|Authors: ||A. Falk Øgaard, M. Bechmann|
|Keywords: ||P fertilization, catch crops, constructed wetlands, carrots, onion, white cabbage|
The water quality in the western part of Lake Vansjø in south eastern Norway is classified as very poor due to excessive growth of blue green algae.
It has been shown that phosphorus (P) losses are high from a subcatchment where potatoes and vegetables are grown on 25% of the agricultural area.
The water quality of the lake is of great concern because it is the drinking water reservoir of 60 000 inhabitants and an important recreation area for people living in the area.
An integrated project funded by the government was started in 2008 in order to improve the water quality of the lake.
Within this project, the public agricultural management, agricultural advisors, farmers and the Norwegian Institute for Agricultural and Environmental Research (Bioforsk) collaborate to attain the target of improved water quality.
The farmers are encouraged to sign a contract where they will receive financial support for covering extra costs for committing to a set of restrictions and mitigation options aiming at reduced P losses.
Vegetable- and potato fields give large challenges when aiming at reduced P losses.
A large part of the research activity is therefore related to possible mitigation options on these fields, e.g., the effect of reduced P fertilization on yields and quality of bulb onion (Allium cepa), carrots (Daucus carota) and white cabbage (Brassica oleracea var. capitata alba), and evaluation of catch crops as a mitigation option for reduced soil erosion from these fields.
Development of constructed wetlands to include filters that adsorb P and measurement of P losses through tile drains are also included in the project.
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