Fræðaþing landbúnaðarins - feb. 2010, Blaðsíða 397

VEGGSPJÖLd | 397
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Christina Stadler 1, Magnús Á. Ágústsson 2, Þórður G. Halldórsson 3
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In Iceland and other northern regions, there is an extremely low natural light level.
That is the major limiting factor for winter glasshouse production. Therefore,
supplementary lighting is essential to maintain yearround vegetable production. So
far, organic vegetable have not been grown in winter in Iceland. However, it is
necessary to get knowledge about yearround vegetable production in organic
horticulture with supplementary lighting. Consulting of conventional production
reveals that the positive influence of artificial lighting on plant growth, yield and
quality of tomatoes (Demers et al., 1998), cucumbers (Hao & Papadopoulos, 1999)
and sweet pepper (Demers & Gosselin, 1998) has been well studied.
Nitrogen (N) fertilizer application in organic horticulture is regulated by the European
Union Standards (EEC no. 2092/91) on organic production of agricultural products
and additionally by standards of organic producer’s organisations. N sources in
organic farming are organic fertilizers such as crop residues, legumes, animal manure
and commercial organic fertilizers. In Iceland, demand of organic N fertilizers has
been increased in the last years. It is common to fertilize vegetable crops mainly with
mushroom compost, residues from the fish industry (fishmeal) (Gunnlaugsson, 1998)
and “residues” from the sea (seaweed). Also, imported industrially processed animal
residues e.g. Nugro (liquid fertilizer based on fishmeal) are getting more popular. It is
reported that organic vegetable, fertilized with mushroom compost, yielded a good
harvest of cucumbers (Gunnlaugsson, 1995) and tomatoes (Gunnlaugsson, 1997).
Yield of organic cucumbers was dependent on the kind of fertilizer and was highest
with fishmeal (Gunnlaugsson & Guðfinnsson, 2004). One reason may possibly be the
influence of fertilizer characteristics on their N mineralization. For instance, it is
known that the N release from plantderived and industrially processed organic N
fertilizers is correlated to the fertilizer N content (Stadler et al., 2006).
The N mineralization of commonly used N fertilizers in organic horticulture (except
compost) in Iceland is expected to be rapid in greenhouses. Therefore, with respect to
a plant growth adapted N supply, it is supposed that fertilizers with a high and rapid N
release should be applied in split doses to result in a high N efficiency (Stadler, 2006).
One preliminary experiment, with a mixture of mushroom compost and fishmeal,
applied at weekly or half a month intervals, has already been conducted and results of
organic grown tomatoes are promising (Gunnlaugsson, 1998). However, more
detailed and continuous observations on how fertilizer application affects nitrate
content in the upper soil layer in connection with yield parameters are needed before
advising for a yearround organic vegetable production.
The objective of this study was (1) to test how to grow organic vegetables the whole
year exemplified by cucumbers and sweet pepper and (2) to find an adequate fertilizer
treatment that enhances yield and quality.