Grass clover swards : A way out for Dutch dairy farms under legislative pressure?

Summary

CONTEXT: Policy measures have been taken to improve water quality in the Netherlands. These measures include the abolishment of derogation, which allowed dairy farmers to go beyond the maximum application of 170 kg nitrogen (N) from organic fertiliser per hectare, and additional measures of the 7^th Nitrates Action program. Grass-clover swards, known for their symbiotic N fixation, could be a strategy to deal with stricter N policies and can potentially improve the environmental sustainability and economic viability of Dutch dairy farms. OBJECTIVE: The aim was to assess the effects of stricter N policies on the farm structure, farm income and environmental performance of a representative Dutch dairy farm on a sandy soil, and to assess the effect of incorporating perennial ryegrass-red white clover (GC_rw) swards and perennial ryegrass-white clover (GC_w) swards into the grassland management of this farm using a model. METHODS: A whole-dairy farm linear programming model was used with the objective function to maximize farm income. The model was combined with a farm nutrient balance and life-cycle assessment to determine the impact on nutrient surpluses and greenhouse gas emissions. We modelled a representative Dutch dairy farm with perennial ryegrass (PRG) before and after implementing stricter N policies. Thereafter, the implications of implementing GC_rw and GC_w swards was assessed. RESULTS AND CONCLUSIONS: Including the policy measures increased the share of maize land (+12%), decreased the number of dairy cows (-9 cows), reduced farm income (€-18,858 yr^-1), led to similar greenhouse gas emissions (∼800 kg carbon dioxide equivalents (CO₂-eq) per tonne (t) of fat and protein corrected milk (FPCM)), and resulted in a lower N surplus (-65 kg ha^-1 yr^-1) and phosphate surplus (-4.4 kg ha^-1 yr^-1) for a scenario with only PRG. The use of GC_rw and GC_w swards could partly compensate for the reduction in farm income (€+9,255 up to +14,706 yr^-1). A combination of PRG, GC_rw and GC_w resulted in the highest farm income. The use of grass-clover swards only had the most positive effect on greenhouse gas emissions (767 kg CO₂-eq t^-1 FPCM) and N surplus (113 kg ha^-1 yr^-1). Sensitivity analysis showed the importance of yields and feed characteristics on the obtained farm income. SIGNIFICIANCE: Grass-clover swards might partly compensate for the negative economic consequences of stricter N policies for Dutch dairy farms. Furthermore, implementing grass-clover swards reduced the GHG emission intensity of milk, but not always nutrient surpluses per hectare of farm land.