Section 4 Selected methods
4.1 Soil loss
In line with the AGRIBALYSE® methodology (Koch and Salou 2015), soil loss was estimated by applying the USDA RUSLE equation.
\[A = R\cdot K \cdot L \cdot S \cdot C \cdot P \cdot f\]
Where:
A: computed spatial and temporal average soil loss per unit area [t·ha-1·yr-1]
R: rainfall-runoff erosivity factor
K: soil erodibility factor
L: slope length factor
S: slope steepness factor
C: cover-management factor
P: support practice factor
f: acre to hectare conversion factor (equal to 2.47)
The AGRIBALYSE ® program computed R and K parameters according to six principal regions of France: central, north, north-east, west, south, and south-west. Furthermore, climate and soil profiles were defined for each region (Koch and Salou 2015).
4.2 Emissions of ammonia (NH3) to the air
In keeping with the AGRIBALYSE® methodology (Koch and Salou 2015), emissions of NH3 from organic fertilizers were calculated by applying the EMEP-EEA (2009) Tier 2. While the emissions of NH3 resulting from the application of mineral fertilizers were calculated according to the EMEP-EEA (2013) Tier 2, which is in line with the World Food LCA Database (WFLDB) (Nemecek et al. 2014). This allowed to consider the effect of both temperature and soil pH in the computation of NH3 emissions.
The NH3 emissions were calculated according to the following equation:
\[NH_3=\frac{17}{14} \cdot \sum_{m=1}^{M}(EF_a \cdot p + EF_b \cdot (1-p)) \cdot N \]
Where:
NH3: ammonia emissions after mineral fertilizer application [kg NH3]
m: fertilizer type (M: number of fertilizer types)
EFa: emission factor on soils with pH ≤ 7 [kg NH3-N/Kg N]
EFb: emission factor on soils with pH > 7 [kg NH3-N/Kg N]
p: fraction of soils with pH ≤ 7 [%/100]
N: fertilizer application [kg N]
17/14 is the conversion factor from N to NH3.
The above equation was simplified by considering that only one value of pH is reported for a given plot, which implies assuming that the pH is homogeneous in the studied agricultural field. In the equation below, i can take the values EFa or EFb, whether the pH is below or above 7.
\[NH_3=\frac{17}{14} \cdot \sum_{m=1}^{M} EF_i \cdot N\]
4.3 Emissions of nitrogen oxides (NOx, NO, NO2) to the air
Nitrogen oxides result principally from the nitrification process. In line with the AGRIBALYSE® methodology (Koch and Salou 2015) and the WFLDB (Nemecek et al. 2014), the EMEP-EEA (2009) Tier 1 was applied to calculate nitric oxide emission generated from the application of organic and mineral fertilizers. Regardless of the type of fertilizer (i.e., organic or mineral) the same emission factor is used:
- Emission factor for NOx-N: 0.012 kg NOx-N/kg N applied
Prior to the computation of NO emissions, N volatized as NH3 was substracted from the amount of N applied.
In ecoinvent, nitrogen oxide emissions are calculated with respect to NO2. In consequence, a conversion factor of 46/14 was applied to the calculated emissions in terms of N.
4.4 Nitrate (NO3-) leaching to groundwater
Faist Emmenegger, Reinhard, and Zah (2009) employed a simple regression model from Willigen (2000) to calculate nitrate leaching to groundwater in the context of the Sustainability Quick Check for Biofuels Project. The main limitation of the SQCB-NO3 model is that it does not account for soil hydrological and biochemical processes. In consequence, the output of this model must be considered as an estimate of nitrate leaching. Nevertheless, the SQCB-NO3 model has been applied in AGRIBALYSE® (Koch and Salou 2015), WFLDB (Nemecek et al. 2014) and ecoinvent (Nemecek and Schnetzer 2011) to calculate nitrate leaching in non-European agricultural fields.
The SQCB-NO3 model was selected over the SALCA-nitrate model because the former was used by AGRIBALYSE ® to calculate nitrate leaching in vineyard fields, which is a research interest of the authors. Furthermore, this model allows to consistently compute nitrate emissions for other crops, and it facilitates updating the VBA application.
Nitrate emissions were calculated according to the following regression model (Faist Emmenegger, Reinhard, and Zah 2009):
\[N=21.37 + \frac{P}{c \cdot L} \Big[0.0037 \cdot S + 0.0000601 \cdot N_{org} - 0.00362 \cdot U \Big]\]
Where:
N: quantity of nitrogen leached [kg N·ha-1·year-1]
P: precipitation and watering, in mm per year
c: soil clay content, in basis 100
L: rooting depth, in meters
S: nitrogen supply, including crop residues [kg N·ha-1]
Norg: quantity of nitrogen in the soil organic matter [kg N·ha-1]
U: nitrogen uptake [kg N·ha-1]
A conversion factor of 62/14 was applied to the calculated emissions of nitrate in terms of N.
4.5 Emissions of nitrous oxide (N2O) to air
Nitrous oxide (N2O) results from nitrification and denitrification processes. The global warming potential (GWP) of N2O for a time horizon of 100 years is 310 times the GWP of CO2 (IPCC 2006).
N2O emissions were calculated according to the following equation (IPCC 2006):
\[N_2O = \frac{44}{28} \cdot \bigg (0.01 \cdot \Big(N_{tot} + N_{cr} + N_{som} + \frac{14}{17} \cdot NH_3 + \frac{14}{46} \cdot NOx \Big) + 0.0075 \cdot \frac{14}{62} \cdot NO_3 \bigg)\]
Where:
N2O: emissions of nitrous oxide [kg N2O·ha-1]
Ntot: total nitrogen in mineral and organic fertilizer [kg N·ha-1]
Ncr: nitrogen contained in the crop residues [kg N·ha-1]
Nsom: nitrogen from mineralisation of soil organic matter [kg N·ha-1]
NH3: losses of nitrogen in the form of ammonia [kg NH3·ha-1]
NOx: losses of nitrogen in the form of nitrogen oxides [kg NO2·ha-1]
NO3: losses of nitrogen in the form of nitrate [kg NO3·ha-1]
With:
\[N_{som}=N_{org} \cdot MR\]
MR: Mineralisation rate (1.6 %) - SQCB-NO3 (Faist Emmenegger et al., 2009).
4.6 Carbon dioxide (CO2) from liming and urea application
The aim of applying lime in agricultural soils is to decrease soil acidity and improve plant development. The addition of carbonates employing limestone or dolomite entails the dissolution of carbonate limes and the release of bicarbonate (2HCO3-). Subsequently, the bicarbonate is transformed into CO2 and water (IPCC 2006).
In agreement with the AGRIBALYSE® methodology (Koch and Salou 2015), the WFLDB (Nemecek et al. 2014), and ecoinvent (Nemecek and Schnetzer 2011), carbon dioxide emissions generated from the application of lime and urea were calculated according to IPCC (2006) Tier 1. The calculated emissions are based on a worst-case approach because it is considered that the total amount of carbon is released in the form of CO2.
CO2 emissions from lime application:
\[CO_2-C_{Emission}=M_{limestone} \cdot EF_{limestone} + M_{dolomite} \cdot EF_{dolomite}\]
Where:
CO2-CEmissions: C emissions from lime application, tonnes C·yr-1
M: annual amount of calcic limestone or dolomite, tonnes·yr-1
EF: emission factor, tonne of C·(tonne of limestone or dolomite)-1
| Product | EF |
|---|---|
| Limestone | 0.12 |
| Dolomite | 0.13 |
| Urea | 1.57 |
Finally, a factor of 44/12 is applied to transform the emissions in terms of carbon into emissions based on carbon dioxide.
\[CO_2= \frac{44}{12} \cdot CO_2-C_{Emission}\]
4.7 Phosphorus emissions
In agreement with the AGRIBALYSE® methodology (Koch and Salou 2015), the WFLDB methodology (Nemecek et al. 2014), and the ecoinvent methodology (Nemecek and Schnetzer 2011), emissions of phosphorous to water were calculated by applying the SALCA-P model (Prasuhn 2006).
The SALCA-P model computes three types of emissions to water according to the mechanism generating them:
- Phosphorus to river (emission by soil loss)
- Phosphate to groundwater (emission by leaching).
- Phosphate to river (emission by run-off)
4.7.1 Phosphorus to river (emission by soil loss)
Emissions of phosphorus by soil loss were calculated according to the following equation (Prasuhn 2006):
\[P_E=A \cdot P_S \cdot F_R \cdot F_{SR} \cdot t\] Where:
PE: phosphorus emitted by soil loss to rivers [kg.ha-1.yr-1]
A: quantity of soil lost [kg.ha-1.yr-1]
t: land occupation time (number of days/365)
| Parameter | Definition | Default value | Units |
|---|---|---|---|
| PS | Phosphorous content in the upper part of the soil | 0.00095 | kg P·kg soil-1 |
| FR | Eroded particle enrichment factor | 1.86 | - |
| FSR | Fraction of soil lost that reaches the river | 0.2 | - |
4.7.2 Phosphate to groundwater (emission by leaching)
The leaching of phosphate to groundwater was calculated according to the following equation (Prasuhn 2006):
\[P_L=P_{LM} \cdot F_{CSS} \cdot t\]
Where:
PL: leached phosphorus [kg.ha-1.yr-1]
PLM: average quantity of phosphorus leached depending on the land occupation category [kg P.ha-1.yr-1]
FCSS: correction factor for fertilization with slurry and/or sludge (see equation below)
t: occupation time (number of days/365)
A conversion factor of 95/31 was applied to convert the emissions of phosphorus into emissions of phosphate.
\[F_{CSS}=1+ \frac{0.2 \cdot (P_2O_{5-slurry\: and\: sludge})}{80}\]
4.7.3 Phosphate to river (emission by run-off)
Emissions of phosphate to river by run-off were calculated according to the following equation (Prasuhn 2006):
\[P_R=P_{RM} \cdot F_C \cdot F_S \cdot t\]
Where:
PR: phosphorus lost by run-off to the rivers [kg.ha-1.yr-1]
PRM: average quantity of phosphorus lost by run-off depending on the land occupation category [kg P.ha-1.yr-1]
FC: correction factor for the form of phosphorus applied (mineral, liquid/solid organic)
FS: slope factor. FS = 0 if slope < 3%, FS= 1, otherwise.
t: occupation time (number of days/365)
\[F_C=1+ \frac{0.7 \cdot P_2O_{5-slurry\: and \: sludge} + 0.2 \cdot P_2O_{5-mineral \: fertilizer} + 0.4 \cdot P_2O_{5-manure\: and\: compost}}{80}\]
A conversion factor of 95/31 was applied to convert emissions of phosphorus into emissions of phosphate.
4.8 Heavy metal emissions to agricultural soil, surface water and groundwater
Emissions of heavy metals to soil, ground, and surface water are calculated based on a mass balance. The inputs considered are seeds, fertilizers, soil amendments, metal-based pesticides, and air deposition. The outputs correspond to the emissions of trace metals into ground and surface water and the products harvested.
4.8.1 Heavy metal emissions to agricultural soils
The mass balance of trace metal (TM) x in soil is calculated according to the following equation (Koch and Salou 2015):
\[\Delta F_{TMx}=\sum_{SFPI_y}IN_y \cdot C_{y,x} - \Big (\sum_{PLR_z} OUT_z \cdot C_{z,x} \Big) \cdot Alloc_x \quad \forall x \in \{Cd,Cu,Zn,Pb,Ni,Cr,Hg\}\]
Where:
ΔFTMx: Flow into the soil of Trace Metal x (TMx)
INy: Quantity of input SFPIy containing TMx:
Seed
Fertilizer (mineral, organic, farm, sludge)
Pesticides
Sundry Inputs
Cy,x: Content of TMx in input SFPIy
OUTz: Quantity of output PLRz carrying the trace metal TMx
Products harvested (including co-products and/or residues exported)
Leaching to groundwater
Run-off to surface water by soil loss
Cz,x: Content of TMx in output PLRz
Allocx: Allocation factor for TMx output flow. This allocation factor only takes account of part of the output flows from the deposition of trace metals. The allocation is calculated for each trace metal:
\[Alloc_x = \frac{ \sum_{SFPIy}IN_y \cdot T_{y,x}}{ \sum_{SFPIy} IN_y \cdot T_{y,x} + Dep_x}\]
4.8.2 Heavy metal emissions to river
Trace metal emissions through erosion are calculated according to the following equation (Koch and Salou 2015):
\[M_{erosion,TMx} = A \cdot S_{TMx} \cdot F_R \cdot F_{SR} \cdot t \cdot Alloc_x\]
Where:
Merosion,TMx: emission of trace metal x to river [kg·ha-1·yr-1]
A: amount of soil lost [kg·ha-1·yr-1]
STMx: the content of trace metal x in the upper part of the soil
FR: eroded particle enrichment factor
FSR: fraction of soil lost that reaches the river
t: land occupation time (number of days/365)
Allocx: allocation factor for trace metal x
The amount of soil lost was calculated by applying the RUSLE equation. An average concentration of trace metals depending on the soil use was considered. The eroded particle enrichment factor and the fraction of soil lost that reaches the river took the default values considered in the AGRIBALYSE® methodology (Koch and Salou 2015). Please refer to Section 4.7 to retrieve the last two parameters.
4.8.3 Heavy metal emissions to groundwater
Trace metal emissions into groundwater were calculated according to the following equation (Koch and Salou 2015):
\[M_{leachng,TMx} = m_{leaching,TMx} \cdot t \cdot Alloc_x\]
Where:
Mleaching,TMx: emission of trace metal x to groundwater [kg·ha-1·yr-1]
mleaching,TMx: average emission of trace metal x to groundwater [kg·ha-1·yr-1]
Allocx: allocation factor for trace metal x.
References
EMEP-EEA. 2009. Web Page. https://www.eea.europa.eu/publications/emep-eea-emission-inventory-guidebook-2009.
EMEP-EEA. 2013. Web Page. http://www.eea.europa.eu/publications/emep-eea-guidebook-2013.
Faist Emmenegger, M, J Reinhard, and R Zah. 2009. “Sustainability Quick Check for Biofuels–Intermediate Background Report.” Journal Article. With Contributions from T. Ziep, R. Weichbrodt, Prof. Dr. V. Wohlgemuth, FHTW Berlin and A, Roches, R. Freiermuth Knuchel, Dr. G Gaillard, Agroscope Reckenholz-Tänikon, Düendorf, Germany.
IPCC. 2006. 2006 Ipcc Guidelines for National Greenhouse Gas Inventories, Prepared by the National Greenhouse Gas Inventories Programme. Book. IGES, Japan.
Koch, Peter, and Thibault Salou. 2015. AGRIBALYSE: Rapport Méthodologique - Version 1.2. Book. Angers, France: ADEME. https://www.ademe.fr/sites/default/files/assets/documents/agribalyse-rapport-methodologique-v1_2.pdf.
Nemecek, Thomas, Xavier Bengoa, J. Lansche, P. Mouron, V. Rossi, and S. Humbert. 2014. “Methodological Guidelines for the Life Cycle Inventory of Agricultural Products. Version 2.0, July 2014.” Journal Article. World Food LCA Database (WFLDB). Quantis and Agroscope, Lausanne and Zurich, Switzerland.
Nemecek, Thomas, and Julian Schnetzer. 2011. “Methods of Assessment of Direct Field Emissions for Lcis of Agricultural Production Systems. Data V3.0 (2012).” Journal Article. Agroscope Reckenholz-Tänikon Research Station ART.
Prasuhn, Volker. 2006. “Erfassung Der Po4-Austräge Für Die ökobilanzierung.” Journal Article. SALCA-Phosphor. Zürich, CH, Agrocope FAL Reckenholz.