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Biofuels Influence on Nutrient Use, Removal in US

15 September 2013

Nutrient use and management will likely be impacted significantly within the next 5 years through grain-based ethanol production, writes Dr. Paul Fixen, International Plant Nutrition Institute Senior Vice President and Director of Research.

Beyond that time period, another round of major impact may occur as cellulosic biofuel production is commercialized.

A major challenge to the fertilizer industry and those conducting research on nutrient management will be the development of nutrient management approaches focused on ecological crop intensification where productivity is increased to meet growing demand and the environment is improved.

Failing to take this challenge seriously will likely lead one day to headlines in the media about the “misadventure” of biofuels and the loss of a tremendous opportunity for agriculture.

“Upon this handful of soil our survival depends. Husband it and it will grow our food, our fuel, and our shelter and surround us with beauty. Abuse it and the soil will collapse and die, taking man with it.”

This quote is attributed to the Sanskrit literature from around 1500 BC (Johnston and Dawson, 2005). It is a clear reminder that agriculture as a source of fuel is far from a new concept. However, the advent of new technology…coupled with a desire to reduce dependence on imported oil…has us in the midst of a modern day agricultural revolution.

This ancient quote also reminds us of the importance of resource stewardship as agriculture strives
to capitalize on the opportunities biofuels provide.

Intensified Interest in Yield Improvement

The increased demand for corn can be met by either increasing acres or increasing production per acre. Higher crop prices offer incentive for both. This production-encouraging market comes at a time when biotechnology and genetics industries are promising leaps in genetic yield potential with
estimates of 3% per year being made by leading biotechnology companies (Fitzgerald, 2006).

Figure 1 shows what a 3% annual rate of increase looks like projected out to 2020 and contains a table translating the yield increases into additional production relative to 2006. The N, P, and K contained in the additional annual production in 2020 amounts to 18, 21, and 13%, respectively, of the entire current U.S. fertilizer use (average of 2004-2006).

Genetic improvement in corn yields promised by the biotech industry
Figure 1: Genetic improvement in corn yields promised by the biotech industry

If the genetics industry can deliver on the promised increased genetic potential, and if agronomic
researchers, educators, crop advisers, and growers can convert that genetic potential into bushels in the bin, we will indeed be in the midst of a revolution not experienced since the hybridization of corn.

Converting genetic potential into harvestable yield should clearly not be taken for granted. Cropping system changes in plant population, fertilization, pest management, tillage, and other cultural practices will likely be necessary on a site-specific basis. The yield drag of increased corn-on-corn acres will need to be overcome.

And, it will be critical for sustainability of the resulting modified system that the changes contribute
positively to environmental impacts…that nitrate and phosphate losses to surface water and groundwater are reduced, soil erosion and soil loss from the field are lessened, nitrous oxide and ammonia emissions to the atmosphere are reduced, carbon is sequestered in the soil or at least maintained, and water is used appropriately.

Increase in Corn Acreage

A substantial increase in corn acreage is predicted in 2007 and about a 10 to 15% increase over the 2004-2006 average acreage (80.3 million) is anticipated over the next couple years by many.

Much of the increase is likely to occur in the traditional corn-soybean rotation region of the Corn Belt, resulting in an increase in corn-on-corn acres. Table 1 gives an estimate of the impact of a 5 million acre shift of soybeans to corn where use per acre on the new corn area is assumed to be the same as reported in the USDA Ag Chemical Use Survey for the 2 most recent survey years, plus an additional 30 lb N/A to compensate for loss of a soybean previous crop credit.



The fertilizer that would have been applied for soybeans is subtracted from the corn fertilizer. The estimation also accounts for the increased N rate needed for the additional corn-on-corn acres that show up in the second year of the increased corn

Since there are 5 million fewer acres of soybeans to rotate with corn, an increase of 5 million acres of corn results in 10 million acres of corn-on-corn. With these assumptions, a 5 million acre increase in corn results in increases of 3.8, 1.7, and 1.3% in U.S. total fertilizer use over the 2004-2006 average. If 10 million acres shift from soybeans, these values would double.

Table 2 shows a second scenario in which 5 million acres of additional corn results from acreage shifts of crops other than soybeans. It is assumed that these will be lower yielding acres and therefore receive lower fertilizer rates than the acres coming from soybeans.

Though enterprise budgets will likely influence which crops will contribute the acres, in this analysis the contributions are based on available acreage and an acreage-weighted average fertilizer rate calculated to subtract from the fertilizer applied to the new corn acres.

Crops contributing acres were wheat, cotton, sorghum, and barley. Since the fertilizer rate differences between corn and the crops contributing the corn acres are smaller, the impact of this scenario on fertilizer use is less than when soybeans were contributing the new corn acreage.


Harvest of Crop Residues and Energy Crops 

The production of ethanol from cellulosic biomass occurs today only on a pilot basis, but progress is being made towards

If cellulosic ethanol production does become a commercial reality as many experts are predicting, the impact on the fertilizer industry and nutrient cycling could be large, especially for K. Corn stover is expected to be a major initial feedstock due in part to a plentiful supply, with current sustainable availability estimated at 75 million tons per year (Perlack et al., 2005).

The nutrient content of this stover is difficult to predict due to the wide range in “typical” nutrient concentrations reported in the literature (Table 3). Nutrient content of stover entering a biorefinery could be even more variable due to variation in foliar leaching during crop senescence, extent of weathering in the field, or harvest techniques.

For the calculations made in this paper, eight reported “typical” stover nutrient concentrations reported in the literature were
simply averaged as shown in Table 3. Using these average figures, the 75 million tons of harvestable corn stover would contain nutrients equivalent to 6%, 5%, and 23% of annual U.S. fertilizer sales of N, P2 O5, and K2 O, respectively.

Table 4 compares the nutrient removal in grain and stover for a 150 bu/A corn crop (average yield for U.S. for 2005 and
2006). Assuming that on average 40% of the stover can be harvested sustainably and maintain soil quality, stover harvest
increases nutrient removal by 20, 14, and 110% for N, P2 O5, and K2 O respectively over grain-only harvest.

Thinking in terms of biorefinery capacity helps visualize how a commercial cellulosic industry might get started. Though the bioenergy literature indicates considerable uncertainty in commercial scale details, an 80 million gallon refinery seems to be in the central range of the capacities presented as does an estimate of 80 gallons of ethanol per dry ton of stover (Table 5).

Therefore, a reasonable estimate of the stover demand for a refinery is a million tons of stover…10 refineries would require 10 million tons per year or 6 to 7 million acres supplying corn stover.

Once cellulosic ethanol production is commercialized, energy crops such as switchgrass or miscanthus (elephant grass) are bound to enter the scene in short order.

These are often described as “low input” species, not requiring fertilization or at most, minimal fertilization (Tilman et al., 2006).
However, studies show these species are highly responsive to N fertilization (Muir et al., 2001; Sanderson et al., 2001) and can remove large quantities of nutrients, especially K (Table 6), though content is extremely variable.

Rainfall during leaf senescence can markedly reduce plant K concentration. At the assumed content of 46 lb K2 O/ton, 10 million acres of switchgrass yielding 8 tons/A would remove a quantity of K equivalent to 36% of total current U.S. fertilizer K

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