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Are sustainable cellulosic ethanol and soil quality possible?

By John Kimble

This sod house on a dryland farm in Eastern Wyoming, circa 1920, is still partly standing, showing the resiliency of the sod, but the cropping failed in a few years. (Provided by John Kimble)There are many people saying we can reduce the dependency on fossil fuel by using renewable resources, such as biomass from crops like corn stubble, for ethanol along with grains. Are we at the Dawning of a New Age on the farm where biomass will provide a new income stream for farmers, or are we back to another point in time where we will be exploiting our soils for a quick-term profit without regard for the sustainability of the soil resource? Many have suggested that biofuel is a possible solution to the continued exploitation of fossil fuel, which is a nonrenewable resource. Recent reports in Science1,2 suggest there may be problems with using biomass and grains for making biofuel. Concerns include loss of cropland for the production of food, increased fertilizer use, impacts to soil quality, increased soil erosion, etc. Ethanol from sugar cane has been shown to be feasible in Brazil, whereas corn has been shown to be a risky proposition due to the possibility of more fuel use in its production, resulting in an overall negative carbon dioxide balance.

Stover is proposed as one source of biomass, while others subscribe to growing specific crops for biomass, such as switch grass. Another proposal is to harvest the biomass and bury it in oceans, where it will become a long-term carbon sink. Strand and Benford3 proposed this, making the point that when crop residue is buried in the oceans it is 92 percent efficient, with cellulosic ethanol production being only 32 percent efficient and soil sequestration of carbon about 14 percent efficient. They,4 however, do not consider the numerous positive effects of leaving the residue on the soil. Crop (biomass) residue has various important soil functions other than just carbon storage. The problem with crop residue removal ideas are that they do not look at the positive benefits of leaving residue on the soil. The naysayers make the point that after 20 years only 10 percent of the original crop residue is still available in the soil. They fail to consider that crop residues are added every year or that, as the crop residue is broken down by soil organisms, it releases back into the soil many nutrients required for crop growth. Saying that SOC (soil organic carbon) sequestration is only 14 percent effective does not look at the soil as a functioning biological system or, likewise, that biomass is needed for a healthy soil system. The actions of the organisms breaking down the biomass builds soil structure, releases nutrients that are utilized by crops, increases the water holding capacity, improves the infiltration rate and reduces evaporation, all of which improve the utilization and storage of rain in the soils. There is also the benefit of the residue providing protection from wind and water erosion.

Some potential biomass users make the point that crop residues should be inexpensive, as the grain crop pays for the production, but like any good businessperson, most farmers will likely seek the best price for their crop residues. There is a large amount of crop residue (globally, 0.6 picogram), but it has many uses other than what was discussed above, some of which are grazing, prevention of wind and water erosion and rebuilding soil carbon after years of depletion. A large portion of the biomass is needed to maintain proper soil function, making it very important to various ecosystems as well as the sustainability of the soils on which agriculture depends

Many wild claims are creating a fog of discourse and double speak with lots of political hype. Most people will agree that we need to wean ourselves from the use of imported oil and to stop our reliance on exploiting a nonrenewable resource. We need to recognize soils as one of the most important resources on the planet and not treat it like “DIRT” when we are promoting using biomass for ethanol. The soils of the grain belt were exploited through tillage in the past, releasing nitrogen and other nutrients. The high native level of the soil organic carbon allowed for sustained yields for a time, but eventually yields decreased as the soil organic carbon levels were reduced to 50 percent or less of the original levels. As yields declined, commercial fertilizers were added to compensate for the loss of native nutrients. The nitrogen fertilizers are made from nonrenewable energy sources, so this must be considered in the equation. There was large-scale erosion as the soil lost its aggregate stability, resulting in the Dust Bowl era in the Great Plains region. There were also major negative impacts to water quality through sediment, nutrient and pesticide runoff. The standard practice was to have a field clean of all surface litter, so we were tilling the soil to death in many areas; we still are doing this today! The practice of no-till farming came along, and each year its use is increasing. The premise of no-till is to leave the biomass on the surface and manage it to keep the soil healthy. Sad to say, in many areas farming of the soil organic carbon (tilling!) still is an ongoing practice. We continue to have extensive wind and water erosion, and we still mine the soil for the nutrients found in soil organic matter. Land that was enrolled in CRP (conservation reserve program) has reverted to production and the resulting tillage is depleting the built-up store of nitrogen, while reducing the levels of SOC. If no-till was used, this exploitation could be avoided but, sadly, in many areas that is not the case.

Here is a simple quote (Albrecht, 1938 Year Book of Agriculture) as to why soil carbon is important: “Up to the present, the policy—if it can be called a policy—has been to exhaust the supply, rather than to maintain it by regular additions according to the demands of the crops produced or the soil fertility removed. To continue very long this practice will mean a further sharp decline in crop yield.” This was written more than a half a century ago, and we still have not developed policies to deal with soil carbon and biomass in a rational way. The importance of soil organic matter has long been recognized, and what we need is a holistic management that does not degrade our soil resource and will allow future generations to farm the land in a productive and sustainable manner. Biomass is the food of the soil!

What needs to be considered is how to maintain soil organic carbon in soils. Maintaining the organic carbon will enhance productivity and lower wind and water erosion. This will also permit nutrients to be recycled, and the biodiversity of organisms in the soil will be stabilized.

When I have talked to farmers, many of them have expressed concerns about biomass removal. One day when I was having breakfast in Imperial, Neb., a farmer asked what I was doing in town, and we got into a discussion about biomass. I said I was working on a proposed biomass removal project, and his unsolicited comment to me was quite telling. He said, “I will not sell my biomass as it is needed to maintain my soil quality.”

What are the concerns that farmers have about large-scale biomass removal and its effect on agriculture sustainability? How much biomass can be removed and under what conditions, and what will be the long and short-term effects?

Farmer concerns are:

* Compaction with more trucks (for every truck of corn grain, there will be 10 more to remove the biomass).

* Sufficient time to remove the biomass (can it be done in a timely manner; farmers are stressed just getting the grain from the fields).

* Loss of material to build soil structure and improve water intake and storage.

* Wind and water erosion.

* Loss of nutrients.

* Soil degradation.

* Short-term gain, long-term soil loss!

* How and where will the biomass be stored until it is used for ethanol production?

Costs/considerations that go into stover removal:

* Soil erosion.

* Soil quality (maintain soil carbon).

* Cost of nutrient removal (how much additional fertilizer will be needed?).

* Tillage practices used—if you use no-till or conservation tillage, maybe some biomass can be removed, but how much? If it is removed, there are still the compaction and storage problems.

* What is the amount of stover that needs to be left in the field to meet sustainability and operational constraints?

* Removal effects on soil water, which in fully appropriated watersheds may become an issue bigger than just on-farm.

How to assess stover removal on soil carbon?

* Century Model has been tested but not for all corn production situations.

* Soil Conditioning Index/RUSLE2 USDA NRCS (2006).

* Wind Erosion Equation USDA NRCS.

* COMET VR.

These are computer models that may show how much biomass can be removed without having an adverse impact on the soils. So far, though, there has been no definitive decision on which model is the most effective.

Ancillary costs that may even exceed the cost of nutrients lost:

* Decreased yields.

* Water-quality impacts.

* Loss of soil water (increased evaporation and increased runoff).

* Air quality (increased wind erosion and greenhouse gases) .

* Wildlife benefits.

* Quality of life?

Key factors that need to be considered first:

* Changes to soil quality/soil carbon.

* Real values of nutrient removal.

* Cost to harvest.

* Net income for farmer.

* Impacts of equipment used to harvest on the soil (compaction, etc.).

* Effects on water usage!

 Provided by John Kimble.Table 1 shows the effect of tillage type and stubble height on wind erosion in Imperial, Neb., using the WEPS–Wind Erosion Protection System. ST is strip tillage, a modified version of no-till; MT is mulch tillage; FP is moldboard plowing. This figure clearly demonstrates that if we continue to plow, we cannot remove any biomass. If we want to maintain soil quality, even with the strip tillage, we need to leave a stubble height of at least 12 inches if we want to keep soil loss in check; with mulch tillage, a height of 46 inches is needed; and with conventional tillage, no biomass can be removed, and even that still has a high level of soil erosion. Moreover, the removal rates will vary based on soil types and climatic conditions.

This shows that it may be possible to remove some stover if you go to no-till, but it is highly dependent on the soil type and the climatic region where it is being removed.

 Provided by John Kimble. Data done by Innovative Cropping Systems group, Va.Table 2 shows the benefits of no-till on runoff, loss of sediment, nitrogen and phosphorus. This benefit comes from maintaining the soil carbon by not removing the biomass. If the stover is removed, these benefits will be lost. In this figure, there are four different no-till treatments shown and one plowed treatment. There is no-till with added litter, with added fertilizer plus sub-soiling and no-till with just added fertilizer. All of the no-till treatments are much better than the conventional tillage.

Dr. Donald Reicosky (ARS Research Soil Scientist, retired) wrote a newspaper article citing the following numbers. Stover removal nutrient replacement cost would be $119.29 per acre, suggesting that the stover must be worth more than $119.29 per acre for a bioenergy source. This value is for the replacement cost of N (nitrogen), P2O5 (phosphorus), and K2O (potassium) only and does not include other costs such as raking, baling and transporting the stover to the bioenergy plant or micronutrients or a payment to the farmer for the stover, which they will not want to give away free.

As stated above, in the past we exploited the soil and the thick sod on its surface and the organic carbon that was in the soil profile by tilling the soils and releasing the nutrients, which for a short time allowed crops to be grown. The soil was tilled and the sod used to build homes. The photo of the sod house was taken in Eastern Wyoming. The sod house is partly standing after about 90 years, but the cropping in this area only lasted at the most a decade before wind, and water erosion made it impossible to continue farming, and the land reverted to range land for cattle grazing. If no-till had been used, maybe there is a possibility that crops could still be grown. In western Nebraska, one farmer uses no-till and gets fairly good yields in dry land farming. His yields are far short of what they are on irrigated land in the same area, but his system is sustainable, whereas the irrigated systems may not be, as there is less and less water available to use for irrigation. In addition, we need to look at more than yield; we need to look at profitability. The cost savings by not irrigating combined with the energy savings of dry land no-till may actually make the lower yields more profitable and more environmentally friendly.

In Ohio where the Richards family operates a farm, Bill Richards was one of the early innovators who switched to no-till more than 30 years ago. Recently, they agreed to provide silage corn to a dairy farmer on land that had been in no-till for 30 years. Within a year or two, the Richards and I observed negative impacts in their soil where the silage was removed, such as fewer earthworms, a notable loss of soil structure and obvious reduced water infiltration rates. The silage corn was still grown using the no-till method, but not enough biomass was left to maintain the soil quality. Consequently, the Richards added cover crops planted right after the silage was harvested and this provided the needed biomass to maintain soil biological functions. We can remove biomass if other changes are made within a given farming system. Cover crops can have beneficial effects; however, cover crops cannot be grown in all areas. In more arid irrigated areas, the use of cover crops may reduce profitability by overusing the limited water supply.

Research work done in Ohio by Blanco-Canqui and Lal5 showed that at rates greater than 25 percent of stover removal on a long-term, no-till, continuous cornfield over a period of 2.5 years, there was a major effect on the health of the soil. Earthworm population decreased, compaction increased and yields were reduced. Blanco-Canqui and Lal point out those effects of removal will be site-specific depending on the soil type and landscape position. This means each removal project needs to assess different soils and regions independently. Some payments for carbon credits on no-till are just based on the practice, i.e., no-till, and do not consider other factors, such as soil type and texture and landscape position. When a proposal is made for stover removal, all relevant factors need to be considered, not just the type of tillage.

Our use of biomass should not result in a negative footprint on overall food production or on soil health and should not add additional greenhouse gases to the atmosphere. Biomass for energy may be one legitimate option among many to reduce reliance on fossil fuels, but this should NOT BE AT THE EXPENSE OF OUR SOILS! As Lal and Pementel6 state, “we do not want to rob Peter to pay Paul.” Stover is needed for soil and water conservation, and excess removal may well have a negative impact on many soil properties that are indispensable to maintaining soil health and long-term farming sustainability. The soils of the U.S. were one of the things that made this country great. Our soils were naturally highly productive, and even after years of what we now know were poor farming practices, they remain quite productive. As more and more lands go into no-till, we are rebuilding our soils. We do not want to reverse this by removing the food for our soils, the BIOMASS!

We do obviously need to develop new income streams for farms. We also need to use more renewable resources for energy production and stop the exploitation of fossil fuels that can never be replaced. We need to look at more than just yields on our croplands, i.e., profitability, sustainability and all the environmental benefits that comes with good stewardship of our soil resources. Biomass may have a future, but most likely it is with the use of dedicated energy crops that do not reduce our food production areas and ultimately will have only minor if any negative impacts on the environment. The important roles that soils provide are detailed in a recent book by Kimble et al.7 This book covers soil carbon management and the economic, environmental and societal benefits of managing our precious soil organic matter. The removal of biomass would likely remove all of the benefits of managing soil carbon as outlined in the book. It is my professional opinion that it would be huge mistake to go down that road. The bottom line is we need to protect and improve our most precious natural resource—the soil.

Endnotes

1. Searchinger, Timothy D. et al., “Fixing a Critical Climate Accounting Error,” Science 326 (2009): 527–528.

2. Jerry M. Melillo et al., “Indirect Emissions from Biofuels: How Important?,” Science 326, no. 5958 (2009), http://www.sciencexpress.org/22October2009/ Page1/10.1126/science.1180251.

3. Strand, Stuart E. and Gregory Benford, “Ocean Sequestration of Crop Residue Carbon: Recycling Fossil Fuel Carbon Back to Deep Sediments,” Environmental Science & Technology (2009), http://pubs.acs.org (accessed Jan. 30, 2009).

4. Ibid.

5. Blanco-Canqui and R. Lal, “Soil and Crop Response to Harvesting Corn Residues for Biofuel Production,” ScienceDirect, Geoderma 141 (2007): 355–362.

6. Lal, R. and D. Pimentel, “Biofuel from Crop Residues,” Soil & Tillage Research 93 (2007): 237–238.

7. Kimble, J.M. et al., “Soil Carbon Management: Economic, Environmental, and Societal Benefits,” (Boca Raton, Fla.: CRC Press, 2007).

 

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