NITROGEN BALANCE IN AN INTENSIVELY UTILISED DAIRYFARM SYSTEM

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Abstract
4 N balance representative of intensive dairyfarming is presented, based on a dynamic model integrating information on N flows for this system. Losses of about 50% of N ingested by animals lead to a negative N balance with predicted annual losses of 40 kg N/ha. Addition of 100 kg fertiliser N is predicted to reduce the N deficit by 13 kg/ ha, with increased leaching and lower clover fixation reducing the effectiveness of applied N. Increasing the level of utilisation from 70 to 75% of herbage produced, by increasing stocking rate, is predicted to increase annual losses to about 60 kg/ ha. Additional losses from excreta and reduced cycling of dead plant material contribute to the increased deficit. The implication of losses of this order to farm productivity are discussed.

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