AGRIC/O: PLANT NUTRIENTS (ELEMENTS)

This Unit is about Plant Nutrients and Nitrogen specifically.

PLANT NUTRIENTS (ELEMENTS)

There are 16 essential plant nutrients and these can be obtained mainly from the soil and also from water (hydrogen) and from the air i.e. carbon and some times Nitrogen.

Essential plant nutrients are those which if not supplied in sufficient amounts to the plants will cause specific injury or growth abnormality but when that particular nutrient is supplied, this can be corrected.

These nutrients can either be macro or micronutrients.

Macro Nutrients

These are required by plans in large amounts and then deficiency will immediately bring about different symptoms .

They are nine (9) i.e

Carbon – CO3 through leaves

nutrients

Micro Nutrients

These are equally important as macro nutrients but are needed by plants in small quantities these include:

  • Iron
  • Zinc
  • Copper
  • Manganese
  • Molybdeum
  • Chlorine
  • Boron

MACRO NUTRIENTS –

NITROGEN:

Sources of Nitrogen

  • Atmosphere when it rains and there is thunder
  • Fixation by symbiotic bacteria found in the roots of legumes.
  • Non symbiotic fixation by free living organisms e.g. Blue green algae, Azotobader, Beijerinktia
  • Mineralisation of organic matter and manure.

Importance of Nitrogen

  1. Nitrogen is an important constituent of all plant cell protein.
  2. It’s responsible for the green colour of the leaves of chlorophyll and this gives the plant ability to manufacture food.
  3. It regulates or influences utilization of many other nutrients e.g: phosphorus and potassium.
  4. It encourages rapid vegetative growth necessary inn pant s like dodo.
  5. It makes the plant succulent and this improves on quality e.g. cucumber, pineapples, etc.
  6. In cereals increases grain size and there content.

Ways through which Nitrogen can be lost from the soil

  • Soil erosion
  • Leaching since its very soluble in water.
  • It can be absorbed by plants which are later harvested
  • Through burning when nitrogen is lost as a gas.
  • Denitrification by the anaerobic this is encouraged by poorly aerated soils, high soil temperature and high soil pH.
  • Through immobilization where nitrogen in the soil is used up by soil organisms is used by soil during decomposition of organic matter.

Deficiency of Nitrogen

  • Chlorosis of leaves: This is when the leaves loose chlorophyll and become yellow starting from the lower leaves.
  • In grasses, tips of lower leaves may become brown discolouration spreads along the mid rib until the leaf dies.
  • Stunted growth: The roots become particularly shot.
  • Premature ripening of fruits and seeds
  • Production of other colours that are not green common in tomatoes anthacynanin.

Excessive symptoms of Nitrogen

  1. The crop will produce abundant very dark green leaves and such crops are very weak and soft and can easily be attacked by diseases.
  2. Weakening of stems and fruits e.g in cotton fibre quality reduces.
  3. Delayed maturity
  4. Scorching of leaves in some plants.
  5. Excessive succulency resulting in lodging.

Management of Nitrogen in plants soil

  • Through addition of organic matter since over 90% of the soil s contained in organic matter.
  • Carrying crop rotation making sure you include a legume.
  • On soil organic matter.
  • Seed inoculation to encourage nitrogen fixing capacity in legumes just before planting the seeds.
  • Include grass bays as part of the rotation to increase on soil organic matter.
  • Add artificial fertilizers, organic manures and after harvesting you dig crop residues in the soil.
  • Regulation of soil Nitrogen labels excessive nitrogen should it be added as it will simply be leached.

THE NITROGEN CYCLE

It is the fate of Nitrogen in nature.  It ensures a continuous supply of Nitrogen in the soil for use by plants.

When legumes are grown, they may develop swellings on their roots called nodules and living in a cymbaitic relationship in the nodules, a group of bacteria known as Rhizohio.  This is capable of capturing fixing nitrogen from the atmosphere to build there body protein.

The excess nitrogen fixed will be used by the host plant and some will remain in the surrounding soil even after the legume has been harvested.

Activity of Micro organisms:  especially where soil does have enough oxygen e.g. during decomposition of organic matter acids are formed.

During the process of nitrification the ions release will increase the soil acidity.

Water logging: which causes hydrolysis resulting in excessive hydrogen ions.

Continuous up take: of nutrients by plants, cautions removed are replaced by H+ e.g. K+, Mg+, NH+, O2+

Leaching in places of high rainfall dissolved ions will be washed away from the top soil layers and they will be replaced by H+

High Amount of sulphur:  in soils especially marsh soils.  HO2 sulphide when such soils are cultivated or drained oxidation occurs forming sulphuric acid.

H2S +2O2           =       H2SO4

Hydrogen                   Sulphuric Acid

Sulphide

THIS VIDEO EXPLAINS MORE ABOUT THE NITROGEN CYCLE

Presence of humus: which may react with ions and aluminium form complex substances which when hydrolysis reduces excess H+ that increase soil acidity.

Another group of organisms, can also fix nitrogen from the atmosphere to the soil especially where the soil is humid and warm for example the Azotobacteria, blue green algae and Beijerenkia.

Plants will take in the Nitrogen compound from the soil to build there body protein and animals will feed on plants to get the proteins.

  • When plants and animals die they decay being acted upon by the purifying bacteria.
  • Animals in addition excrete and produce faeces that can also be purified.
  • Ammonium compounds are formed and the process is known as mineralization.
  • Ammonium compounds formed may either be used by soil organisms.
  • Absorbed by certain species of higher plants e.g. Paddy rice.
  • Fixed by day organic matter so that it became temporarily un available to plants.
  • It may be oxidized in a process known as Nitrification.

Nitrates can either be lost as a gas or dissolved and last through loaching.  During thunder, Nitrogen is fixed by electrical discharge of lightening. This will dissolve in rain water to form Nitric acid which is washed into the soil where it is converted to Nitrates and absorbed by crops.

In soils that are poorly aerated, the denitrifying bacteria and some fungi will use up the oxygen in the Nitrates so that the Nitrogen can escape back to the atmosphere then the cycle continues.  After the dry season or on set of the rain, a lot of Nitrogen will be washed down by rain which is known as the Nitrogen Flush.

 

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ASSIGNMENT : PLANT NUTRIENTS (ELEMENTS) assignment MARKS : 10  DURATION : 1 week, 3 days

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