The performance of a white clover based dairy system in comparison with a grass/fertiliser-N system. II. Animal production, economics and environment

The performance of a white clover based dairy system in comparison with a grass/fertiliser-N system was studied during three years. Both systems had 59 cows, plus young stock, on an area of 40.6 ha for grass/clover and 34.4 ha for grass/fertiliser-N. During the grazing season, the cows in both groups were supplemented with 3.5 kg concentrates day-1. The daily Fat and Protein Corrected Milk (FPCM) production was 25.7 and 26.5 kg cow-1 for grass/fertiliser-N and grass/clover, respectively. The difference in milk production occurred from July onwards. Despite preventive measures in the grass/clover system, bloat occurred several times between August and October. During the housing season, cows received ad libitum grass or grass/clover silage with 6 kg concentrates cow-1 day-1. Although the intake of grass/clover silage was consistently higher, there were no differences in milk production. The grass/clover system had a lower N surplus, but this was related to the lower intensity of the system. The overall N utilisation was 25% in both systems. The average nitrate concentration in drain water, measured on a selection of fields, was 26 and 28 mg 1-1 for grass/fertiliser-N and grass/clover, respectively. The nitrate concentrations in drain water from grass/clover fields were positively related with the clover content in the sward. The energy use of the grass/clover system was 15% lower than that of the grass/fertiliser-N system, with the fertiliser use as the main source of difference. Compared to the grass/fertiliser-N system, the gross margin per cow was slightly higher for grass/clover, but the gross margin per ha was 10% lower for grass/clover. Considering agronomic and environmental aspects only, white clover based dairy systems are a viable option for the future, but from a financial viewpoint the use of white clover will be restricted to systems which produce approximately 12 t FPCM ha-1 year-1 or less