The Republic of Ireland was one of a minority of EU member states to include direct controls on chemical phosphorus (P) fertilisers in its EU Nitrates Directive National Action Plan, first introduced in 2006. This study estimates farm gate phosphorus balances and use efficiencies across 150 specialist dairy farms over the seven year period since these controls were introduced (2006-2012) using nationally representative data. Results indicate that P balances declined by 50% over the study period from 11.9 in 2006 to 6.0kgha-1 in 2012. This decline was driven by a reduction in chemical fertiliser imports of 6.5kgha-1. This is equivalent to a reduction of 281kg of P and represents a cost saving of €812 per annum across the average farm. Phosphorus use efficiency also improved over the period from 60% in 2006 to 78% in 2012, peaking in 2011 at 88.3%. This was achieved while increasing milk solids output per hectare and per cow. Results of a random effects panel data model indicated that P balance and use efficiency are significantly influenced by factors such as fertiliser prices, stocking rates, land use potential, use of milk recording technology, contact with extension services and rainfall patterns.