Exploratie van de variabiliteit in N-excretie bij melkvee voor de monitoring van regionale N-balansen

Animal nutrient excretion is a key factor in manure legislation and environmental monitoring. As it can not be measured directly, total emissions are usually estimated using flat-rate coefficients. This is also the case for dairy cows, whose productivity has constantly increased over the past decades. It thus seems odd to use constant, flat-rate coefficients for N excretion/cow, instead of linking it to milk production/cow. For environmental monitoring, however, the problem is in getting milk production data at farm level. As milk production in turn is closely correlated to feed uptake, estimating nutrient excretion indirectly, by means of fodder acreage available, was explored. A significant relation was found between N excretion per cow and the grassland and maize acreages per cow, in which the effect of grassland acreage is over 2,5 times larger than that of maize. Although average N excretion has increased to 118 kg N/(cow x year) on specialised dairy farms, at the regional level, the cows’ increasing productivity predominates, resulting in an increased eco-efficiency.