Document ID: EPA-HQ-OAR-2015-0091-0018
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2015-03-20T04:00Z

MEMORANDUM
TO: 		Air and Radiation Docket EPA-HQ-OAR-2015-0091
FROM: 	EPA Office of Transportation and Air Quality
DATE:		March 11, 2015
SUBJECT: 	Supporting Documentation for Pennycress Cultivation Emissions

The document "Pennycress data and calculations  -  for docket.xlsx" contains data and calculations used in the analysis of greenhouse gases attributable to the production of pennycress oil, including:
   * Assumptions about fertilizer use and other inputs for growing pennycress, and calculations of the greenhouse gas emissions from these inputs.  
   
   There is currently limited published data on the optimal amount of fertilizer appropriate for pennycress production.  Therefore, we used a range of fertilizer inputs.  Some sources suggest that minimal fertilizers would be needed for pennycress.[,][,]  Therefore, we used zero fertilizer application rates for nitrogen, phosphorus, and potassium as a lower bound for our greenhouse gas estimates.  
   
   As the upper bound of our greenhouse gas estimate of nitrogen inputs, we used 50 lbs/acre.  This assumption is based on a study that suggests that a nitrogen input of 50 lb/acre, split between the spring and fall, is optimal for pennycress.  This study tested fertilizer inputs between 0 and 125 lb N/acre in a growth chamber experiment, and 0 and 100 lb N/acre in a field experiment.  In the growth chamber experiment, the seed yield for 50 lb N/acre was higher than when lower inputs were used, but fertilizer inputs above 50 lb N/acre did not increase the yield.  In the field experiment, inputs of 75 and 100 lb N/acre did not result in seed yields that were significantly higher than the seed yield when 50 lb N/acre was split between the fall and spring.  Therefore, the study concluded that 50 lb N/acre, split between the fall and spring, was likely the optimal nitrogen input.  A nitrogen input of 50 lb/acre is lower than the nitrogen removal for one acre of pennycress production (for 2000 lb pennycress seed per acre, 76 lbs nitrogen are removed from the soil).  However, pennycress will also use the residual nitrogen in the soil from planting corn.[3]
   
   As the upper bound of our greenhouse gas estimate of phosphorus and potassium inputs, we used 20 lbs/acre each, as recommended by USDA.  These values are supported by a study that calculated the phosphorus and potassium inputs needed to exactly replace the nutrients removed from the field by harvesting pennycress.[5]  Using their phosphorus and potassium content of pennycress, and our yield of 1800 lbs pennycress seed/acre, we calculated a phosphorus input of around 35 lbs/acre and a potassium input of around 25 lbs/acre.  However, this study is based on calculated values rather than actual farming practices.  The study that looked at nitrogen inputs for pennycress did not mention phosphorus or potassium inputs, which suggests that the researchers did not believe additional phosphorus or potassium would be needed to increase yields.  Input from industry suggests that one of the benefits of growing pennycress as a winter cover crop is that it uses the existing nitrogen and phosphorus available in the soil after corn plantings to reduce nutrient runoff.[3]  Because pennycress is grown in rotation with corn and soybeans, it is likely that there would be excess phosphorus and potassium in the soil from these crops.  Therefore, we assumed slightly less phosphorus and potassium would be needed than calculated based on an exact replacement of nutrients. 

   * Pennycress yield

   * Conversion factors

   * Calculations of the N2O emissions from fertilizer and crop residues, for pennycress and soybeans. 
   
   Equations for direct and indirect emissions from these sources are from the Intergovernmental Panel on Climate Change.  To calculate the amount of crop residues from pennycress, and the nitrogen content of these crop residues, we used data on canola as a substitute for pennycress, because data on pennycress were not available, and both canola and pennycress are oilseed plants in the Brassicaceae family.  The nitrogen fertilizer application rates for soybeans are based on regional application rates used in the FASOM model.  These application rates are documented in the Final RFS2 Rulemaking Docket: EPA-HQ-OAR-2005-0161-3178. 
      
   * Net returns for growing pennycress

   Planting, harvesting, and price per pound of pennycress seed were based on information from the petitioner.  The petitioner also provided information on the amount of seed that would need to be planted (lbs/acre) for yields of 1500 lbs seed/acre and 2500 lbs seed/per acre.  We interpolated these values to get the amount of seed that would need to be planted for a yield of 1800 lbs/acre.  
   
   We have also received information from industry that suggests that farmers will be compensated $0.06/lb of pennycress, with industry paying for the seed, fertilizers, planting, harvesting, and transportation.[3]  At yields of 1800 lbs/acre, this translates to a return of $108/acre, which is similar to our calculated return of $121/acre using data from the petitioner.  

   * Energy inputs and greenhouse gas emissions from extracting oil from pennycress seeds