Nitrogen
Main Nutrient
Nitrogen is one of the most important components for plants. It is mainly used
for the construction of proteins, but it is also responsible for the growth
of plants. The chemical symbol for nitrogen is N. The amount of nitrogen in
fertilizers is expressed in % (pure) N. Divided in nitrate N, ammonium-N, Urea-N
and organic-N.
Ammonium Nitrate
When organic fertilizer is digested, ammonium nitrate is released. If the soil
life, the oxygen supply and the soil structure are in good shape, then the ammonium
nitrate will be quickly transformed into nitrate nitrogen.
Nitrate Nitrogen
Nitrate is formed from organic fertilizer or it is added directly to the soil
in the form of fertilizers, especially during the summer. If there is much rainfall,
then nitrate is easily washed out below the root zone (loss). For this reason,
the amount of nitrate can fluctuate very highly throughout the year. The nitrate
number assessed can only give an impression of the momentary provision of nitrogen.
Especially leaf crops absorb a lot of nitrogen. A high content of plant available
nitrogen in the soil will increase the amount of nitrogen in the crop. Most
plants grow quicker than, but the resistance to plant diseases decreases. On
the other hand, crops grow too slow and form little leaves if the content of
nitrogen is low or poor.
The use of organic fertilizer and compost will provide for a regular subsequent
delivery of nitrogen throughout several years after applying that manure. The
need for nitrogen rather differs between crops. For carrots and chicory a relatively
low nitrogen level is sufficient, but for grass and potatoes a higher level
of nitrogen is recommended.
Contents of nitrate in the Winter are usually lower than in the Summer. A bad
growth (small, light-green leaves) can be caused by lack of nitrogen. If there
is too much nitrogen present in the crop, then potatoes, for example, and also
beans will produce many leaves but not as many potatoes and beans.
Soil life
When the amount of total organic nitrogen is good and the C/N quotient is not
too high, and the total amount of soil biota is good, much nitrogen can be expected
from a soil without even applying fertilizers in that same year. In biological
glasshouse cultures we advise to analyse the soil biota (soil life screening
analysis package) once a year.
Loss of nitrate
When the soil has a high oxygen consumption and / or the soil is compact, nitrate
can be easily decomposed into nitrogen oxide of nitrogen-gas. The efficiency
of nitrogen fertilization is than lowered. In the EU, where the fertilization
with nitrogen is limited, not only a good fertilizer management is needed, but
also a soil with enough oxygen for the soil life and the plant roots. See the
article about oxygen.
Environmental Aspects for Nitrogen Fertilization
If the content of nitrogen in the soil is too high, then especially green vegetables
like lettuce and spinach can obtain a nitrate content which is too high. Besides,
nitrogen washes out easily in the form of nitrate, on all soils but more easy
on sandy soils than on clay soils, so that nitrate ends up in the ground water.
When in the soil is a layer that denitrificates, such as in peat soils among
others, the nitrate will microbially decompose into nitrogen gas. Leaching of
nitrates is in that case prevented. In the Autumn or in the early Winter, nitrogen
fertilization is normally less effective because, during the Winter, mineral
nitrogen washes out (and, on sandy soils, potassium as well).
EUROLAB / KOCH BODEMTECHNIEK – DEVENTER – THE NETHERLANDS
Pastures
