Page 168 of RuFaS Documentation states that Manure CH4 is calculated using an adaptation from a method of Sommer, Petersen, and Moller, 2024 based on degradable and non-degradable VS in manure. I am confused as to why the RuFaS values are so low.
I calculated manure CH4 (g/d) using the following equation: ((dVS x B0 x 0.67 x MCF/100) x 1000) (IPCC Tier 2 Approach, Equation 4-15; Leytem et al., 2024) where dVS = digestible volatile solids, B0 = maximum manure CH4 producing capacity (0.24 m3 CH4/kg VS) (Leytem et al., 2024), 0.662 = conversion factor of CH4 (m3) to CH4 (kg), and MCF= Methane Conversion Factor (%) was based on manure management strategy (EPA, 2023, Leytem et al., 2024, Luke, 2025, Ray 2025, Rodriguez et al., 2025). Manure management strategies greatly impact GHG emissions, varying by farm and region. Use of anaerobic digesters is rising, with 30% of California (West) (Rodriguez et al., 2025), 5% of Michigan (Great Lakes) (Luke, 2025), and 12% of New York (Northeast) (Ray, 2025) dairy manure managed with these systems since 2024. Manure conversion factors (MCF) were calculated using anaerobic lagoon, liquid/slurry, and deep pit estimates (Tables A-164 and A-165; EPA,2023) for each state and an anaerobic digester estimate of 10 (Table 4-39; Leytem et al., 2024), weighted according to anaerobic lagoon usage (West (54%); Great Lakes (37%); Northeast (30%)) (Table A-161; EPA, 2023) and anaerobic digester usage (West (30%); Great Lakes (5%); Northeast (12%)), with remaining manure assumed to be managed using liquid/slurry and deep pit (West (16%); Great Lakes (58%); Northeast (58%)). Average regional MCF, weighted according to state milk production, were: West (48.94), Great Lakes (40.78), and Northeast (36.16).
| |
GL0BP |
GL31BP |
GL42BP |
GL45BP |
NE0BP |
NE23BP |
NE41BP |
NE48BP |
| Manure CH4 (g/d) (NDS dVS) |
369.92 |
379.91 |
399.65 |
389.25 |
313.30 |
320.98 |
326.92 |
346.64 |
| RuFaS Manure CH4, g/d |
237.09 |
228.45 |
234.29 |
232.88 |
219.11 |
221.05 |
223.23 |
225.13 |
| |
W0BP |
W37BP |
W48BP |
W51BP |
| Manure CH4 (g/d) (NDS dVS) |
425.42 |
465.78 |
465.58 |
469.26 |
| RuFaS Manure CH4, g/d |
229.72 |
228.60 |
227.65 |
227.40 |
| |
GL0BP |
GL31BP |
GL42BP |
GL45BP |
NE0BP |
NE23BP |
NE41BP |
NE48BP |
| NDS Manure VS, kg/d |
6.60 |
6.67 |
7.15 |
6.90 |
6.28 |
6.37 |
6.57 |
6.93 |
| NDS Manure dVS, kg/d |
5.64 |
5.79 |
6.10 |
5.94 |
5.39 |
5.52 |
5.62 |
5.96 |
| RuFaS Manure VS, kg/d |
8.64 |
8.66 |
8.65 |
8.60 |
8.31 |
8.36 |
8.34 |
8.36 |
| |
W0BP |
W37BP |
W48BP |
W51BP |
| NDS Manure VS, kg/d |
6.28 |
6.95 |
6.97 |
6.88 |
| NDS Manure dVS, kg/d |
5.41 |
5.92 |
5.92 |
5.96 |
| RuFaS Manure VS, kg/d |
8.51 |
8.53 |
8.49 |
8.55 |
For the above initial RuFaS calculations, it was assumed that all manure was handled with a freestall/slurry system. In a second RuFaS run (below), it was assumed that an open lot/anaerobic lagoon system was used for the West while the Great Lakes and Northeast still used the freestall/slurry system. Also, the impact of forages being homegrown was considered in this second run. As expected, RuFaS predicted manure VS (kg/d) is relatively unchanged. Manure CH4 is slightly reduced for the Great Lakes and Northeast regions and significantly reduced for the West.
| |
GL0BP |
GL31BP |
GL42BP |
GL45BP |
NE0BP |
NE23BP |
NE41BP |
NE48BP |
| RuFaS Manure VS, kg/d |
8.64 |
8.65 |
8.64 |
8.59 |
8.31 |
8.30 |
8.28 |
8.32 |
| RuFaS Manure CH4, g/d |
199 |
199 |
202 |
200 |
186 |
189 |
186 |
189 |
| |
W0BP |
W37BP |
W48BP |
W51BP |
| RuFaS Manure VS, kg/d |
8.51 |
8.53 |
8.49 |
8.55 |
| RuFaS Manure CH4, g/d |
10 |
10 |
10 |
10 |
Page 168 of RuFaS Documentation states that Manure CH4 is calculated using an adaptation from a method of Sommer, Petersen, and Moller, 2024 based on degradable and non-degradable VS in manure. I am confused as to why the RuFaS values are so low.
I calculated manure CH4 (g/d) using the following equation: ((dVS x B0 x 0.67 x MCF/100) x 1000) (IPCC Tier 2 Approach, Equation 4-15; Leytem et al., 2024) where dVS = digestible volatile solids, B0 = maximum manure CH4 producing capacity (0.24 m3 CH4/kg VS) (Leytem et al., 2024), 0.662 = conversion factor of CH4 (m3) to CH4 (kg), and MCF= Methane Conversion Factor (%) was based on manure management strategy (EPA, 2023, Leytem et al., 2024, Luke, 2025, Ray 2025, Rodriguez et al., 2025). Manure management strategies greatly impact GHG emissions, varying by farm and region. Use of anaerobic digesters is rising, with 30% of California (West) (Rodriguez et al., 2025), 5% of Michigan (Great Lakes) (Luke, 2025), and 12% of New York (Northeast) (Ray, 2025) dairy manure managed with these systems since 2024. Manure conversion factors (MCF) were calculated using anaerobic lagoon, liquid/slurry, and deep pit estimates (Tables A-164 and A-165; EPA,2023) for each state and an anaerobic digester estimate of 10 (Table 4-39; Leytem et al., 2024), weighted according to anaerobic lagoon usage (West (54%); Great Lakes (37%); Northeast (30%)) (Table A-161; EPA, 2023) and anaerobic digester usage (West (30%); Great Lakes (5%); Northeast (12%)), with remaining manure assumed to be managed using liquid/slurry and deep pit (West (16%); Great Lakes (58%); Northeast (58%)). Average regional MCF, weighted according to state milk production, were: West (48.94), Great Lakes (40.78), and Northeast (36.16).
For the above initial RuFaS calculations, it was assumed that all manure was handled with a freestall/slurry system. In a second RuFaS run (below), it was assumed that an open lot/anaerobic lagoon system was used for the West while the Great Lakes and Northeast still used the freestall/slurry system. Also, the impact of forages being homegrown was considered in this second run. As expected, RuFaS predicted manure VS (kg/d) is relatively unchanged. Manure CH4 is slightly reduced for the Great Lakes and Northeast regions and significantly reduced for the West.