Phosphorus Mobility in Soil Columns Treated with Dairy Manures and Commercial Fertilizer.

The concentration of animal production in some areas of the United States has led to concern about the environmental fate of manure derived phosphorus (P) in soils.  A column study was conducted to quantify P leaching in a calcareous soil treated with mono-ammonium phosphate (MAP), two solid dairy manures (D1S and D2S) and two liquid dairy manures (D1L and D2L).  A control with no P application was also included. Treatments were applied at 166 kg P/ha to columns containing 20 cm of a Warden fine sandy loam (coarse-loamy, mixed superactive, mesic Xeric Haplocalcids) in a completely randomized design with four replications and housed in a climate controlled growth chamber. Simulated irrigation water was added to the columns at a rate of 450 ml during thirteen events over a nine-week period with leachate collected, volume recorded, and concentrations of total organic C (TOC) and total P (TP) determined for each event.  At the end of the leaching events the soil from each column was collected in 2.5 cm increments to 20 cm, air dried, ground, and analyzed for TP, total Ca, total Fe, total Mn, water soluble P (WSP), and total carbon (TC). The masses of TP and TOC in leachate were in the order D1L = D2L > MAP = D1S = D2S = Control. There was a positive linear relationship between the cumulative mass of TOC and cumulative mass of TP lost in leachate over all manure treatments (r² = 0.98).  The masses of TP and WSP for treatments in the entire soil columns were in the order MAP > D1L = D2L > D1S = D2S = Control. Masses of  P and C in leachate and soil show that P mobility in soil were in the order liquid dairy manures > MAP > solid dairy manures.  At the end of the study, the total C was greater in the surface 2.5 cm of the soil columns for the solid manure treatments compared to the other treatments/depth combinations. The greater leaching of P in the liquid manure treatments compared to the solid manure treatments may be due a combination of factors including microbial activity, organically complexed metals, coating of P adsorption sites on clay particles by organic C compounds, and P-Ca and P-Al reactions.