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

统计数据显示，每年约有3.8千克磷(P)出口到魁北克南部的圣劳伦斯河。这导致68%的监测站磷含量超过省级水质标准(0.03 mg L-1)的容许负荷量。最近的研究表明，地下瓦片排水农田是这些地区水质恶化的主要原因。在加拿大东部，养分流失主要发生在12月至5月的非生长季。尽管大孔隙和土壤纳米颗粒促进的磷素输运是排水区磷素流失的主要机制，但很少有人研究冻融条件下的水文过程和磷素流失。另一方面，可以采用管理措施来减少非生长季的养分流失。覆盖作物和减少耕作是瓷砖排水田地上使用的主要选择；然而，并不是所有潜在的做法都是有用的，事实上，没有发现耕作能增加田间溶解磷的出口。这可能是由于免耕土壤中的大孔隙较多所致。然而，目前还没有针对这一问题或将这些管理做法与地下水位管理战略相结合的研究。因此，这项田间研究的目标是制定最佳管理措施，以减少融雪和融雪后磷的流失，并了解冬季水文和微孔隙度对瓷砖排水中纳米颗粒促进的磷流失的影响。试验将在魁北克的一个24块地下排水场地进行，采用完全随机区组设计，因子为2×2×2。这三个因素是地下水位管理、种植制度和耕作。对于每个因素，将有2个水平：控制排水与自由排水、玉米-大豆轮作(覆盖和不覆盖作物)、串联式圆盘+田间耕作机(对照)与免耕。因此，将有8个处理，每个处理分配3个地块。将对天气、瓦片排水、地表径流、降雪、积雪、土壤冰和液态水含量、雪升华、土壤大孔隙度和纳米颗粒以及水中各种形态的磷进行密集测量，特别是在融雪和融雪后。由加拿大创新基金会赞助，最近购买了一台NanoBrook Zetasizer、一台闪烁仪和一台Snow Pack Analyzer(SPA)，以促进这种测量(价值247,208美元)。

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 x 2 x 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).