Nutrient leaching from clay soil monoliths with variable past manure inputs.

Overall, arable soils in Sweden are currently generally close to phosphorus (P) balance, but excessive P accumulation has occurred on animal fur farms, i.e., those rearing mink ( Mustela vison) and foxes ( Alopex lagopus and Vulpes vulpes). Manure P from these farms has sometimes regarded as sparingly soluble. Laboratory lysimeter topsoil trials with simulated rain demonstrated that potential leaching of P in dissolved reactive form (DRP) can be very high, even for heavy clay (50%-65%) soils. The Swedish/Norwegian soil test P-AL (soil P extracted with acid NH₄ lactate, AL) proved useful as a potential indicator of DRP leaching risk (regression coefficient [ R<?h.3>²] = 0.89) from fur farms. The upper 5-cm soil layer, with 190% higher (median) soil P status than the 5-20 cm layer, was the major source of potential DRP leaching through soil columns at the site, despite having been under grass or green fallow for the past 8 y. In percolate from topsoil lysimeters, DRP concentration increased by 0.29 mg L^-1 after the long-term manure application but only by 0.14 mg L^-1 after the single slurry application when compared to no addition of slurry. Therefore, the build-up to a high soil P status due to the long-term application of mink manure was more important than a single application of pig slurry at a rate corresponding to 22 kg P ha^-1 with respect to soil leachate DRP losses in this lysimeter study. The study stresses the importance of precision farming, in which the amount of slurry-P applied is based on testing the already existing soil P content. [ABSTRACT FROM AUTHOR]