Effects of Poultry Manure Amendment on Phosphorus Uptake by Ryegrass and Soil Phosphorus Fractions.

Soil phosphorus (P) exists in numerous forms that differ in plant availability.  Poultry manure (PM) and other organic fertilizers with a high proportion of stable P can alter the balance of P forms, thus affecting soil nutrient status.  To investigate effects of PM on soil distribution and plant utilization of P, we conducted a greenhouse study with perennial ryegrass (Lolium perenne) in soil with PM at rates of 0, 22, and 112 mg P kg^-1 of soil. Ryegrass biomass was harvested at 4, 8, and 16 weeks, and soil separated into rhizosphere and bulk fractions.  Soil P was sequentially extracted by H₂O, 0.5 M NaHCO₃, 0.1 M NaOH, and 1 M HCl, followed by quantitation of inorganic P (P_i) and enzymatically hydrolysable organic P (P_oe).  Manure at 112 mg P kg^-1 increased root P concentrations 1.4-fold and total P uptake 1.6-fold, but did not change plant biomass yield.  PM had short-term effects on both P_i and P_oe, with increased NaOH- and HCl-P_i, and decreased NaOH- and HCl-P_oe at week 4.  Labile-P_i (H₂O and NaHCO₃ fractions) was higher at week 16 with PM, suggesting replenishment of this fraction from stable P forms.  Plant roots also affected P distribution, as labile-P_i in rhizosphere with PM was 16-20% higher than bulk soil at 8 weeks.  These results demonstrate that a single PM application does not lead to accumulation of stable P, including HCl-P.  Furthermore, PM may promote redistribution of specific soil P fractions, leading to plant utilization of stable P forms.