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In
onion cultivaton the fertilization requires special carefulness,
because apart from a high yield, the achievement of good quality
products should be pursued. The nutrient uptake from the soil, and
thus the demand of fertilizers, increases almost parallely with
the yield, whereas the assumption that excessive fertilization leads
to infinite yield increase is wrong.
Basic fertilization:
In autumn or before sowing in spring (2 - 3 weeks before) aprox.
100 - 200 kg/ ha P2O5
and 150 - 170 kg/ ha K2O should be applied.
The
application of lime fertilizer depends on the existent content in
the soil The use of chloride-containing fertilizers must be avoided
in any case.
Important:
Sufficient magnesium supply (examination of the soil).
The proportioning and the control of the nitrogen supply is especially
important. In practice usually too much nitrogen is applied rather
than too few.
The application of fertilizers on a population should always be
in accordance with the nutrient uptake.
In
consideration of the nutrient content of the soil, a total nutrient
supply of aprox. 120 - 140 kg N, 50 - 60 kg P2O5
and 180 kg/ha K2O should be guaranteed in
the upper 60 cm (extraction depth of the onion).
Depending on the relation of the required additional fertilization
and the nutrient content of the soil, a maximum of 50 kg pure nitrogen
should be applied before sowing. The second nitrogen fertilization
includes the remaining supplementary fertilization and must be applied
before the beginning of the bulb formation.
The consequences of a too high nitrogen supply after the beginning
of the bulb formation are: no increase of the yields, delayed maturity,
excessive growth and overproduction of leafage, and disease susceptibility,
reduced firmness and storage life, loose skins.
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Onions
