Recession of phosphorus and nitrogen concentrations in tile drainage water after high poultry manure applications in two consecutive years

High application rates of poultry (Gallus gallus domesticus) manure can impair drainage water quality through enhanced leaching of phosphorus (P) and nitrogen (N). In two years with application rates of broiler chicken manure corresponding to 99 and 79kgPha−1year−1 to a tile-drained field with loamy soil in SW Sweden, mean concentrations of dissolved reactive P (DRP) were significantly higher (p<0.05) elevated in peak water flows in the two winter periods than in 19 previous years without manure application of any kind. With the water sampling strategy used, this effect was observed 5 and 4 months after application, when 160 and 140mm of water, respectively, had discharged. Flow recession of distinct peak flows was illustrated as exponential decay to time, with half-life 48h, while recession of elevated DRP concentrations had approximately 2h half-life. In the following 12 years, only moderate amounts of mineral P were applied (on three occasions) to this topsoil with 11% degree of P saturation measured in acid soil extract (DPS-AL). Mean DRP concentrations in peak, base and intermediate flow in that period were moderate, i.e. similar to those before manure application. In contrast, high concentrations of nitrate N (NO3-N) in peak, base and intermediate flows occurred in the 8-year period following manure application. Mean NO3-N concentration in peak flows decreased approximately linearly, by 5.6μgL−1, for every mm of total water discharge. Thus poultry manure should not be applied in repeated high loads in order to avoid the risk of enhanced P leaching losses during subsequent peak flows. Furthermore, N leaching losses during peak and base flow conditions can persist for longer than a 5-year crop rotation and were shown here to recede at a slower relative rate than P.