3.1. Direct Energy Intensity
The average yearly energy consumed (Table 1
) by farms accounted for 13,675 kg of diesel, 26,245 kWh of electricity and 115 kg of LPG. Diesel fuel requirements were about 260 kg·LC−1
, 369 kg per hectare cultivated and 40 kg per tonne of FPCM. For the electricity, the EUI were 491 kWh per lactating cow and 73 kWh per tonne of milk. The annual energy indicators associated with LPG usages amounted to 2 kg per lactating cow and 0.4 kg per tonne of FPCM. Expressing the above mentioned data in terms of primary energy requirements, Table 1
shows a global consumption of 7678 MJ per head, 16,514 MJ per LC and 2522 MJ of primary energy per tonne of FPCM.
Battini et al. [39
] quantified lower diesel usage in four typical dairy farms located in the Po Valley (North Italy), ranging from 154 to 183 kg of diesel fuel per lactating cow.
The analysis of the electricity usages indicates that milk harvesting and refrigeration were the most demanding processes, requiring 23% and 19% of the annual electricity consumption, respectively (Figure 1
). The other processes that affect significantly the electricity consumptions were: water heating (15%), water pumping (13%), and pumping for irrigation (9%), followed by slurry management and fan-misting (5% each), lighting and cow brushing (4% each). The total activities carried out at the milking parlor level accounted for 57% of the total electricity requirement. The results obtained from the electricity analysis are higher (17% expressed in terms of kWh for lactating cows and 24% higher if referred to the unit of milk) than those found from a French study conducted by L’Institut de l’Elevage (2009) [25
] which investigated 60 dairy farms (milk yield 7.2 t cow−1
). Comparable results were obtained in 60 Italian dairy farms (milk yield 8 tonne cow−1
) located in the Emilia Romagna region [40
]: 510 kWh per cow per year and 0.064 kWh per kg of milk per year. Although, a study conducted in 41 German dairy farms shows an average EUI of 90 kWh per tonne of milk, a value that is 23% higher of the present results [26
]. The EUI of 44 kWh per tonne of milk obtained from Sardinian dairy farms [24
] is lower than the results of the present study. The differences in farm mechanization level and milk yield expressed per raised head significantly affect the EUI.
Moreover, diesel fuel requirements related with on-farm and field operations (Figure 2
), feed preparation and distribution represent 39% of the overall diesel fuel utilization; field activities associated to crop cultivation accounted for 38%; slurry treatment for 16%; and irrigation pumping for 7% of the total.
Feeding operations were also evaluated by Kraatz (2012) [41
] in German dairy farms, showing higher levels of input requirement in feed supply corresponding to about 50% of the on-farm energy intensity.
Diesel usages for land operations are allocated into four phases which contributed to the total consumption in the following way: 15% for manure distribution; 31% for soil preparation; 9% for sowing, crop treatments and fertilization; and crop harvesting and transportation represent the most demanding procedures, necessitating 44% of the total (Figure 2
). However, the purchase of feed from the outside of the farm may occur. This aspect has been considered in Part 2 [42
] of this paper-series since animal feed represents an indirect energy items.
The most representative crop selections in the investigated farms were grass and legume crops for forage production (52%), maize for corns silage (33%) and cereals for the production of grains (26%).
Additional assessments about diesel consumption were assessed for each cultivated crop. Obviously, crops which required more mechanized actions accounted for higher fuel demand: 110 kg ha−1 for hay production; 133 kg ha−1 for hay silage; 134 kg ha−1 to harvest cereal grains; 163 kg ha−1 for alfalfa products (hay and silo hay); and, the largest value, 171 kg ha−1, related to corn silage.
When diesel fuel requirements per land extent (ha) were reported to the associated crop yield, stated as tonne of harvested Dry Matter (DM), the assessment revealed reversal outcomes. In fact, corn silage and alfalfa crops held the highest diesel fuel consumptions per cultivated hectare (Figure 3
), but with the lowest amounts of diesel requirements per unit of product harvested (11.5 and 17.8 kg tDM−1
, respectively). The production of cereal grain presented the highest consumption of fuel per unit of product harvested (about 68 kg tDM−1
) since the production yield of cereal grain was commonly low (from 1.8 t ha−1
to 3.1 t ha−1
). Grass forage and spring silage required a consumption of 26.3 and 26.6 kg of diesel per tonne of DM produced, respectively. These results were also expressed as useful energy based unit (g of diesel per MJ), analyzing the consumption of diesel fuel for the respective energy content of each feed [43
], expressed in terms of megajoules of metabolizable energy per kilogram of dry matter (MJ/kg DM). Thus, corn silage and alfalfa showed, respectively, 1.10 and 1.98 g of diesel MJ−1
, while hay silage and hay required about 2.21 and 2.92 g of diesel MJ−1
, respectively. The highest value was obtained for the production of grains with about 5.68 g of diesel MJ−1
of product harvested.
3.2. Carbon Dioxide Emissions
The yearly CO2
emissions related to electricity consumptions accounted for 201 kg CO2
and 30 kg CO2
-eq per tonne of FPCM (Table 2
The yearly emissions from diesel fuel combustion accounted for 819 kg CO2-eq per lactating cow and 125 kg CO2-eq per tonne of FPCM per year. This index accounted for 1162 kg CO2-eq ha−1 per year when referred to the cultivated land extent. Furthermore, the emission associated to the utilization of LPG were negligible: 1 kg CO2-eq per tonne of FPCM and 7 kg CO2-eq per lactating cow.
The on-farm average emission of CO2-eq, ascribable to the overall energy usages, was around 54 tonnes of CO2-eq per year, which corresponded to 1027 kg CO2-eq per lactating cow and 156 kg CO2-eq per tonne of milk.
Lower levels of carbon dioxide emissions, related to energy consumptions, were found [24
] in a study conducted in 20 Italian conventional dairy farms emitting 834 kg CO2
-eq per lactating cow and 85 kg CO2
-eq per tonne of milk sold. Milk yield and herd size affect carbon dioxide emission indices when emissions are reported per unit of milk sold.
The overall CO2
-eq emissions associated to diesel fuel and electricity ascribed to each on-farm activities is shown in Figure 4
. Diesel consumptions represent the most pollutant source, accounting for 72% of the total carbon emissions, while electricity represents about 27%. Feed management and land operations contribute each for 31% of the total energy carbon footprint followed by slurry management (9%), while electricity requirements accounted for a lower quantity of the overall CO2
emissions. Milk harvesting and refrigeration both denote 4% of CO2
emissions, while water pumping and water heating amounted about 3% each.
Further analyses were carried out to identify more accurate energy related indices per farm characteristics, as herd size and annual milk yield per lactating cow. As shown in Table 3
, the energy consumptions and the associated emissions of CO2
-eq were classified based on four categories of herd size, from less than 50 heads to over 200 heads.
The group “50–100” held the highest number of farms (100), whereas only 44 farms were located in the group “greater than 200”. Larger farms, with higher yield of milk (tonnes LC−1 per year), were associated with lower levels of CO2 emissions per unit of FPCM: 10 kg CO2-eq per 100 kg FPCM per farms with more than 200 heads versus 24 kg CO2-eq per 100 kg FPCM in farms with fewer than 50 heads. It resulted that larger farms were capable to produce milk emitting 2.4 times less CO2 than smaller farms in terms of emissions from on-farm direct energy consumption.
Global results were also grouped based on the annual milk yield production per lactating cow, as shown in Table 4
; where direct energy consumptions and associated emissions of CO2
-eq were referred to four categories, from less than 5 t of milk to over 9 t of milk per cow.
The majority of farms were located in the class “7 to 9 t of FPCM” and “≥9 t of FPCM” groups, 88 and 85, respectively, while 40 farms held to the group “less than 5 t of FPCM”. The results of this analysis indicated that farms with higher milk yields (milk tonnes·LC−1) were related with higher herd dimension.
The analysis demonstrated that the direct energy carbon footprint was higher in farms belonging to the lowest milk yield class: 36 kg CO2-eq per 100 kg of milk in farms with yield lower than 5 t per cow; 16 kg CO2-eq 100 kg FPCM−1 in farms belonging to yield class between 5 and 7 t; 12 kg CO2-eq 100 kg FPCM−1 in farms with milk yield between 7 and 9 t and reaching the minimum value of 10 kg CO2-eq 100 kg FPCM−1 when milk yield was greater than 9 t.
Dairy farms which held higher level of milk production were capable to produce milk emitting around 3.6 times less CO2 than farms with lower milk yield (group “>9” vs. group “<5”).
Characterization and typification of mechanization, structural and energy profiles of dairy farms were observed and discussed by Todde et al., in 2016 [18
], underlining how the high technological investments, the locations and the management significantly affect small and large size farms.
In this two-part series, a comprehensive analysis of direct and indirect (Part 1 and Part 2) energy requirements and related carbon footprint of conventional dairy farms has been carried out. The overall results are reported in Part 2 [42
], where total direct and indirect energy demand, expressed in GJ per farm, has been shown as well as the related carbon emissions.