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Agricultural Science

PLANT NUTRIENTS AND NUTRIENT CYCLES

Plant nutrients are classified into two, these includes macronutrient and micronutrient.

 

MACRONUTRIENTS

These are mineral elements or nutrients required by crops in large quantities. Examples are: nitrogen, phosphorus, potassium, magnesium, calcium and sulphur.

 

MICRONUTRIENT OR TRACE ELEMENTS

These are mineral elements or nutrients required by crops in small quantities. Examples are: Zinc, Copper, boron, molybdenum, Iron, Chlorine and Manganese.

 

FUNCTIONS AND DEFICIENCY SYMPTOMS OF PLANT NUTRIENTS

S/N ELEMENT FUNCTION DEFICIENCY SYMPTOMS
1. Nitrogen i.       Aids plant’s growth and reproduction

ii.     Promotes vegetative and short system growth

iii.   Excess Nitrogen delay maturation and fruiting

iv.   Promotes chlorophyll formation

v.     Necessary for synthesis of plant hormones

i.           Stunted growth

ii.         Yellowing of leaves

iii.       Leaves tend to drop

iv.       Poor formation of fruits and flowers

2. Phosphorus i.       It aid enzyme reactions

ii.     It is a constituent of cell division

iii.   Increases soil resistant to diseases

iv.   Helps in ripening of fruits

v.     Help in root development and seed germination

vi.   Aids seed germination

i.           Logging results in cereal crops

ii.         Stunted growth

iii.       Leaves turn purple and brownish in colour

iv.       Poor root development

v.         Immature fruit drop

 

3 Potassium i.       Important constituent of plant tissues

ii.     Aids synthesis of carbohydrates

iii.   Activates various plant enzyme reactions

iv.   Promotes development of young plants

v.     Helps in nitrate uptake in the soil

i.           Weak slender stems

ii.         Delayed growth

iii.       Premature loss of leaves

iv.       Brown colour at margin of leaves

4 Calcium i.             Strengthens plant cell with calcium pectate

ii.           Helps in translocation and storage of carbohydrate and proteins in seeds and tubers

iii.         Necessary for normal growth of root tips

iv.         It controls toxicity of aluminum, manganese and sodium ions

v.           It improves soil PH

i.           Causes stunting of root system

ii.         Weak slender plants

iii.       Pale yellow colour of leaves

5 Magnesium i.              It is important in the synthesis of carbohydrate as it is a constituent of chlorophyll

ii.           It assists in transportation of phosphate for fruit seeds development

iii.         It enhances plant growth

iv.         It is required for normal cell division

v.           Necessary for synthesis of soil in plants

i.           Chlorosis along leaf veins

ii.         Stunted growth Premature leaf fall

 

EVALUTION

  1. Give five examples each of macro and micro nutrients.
  2. State the functions and deficiency symptoms of sulphur, iron, manganese copper, zinc, boron and molybdenum.

 

NITROGEN CYCLES

Nitrogen cycles refer to the circulation of certain nutrients like nitrogen, carbon and water in nature.

Nitrogen cycle is the nature’s way of regulating the amount of Nitrogen in the soil and air

 

Ways by which Nitrogen is added to the soil in Nitrogen Cycle

  1. Direct fixation by lightening during rainfall.
  2. Incorporation into the soil by free living bacteria or non-symbolic bacteria.
  3. Nitrogen fixing bacteria in the root nodules.
  4. Decomposition of organic matter.
  5. Application of Nitrogen fertilizer.

 

Soil can gain Nitrogen through the following ways

  1. Symbiotic Nitrogen Fixation
  2. Electrical discharge
  3. Non symbiotic Nitrogen Fixation
  4. Ammonification and Nitrification
  5. Application or organic manure and Nitrogen fertilizers

 

Ways by which nitrogen is lost from the soil are: 

  1. By Denitrification
  2. Soil erosion
  3. Leaching
  4. Soil PH
  5. Bush burning
  6. Crop removal
  7. Volatilisation
  8. Oxidation reaction
  9. Reduction reaction

 

Processes that lead to formation of Nitrate from organic matter in Nitrogen Cycle

  1. Putrefaction: Delay of plant and animal remains into similar nitrogenous compounds by microorganism
  2. Amminization: Products from putrefaction reactions converted to simple amino compounds and animal
  3. Ammonization: Conversion of amino compounds and amines into ammonium compounds
  4. Nitrification: Oxidation of ammonium compounds into nitrites and Nitrates

 

CARBON CYCLE

This involves the series of processes which contribute to the circulation of carbon in nature.

 

Explanation

  1. Carbondioxide is removed from the air mainly by photosynthesis
  2. Carbon is lost in form of carbonates of calcium and magnesium through leaching and drainage.

The atmosphere gains carbondioxide through

  1. Burning of fuel like coal and wood
  2. The action of volcanoes which releases carbon dioxide
  3. The respiration of plants and animals
  4. Death and delay and putrefaction of plants and animals
  5. Diffusion of carbon dioxide from seas and other bodies of water

IMPORTANCE OF CARBON CYCLE

  1. Plant use carbondioxide obtained from the air to manufacture their food during photosynthesis
  2. Provision of carbon which is the essential building block of all organic matters
  3. Organic matter which is made from carbon helps to replenish soil nutrients.

 

WATER CYCLE

This is the continuous movement of water from the atmosphere to the earth and from the earth to the atmosphere.

 

The atmosphere receives water through

  1. Evaporation from oceans and land
  2. Transpiration from plants
  3. Breathing and respiration by plants and animals

 

Land receives water through:

  1. Rainfall and precipitation
  2. Infiltration and percolation

 

FORMS IN WHICH WATER EXISTS IN THE SOIL

  1. Hygroscopic water
  2. Capillary water
  3. Gravitational water

 

Ways of conserving water in the soil

  1. Stoppage or reduction of water-run-off
  2. Addition of humus or organic mature
  3. Removal of weeds to reduce transpiration and water loss
  4. Mulching
  5. Cover cropping
  6. Contour ridging
  7. Appropriate tillage
  8. Strip cropping

 

EVALUATION

  1. Explain Nitrification.
  2. List five ways the soil can gain nitrogen.

 

IMPORTANCE OF WATER TO CROPS

  1. Water provides the medium for absorption of minerals salts
  2. It facilitates transfer of nutrients to other parts of plants
  3. It is an essential raw material during photosynthesis
  4. Facilities enzymatic activities occurring in crop plant protoplasm
  5. It is a constituent of protoplasm
  6. It has cooling effect on crops
  7. It helps to sustain life
  8. It helps in seed germination
  9. It helps to maintain plant turgor or turgidity

 

GENERAL EVALUATION

  1. List five importance of water to crops.
  2. List three form which water exist in the soil.
  3. List three ways by which Nitrogen is lost from the soil.
  4. What is macro nutrient? List five examples.
  5. What are micronutrients? List five examples.

 

WEEKEND ASSIGNMENT

  1. The conversion of nitrates to nitrogen gas by certain bacteria is ___ (a) oxidation (b) reduction (c) nitrification (d) de-nitrification
  2. Microbial delay of plant and animal remains into simpler nitrogenous compound is ___ (a) nitrification (b) putrefaction (c) leaching (d) burning
  3. The washing away of soil nutrient down beyond the reach of the root is called ___ (a) erosion (b) mulching (c) leading (d) fertilization
  4. The following are macro nutrients expect (a) boron (b) nitrogen (c) magnesium (d) calcium
  5. Which of these is not a micro-element? (a) copper (b) zinc (c) boron (d) potassium

 

SECTION B

  1. (a) Differentiate between macro and micro nutrients

(b) List three factors influencing nutrient availability in the soil

  1. (a)  State three function of Nitrogen to plants

(b)  State three importance of organic matter in Agricultural

 

See also

AGRICULTURAL PRODUCTION

IRRIGATION AND DRAINAGE

SURVEYING AND PLANNING OF FARM STEAD

FARM MACHINERY

FACTORS OF SOIL FORMATION

 

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