Tuesday, November 14, 2006

Chemical Behavior of Phosphorus in a Sandy Loam Soil Long-Term Applied with Dairy Slurry.

Aruna Herath1, Tiequan Zhang2, Tom Forge3, Chantal Hamel3, and Michael Goss1. (1) Univ of Guelph, Gorden St, Guelph, ON N1G 2W1, Canada, (2) Agric & Agri-Food Canada, 2585 County Road 20, Harrow, ON N0R 1G0, Canada, (3) AAFC, 6947 Highway 7 - 6947 Autoroute 7, Agssiz, BC V0M 1A0, Canada

Soil P fractions and their distribution govern the fate and bio-availability to crops.  A better understanding of changes in P fraction would improve soil P management and thereby restrain the unwanted soil P losses to the environment.  The objective of this study was to assess the long-term effects of soil P inputs from both dairy slurry and inorganic fertilizer on soil P forms and its distribution in soil profile. A field experiment was conducted in a sandy loam soil under sward of tall fescue from 1992 to 2005. There were six treatments including two rates of dairy slurry (50 and 100 N kg ha -1),  two rates of inorganic fertilizer maintaining  the same N rates as that of dairy slurry,  alternating dairy slurry and inorganic fertilizer each at 100 kg mineral-N ha-1, and the unfertilized control. Soil samples were collected at depths down to 60cm and analysed for P fractions using the modified Hedley’s technique.  In soils added with dairy slurry at 100 kg N ha -1 had the highest concentrations of both inorganic and organic P fractions amongst all treatments. Most of the residual P was found in labile P. Residual P accumulated mainly on the surface layer of 0-15 cm, regardless of the treatments. The results confirm that long-term accumulated residual P from either inorganic fertilizer or dairy slurry can be available to crops or susceptible to loss in soluble forms.