provides producers with almost complete planting flexibility by decoupling planting decisions from program payments and by eliminating annual supply control programs. Target prices and deficiency payments are eliminated and replaced by fixed contract payments that are independent from market prices...In addition to a more market-oriented commodity policy, reduced trade barriers through passage of GATT and NAFTA are leading to freer trade and closer linkage of commodity prices between domestic and world markets. Under the old program rules, acreage response largely depended on program rules and planting restrictions.

Increased grain prices have caused four dry mill ethanol plants to close since May 1995, and some may not reopen...One of the plants closing was in North Dakota where the State legislature has limited funding for ethanol subsidies. Minnesota and Nebraska have incentives to encourage production of alcohol and new plants have opened in these States. In an effort to encourage ethanol use, EPA announced a proposed rule change permitting 10-percent ethanol blends in reformulated gasoline year-round.

Note, though, that, as shown below, the national average total energy use -- fertilizer energy plus on farm fuel and-power -- on corn farms in 1991 was less than the average for Illinois, which produces the most ethanol, and less than the average for Nebraska, which has one of the fastest-growing corn outputs. Thus, a marginal analysis might conceivably come up with higher total energy inputs (fertilizer plus on-farm use) than the estimated national average inputs here.

where:

FB = the amount of fertilizer applied per bushel harvested (lb/bu)

FH = the amount of fertilizer applied to harvested acres (lb/harvested-acre) (discussed below)

YH = the crop yield (bushels per harvested acre)

(data for corn, 1951-1996, from ERS, Feed Situation and Outlook Yearbook, 1997; data for soybeans, 1955-1996, from Oil Crops Situation and Outlook Yearbook, 1996)

Taylor (1994) reports the total amount of fertilizer applied to corn and soybeans from 1964 to 1993. This total amount is calculated as the application rate per acre multiplied by the total number acres. Now, from 1964 to 1985, the fertilizer-use surveys collected data on harvested acreage only, and hence the reported application rate was the rate per harvested acre specifically. Thus, the parameter FH for the years 1964 to 1985 be estimated directly from the data in Taylor (1994).

Calculation of FH after 1985. However, after 1985, the ERS surveyed and reported the average rate of fertilizer use per planted (and fertilized) acre, rather than per harvested acre (Taylor, 1994).Thus, the published data on fertilizer use from 1986 to 1995 must be adjusted to account for the greater use of fertilizer on acreage that eventually is harvested than on acreage that is planted but not harvested.

where:

FH = the amount of fertilizer applied to harvested acres (lb/harvested-acre)

FP = the amount of fertilizer applied to planted acres (i.e., all acres, harvested and non-harvested) (lb/planted-acre) (Taylor reports FP . P for corn and soybeans from 1986 to 1993; the Agriculture Chemical Usage reports [National Agricultural Statistics Service, annual] reports data that can be used to calculate FP for 1994, 1995, and 1996)

P = all planted acres, harvested plus non-harvested (see data sources for yield, YH, above)

H = the amount of acres harvested (see data sources for yield, YH, above)

R = the fertilizer application rate on non-harvested acres, relative to the application rate on harvested acres (see the discussion below)

 

The same adjustment is made to the original USDA data on pesticide use, which are reported in lbs of pesticide per planted acre (Lin et al., 1995).

Finally, essentially the same adjustment must be made to the data on fuel and electricity use per acre, which are reported per planted acre (Ali and McBride, 1994a, 1994b) and discussed below. The adjustment equation is of the same form as that given above for fertilizer; substitute "fuel and electricity" for "fertilizer," and the appropriate energy units in place of lbs of fertilizer.

 

The R factor. The rate of energy use, fertilizer use, and pesticide use on non-harvested relative to harvested acres depends on how the use of energy, fertilizers, and pesticides are distributed over the growing season, and at what point non-harvested acreage is left alone. I assume that the bulk of fertilizer is applied relatively early in the season, and that energy and pesticides are used more uniformly throughout the season. I also assume that non-harvested acreage is abandoned relatively early. Thus, I assume:

 

Fertilizer	R = 0.60
Pesticides	R = 0.40
Energy	R = 0.40

My new base-year assumptions for corn can be compared with my previous assumptions, and those of Conway et al. (1994):

Previously, I accounted for emissions associated with the manufacture and use of pesticides (herbicides, insecticides, fungicides, and related products) by multiplying fertilizer-related emissions by 1.20. Now, emissions from pesticide use are modeled explicitly.

Lin et al. (1995) report pesticide use per planted acre of corn and soybeans for various years from 1964 to 1992, and the Agricultural Chemical Usage series (National Agricultural Statistics Service, annual) reports pesticide use planted acre in 1994, 1995, and 1996. With these data, and data on yields and planted and harvested acreage, and an assumption regarding the application rate on non-harvested acres relative to that on harvested acres, I calculate pesticide use per bushel, with the equation used to calculate fertilizer use per bushel. (As noted above, I assume that for pesticides, R = 0.40.) The calculated pounds of pesticide active ingredient per bushel harvested is:

It appears that pesticide use per bushel has dropped slightly since 1990, most likely on account of higher yields. With consideration of these results, I make the assumptions shown in Table XIV.

where:

EB,S = the energy use per bushel in state S

EA,S = the energy use per harvested acre in state S from step 1 above

YP,S = the yield per planted acre in state S, for the farms in the FCRS survey

Ps = the planted acreage in state S, for the farms in the FCRS survey

Hs = the harvested acreage in state S, for the farms in the FCRS survey

where:

EB = the average bushel-weighted energy use per bushel for all of the states in the FCRS

EB,S = the energy use per bushel in state S, from step 2 above

BS = the total bushel yield from all farms (not just those in the FCRS) in state S (USDA/NASS crop production data by state; available from the USDA/NASS website: www.usda.gov/nass)

 

At this stage, the results of the analysis for corn, expressed in 106 BTU of energy embodied in fertilizers, and 106 BTU of farm fuel and power, per bushel of production, are:

	CO	IL	IN	IA	MI	MN	NE	OH	SD	WI	Ave.
Fuel, power	0.021	0.013	0.013	0.012	0.018	0.013	0.039	0.015	0.021	0.016	0.018
Fertilizer	0.021	0.040	0.036	0.027	0.035	0.018	0.022	0.039	0.016	0.024	0.029
Total	0.042	0.053	0.049	0.039	0.053	0.030	0.061	0.055	0.036	0.040	0.047

 

4) Finally, I adjust average energy use per bushel from step 3 to account for the likely underestimation of relevant average energy use in the FCRS. For three reasons, the bushel-weighted average energy use per bushel for the farms in the 10 states in the FCRS probably slightly underestimates the national average energy use per bushel. First, it appears that the farms in the survey were a bit more productive than the average farm. The acre-weighted average bu/acre yield of the farms in the survey was about 7% higher than the average bu/acre yield of corn farms nationally. And bushel-weighted fertilizer use per bushel on the farms in the survey was 10-20% less than the national average use. Second, the FCRS estimates of fuel use do not include the minor amount of "other" fuels -- coal, kerosene, and wood -- reported in the USDA’s Farm Production Expenditures report (see Appendix K of Volume 2). In Table K.6, I estimate that these other fuels supply 1-10% of total energy use per acre on corn farms. Third, the FCRS estimates of fuel use probably do not include energy use by purchased service providers, such as crop dusters.

To account for these sources of underestimation, I multiply the calculated FCRS energy-use rates per bushel by 1.10, to arrive at the values of Table XIV.

The revised analysis of Table XIV results in an energy consumption of about 19,000 BTU/bushel-corn in the year 2000, which is a bit less than the 22,000 BTU/bushel-corn assumed in the original report. This reduction in farm energy consumption results in about a 3% reduction in fuelcycle GHG/mi emissions.

 

Collection, grinding, baling, and transport of corn residue

In Table K.13, I estimated that the collection, grinding, and baling of corn residue, for use as a fuel, required 0.28 to 0.56 million BTU of diesel fuel per ton of residue, and assumed a value of 0.42. In comparison with the energy requirements for grass harvesting, this seems high. I now assume a value of 0.30.

 

Inputs to woody-biomass production (SRIC)

Most of the assumptions about productivity, fertilizer user, and N2O emissions of woody-biomass SRIC (short-rotation intensive-cultivation) systems have been changed. The model structure also has been changed: as indicated by Table XIV, the inputs are now treated explicitly, in terms of lbs of fertilizer or gallons of fuel (and so on) per ton of wood.

1). Graham et al. (1992) estimate that present wood plantations yield 11.3 metric tons of dry wood per hectare, after harvesting and transportation losses (5.0 short tons/acre), and that future plantations will yield 18.5 metric tons/ha (8.3 short tons/acre). Mann et al. (1995) and the Oak Ridge National Lab BIOCOST production model (Walsh, 1997) also assume 5 t/acre/year, apparently based on the same work. Perlack et al. (1992) assume 5.9 t/acre/year, after harvesting and transportation losses, for several sites. I assume a value of 5.0 net short tons dry wood/acre in 1994, and increase in the per-acre yield of 1.75%/year.

These values are used here to calculate fertilizer and fuel input data per ton of wood, below, and to calculate loss of soil carbon per ton of wood produced.

2). Turhollow and Perlack (1991) estimate that the production of woody biomass requires 50-kg N/ha, 15-kg P2O5/ha, and 15-kg K2O/ha, with future as well as present technology. The National Renewable Energy Lab’s (NREL) detailed evaluation of the biomass fuelcycle assumes these values for tree plantations (Perlack et al., 1992). If 100% of the acreage is fertilized (Turhollow and Perlack [1991] and Graham et al. [1992] appear to assume that all SRIC acreage is fertilized), the application rates above result in 7.6 lbs-N and 2.3 lbs K2O and P2O5 per net ton of wood.

The latest version of Oak Ridge National Lab’s BIOCOST model (Walsh, 1997) assumes the following inputs, per ton of dry wood or grass produced:

	N (lbs)	P2O5 (lbs)	K2O (lbs)	lime (lbs)	pesticide (lbs)	diesel (gal)
Poplar	7.71	1.18	1.88	0.04	0.13	2.19
Switch grass	18.61	3.00	5.00	0.02	0.08	1.61

 

I assume that these rates apply to the year 2000, and decrease thereafter as plantation productivity increases (Table XIV).

3). Turhollow and Perlack (1991) estimate that the energy embodied in pesticides used in SRIC is 12% of the energy embodied in the fertilizer. Mann et al. (1995) report application rates on tree plantations of up to 10 lbs/acre. NREL’s detailed evaluation of the biomass fuelcycle assumes 0.23 lbs/acre for tree plantations (Perlack et al., 1992), or 0.04 lbs/ton-wood. I will use this last value, and assume that it is constant throughout the projection period.

4). Turhollow and Perlack (1991) use data from Blankenhorn et al. (1985) to estimate that the establishment, harvesting, and use of equipment for SRIC consumes 0.69 gJ diesel fuel per Mg of wood (4.3 gallons/ton) (excluding energy embodied in fertilizer and pesticides), and that hauling from field to production facility (40 km away) consumes 0.23 gJ diesel fuel per Mg wood. Mann et al. (1995) also assume a haul of 40 km, to biomass power generation facility. Perlack et al. (1992) estimate diesel fuel use to be 2.3 gallons/ton, including energy for moving equipment and materials to the field. As indicated above, the BIOCOST model (Walsh, 1997) assumes about 2.2 gal/ton for wood, and 1.6 for grass. Consistent with this lower figure for grass, Mislevy and Fluck (1992) used only 1.3 gal/ton to establish, fertilize, and harvest grass on an experimental plot in Florida.

My assumptions are shown in Table XIV. Note that I have assumed that a minor amount of gasoline and electricity is used.

 

Inputs to the production of perennial grasses

Perennial grasses have been added as a feedstock for ethanol production. The chemical and energy inputs, based on analyses done by Oak Ridge National Laboratory (Perlack et al, 1992; Walsh, 1997) are shown in Table XIV. I assume that parameters for transportation of grass feedstock from field to production plant are the same as those for woody biomass. The fuel production parameters are from Perlack et al. (1992).

In the model output, grass and wood feedstocks are combined into a single "biomass" fuelcycle. Thus, the user specifies the proportion of ethanol derived from grasses, and the proportion derived from trees, and the model calculates the weighted-average fuelcycle GHG emissions. Results for 100% grass or 100% wood are shown in the summary tables.

Perlack et al. (1992) assume that a mix of wheat grass and switch grass has a higher heating value of 15.00. 106 BTU/ton.