Phytoextraction of phosphorus-enriched grassland soils

Area of Science:

• Agricultural Science
• Environmental Science
• Soil Science

Background:

• High phosphorus (P) levels in Dutch agricultural soils lead to excessive P loss into surface waters.
• Current manure policies are insufficient to meet European Water Framework Directive (2015) water quality standards.
• Additional strategies are required to mitigate P loading into surface waters.

Purpose of the Study:

• To evaluate the effectiveness of phytoextraction as a method for reducing soil P concentrations in agricultural grasslands.
• To confirm greenhouse findings on zero P application with field data.
• To assess the impact of prolonged P mining on soil P pools and P mobility.

Main Methods:

• A five-year phytoextraction field experiment was conducted on four grassland sites with varying soil types (sand, peat, clay).
• Phytoextraction plots received zero P and 300 kg N ha⁻¹ yr⁻¹, with harvested grass removed.
• Soil solution P concentrations and soil solid phase P pools (water-extractable P(w), ammonium lactate-extractable P-AL) were analyzed over time.

Main Results:

• Zero P application over five years significantly reduced P concentrations in the upper soil layer (0-0.05 m) by 30-90%.
• P reduction diminished with increasing soil depth.
• Weakly bound P pools (P(w), P-AL) showed the largest decline (10-60%), while strongly bound P forms decreased minimally.

Conclusions:

• Phytoextraction is an effective strategy for rapidly reducing soil P concentrations in the topsoil layer of grasslands.
• Sustained P mining through phytoextraction can substantially decrease P leaching and runoff.
• This method offers a viable approach to improve water quality by managing soil P levels.