Phosphorus losses from grasslands in short-term ley rotations under boreal conditions

• Main Author: Räty, Mari
• Other Authors: Ventelä, Anne-Mari, University of Helsinki, Faculty of Agriculture and Forestry, Department of Agricultural Sciences, Doctoral Programme in Sustainable Use of Renewable Natural Resources, Natural Resources Institute Finland (Luke), Maaninka, Finland, Helsingin yliopisto, maatalous-metsätieteellinen tiedekunta, Uusiutuvien luonnonvarojen kestävän käytön tohtoriohjelma, Helsingfors universitet, agrikultur-forstvetenskapliga fakulteten, Doktorandprogrammet i hållbart utnyttjande av förnybara naturresurser, Yli-Halla, Markku, Soinne, Helena, Virkajärvi, Perttu
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Helsingin yliopisto 2020
• Subjects: maataloustiede; ympäristötiede; Northern Finland
• Online Access: http://hdl.handle.net/10138/321521

Grasslands occupy 45% of agricultural land in Finland, but in provinces characterised by grassland-based dairy production the proportion can be 67%. Phosphorus (P) loads from grasslands to inland waters have received relatively little research attention. In the Finnish climate, soils are subjected to frost in winter and snowfall comprises a considerable part of total annual precipitation. Surface runoff is generated by limited infiltration of snowmelt water into partially frozen soil in spring, which is a crucial period for dissolved nutrient and soil particle transport, especially in central and northern Finland. This thesis examined the role of perennial grass vegetation in P dynamics in the soil-plant-water continuum and quantified P losses from grasslands under boreal conditions. Potential contributions of perennial vegetation to P losses were estimated indirectly, by determining changes in nutrient content of aboveground vegetation. Susceptibility of overwintering perennial ley regrowth to deliver P was assessed in a simulated snowmelt-induced surface runoff study. These approaches were complemented with five-year monitoring of a small (3.2 km2) agricultural and forested catchment, representing grassland-based dairy production areas in east-central Finland. Amount and inter-annual variation in P losses and erosion rate were quantified. The results showed that grasslands can release substantial amounts of plant-derived P when exposed to frost, freezing and thawing. Elevated P concentrations and losses of up to 0.69 kg ha-1 were detected in simulated snowmelt-induced runoff outflow. Higher P concentrations were also occasionally measured in early spring runoff at small catchment scale. More frequent freezing/thawing will enhance plant-derived P release, especially under a reduced snow layer and lack of insulating cover. In five-year monitoring of an agricultural sub-catchment with short-terms leys, where some fields were under grassland and others under cereals, mean annual total P (TP) losses were 1.0 kg ...