Effect of management practices on hydrology and nutrient losses from a tile-drained field under freeze-thaw conditions

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Statistics have shown that about 3.8 Gg of phosphorus (P) per year was exported to the St. Lawrence River in southern Quebec. This resulted in tolerable loads of P under provincial water quality standards (0.03 mg L-1) being exceeded at 68% of monitoring stations. Recent studies have shown that subsurface tile-drained cropland was the major contributor to water quality degradation in those regions. In eastern Canada these nutrient losses occurred mainly during the non-growing season of December to May. Notwithstanding the fact that macropore and soil nanoparticle-facilitated phosphorus transport are the key mechanisms of P losses from tile-drained regions, very few study have been conducted to investigate the hydrological processes and P losses under freeze-thaw conditions. On the other hand, management practices can be applied to mitigate nutrient losses during the non-growing season. Cover crops and reduced tillage are the primary options used on tile-drained fields; however, not all potential practices are useful, indeed, no till was found to increase dissolved phosphorus export from fields. This phenomenon might be attributed to there being more macropores in no-till fields. However, no study has been developed to focus on this question or combining those management practices with water table management strategies. Therefore, the objectives of this field study are to develop best management practices to mitigate P losses during the snowmelt and post-snowmelt periods and to understand the effect of winter hydrology and microporosity on nano-particle facilitated P loss in tile drainage. The experiment will be conducted at a 24-plot subsurface drainage site in Quebec with a complete randomized block design with a 2 2 2 factorial. The three factors are water table management, cropping system, and tillage. For each factor, there will be 2 levels: controlled drainage vs. free drainage, corn-soybean rotation with and without winter cover crop, and tandem disk + field cultivator versus no-till. Therefore, there will be 8 treatments and 3 plots will be assigned to each treatment. Weather, tile drainage, surface runoff, snowfall, snowpack, soil ice and liquid water content, snow sublimation, soil macroporosity and nano-particles, and all forms of P in water will be intensively measure, in particular during snowmelt and post-snowmelt period. Sponsored by the Canadian Foundation of Innovation, a NanoBrook Zetasizer, a scintillometer, and a Snow Pack Analyzer (SPA) were recently purchased to facilitate such measurements (value $247,208).