The effect of grass yield on economic and environmental performance of dairy farms

In this study we explored the importance of grass yield for the economic and environmental performance of
dairy farms that apply grazing. A whole-farm optimization model was used to analyse the effect of grass yield
on labour income, nitrogen (N) and phosphate (P2O5) losses and greenhouse gas emissions (summed in kg
CO2-equivalents per kg fat-and-protein-corrected milk (FPCM)). The model contains all relevant activities
and constraints present on Dutch dairy farms and represents a typical farm in 2016. The objective function of
the model maximizes labour income. The model was used to optimize farm management for a dairy farm of
50 ha with different grass yields. Data on grass yields were derived from 23-26 Dutch dairy farms that apply
grazing for the years 2012-2014. Grass yield varied between farms from 34.5 to 69 MJ NEL/ha (NEL = net
energy for lactation) at the same fertilization level of about 225 kg N/ha. The model results show that, based
on the lowest and highest grass yield, labour income varied from -€9,300 to €23,700 yr-1. A higher grass yield
led to a higher labour income mainly due to lower costs for feed purchases. A higher grass yield also resulted
in lower on-farm surpluses, i.e. 181 kg N/ha and 7 kg P2O5/ha (highest grass yield), compared to 245 kg N/
ha and 22 kg P2O5/ha (lowest grass yield), and lower greenhouse gas emissions, i.e. 970 kg CO2-eq/kg FPCM
(highest grass yield) compared to 1,047 kg CO2-eq/kg FPCM (lowest grass yield). Results show the importance
of grass yield to improve the economic and environmental performance of dairy farms. To identify options
to increase grass yields further research will focus on quantifying relations between grassland management
and grass growth, utilization and intake on modern dairy farms.