Overwinter Changes in Soil P Fractions With Tillage and P Fertilization in Eastern Canada.

Determining how agricultural management practices affect changes of soil P over winter could further our understanding of soil P cycle as influenced by the specific climatic conditions of eastern Canada. This study assessed the effects of tillage and P fertilization, as well as climatic conditions on changes of soil P fractions occurring during overwinter. 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 soybean harvest, and in the following spring (2002 and 2008) before corn seeding in plots under moldboard plow (MP) and no till (NT) management and fertilized with 0, 17.5, or 35 kg P ha^-1 and 160 kg N ha^-1. Soil samples were analyzed for different attributes including P fractions, and other chemical properties to assess changes over periods 1 (spring 2002 subtracted from fall 2001) and 2 (spring 2008 subtracted from fall 2007). Results show that changes of all soil P fractions were profoundly different between the two periods suggesting that soil P changes were largely dependent on climatic conditions. The increasing trend of resin-P, NaOH-Pi and NaOH-Po in period 1 and NaOH-Pi in period 2 indicates these fractions could be the sink of soil P involved in mineralization/immobilization process. No till had a positive effect on changes of resin-P, NaOH-Pi and total P in period 1, but had no effect on any fractions in period 2. The positive effect of P fertilization on changes in soil Pi and NaOH-Po fractions over the two periods indicates the residual fertilizer P involved in soil P cycling during winter, but differentiating in tillage systems and periods. We conclude that NT combined with P fertilization could affect soil P transformation during winter, and these effects were largely influenced by climatic conditions.