Phosphor-Bodenbilanzen von Grünland- und Ackerflächen auf einem ökologischen Milchviehbetrieb

Summary in the original language of the document

Mineral phosphorus (P) fertilizers from fossil reserves are finite which puts agriculture at risk of losing soil fertility. This study calculates P soil balances of an organic dairy farm in Northern Germany to focus on potentials and variations in the farm P cycle. P flows were different between the years because yield levels and amount of manure application varied. Different plant species showed different P export which depended mainly on biomass export. This can also be seen as their site specific mobilization potential. The highest mean P export between 2010 and 2012 was measured with maize (mean 30.4, range 17.7-38.2 kg P ha-1 a-1) and grass-clover (mean 23.7, range 17.3-29.5 kg P ha-1 a-1). By grazing, permanent grassland showed a mean P mobilization from soil P of 15.9 kg ha-1 a-1. The annual soil P balance was -7.96 kg P ha-1 (range -6.16 to -9.3 kg P ha-1) at permanent grassland and -11.1 kg P ha-1 at arable land (range -1.5 to -17.7 kg P ha-1). Because of the high ranges it is reasonable to analyze a few years to get a better view on P flows at farms. High PCAL values from historical fertilizer inputs can be seen as a P source in short term and can especially be mobilized by permanent grassland. It is necessary to change the P flows into a more sustainable way before the P gap cannot be closed by soil reserves anymore and P deficit will limit plant growth.