Soil Phosphorus Fractions Change in Winter in a Corn-Soybean Rotation with Tillage and Phosphorus Fertilization

Determining how agricultural management practices affect soil phosphorus (P) over the winter may further our understanding of the soil P cycle under specific environmental conditions in eastern Canada. This study assessed changes over winter for soil P fractions and other selected chemical properties as affected by tillage and P fertilization. In 1992, a long-term corn (Zea mays L.) and soybean (Glycine max L.) rotational experiment was established in the province of Quebec, Canada. Soil samples (0-15 cm) were collected in fall 2001 and 2007 after a soybean harvest, and in the following spring 2002 and 2008 before corn seeding, in main plots under moldboard plow and no-till managements and selected subplots fertilized with 0, 17.5, or 35 kg P ha-1 and 160 kg N ha-1. Soil samples were analyzed for P fractions and other chemical properties to assess changes over winter for 2001-2002 and 2007-2008. Changes over winter of all soil P fractions were significant for the two periods, indicating the occurrence of soil P transformation and movement over winter. The Mehlich-3-extractable Fe, Al, Ca, and Mg decreased during the two studied periods. Tillage had no significant effect on all soil P fractions. The resin-extractable P in 2001-2002 and NaHCO3-extractable inorganic P and NaOH-extractable organic P during the two winters were significantly increased under P fertilization. This study demonstrated that P in cultivated soils changed during winter as a result of changes in labile P fractions possibly due to the solubilization of residual fertilizer P combined with environmental factors.