Effects of drainage duration on mineral wetland soils in a Prairie Pothole agroecosystem

- Agricultural surface drainage improves growing conditions and nutrient availability.
- Effects of drainage on soil properties varies with duration of drainage.
- Soils drained up to 34 years may have greater nutrient losses to drainage water.
- Soils drained longer than 36 years appear to become more similar to upslope soils.

Recent flooding of agricultural land in the northern Prairie Pothole Region - coupled with intensification of agriculture - has resulted in renewed efforts to drain Prairie Potholes. Drainage is used to improve growing conditions and increase the amount of land that can be cultivated. The aim of this study was to determine if duration of agricultural drainage improved growing conditions and nutrient availability, by measuring physical (i.e. structure and bulk density) and chemical properties (i.e. C, N, and P). Forty-two wetlands and paired midslopes were selected in the Prairie Pothole Region in the Black soil zone of southeastern Saskatchewan. Drainage duration of wetlands ranged from 0 to 50 years. Results suggest drainage does improve growing conditions and nutrient availability for agricultural production, but these changes vary across wetlands drained for different durations of time. Compared with undrained soils, changes were greatest in soils drained from 20 to 34 years, but decreased after 36 years becoming more similar to cultivated midslope positions. Some drainage benefits include increased nitrification and greater available PO4−3 at a depth of 0-15 cm. Phosphorus sorption decreased with drainage duration and P desorption increased in soils drained from 7 to 34 years. This could result in greater available N and P for crop uptake, but could also lead to greater nutrient losses. Additionally, bulk density increased and microaggregates decreased with drainage duration. Compared with undrained soils, drainage did not have a significant effect on macroaggregates, soil organic carbon, water extractable organic carbon, light fraction, total N, NO3− , and mineralization. It is likely other agricultural practices used in conjunction with drainage, such as tillage, fertilizer additions, and crop removal, are affecting how these soil properties change over time. The resulting quantitative data from this study provides an excellent resource for planning management strategies to improve nutrient use efficiency and reduce losses to the environment.