Plant Nutrition from the Root
Environment
The need to feed
• We have already made the point that what is
taken out of the soil must be put back,
• and therefore part of the soil management is
the use of compost, manure or fertilisers to
maintain soil fertility.
Sources of added Nutrients
• Organic matter is usually some form of
compost or manure. Its primary benefit is to
improve the quality and structure of the soil,
although it also provides some nutrients.
• Fertilisers are concentrated forms of nutrients
that have been produced by some form of
processing.
• Note that these are not really alternatives.
Organic matter is a soil conditioner that
improves the quality of the soil, and soils that
are only fertilised will deteriorate over a period
of time.
Organic matter
• Of all the nutrients, nitrogen is the one most
likely to be needed, as plants require a
significant amount, and it is easily leached
from the soil.
• The others likely to be needed are phosphorus
and potassium, and many proprietary
fertilisers contain all three.
• Remember that an excess of fertilisers can
harm the plants and the environment.
Organic matter
• The nutrient content of compost and manure is
low compared to fertilisers but
• because they are applied in bulk the effect can
be similar
• They can be incorporated into the soil when it is
cultivated or they can be applied as a surface
mulch,(gradually incorporated by earthworms).
• Amount: One barrowload per 4 sq m.
• The best time to apply it:
– to clay soils is in the autumn so that it can be
broken down over the winter,
– but in sandy soils leave it to late winter or early
spring to avoid it being leached out.
Green manures
• These are different to other manures as
they are plants that-are grown on the soil to
be manured, and are incorporated directly
into that soil a few weeks before a crop is to
be planted.
• The plants are grown and used in one
season and should be incorporated into the
soil before they start to turn woody.
• Ones that can be sown in late summer and
dug in the following spring are probably the
most useful as they cover the bare soil in
winter and protect the soil structure.
Advantages of Green Manuers
• 1. Provides organic matter and nutrients to
the soil particularly when nitrogen fixing
plants are used.
• 2. Protects the surface of the soil and prevents
erosion or the leaching of nutrients
• 3. Prevents- the proliferation of weeds.
Plants Suitable as Green Manures
1. Clover (Trifolium pratense)
• Clover has the advantage of fixing
nitrogen and can be left to
overwinter. Sow from April to
July.
2. Mustard (Sinapis alba)
• A fast growing summer crop. Sow
between March and August and
dig in before flowering.
3. Winter rye (Secale cereale)
• Sow from August to October to
overwinter.
Fertilisers
• Fertilisers can be organic or inorganic.
• Organic fertilisers, such as bonemeal, are
derived from material which was once living.
• Inorganic fertilisers, such as sulphate of
ammonia, are manufactured or- derived from
minerals. Inorganic fertilisers are probably
more precise in their nutrient content, and
may be quicker acting.
• Also, since the BSE crisis are considered safer
to handle.
Fertilisers
• Fertilisers can also be straight, which means theycontain one nutrient, usually nitrogen,
phosphorus or potassium,
• Or compound; which means they contain more
than one. 'Growmore' and 'Fish, blood and bone'
-are examples of compound fertilisers.
• Fertilisers can come as a powder to be used
directly on the soil, or in a solution, or as
granules.
Controlled Release Fertilisers
• Most fertilisers are quick acting but a
comparatively recent development is
the use of controlled release fertilisers
which allow the nutrients to be
released over a period of time.
• This is particularly useful for nutrients
which are easily leached from the soil
such as nitrogen.
• Originally aimed at crop production
such fertilisers are now available for a
wide variety of environments
including pot plants and lawns.
Application of fertilisers
Base dressing
• The fertiliser is incorporated in the soil. In a domestic
garden situation it would be dug in, but in a
commercial situation more sophisticated methods are
used:
– distributing it with the seed directly into the drill,
– or applying it as a band alongside the drill.
Top dressing
• The fertiliser is applied to the surface of the soil and
relies on rain or irrigation to carry it down to the roots.
For this reason the fertiliser must be soluble.
Application of fertilisers
Liquid
• The fertiliser is dissolved in water and applied to
the soil surface. This will give a faster reaction
than a top dressing.
Foliar feed
• The fertiliser is dissolved in water and applied as
a spray to the leaves of the plant. Foliar feeds are
quick acting and are particularly useful where the
soil conditions prevent the uptake of some
nutrients.
Timing of Fertilisers
• Nitrogen fertilisers are best applied 2-4 weeks before
planting because of the possibility of them being
leached out.
• Also, since they encourage vegetative growth, they are
not applied in late summer or autumn when new
growth may be damaged by winter weather.
• The application of other fertilisers is not so critical, but
as a general rule apply in spring before new growth
begins. Some crops may also require additional
applications during the growing season.
• Whatever the method or time of application it is
important to follow the manufacturer's instructions.
Comparison of bulky organic matter
with fertilisers
Nutrient content of organic matter
and fertilisers