Crop Residue May Be Too Valuable to Harvest for Biofuels

Jul 15, 2008

(PhysOrg.com) -- In the rush to develop renewable fuels from plants, converting crop residues into cellulosic ethanol would seem to be a slam dunk.

However, that might not be such a good idea for farmers growing crops without irrigation in regions receiving less than 25 inches of precipitation annually, says Ann Kennedy, 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,” she said. “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.”

Ideally, according to Kennedy, soils in the Palouse should have about 3.5 percent organic content. In most farm fields, she said, it is now closer to 2 percent.

She said organic matter provides nutrients crops need, helps the soil hold water and contributes to the formation of soil clods that help prevent wind erosion. The percentage of organic matter in a given soil varies naturally from region to region, depending on climate, soil disturbance, moisture and vegetation. Generally speaking, more moisture leads to more vegetation, which is the feedstock for the microbes that break down residue into organic matter.

“A lot of people think residue is part of organic matter,” Kennedy said, “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.”

Kennedy, who researches the composition of cereal crop residues and the amount of residue needed to maintain soil quality, said that the tillage system used to prepare the soil for planting has a big effect on the conversion of residue to soil organic matter. In no-till (direct seed) or one-pass tillage systems, she said, at least a ton of residue per acre per year is needed to build soil organic matter over time. In these minimum tillage systems, the intact and slowly decomposing roots also add to organic matter. She found that the percentage of organic matter in no-till research plots at the Palouse Conservation Field Station increased from 1.9 percent to 3.6 percent over the course of 20 years.

In fields with multiple tillage passes, on the other hand, organic matter may not increase even if all the drop residue is left in the field.

Kennedy thinks multiple tillage may mix the soil and residue too well, in essence over-feeding the microbes. The microbes will consume the incorporated residue too quickly and release most of it into the air as carbon dioxide.

“It is like going to an all-you-can-eat restaurant every day and eating too much,” she said “You cannot adequately metabolize all the food you ate. Cultivated soil is like a ‘pig out’ for microbes.”

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. And about proposals to bale off crop residue for production of biofuels?

“You could remove the extra residue,” she said, “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.”

If residue were harvested, she said, 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.”

Provided by Washington State University

Explore further: Predicting bioavailable cadmium levels in soils

add to favorites email to friend print save as pdf

Related Stories

Black carbon is ancient by the time it reaches seafloor

Apr 08, 2014

(Phys.org) —A fraction of the carbon that finds its way into Earth's oceans—the black soot and charcoal residue of fires—stays there for thousands for years, and a new first-of-its-kind analysis shows ...

Is reducing environmental impact in the EU feasible?

Jan 30, 2014

By 2023 all EU member states must be complying with more stringent guidelines related to Integrated Pest Management (IPM). "The essence of the new guideline is reducing the environmental impact of pesticides," ...

Loss of biodiversity limits toxin degradation

Jan 16, 2014

You might not think of microbes when you consider biodiversity, but it turns out that even a moderate loss of less than 5% of soil microbes may compromise some key ecosystem functions and could lead to lower degradation of ...

Recommended for you

Predicting bioavailable cadmium levels in soils

14 hours ago

New Zealand's pastoral landscapes are some of the loveliest in the world, but they also contain a hidden threat. Many of the country's pasture soils have become enriched in cadmium. Grasses take up this toxic heavy metal, ...

Oil drilling possible 'trigger' for deadly Italy quakes

18 hours ago

Italy's Emilia-Romagna region on Tuesday suspended new drilling as it published a report that warned that hydrocarbon exploitation may have acted as a "trigger" in twin earthquakes that killed 26 people in ...

Snow is largely a no-show for Iditarod Trail Sled Dog Race

18 hours ago

On March 1, 65 mushers and their teams of dogs left Anchorage, Alaska, on a quest to win the Iditarod—a race covering 1,000 miles of mountain ranges, frozen rivers, dense forest, tundra and coastline. According ...

UN weather agency warns of 'El Nino' this year

19 hours ago

The UN weather agency Tuesday warned there was a good chance of an "El Nino" climate phenomenon in the Pacific Ocean this year, bringing droughts and heavy rainfall to the rest of the world.

Study shows less snowpack will harm ecosystem

19 hours ago

(Phys.org) —A new study by CAS Professor of Biology Pamela Templer shows that milder winters can have a negative impact both on trees and on the water quality of nearby aquatic ecosystems, far into the warm growing season.

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

irjsi
5 / 5 (1) Jul 16, 2008
God, the Primo Soil Builder!
Walk in the forest . . . that
wonderful fragrance eminating from
the 'soft' carpet of decomposing matter
upon which we tread.
see also: "terra preta"
http://www.eprida.com
/news/nature_viewpoint_on_charcoal.pdf

Roy Stewart
Phoenix AZ
Natural_Philosopher
not rated yet Jul 16, 2008
The effete a$$cavities drinking their Chablis and eating their cheese have never walked in a park never mind a forest or farm.

They also have never taken even a rudimentary course in Science.

hese effete snobs think they know-it-all. How has it taken this long to contradict the novel idea that you can remove organic material totally from a field every year and not think it will degrade the Soil?

Its as stupis as saying new dead plants are preferabel to old dead plants as a source of fue. A poliitical 'truth' that bears absolutely no relation to any reality except the minds of the would-be resurrected Politiburo.



What Uppah Westside cityscape do these ignorami inhabiot. its certianly not Earth or Reality.

More news stories

UN weather agency warns of 'El Nino' this year

The UN weather agency Tuesday warned there was a good chance of an "El Nino" climate phenomenon in the Pacific Ocean this year, bringing droughts and heavy rainfall to the rest of the world.

Patent talk: Google sharpens contact lens vision

(Phys.org) —A report from Patent Bolt brings us one step closer to what Google may have in mind in developing smart contact lenses. According to the discussion Google is interested in the concept of contact ...

Tech giants look to skies to spread Internet

The shortest path to the Internet for some remote corners of the world may be through the skies. That is the message from US tech giants seeking to spread the online gospel to hard-to-reach regions.

Wireless industry makes anti-theft commitment

A trade group for wireless providers said Tuesday that the biggest mobile device manufacturers and carriers will soon put anti-theft tools on the gadgets to try to deter rampant smartphone theft.