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

Pawlowski, Meghan; Meki, Manyowa N.; Kiniry, James R.; Crow, Susan E.

doi:10.1186/s13021-018-0102-8

Carbon Balance and Management

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 C_eq ha⁻¹ year⁻¹
C inputs and outputs	Description	Sugarcane 100%	Sugarcane 50%	Napiergrass 100%	Napiergrass 50%
Fossil emission
Field operations
Field preparation^a
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
Harvest^b
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/maintenance^c
Farm machinery	Tractors, implements and trucks	45.7	45.7	45.7	45.7
Seed propagation^d		1950.0	1950.0	1300.2	1300.2
Irrigation^e		58.7	29.9	58.7	29.9
Field operations subtotal		2181.2	2152.3	1531.4	1502.5
Agricultural inputs
Fertilizer application^f	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
Herbicide^g	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 emissions^j
Burn emissions of CH₄ and N₂O			320.3	141.0	0.0
Black carbon		1644.0	797.7	0.0	0.0
Soil emisisons^k
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

^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
^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
^cValues for fabrication and maintenance of equipment from Samson et al. [5]
^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
^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
^fEF for N fertilization used from Lal [20] and Macedo et al. [11]. EF used 0.97; SC sugarcane, N napiergrass
^gIndividual herbicide EF were calculated from Lal [20], EF used 5.64
^h EF used 0.12 from Macedo et al. [11]
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])
^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])
^kUsed IPCC (2007) GWP of 25 for CH₄ and 298 for N₂O
^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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ISSN: 1750-0680

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