harvesting residues, in short, requires farmers to find other ways to increase the amount of organic matter in their soils. "'We need to constantly replenish organic matter -- so removing valuable residue, especially in areas with low rainfall, may not be the best practice'," says Kennedy.

This is clearly vital research, especially given plans to produce massive amounts of cellulosic ethanol -- in part from crop residues -- in the future. However, the continuation of this research now looks uncertain. According to a report in Wednesday's Capital Press, the WSU land and water conservation unit, for which Kennedy works, is one of many such units nationwide that are potential candidates for closure.

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12 Comments | Post a Comment

Eureka!

Over feeding soil bacteria! This is an illuminating concept. By tilling it in you also expose it to anaerobic digestion in wet seasons.

This breaks down cellulose, containing the carbon removed from the atmosphere by photosynthesis. Add on ammonia fertilizer and you get a GHG disaster of methane and nitrous oxide release.

Use crop "waste" (residue) as mulch and it preserves soil moisture in dry times and sequesters carbon, releasing it slowly over decades as the less harmfull GHG cO2 (methane 21x CO2 and nitrous oxide 296x GHG effect of cO2).

The estimate of soil organic matter from tilling and chemical ag maybe a bit low though. Go down under the surface, 20 feet down. Praitie soil was 20 feet thick before being busted by sodbusters. Now it's a few inches of insert chemically toxic dust ready to blow into every lung around in the next dust bowl. An iminent possibility in GHG climate weirding.

Overall, organic no-till, mulch agriculture fed by biodigestion of manure and the portion of crop residue removed in food processing added to biomass vulnerable to massive firestorms, the dead wood in drought and disease wracked forests; could really reverse GHG disaster. By halting methane and nitrous oxide release and sequestering carbon in the soil.

The biogas produced is a great backup energy source that offsets CO2 release from combustion.

http://amazngdrx.blogharbor.com/blog John Schneider, Northern Wisconsin

by amazingdrx at 7:35 AM on 17 Jul 2008

Cover Crops to Offset Loss of Crop Residue?

Encouraging news about the potential of cover crops to sequester carbon has been coming from various parties lately (USDA, researchers, Big Sky Initiative to name a few). If the farmers who choose to use their agricultural residues for cellulosic biofuels could be encouraged or even subsidized to plant cover crops, perhaps that would provide at least as much organic matter as the use of the residues currently does.

by Beth in Ohio at 10:06 AM on 17 Jul 2008

Can't wait till cellulosic gets going commercially

It will show its true colors then. Should be interesting.

In the end, it all comes down to biodiversity. Poison Darts--Protecting the biodiversity of our world

by biodiversivist at 10:45 AM on 17 Jul 2008

Cooking trees in biodiesel

http://www.jsonline.com/story/index.aspx?id=772398

They are going to try this here bio-d, I bet the energy/GHG equation will render it a huge mistake. But pork barrel subsidies will keep it cooking. Will they add crop residue too? Most likely.

They burn diesel getting the logs out of the woods to the mill, then a whole lot of coal fired electricity is used to process it. And a whole lot of natural gas will be burned to cook it.

http://amazngdrx.blogharbor.com/blog John Schneider, Northern Wisconsin

by amazingdrx at 11:02 AM on 17 Jul 2008

Whoops.. I meant

Cooking trees into biodiesel. Just like they want to cook coal into diesel. Fischer-Tropsch style.

Both idiotic plans, cooked up by morons. Hehey.

http://amazngdrx.blogharbor.com/blog John Schneider, Northern Wisconsin

by amazingdrx at 11:05 AM on 17 Jul 2008

Some More Fodder for Thought

Ron, good write up.

One main point as this might affect soil health:
the combined impact of reduced residues and organic matter with increased wheel traffic on farm fields from the bailing and fetching of crop residues from the field to transport trucks. Farmers are very sensitive about soil compaction. More compaction means more tillage, more costs, and less yield to boot.

I don't anticipate many farmers being interested in purchasing or leasing all the additional machinery, trucks and trailers that would be needed to make this extra residue harvesting operation possible. It would involve heavy investments plus potential economic opportunity costs as it competes for timely harvesting, transport and storage of their grain crops. And, it would involve hiring more farm labor which is not that easy to find in the Midwest. Plus, farmers are already seeing some major bucks going out for diesel fuel. Why add another significant drain?

I anticipate that the companies processing the residues into ethanol would have to vertically integrate much of the harvesting and transport of residues to their plants. I can't imagine too many farmers being interested in having these companies mucking up wet fields and compacting soils with their heavy equipment. And as to the economics of vertical integration, well, there just have not been too many of these agriculturally based companies surviving. If they have, they are in very concentrated locations and are processing very high value commodities.

It is easy for arm chair pipe dreamers to come up with schemes like converting residues to ethanol. But it seems like bad design building another monster to perpetuate bad design with liquid fuels.

by justlou at 4:16 AM on 18 Jul 2008

Thanks for the informative comment, Justlou

Yes, I have wondered about the effects of soil compaction as well. I assume (perhaps naively) that somebody in one of the USDA-ARS units or land-grant universities is looking into that.

The way you describe the harvesting, it would be carried out as a separate, additional operation, conducted about 40 days after harvesting the grain. That was certainly the thinking a decade ago. (See this good summary of a 1995 investigation into harvesting corn stover for a proposed corn-based pulp mill in northwest Indiana, for example.) That method creates all kinds of challenges, not least to the problem of contaminating the residues with dirt.

I would have assumed that what the industry has in mind these days is harvesting the residues at the same time that the grain or oilseeds are harvested -- in the case of corn, what some call "Whole Stalk Harvest". That, in the least, would require either replacing or modifying existing harvesters, and towing or driving additional wagons to collect the residues. But I am not an expert in such matters.

In either case, I think your vision of the service being largely contracted out seems likely.

These are only my personal opinions.

by Ron Steenblik at 4:39 AM on 18 Jul 2008

Corn Silage

The dairy farmers have pretty well perfected this system. Just one thing missing from the ethanol operation: cow crap to go back on the fields.

It takes quite a fleet of trucks to harvest 200 bushels per acre of corn grain. Multiply that by about 10 for the whole stalk and what do you get?

by justlou at 5:22 AM on 18 Jul 2008

Yup, Justlou

Just one thing missing from the ethanol operation: cow crap to go back on the fields.

Which brings us back to Ann Kennedy's observation: If residue were harvested, soil fertility would drop and farmers would have to find other ways to increase the amount of organic matter in their soils. "We need to constantly replenish organic matter -- so removing valuable residue, especially in areas with low rainfall, may not be the best practice."

These are only my personal opinions.

by Ron Steenblik at 5:41 AM on 18 Jul 2008

Feasibility

Where organic matter would be depleted rapidly, fields harvested for residue could possibly only sustain such a harvest maybe once every 5 years or so. So, this would expand the range of harvesting around any plant. Which would add to transport costs.

Adding up all these factors I wonder how the biomass to biofuel logistics, yield and efficiencies compare with direct combustion as as source of heat or electric generation in small scale, local facilities?

by justlou at 6:08 AM on 18 Jul 2008

Liquid fuels vs. biomass to heat or electric power

I wonder how the biomass to biofuel logistics, yield and efficiencies compare with direct combustion as as source of heat or electric generation in small scale, local facilities?

Poorly, in all the studies I have seen. But for policy-makers who are strong motivated by notions of energy independence, that difference in cost and efficiency doesn't matter very much. What matters is finding substitutes for (imported) petroleum

These are only my personal opinions.

by Ron Steenblik at 7:11 AM on 18 Jul 2008

Biogas/natural gas

"What matters is finding substitutes for (imported) petroleum"

Biogas can do this. And if only 5% of the total natural gas use is from biogas from waste, the rest of the CO2 from combustion is offset.

Also biogas production yields organic fertilizer and soil ammendment in the form of partially digested cellulose. Clean GHG offsetting biofuel.

With new nano tech methane storage, gas tanks would be similar size and safety. No high pressure tanks necessary.

Turning to natural gas/biogas to continue standard gas guzzling would cause gas prices to soar, just like oil products have. Tha's a good thing. Why?

Because it insures that plugin hybrids will still be the ultimate answer. with only maybe 20% of present miles driven on natural gas/biogas. The rest would be driven on renewable electricity in batteries and electrified rail.

http://amazngdrx.blogharbor.com/blog John Schneider, Northern Wisconsin

by amazingdrx at 10:19 AM on 18 Jul 2008

ADVERTISING POLICY

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