Phosphorus offtake and optimal phosphorus fertilisation rate of some fodder crops and potatoes in temperate regions
Agrokémia és Talajtan
I ntrod uctio n Phosphorus (P) is a major factor in eutrophication of surface waters as P is typically the limiting factor for algal blooming in freshwater systems (STERNER, 2008) . Negative environmental effects are the reduced biodiversity of aquatic ecosystems and the decline in water quality. The algae produce toxic substances that kill fish and cause diseases in animals and humans. In some European countries agriculture has become the main P source in water bodies (KRONVANG et al., 2005) .
... ANG et al., 2005) . In Flanders, the share of agriculture in total P load to ground-and surface waters was estimated to be 44% in 2011 (ANONYMOUS, 2015c). The attention of the Manure Action Plan (MAP) legislation is shifting from nitrate to P, as the average ortho-P concentration in the MAP network surface water is about 0.4 mg ortho-P·l -1 (PEETERS, 2014) which is about four times higher than the environmental limit of 0.07-0.14 mg ortho-P·l -1 , depending on the type of watercourse (ANONYMOUS, 2010). The diffuse P losses into ground-and surface water from agriculture in northwest Europe are caused by the historically large P fertiliser additions resulting in a large acreage of soils with a high P content (KRONVANG et al., 2005) . As P fertilisation rates affect the soil P content, one of the most commonly followed strategies to reduce P losses from agricultural soils is a rational P fertilisation rate. Fertilisation advice should envisage an equilibrium maintenance P fertilisation rate for fields with optimal soil P content, with differentiation for other fields taking into account the soil P content. Phosphorus fertility categories, as a function of soil P values, are used in 25 European regions, studied by JORDAN-MEILLE et al. (2012) . In this paper, up-to-date information is given on the phosphate (P 2 O 5 ) removed by cut grassland without clover, silage maize or potatoes and this is confronted with the maximum allowed P fertilisation rates in Flanders' new MAP in the framework of the implementation of the Nitrates Directive and Water Framework Directive.