Daniel G. De La Torre Ugarte

Biomass and bioenergy applications of the POLYSYS modeling framework

Abstract The Policy Analysis System (POLYSYS) is a national simulation model of the US agriculture sector which can incorporate agricultural supply and demand and related modules to estimate agricultural production response, resource use, price, income, and environmental impacts of projected changes from an agricultural baseline. The framework recursively incorporates linear programming, econometric, and process models to estimate an impact path resulting from changes imposed on a baseline scenario and its underlying assumptions. POLYSYS estimates crop production and supply at a disaggregated regional level, whereby the 48 contiguous states are subdivided into 305 geographic regions with relatively homogeneous production characteristics. POLYSYS is capable of estimating a wide range of policy alternatives and economic and environmental conditions and simulations may be tailored to a variety of specific analytical needs. This paper presents a broad overview of the structure and approach of the POLYSYS model with emphasis on biomass and bioenergy related applications of the model.

Projecting Yield and Utilization Potential of Switchgrass as an Energy Crop

The potential utilization of switchgrass (Panicum virgatum L.) as a cellulosic energy crop was evaluated as a component of a projected future national network of biorefineries designed to increase national reliance on renewable energy from American farms. Empirical data on yields of switchgrass from a network of experimental plots were coupled with data on switchgrass physiology and switchgrass breeding progress to provide reasonable expectations for rates of improvement over current yields. Historical breeding success with maize (Zea mays L.) was found to provide a reasonable model for projected linear rates of yield improvement of switchgrass based on documented progress to date. A physiologically based crop production model, ALMANAC, and an econometric model, POLYSYS, were utilized to estimate variability in switchgrass yield and resource utilization across the eastern two‐thirds of the United States. ALMANAC provided yield estimates across 27 regional soil types and 13 years of weather data to estimate variability in relative rates of production and water use between switchgrass and maize. Current and future yield projections were used with POLYSYS to forecast rates of adaptation and economic impacts on regional agricultural markets. Significant positive impacts on US markets, including significant increases in farm income and significant reduction in the need for government subsidies, were projected. This was based on expected technological progress in developing biorefineries that will significantly increase national energy self‐sufficiency by producing feed protein, transportation fuel, and electrical power from cellulosic feedstocks.

Cropland carbon fluxes in the United States: increasing geospatial resolution of inventory-based carbon accounting.

Net annual soil carbon change, fossil fuel emissions from cropland production, and cropland net primary production were estimated and spatially distributed using land cover defined by NASAs moderate resolution imaging spectroradiometer (MODIS) and by the USDA National Agricultural Statistics Service (NASS) cropland data layer (CDL). Spatially resolved estimates of net ecosystem exchange (NEE) and net ecosystem carbon balance (NECB) were developed. The purpose of generating spatial estimates of carbon fluxes, and the primary objective of this research, was to develop a method of carbon accounting that is consistent from field to national scales. NEE represents net on-site vertical fluxes of carbon. NECB represents all on-site and off-site carbon fluxes associated with crop production. Estimates of cropland NEE using moderate resolution (approximately 1 km2) land cover data were generated for the conterminous United States and compared with higher resolution (30-m) estimates of NEE and with direct measurements of CO2 flux from croplands in Illinois and Nebraska, USA. Estimates of NEE using the CDL (30-m resolution) had a higher correlation with eddy covariance flux tower estimates compared with estimates of NEE using MODIS. Estimates of NECB are primarily driven by net soil carbon change, fossil fuel emissions associated with crop production, and CO2 emissions from the application of agricultural lime. NEE and NECB for U.S. croplands were -274 and 7 Tg C/yr for 2004, respectively. Use of moderate- to high-resolution satellite-based land cover data enables improved estimates of cropland carbon dynamics.

Energy use and carbon dioxide emissions from cropland production in the United States, 1990-2004.

Changes in cropland production and management influence energy consumption and emissions of CO(2) from fossil-fuel combustion. A method was developed to calculate on-site and off-site energy and CO(2) emissions for cropping practices in the United States at the county scale. Energy consumption and emissions occur on-site from the operation of farm machinery and occur off-site from the manufacture and transport of cropland production inputs, such as fertilizers, pesticides, and agricultural lime. Estimates of fossil-fuel consumption and associated CO(2) emissions for cropping practices enable (i) the monitoring of energy and emissions with changes in land management and (ii) the calculation and balancing of regional and national carbon budgets. Results indicate on-site energy use and total energy use (i.e., the sum of on-site and off-site) on U.S. croplands in 2004 ranged from 1.6 to 7.9 GJ ha(-1) yr(-1) and from 5.5 to 20.5 GJ ha(-1) yr(-1), respectively. On-site and total CO(2) emissions in 2004 ranged from 23 to 176 kg C ha(-1) yr(-1) and from 91 to 365 kg C ha(-1) yr(-1), respectively. During the period of this analysis (1990-2004), national total energy consumption for crop production ranged from 1204 to 1297 PJ yr(-1) (Petajoule = 1 x 10(15) Joule) with associated total fossil CO(2) emissions ranging from 21.5 to 23.2 Tg C yr(-1) (Teragram = 1 x 10(12) gram). The annual proportion of on-site CO(2) to total CO(2) emissions changed depending on the diversity of crops planted. Adoption of reduced tillage practices in the United States from 1990 to 2004 resulted in a net fossil emissions reduction of 2.4 Tg C.

Land Use Implications of Expanding Biofuel Demand

The Renewable Fuel Standard mandates in the Energy Independence and Security Act of 2007 will require 36 billion gallons of ethanol to be produced in 2022. The mandates require that 16 of the 36 billion gallons must be produced from cellulosic feedstocks. The potential land use implications resulting from these mandates were examined using two methods, the POLYSYS model and a general equilibrium model. Results of the POLYSYS analysis indicated that 72.1 million tons of corn stover, 23.5 million tons of wheat straw, and 24.7 million acres would be used to produce 109 million tons of switchgrass in 2025 to meet the mandate. Results of the CGE analysis indicated that 10.9 billion bushels of corn grain, 71 million tons of corn stover, and 56,200 tons of switchgrass is needed to meet the mandate.

Economic Competitiveness of Bioenergy Production and Effects on Agriculture of the Southern Region

The economic competitiveness of biobased industries is discussed by comparing the South relative to other regions of the United States and biomass as a feedstock source relative to fossil fuels such as coal and petroleum. An estimate of the biomass resource base is provided. Estimated changes in the agricultural sector over time resulting from the development of a large-scale biobased industry are reported, and a study on the potential to produce electricity from biomass compared with coal in the southern United States is reviewed. A biobased industry can increase net farm income and enhance economics development and job creation.

Estimating Price Variability in Agriculture: Implications for Decision Makers

Using a stochastic version of the POLYSYS modeling framework, an examination of projected variability in agricultural prices, supply, demand, stocks, and incomes is conducted for corn, wheat, soybeans, and cotton during the 1998-2006 period. Increased planting flexibility introduced in the 1996 farm bill results in projections of significantly higher planted acreage variability compared to recent historical levels. Variability of ending stocks and stock-to-use ratios is projected to be higher for corn and soybeans and lower for wheat and cotton compared to the 1986-96 period. Significantly higher variability is projected for corn prices, with wheat and soybean prices also being more variable. No significant change in cotton price variability is projected.

Economic and environmental impacts of the corn grain ethanol industry on the United States agricultural sector

This study evaluated the impacts of increased ethanol production from corn starch on agricultural land use and the environment in the United States. The Policy Analysis System simulation model was used to simulate alternative ethanol production scenarios for 2007 through 2016. Results indicate that increased corn ethanol production had a positive effect on net farm income and economic wellbeing of the US agricultural sector. In addition, government payments to farmers were reduced because of higher commodity prices and enhanced net farm income. Results also indicate that if Conservation Reserve Program land was converted to crop production in response to higher demand for ethanol in the simulation, individual farmers planted more land in crops, including corn. With a larger total US land area in crops due to individual farmer cropping choices, total US crop output rose, which decreased crop prices and aggregate net farm income relative to the scenario where increased ethanol production happened without Conservation Reserve Program land. Substantial shifts in land use occurred with corn area expanding throughout the United States, especially in the traditional corn-growing area of the midcontinent region. Production of other crops, such as soybeans and cotton, shifted out of traditional growing areas to accommodate increased corn production. Fertilizer and chemical usage also increased. When conservation tillage adoption was assumed to remain at 2007 levels for the 10-year period, regional tillage intensity, soil erosion, and fossil fuel-based carbon emissions increased, while soil carbon stocks decreased as a result of increased corn production. However, the simulation demonstrated that additional adoption of conservation tillage above 2007 levels mitigated the adverse effects of increased corn production on soil erosion and net carbon emissions to the atmosphere.

Agricultural Impacts of Biofuels Production

Analysis of the potential to supply 25% of projected 2025 U.S. transportation fuels indicates sufficient biomass resources are available to meet increased demand while simultaneously meeting food, feed, and export needs. Corn and soybeans continue to be important feedstocks for ethanol and biodiesel production, but cellulose feedstocks (agricultural crop residues, energy crops such as switchgrass, and forestry residues) will play a major role. Farm income increases, mostly because of higher crop prices. Increased crop prices increase the cost of producing biofuels.

Evaluating possible cap and trade legislation on cellulosic feedstock availability

An integrated, socioeconomic–biogeophysical model is used to analyze the interactions of cap‐and‐trade legislation and the Renewable Fuels Standard. Five alternative policy scenarios were considered with the purpose of identifying policies that act in a synergistic manner to reduce carbon emissions, increase economic returns to agriculture, and adequately meet ethanol mandates. We conclude that climate and energy policies can best be implemented together by offering carbon offset payments to conservation tillage, herbaceous grasses for biomass, and by constraining crop residue removal for ethanol feedstocks to carbon neutral level. When comparing this scenario to the Baseline scenario, the agricultural sector realizes an economic benefit of US