The Effects of surface drainage on soil physical and chemical properties in the Black soil zone of Saskatchewan
Recent flooding of agricultural land in the northern and eastern Saskatchewan Prairies coupled with intensification of agriculture has resulted in renewed efforts to drain prairie potholes. Drainage is used to increase land available for farming, reduce costs of manoeuvring equipment around wetlands, allow for earlier seeding, and improve growing conditions. Given that low-lying areas tend to have higher nutrient and organic matter concentrations than surrounding uplands, drainage may create some of the most productive land in the province. However, agricultural drainage has been identified as a large nonpoint contributor of N and P loading to waterbodies and could result in degradation of downstream water quality in the Prairies. The objectives of this research were: 1) to determine if agricultural drainage improved growing conditions and nutrient availability in soils over time by measuring physical (i.e. structure and bulk density) and chemical properties (i.e. C, N, P and K), 2) to determine if drainage causes wetland soils to become more similar to midslope soils in terms of properties and nutrient dynamics, and 3) to investigate how forms and fates of nutrients (N and P) vary under different precipitation scenarios to reveal the potential productivity and potential nutrient loss to drainage water of drained soils. To achieve objectives 1 and 2, 42 wetlands and corresponding midslopes were selected in the Black soil zone of eastern Saskatchewan, approximately 60 km southeast of Yorkton. The drainage age of wetlands ranged from 0 to 50 years. In the fall of 2014, intact cores were collected for analysis of bulk density, aggregate stability, macronutrients, and carbon. Overall, drainage improved growing conditions and nutrient availability in soil. The field study showed greater nutrient availability, evident by greater available 〖"PO" 〗_"4" ^"-3" and increased nitrification. These improvements were greatest in soils that had been drained from 7 to 34 years, but decreased in soils drained from 36 to 50 years. Soils that had been drained for longer durations appeared to become more similar to the midslope position. Disadvantages following drainage, such as increased bulk density and decreased quantity and quality of OC, were greatest in soils drained from 36 to 50 years. To achieve the third objective, a greenhouse study was completed using bulk soil collected from an undrained (UD), recently drained (RD), medium drained (MD), longest drained (LD) and midslope (MS) sampling location. Wheat was planted and three different precipitation treatments (below, normal and above-normal) were applied. Nitrogen and P were analyzed in plant, soil, and leachate, and nutrient budgets were developed. The greenhouse study demonstrated that drained soils have greater plant N and P uptake, and plant yield. The greenhouse study also identified that not all soils contribute equally to nutrient losses in drainage water and that recently drained soils may be a larger contributor under below and normal precipitation, but a lower contributor under above-normal precipitation. The findings of both the field and greenhouse study are of significance because they identify that perceived benefits may decline with time. Results are useful for developing management practices that may further extend the benefits of drainage and for developing mitigation strategies to reduce N and P exports to drainage water.
DegreeMaster of Science (M.Sc.)
SupervisorBedard-Haughn, Angela K.
CommitteePennock, Daniel J.; Schoenau, Jeff J.
Copyright DateApril 2016