In the development of the Dutch National Ecological Network, many hectares of arable land are converted to nature areas to protect plant and animal species. This encompasses development of species-rich grasslands. On former agricultural land on sandy soils, this development is often hampered by relatively high phosphorus (P) levels, which also cause eutrophication. Standard practices to decrease the amount of P are either topsoil removal or long-term mowing of low-yielding established grassland. Both methods have disadvantages, and there is a need for additional techniques. As an alternative, phytoextraction ("mining") of soil P has been proposed. We tested a new technique of mining without mineral N fertilizer by cropping an intensively mown grass-clover with potassium (K) fertilization that could potentially be used as cattle feed. A long-term field experiment was conducted, comparing soil P removal by grass-clover swards with and without supplementary K fertilization on a sandy soil. During the experiment, which ran from 2002 to 2009, soil P levels and nutrient contents of grass-clover were measured, and P and K balances were calculated. Our results show that grass-clover with K fertilization removed excess soil P (also at lower P levels) at a relatively high rate (34 kg P ha −1 yr −1, significantly higher than without K fertilization; P < 0.05) and produced reasonable yields of grass-clover. Our P balance suggested reduced leaching from the topsoil during this experiment. For nature restoration in agricultural areas, this tool opens many possibilities.
Phytoextraction of Soil Phosphorus by Potassium-FertilizedGrass-Clover Swards Bart G. H. Timmermans* and Nick van Eekeren O n a global scale, awareness is growing that the amount of phosphorus (P) available for fertilizer production and crop growth is limited and that a potential P crisis is looming (Abelson, 1999;Herring and Fantel, 1993). At the same time, some western European countries, including The Netherlands, are having problems with excessive P levels in agricultural soils. In The Netherlands, an extensive network of green corridors, called the National Ecological Network, is being implemented (Bakker et al., 2015). The idea originated in the 1990s and aims to protect species of animals and plants. The National Ecological Network encompasses various types of nature areas. In this context, many hectares of arable land have been transferred to nature reservations, and many more are planned (originally the plan was to implement 728,500 ha in 2018, but the ambition has decreased somewhat in terms of area and planning). In most of these former agricultural soils, long-term applications of fertilizers and animal manure in the past, which were stopped after land acquisition by nature organizations, have led to an imbalance in the levels of soil nutrients. Although these soils often have high levels of relatively immobile soil P, the more mobile nitrogen (N) and potassium (K) have often become suboptimal according to agricultural standards because of ...