Life cycle analysis of greenhouse gas emissions from organic and conventional food production systems, with and without bio-energy options

Figures & data

Table 1 Details of the crop rotations used in the Nafferton Factorial Systems Comparison experiments.

Crop rotation	Rotation year
	1	2	3	4	5	6	7	8
Conventional	Winter wheat	Winter wheat	Winter barley	Potato	Winter wheat	Winter barley	Grass/clover	Grass/clover
Organic	Winter wheat	Potato	Spring beans	Cabbages	Spring barley	Grass/clover	Grass/clover	Grass/clover

Table 2 Overview of sources of default values and variables used in greenhouse gas estimates from organic and conventional production systems.

Parameter	Baseline scenarios (ORG and CON)^a	Alternative scenarios (O-SL, O-BC, O-BG, C-BC, C-ST, C-BG)^b
Crop yields	Measured values from NFSC experiments	Same as baseline except where straw was incorporated (10% reduction in yield)
Crop moisture contents	Average measured values from NFSC experiments	Not adjusted
Crop nutrients	Average measured values from NFSC experiments	Not adjusted
Crop inputs	Recorded values from NFSC experiments	Not adjusted
Field activities	Recorded values from NFSC experiments; default emission factors (see Table 4)	Emissions adjusted where crop yield affected energy use, e.g., baling
Stocking density	Based on measured crop yields with assumptions (see text)	Based on alternative scenario crop yields
Milk yield (l y^−1)	Based on Nafferton farm records for organic (6758 l y^−1) and conventional herds (8250 l y^−1)	Same as baseline scenarios
Dry matter intake derived from forages (%)	Based on QLIF project survey data	Same as baseline scenarios
Straw N content (%)	Based on NFSC experiments results	Same as baseline scenarios
N2O emissions	Based on actual amounts of fertilizer or compost applied, and IPCC default emission factors	Adjusted for scenarios where no compost was used
CH4 emissions	Based on estimated stocking density and emission factors from the literature for organic (173.6 kg y^−1) and conventional (155 kg y^−1) cows	Same as baseline scenarios

a ORG: organic stocked rotation with composted manure returned to the field; CON: conventional stockless rotation.

b O-SL: organic stockless rotation with crop residue return to soil; O-BC: organic stockless rotation with on-farm bio-energy (pyrolysis); O-BG: organic stocked rotation with on-farm bio-energy (biogas); C-BC: conventional stockless rotation with on-farm bio-energy (pyrolysis); C-ST: conventional stocked rotation with composted manure returned to the field; C-BG: conventional stocked rotation with on-farm bio-energy (biogas).

Table 3 Details of the agricultural systems used for baseline scenarios and alternative scenarios.

Code	System
ORG	Organic crop rotation with organic management; forage crops fed to dairy cattle; straw for bedding; composted manure returned to the field; potatoes sold off the farm (stocked)
O-SL	Organic crop rotation with organic management; straw and forage crops incorporated into the soil; cereals, potatoes and cabbages sold off the farm (stockless)
O-BC	Organic crop rotation with organic management; forage crops and straw used for on-farm pyrolysis with biochar as a by-product; cereals, beans and potatoes sold off the farm (stockless)
O-BG	Organic crop rotation with organic management; cereals, beans and forage crops fed to dairy cattle; straw returned to the soil; manure slurry used for biogas, then returned to the field; potatoes and cabbages sold off the farm (stocked)
CON	Conventional crop rotation with conventional management; all crops (and straw) sold off the farm (stockless)
C-BC	Conventional crop rotation with conventional management; straw and forage crops used for on-farm pyrolysis with biochar as a by-product; cereals and potatoes sold off the farm (stockless)
C-ST	Conventional crop rotation with conventional management; forage crops fed to dairy cattle; straw for bedding; composted manure returned to the field; potatoes sold off the farm (stocked)
C-BG	Conventional crop rotation with conventional management; straw returned to the soil; manure slurry used for biogas, then returned to the field; potatoes sold off the farm (stocked)

Table 4 Default figures used for calculating greenhouse gas emissions from field activities (direct emissions) for the Nafferton Factorial Systems Comparison experiments.

Type	kg CO2e ha^−1	Reference
Emissions calculated on an area basis
Ploughing	131.6	[7]
Seeding	23.7	[7]
Rolling	23.7	[7]
Pesticide spraying	41.2	[7]
Weeding	23.7	[7]
Fertilizer spreading	36.2	[7]
Combining	91.2	[7]
Secondary tillage	43.1	[7]
Mowing	16	[8]
Ridging	19.2
Potato harvest	54.4
Potato planting	19.2
Flailing	16
Type	kg CO2e ton^−1	Reference
Emissions calculated on a weight basis
Baling	6.4	[8]
Compost application	1.92	[8]

Emissions for baling straw and silage were based on 2 l diesel fuel per ton of biomass; diesel fuel use was converted to CO₂ emission using a factor of 3.2 kg CO₂e emitted per litre of diesel fuel burned; ridging and potato planting were assumed to be equivalent in energy use to heavy seedbed harrowing; emissions for rolling were assumed to be equivalent to sowing; potato harvesting was assumed to be equivalent to sugar beet harvest; flailing was assumed to be equivalent to mowing; compost application figures were based on the values for loading and spreading manure [8].

Table 5 Ruminant metabolizable energy (ME) and digestible energy (DE) (pigs) conversion factors.^a

Crop	Ruminant ME per kg DM (MJ)	DE (pigs) per kg DM (MJ)
Winter wheat	13.6	14.0
Winter barley	12.8	12.9
Spring beans	13.4	12.7
Spring barley	12.8	12.9
Grass and clover	10.8	NA

a All data from [49] except for grass and clover, which are estimated based on 68% digestibility of the dry organic matter.

Fig. 1 Gross greenhouse gas emissions from 8 different scenarios calculated using either the farm gate or wider society as system boundaries. For detailed descriptions of the scenarios see Table 3.

Fig. 2 Average crop yields in two different crop production systems over the first 4 years of the Nafferton Factorial Systems Comparison experiments. Conventional rotation is a cereal intensive crop rotation under conventional crop management. Organic rotation is a diverse crop rotation under organic management. WW: winter wheat; WBAR: winter barley; POT: potatoes; GC: grass/clover; BEANS: spring beans; CABB: cabbages; SBAR: spring barley.

Fig. 3 Human food energy produced (MJ) per hectare of land over 8 years in each of the scenarios compared. For detailed descriptions of the scenarios see Table 3.

Fig. 4 Net total greenhouse gas emissions for 8 different food production scenarios including C offsets for bio-energy in the balance calculation. For detailed descriptions of the scenarios see Table 3.

Fig. 5 Relationship between net GHG emissions and food energy production for eight different production scenarios. For detailed descriptions of the scenarios see Table 3.