NITROGEN TURNOVER ON ORGANIC AND CONVENTIONAL MIXED FARMS

Separate focus on crop fertilization or feeding practices inadequately describes nitrogen (N) loss from mixed dairy farms because of (1) int eraction between animal and crop production and between the production system and the manager, and (2) uncertainties of herd N production an d crop N utilization. Therefore a systems approach was used to study N turnover and N efficiency on. 16 conventional and 14 organic private Danish farms with mixed animal (dairy) and crop production. There were significant differences in N surplus at the fan level (242 kg. N/ha. vs. 124 kg. N/ha. on conventional and organic dairy farms respectively ) with a correlation. between stocking rate and N surplus. N efficienc y was calculated as the output of N in animal products divided by the net N import in fodder, manure and fertilizer. N turnover in herd and individual crops calculated on selected farms showed differences in or ganic and conventional crop N utilization. This is explained via a dis cussion of the rationality behind the current way of planning the ''op timum fertilizer application'' in conventional agriculture. The concep t of marginal N efficiency is insufficient for correcting problems of N loss from dairy farms. Substantial reductions in N loss from convent ional mixed dairy farms is probably unlikely without lower production intensity. The concept of mean farm unit N efficiency might be a way t o describe the relation between production and N loss to facilitate re gulation. This concept is linked to differing goals of agricultural de velopment-i.e. intensification. and separation vs. extensification and integration. It is discussed how studies in private farms-using organ ic farms as selected critical cases-can demonstrate possibilities for balancing production and environmental concern.