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Table 1 Agricultural carbon (C) balance of bioenergy cropping scenarios in Maui, Hawaii

From: Carbon budgets of potential tropical perennial grass cropping scenarios for bioenergy feedstock production

C inputs and outputs Description kg Ceq ha−1 year−1
Sugarcane 100% Sugarcane 50% Napiergrass 100% Napiergrass 50%
Fossil emission
 Field operations
  Field preparationa
   Lime application John Deere 5000–7000 (140–360 HP) 5.2 5.2 5.2 5.2
   Subsoiler John Deere 9000 (540 HP) 12.4 12.4 12.4 12.4
    Harrow John Deere 9000 (540 HP) 3.8 3.8 3.8 3.8
    Strip tillage John Deere 9000 (540 HP) 5.4 5.4 5.4 5.4
    Planter Game (250–300 HP) 5.7 5.7 5.7 5.7
    Herbicide application John Deere 5000–7000 (140–360 HP) 2.1 2.1 2.1 2.1
  Harvestb
   Cane harvester John Deere 3522 (337 HP) 63.1 63.1 63.1 63.1
   Loader Cat 950 and John Deere 624 (175–200 HP) 10.8 10.8 10.8 10.8
   Hauler Cat 773B-E (650–675 Hp) 18.1 18.1 18.1 18.1
  Fabrication/maintenancec
   Farm machinery Tractors, implements and trucks 45.7 45.7 45.7 45.7
  Seed propagationd   1950.0 1950.0 1300.2 1300.2
  Irrigatione   58.7 29.9 58.7 29.9
Field operations subtotal 2181.2 2152.3 1531.4 1502.5
Agricultural inputs
  Fertilizer applicationf 344.68 kg ha−1 year−1 for SC, 243.63 kg ha−1 year−1 for N 355.0 355.0 236.8 236.8
  Herbicideg Applied at a rate 20.307 kg ha−1 year−1 for first year 114.5 114.5 114.5 114.5
  Lime (CaO)h Applied at a rate of 2569 kg ha−1 every 2 years 308.3 308.3 308.3 308.3
 Agricultural inputs subtotal 777.8 777.8 659.6 659.6
Fossil emission subtotal 2959.0 2930.1 2190.9 2162.1
Non-fossil emissions
  Litter decompositioni   10.3 4.6 41.3 18.2
  Pre-harvest burning emissionsj
   Burn emissions of CH4 and N2O   320.3 141.0 0.0
   Black carbon   1644.0 797.7 0.0 0.0
   Soil emisisonsk
    N2O emission   44.5 31.7 62.1 54.0
    CH4 emission   − 29.4 − 19.7 − 40.9 − 35.4
Non-fossil emissions subtotal 1989.7 955.1 62.5 36.9
Total emissions 4948.6 3885.2 2253.5 2198.9
Outputs
  Δ Soil carbon (surface layer)l 0 0 − 6828 − 6820
  Δ Soil carbon (deep profile)l 0 0 − 14,571 − 17,359
Net flux (surface layer)    − 4574.5 − 4621.1
Net flux (deep profile)    − 12,317.5 − 15,160.1
  1. aData from Lal [20] and Macedo et al. [11] for emissions and EF related to fuel consumption from farming operations during field preparation. Equipment description and HPs gathered from personal communication with HC&S (2013). EF used 0.853
  2. bData from Lal [20] and Macedo et al. [11] for emissions and EF related to fuel consumption from harvest operations. Equipment description and HPs gathered from personal communication with HC&S (2013). EF used 0.853
  3. cValues for fabrication and maintenance of equipment from Samson et al. [5]
  4. dEF 0.3 used from Six and Jastrow [21], based on total seed weight of 6500 kg ha−1 for sugarcane and 4334 kg ha−1 for napiergrass
  5. eUsed Lal [20] conversion factor of kWh = 7.25 × 10−2 CE for conversion of total energy used to pump 1 MG of water. Total energy was reduced by 75% based on personal communication with HC&S to account for renewable energy
  6. fEF for N fertilization used from Lal [20] and Macedo et al. [11]. EF used 0.97; SC sugarcane, N napiergrass
  7. gIndividual herbicide EF were calculated from Lal [20], EF used 5.64
  8. h EF used 0.12 from Macedo et al. [11]
  9. iAssuming trash input is 15% of total biomass yield. Based on N content in residual litter of 45 kgN ha−1 in unburnt systems and 7 kgN ha−1 in burnt systems (Cerri [42]; Galdos et al. [12]; Lisboa et al. [3])
  10. jAssuming 15% residue. EF 0.07 kg N2O DM burnt and 2.70 kgCH4 DM burnt (IPCC 2006; Macedo et al. [11]). BC based on 1.0 kg BC Mg trash burnt and a GWP of 500 relative to CO2 (Sanhueza [23])
  11. kUsed IPCC (2007) GWP of 25 for CH4 and 298 for N2O
  12. lChange (Δ) in SOC was measured by the equivalent soil mass method in year one and two of cultivation, reported value is the mean annual Δ
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Carbon Balance and Management

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