Recent research has shown that the carbon footprint (CF) of milk produced on Irish dairy farms is approximately 1.23 kg CO2eq. per litre of fat and protein corrected milk. The objective is evaluate the feasibility of a Low Carbon (LC) System of milk production where emissions per litre of FPCM are substantially lowered, while maintaining current levels of milk output per ha and profitability.
Two dairy systems were established at Solohead Research Farm (52° 51' N; 08° 21' W) in January 2017 and will run for three years: LC and control and each system with an overall farm stocking density of 2.5 cows per ha. The entire herd of 130 spring-calving cows at Solohead was divided into seven main groups on the basis of lactation number. The cows with the highest economic breeding index (EBI) in each group were selected for the LC herd of 24 cows. The remainder of the herd was then divided into seven main groups as above and then sub-divided into sub-groups of four on the basis of calving date. From within each subgroup, one cow was randomly assigned to the control with the same number of cows per lactation group as the LC herd.
Annual fertilizer N input was be 150 kg/ha on the LC system, which also relies on biologically fixed N in association with white clover in the sward, and 280 kg/ha on the control system, which is the maximum allowed under nitrates directive regulations at this stocking density. Fertilizer N was applied in the form of NBPT treated urea to the LC in February, March and August and September, and as urea between February and April and as calcium ammonium nitrate from May to September to the Control. Slurry produced during housing was applied back in equal volumes to both systems using a trailing shoe for LC and a downward facing splash-plate for control (which represents current common practice on farms).
To date milk production on the LC system was 6076 L per cow or 517 kg of milk fat and protein (MS) compared with the control; 5704 L per cow or 471 kg MS. The LC system has given higher output with lower inputs. Field measurements of N2O emissions from both systems are ongoing. The CF of both systems will be determined using life cycle assessment in due course. A PhD student was recruited for this project in June but resigned in November.