Relationship between nourishing performance, carbon footprint and nitrogen balance in Walloon dairy

The objective of this study was to highlight, in 21 dairy farms, the correlations between farm structure and 3 environmental indicators: the nourishing performance index (NPI- number of people fed by animal protein per hectare), net carbon footprint of milk (CF -CO2 equivalent per litres of energy corrected milk; ECM) and the excess nitrogen balance (NB -kg of nitrogen per hectare). To conduct this study, the CAP’2ER tool developed by the Institut de l’Elevage (IDELE) in France was used. More than 150 data from 2018 were collected during interviews led with 21 dairy farmers from Wallonia (Belgium). The indicators of interest here are NPI, CF and NB. Milk yield (kg) was converted in ECM using the following values: fat%: 4% and protein%: 3.3% milk. The CO2 conversion factors are estimated at 25 for methane (CH4) and 298 for nitrous oxide (N2O). A correlation matrix was run on SAS (SAS 9.3) between the selected environmental indicators and the following parameters: the agricultural surface of the farm (ha), the number of dairy cows/farm and ECM produced per cow. Regarding NPI, we noted a positive correlation with the number of cows per farm, ECM per cow, NB per ha and CF per kg ECM. This latter observation was not confirmed when expressed by ha. The higher NPI, the higher high producing cows on the farm. The highest NPI was observed at highest nitrogen surplus per ha and the highest milk CF. For the excess nitrogen balance, we observed a positive correlation with the number of cows, ECM per cow and milk CF but not with the area. The more there is a nitrogen balance surplus, the more cows produce more on the farm. The more excess of nitrogen per ha there is, the higher is the milk CF. Milk CF did not correlate with area, number of cows per farm or milk production per ha, but did with NPI and excess NB per ha. In conclusion, the NPI of a farm, the excess nitrogen balance per ha and the net carbon footprint of milk demonstrated positive correlation between each other, in these 21 Walloon farms. However, it is interesting to note that the CF per kg ECM is not influenced by farm factors like the surface, the milk yield per cow and the number of cows per farm