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Management Options to Reduce Phosphorus Leaching from Vegetated Buffer Strips

Hille, Sandra, Graeber, Daniel, Kronvang, Brian, Rubæk, Gitte H., Onnen, Nils, Molina-Navarro, Eugenio, Baattrup-Pedersen, Annette, Heckrath, Goswin J., Stutter, Marc I.
Journal of environmental quality 2019 v.48 no.2 pp. 322-329
agricultural land, ammonium, conservation buffers, harvesting frequency, leaching, models, phosphorus, risk, soluble phosphorus, surface water, topsoil, vegetation
Vegetated buffer strips (VBS) between agricultural areas and surface waters are important retention areas for eroded particulate P through which they may obtain critically high degrees of P saturation imposing high risk of soluble P leaching. We tested topsoil removal and three harvesting frequencies (once, twice, or four times per year) of natural buffer vegetation to reduce P leaching with the aim to offset erosional P accumulation and high degrees of P saturation. We used a simple numerical time-step model to estimate changes in VBS soil P levels with and without harvest. Harvesting offset erosional deposition as it resulted in an annual ammonium oxalate-extractable P reduction of 0.3 to 2.8% (25-cm topsoil content) in soils of the VBS and thus, with time, reduced potential P leaching below a baseline of 50 μg L⁻¹. Topsoil removal only marginally reduced potential leaching at two sites and not anywhere near this baseline. The harvest frequency only marginally affected the annual P removal, making single annual harvests the most economical. We estimate 50 to 300 yr to reach the P leaching baseline, due to substantial amounts of P accumulated in the soils. Even in high-erosion-risk situations in our study, harvesting reduced soil P content and the P leaching risk. We suggest harvesting as a practical and efficient management to combat P leaching from agricultural VBS, not just for short-term reductions of dissolved P, but also for reductions of the total soil P pool and for possible multiple benefits for VBS.