Long term studies (1989-2012) of soil nutrients and ley yields on a Norwegian organic dairy farm (Tingvoll experimental farm) showed that soil nutrient concentrations decreased over time after conversion. A potential decline in yields due to reduced nutrient concentrations will be difficult to detect, because of large annual variations in yield levels. The sustainability of the nutrient management on the farm should be considered, aiming at keeping soil nutrient concentrations above levels impacting negatively on the yields
