Soil phosphorus fractions following annual paper mill biosolids and liming materials application

Industrial by-products such as paper mill biosolids (PB) and different liming materials have been used as fertilizers and amendments in agricultural soils for many decades. However, little isknown about the effectsof their repeated application on soil nutrient availability, particularly phosphorus (P). A 6-yr field study (2000-2005) wasconducted in the province of Quebec to investigate the effect of repeated annual applications of different PB and industrial by-products on selected soil chemical properties, especially soil P fractions. Different PB rates (0 to 90 Mg wet ha-1) and several liming products (lime mud, wood ash, calcitic lime, and Mg by-products) were annually applied to field crops after seeding. Soils were sampled before seeding in May 2003 and at harvest in October 2005. Results showed that HCl-P was the largest P pool, accounting for about 64% of the total P fraction, and that the repeated applications of liming products significantly increased this pool and decreased the organic P pools. The NaOH-Po and residual-P were significantly lower in 2005 than in 2003, indicating that PB application without supplemental P fertilizer inputs enhanced the mobility and/or mineralization of NaOH-Po and the transformation of recalcitrant P to more labile formswith time. Lime mud (LM) wasfound to be the best liming material owing to itshigh neutralization capacity and positive effect on soil P availability over time.