Phosphorus in soils of riparian and non‐riparian wetland and buffer strips in the Waikato area, New Zealand uri icon

abstract

  • This paper examines the potential for phosphorus (P) release from intensively grazed pasture to waterways. In particular it describes the P release processes occurring in riparian buffer strips. Soil samples at three depths (0-2.5, 2.5-7.5, and 7.5-15 cm) were collected from riparian buffer strips, including wetland and non-riparian areas at three pasture sites. These soil samples were analysed for total P, plant available P as measured by Olsen P, and soil solution P as measured by 0.01M CaCl2-extractable P. The P retention capacity and P buffering capacity of the riparian soils were also measured. A significant relationship was found between Olsen P and 0.01M CaCl2-extractable soil P, indicating that soils with a high plant available P pool (measured as Olsen P) potentially have a high P loss in subsurface flow (as represented by CaCl2- extractable P). All of the CaCl2-P concentrations in the top 2.5 cm soil depth at the study sites were higher than the threshold concentration (0.01 mg CaCl2-P litre(-1)) considered to stimulate fresh water algal growth. This P could contribute to P losses through leaching and surface runoff. However, soils at lower depths (2.5-7.5 and 7.5-15 cm) were found to have higher P sorption and higher P buffering capacity, thus potentially can trap more (15-45 kg P ha(-1)) than the surface profile (0-2.5 cm). Subsoils may therefore play an important role in controlling P release. The P release may vary depending on the P sorption characteristic of soils and flow pathways. Development of riparian buffer strips for an effective decrease in P losses from intensively grazed systems should take into account P release characteristics of the soil, the distribution of Pin soil profile, and the time necessary for plant available P (i.e., Olsen P) to decline to acceptable levels.

publication date

  • 2006
  • 2006