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The longevity of cultivation in decreasing the potential for phosphorus loss in runoff

journal contribution
posted on 2024-06-21, 03:51 authored by Rich McDowellRich McDowell, Chris SmithChris Smith
Phosphorus (P) loss from highly fertilised grazed pastures can impair surface water quality. High P concentrations in grazed pastures are maintained to boost legume production, but systems that use monocultures of grass and clover can be more profitable and decrease P losses by lowering soil P in grassed areas. In contrast with using a direct drill to establish new pastures, conventional cultivation can lower topsoil P quickly and can be used as part of a farm re-grassing programme every six years. We tested if the potential for low P losses (measured by water extractable P; WEP) could be maintained over six years in pastures (ryegrass and white clover monocultures and a ryegrass and clover mixed sward) despite being fertilised (10, 35 and 100 kg P ha-1) and grazed. Cultivation (0-20 cm) decreased WEP and Olsen P in all three pastures and P rates by 30-50 % compared to direct drill and maintained this decrease for six years. A threshold in Olsen P (22 mg L-1) was noted where WEP concentrations increased at a greater rate relative to Olsen P than below. This threshold was like the critical point in Olsen P for 97 % relative yield in the pastures (22-28 mg L-1) and could be used to advise on cultivation and P fertiliser strategies to help avoid the potential for P loss without significantly compromising yield. The data indicated that cultivation could be used to quickly establish and maintain lower soil P concentrations as part of a strategy to decrease P losses and improve profit by using a split grass-clover system. Highlights:
  • Phosphorus runoff from land can impair surface water quality.
  • Splitting pastures into monocultures maintains production and enables low P plants to grow in runoff prone areas.
  • Conventional cultivation can be used to quickly decrease enriched soil P for low P plants.
  • Potential for runoff was maintained despite fertiliser P and grazing returns over 6-year period.
  • Conventional cultivation is a suitable method for re-grassing programme to lower runoff P losses.

Funding

Funded by the New Zealand Ministry for Business, Innovation and Employment's Our Land and Water National Science Challenge (Toitū te Whenua, Toiora te Wai) as part of project Linking Legacies to Wai

History

Publication date

2023-03-07

Language

  • English

Does this contain Māori information or data?

  • No

Journal title

Soil and Tillage Research

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