White clover utilisation on dairy farms in the Netherlands

Keywordsbotanical composition, carbon, cutting frequency, dairy system, energy, fixation, gross margin, herbage quality, milk production, MINAS, nitrate leaching, nitrogen, nutrient balance, nutrient efficiency, perennial ryegrass, phosphorus, rotational grazing, soil, strategic nitrogen application, sward utilisation, white clover The present efforts to reduce the nitrogen (N) losses on dairy farms have reduced the use of fertiliser N and consequently renewed interest in white clover ( Trifolium repens L.).The general objective of this thesis was to provide a scientifically sound basis for the use of white clover on dairy farms in the Netherlands. The research consisted of a system comparison between a traditional grass/fertiliser-N system and a new grass/clover system. The aim was to design and demonstrate an agronomically, environmentally and economically sound white clover-based dairy system, and to identify potential problems with the utilisation of white clover in dairying. Simultaneously, specific research questions on processes within the new grass/clover system were addressed in separate field experiments with detailed measurements. The field experiments aimed to quantify the potential herbage yield and herbage quality of mixed swards, under a range of management practices, such as N and phosphorus (P) application, and cutting and grazing management.Both the clay and sandy soils in the experiments showed a good potential for perennial ryegrass/white clover swards with average annual DM yields of 13.3 t ha -1, respectively. The yields were among the highest recorded for unfertilised mixed swards in the Netherlands.The year-round application of N is not considered to be economic, but N can be used effectively on grass/clover swards if its use is restricted to spring application. This so-called 'strategic' application of N increases the DM yield in the first cut, only temporarily reducing white clover content in the sward. Phosphorus application did not increase clover yield. The results suggested a negative effect of P application on clover proportions in mixed swards.The results of the system experiment demonstrated the potential of mixed swards of perennial ryegrass and white clover in a rotational grazing and cutting system. In a field experiment, the average annual DM yields were 13.4 t ha -1with rotational grazing and cutting, compared to 12.8 t ha -1with cutting only.The herd of the white clover based system produced 85% of the milk yield per ha of the grass/fertiliser-N based system. The N utilisation at farm level was nearly 25% in both systems, and there was no difference in the average nitrate concentrations in drain water. The total energy use of the clover based system was 15% lower than that of the fertiliser-N based system.The agronomic and environmental performance show that 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 milk ha -1year -1or less. However, within the MINAS system more intensive farms can benefit from a partial conversion to grass/clover. The prospects for white clover will certainly be affected by the developments in the nutrient policy.