Phytoextraction of soil phosphorus by grass-clover as a synergy between agriculture and nature restoration

In the development of the Dutch National Ecological Network, arable land is converted to nature areas. This development is often hampered by high phosphorus (P) levels. Standard practices to decrease the amount of P are either top-soil removal or mowing of low yielding established grassland. Both methods have their disadvantages and there is a need for additional techniques. As an alternative, phytoextraction (‘mining’) of soil P has been proposed. We tested a phytoextraction by cropping an intensively mown grass-clover with potassium (K) fertilisation, which 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, K fertilization on a sandy soil. Our results show that grass-clover with K fertilization is an effective method that removed excess soil P at a relatively high rate (34 kg P ha^-1 year^-1, significantly higher than without K fertilization, P<0.05). Therefore phytoextraction can be an important synergy between agricultural production and nature restoration.