Leaving Certificate Agricultural Science

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Leaving Certificate Agricultural Science
Soil 6 Soil Fertility
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Soil Fertility

• All plants require certain elements and minerals
  to carry out functions in the plant.
• These minerals allow for proper growth of the
  plant.
• A lack of the minerals results in a deficiency
  disease or stunted growth.
• An essential element is defined as a chemical
  element required for the normal growth of the
  plant.
• Some elements are required in large amounts and
  they are called macro elements. The others are
  called micro elements and are only required in
  small amounts.

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Macro Elements
Macro Mineral Role in Bodily Function Deficiency Symptom
Calcium Ca Builds bones and Teeth Secretions in milk Hypocalcaemia (Milk Fever) Rickets Lameness
Phosphorus P Formation of nucleic acids Carbohydrate metabolism Depraved appetite Poor fertility / Milk yield
Potassium K Muscle and nerve excitability Osmotic Regulation Dehydration
Sodium Na Transmission of nerve impulses Active Transport Dehydration Poor Growth
Chlorine Cl Gastric Juices Alkalosis
Magnesium Mg Metabolic Function Hypomagnesaemia (Grass tetany)
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Micro Elements
Micro Minerals Role in Bodily Function Deficiency Symptom
Iron Fe Haemoglobin formation Anaemia in milk only fed Animals
Copper Cu Protein formation Poor Growth / Infertility
Manganese Mn Metabolic functions Reproductive failure Depressed. Delayed Oestrous Abortion
Zinc Zn Skin, hair, wool and hoof Weak hooves, lameness, Mastitis, high S.C.C.
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Nitrogen

• Nitrogen is an important component of plant
  proteins, chlorophyll and nucleic acids
  therefore it is vital for growth, photosynthesis
  and cell reproduction.
• It is the most important and widely used
  fertiliser element.
• A deficiency in N causes sharp reductions in crop
  yields.
• When N is abundant in soil, the crop grows
  quickly, is dark green in colour and fruits and
  seeds have high protein levels.
• When N is short, growth is restricted and the
  plant goes yellow.

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The Nitrogen Cycle
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The Nitrogen Cycle

• The significant parts of the Nitrogen Cycle are
  as follows
•  
• i. Fertiliser Application
• Organic and Inorganic fertilisers contain N in
  Urea, Ammonium and Nitrate forms.
• ii. Nitrogen Fixation
• Nitrogen fixation is the process of changing
  atmospheric nitrogen into other simpler forms
  (e.g. NH4)
• Rhizobium bacteria are found on root nodules on
  legumes convert Nitrogen into a usable form.
  (E.g. Clover)
•  
• iii. Organic Matter Breakdown
• When organic matter or manure is applied to
  soil, the complex forms of N in the material are
  converted in NH4

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The Nitrogen Cycle

•  iv. Nitrification
• Nitrification is the conversion of NH4
  (Ammonium) into Nitrates using O2
• v. Plant Uptake
• The uptake of NO3- by plants completes the cycle
  N begins at plants and end at plants.
•  
• vi. De-nitrification and Leaching
• De Nitrification occurs in wet, anaerobic or
  waterlogged soils. It results in a loss of N from
  the soil and its conversion to N2O or Nitrous
  Oxide and N2 gas.

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Soil Analysis

• Soil must be analysed to measure its fertility
  and the fertiliser requirements. It involves
  three steps
• Soil Sampling
• Soil must be sampled in various areas of the
  field considering different coloured areas
  sloped areas.
• Take a minimum of 25 samples, usually in a W
  shape throughout the field are taken at root
  level.
• Mixing all of these samples makes a composite
  sample.
•  

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Soil Analysis

•  Soil Analysis
• Soil analysis generally means determining lime
  requirements, available P and available K.
• Most testing is carried out by Teagasc, in their
  soil testing lab at Johnstown Castle.
•  
• Interpretation of soil analysis
• The results of the soil analysis are compared to
  previous reference tests carried out by Teagasc.
• This allows the technician to give guidelines
  for the farmer on P and K application and liming
  requirements.

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Nutrient testing in soils
Test Reagent Positive Result
Nitrates Diphenylamine Blue colour
Phosphates Ammonium Molybdate Yellow precipitate
Sulphates Barium Chloride White cloudiness
Chlorides Silver Nitrate White precipitate