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TECHNICAL REPORTS

Waste Management

Phytase Supplemented Poultry Diets Affect Soluble Phosphorus and Nitrogen in Manure and Manure-amended Soil

^a Centre for Mined Land Rehabilitation, The Univ. of Queensland, St. Lucia, Qld. 4072, Australia
^b Department of Environmental Science, Univ. of Technology Sydney, Broadway, NSW 2007, Australia
^c School of Land, Crop and Food Sciences, The Univ. of Queensland, Gatton Qld. 4343, Australia
^d School of Animal Studies, The Univ. of Queensland, Gatton Qld.4343, Australia

^* Corresponding author (u.pillaimcgarry{at}uq.edu.au).

Received for publication May 21, 2008. Understanding P and N dynamics in manure-amended soil is essential for estimating the environmental impact of manure utilization in land applications. A laboratory incubation study was conducted to assess, (i) the effect of feeding a standard Australian commercial diet, and diets modified with phytase supplementation and reduced nonphytase phosphorus (NPP), on the concentrations of P and N (total and soluble) in the manure derived from layer hens (Gallus domesticus L.), and (ii) the change in water-soluble phoshorus (P_WSP) and mineral N (NH₄–N and NO₃–N) when used as a soil amendment, applied at rates equivalent to 200 kg ha^–1 (200N) and 400 kg ha^–1 (400N). Phytase supplementation increased %P_WSP by 8 to 12% in the manures, regardless of the levels of NPP in the diets, and in the manure-amended soils by 27 to 30% at the 200N application rate, and up to 54% at the 400N rate. Phytase significantly (P < 0.05) reduced total nitrogen (TN) content (by 12–31%) of the manures but generally produced greater nitrate accumulation in the manure-amended soils. Net nitrification, which commenced 4 wk after incubation, was accompanied by a simultaneous decrease in soil pH (by one pH unit) and a concomitant decline in %P_WSP. The decline in %P_WSP was primarily attributed to P retention by the soil as it became more acidic. This study suggests that phytase addition not only reduces manure total N content, and increases water-soluble P, but its effects on manure total phosphorus (TP) and 2 mol L^–1 KCl extractable mineral N is influenced by the NPP level in the diet.

Abbreviations: N_min, mineral nitrogen • NPP, nonphystase phosphorus • P_WSP, water-soluble phosphorus • PA, phytic acid • SO, soil only • TN, total nitrogen • TP, total phosphorus • WSP, water-soluble phosphorus