Phosphorus dynamics in soils amended with acidified pig slurry and derived solid fraction

A laboratory incubation was performed in soil amended with acidified and non acidified pig slurry and derived solid fraction to assess changes in mineral and organic phosphorus (P) resorting to the Hedley fractionation. Five treatments were considered: non acidified pig slurry (S), acidified pig slurry (AS), non acidified solid fraction (sF), acidified solid fraction (AsF) and a control (soil only). Slurry and derived fractions were applied at a rate of 120 mg P kg− 1 dry soil to a sandy soil and P fractionation in soil was followed over 182 days using a modified Hedley fractionation procedure.At the beginning of the incubation, the more labile P fraction (cation–anion exchange resins membrane fraction — CAEM) had the highest amount of slurry derived P. Application of AS increased in 87.4% the more labile P fraction relative to soil only, whereas application of S led to an increase of only 75.8%. Increases in the other inorganic fractions (NaHCO3 Pi, NaOH Pi, NaOH u.s. Pi and HCl) were also observed after soil application of S and AS, even if at a lower extent, but no effect was observed in the organic P fractions.Mineralization of occluded organic P and the subsequent increase of labile and plant available fractions in soil increased over time. The NaOH and NaOHu.s. organic fractions decreased significantly during the incubation whereas there was a significant increase in the NaHCO3 Po, NaOH Pi and the NaHCO3 Pi fractions.At the beginning of the incubation, significant differences were observed between S and sF treatments, particularly in labile Pi (CAEM). The solid fraction presented lower increases (70.8%) when compared to the slurry (75.8%). Conversely, for the NaHCO3–Pi fraction higher increases were registered in the solid fraction, 9.8%, when compared to the slurry, 4.3%. Separation of acidified slurry resulted in non significant differences among the most labile Pi fractions.

► Soil incubation with pig slurry increased predominantly the most labile Pi fraction.
► Pig slurry application had a small impact on soil organic P.
► Slurry acidification promotes increases of the most labile soil Pi fractions.
► The effect of acidification persists after solid fraction separation.