Nitrate and Phosphate Desorbed From Anionic Exchange Membranes Over Winter As Affected By Tillage and Fertilization.

Projected global warming may result in large climatic conditions variations in soil temperatures and in the number of soil freezing and thawing cycles during winter in cool temperate and high-latitude regions. Determining how agricultural management practices affect changes of soil nitrogen (N) and phosphorus (P) over winter could further our understanding of soil N and P cycle. Anionic exchange membranes (AEMs) have been successfully used to estimate the availability of soil N and P under different agro-ecosystems. The main objective of this study was to assess the effects of tillage systems, mineral N and P fertilization on NO₃^- and PO₄^- accumulation on AEMs (AEM-N and AEM-P, respectively) over winter. The AEMs were buried in the surface horizon (0–15 cm) over winter (mid-Nov. to mid-April) in three consecutive years (2009/2010, 2010/2011, and 2011/2012) in a long-term corn-soybean rotation experiment established since 1992 in eastern Canada. Treatments consisted of two tillage systems including moldboard plow (MP) and no till (NT) and nine combination of fertilization application including three N rates (0,80,160 kg N ha^-1) and three P rates (0,17.5 and 35 kg P ha^-1) in a split plot design with four replications. Results show that AEM-N and AEM-P were significantly greater under NT than MP across all N and P treatments and years. The effect of N fertilization on AEM-N was year-depended; AEM-N was not affected by N application after winter of 2009/2010 but was greater with 160 kg N ha^-1 compared with no N applied after winter of 2011/2012; in addition, AEM-N increased by the increasing of N application under NT but not under MP after winter of 2010/2011. The AEM-P increased by increasing P application under NT in all three winters, while AEM-P was greater with no N applied than with N applied under NT.  No significant change was observed on AEM-P under MP. We conclude that the fertilized NT had a greater potential than MP for sustaining production in the following growing season and also for N and P losses via surface runoff in early spring.