NUTRIENT REQUIREMENTS OF PASTURES

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NUTRIENT REQUIREMENTS OF PASTURES
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Why pastures have to be fertilized

• Nutrients are removed from soil by pastures
• Soil is not able to completely supply the
  required nutrients

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Nutrient uptake per year (kg/ha)
Species Yield t/ha N P K Ca Mg
Brachiaria ruziziensis 32.9 333 54 442 150 77
Pennisetum purpureum 27.7 332 70 554 105 69
Panicum maximum 25.3 317 48 399 163 109
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Deficiency Symptoms

• NITROGEN General chlorosis of leaves with older
  leaves first showing symptoms

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NITROGEN DEFICIENCY

• Potato leaves
• Left normal green leaf with sufficient nitrogen
  supply
• Right nitrogen deficient leaf, pale green and
  yellow tinted

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Deficiency symptoms

• Phosphorus Leaves become purple or red in the
  veins. Early symptoms, leaves dark green in
  colour

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PHOSPHORUS DEFICIENCY

• May develop purplish or reddish colour on leaves
• Premature leaf loss
• Poor root development
• Delayed maturity
• Decreased yield

Rice plant under P-deficiency, stunted with
limited tillers, narrow, short, erect and dirty
dark green leaves.
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Deficiency Symptoms

• Potassium (K) yellow spots leaves scorching on
  leaf margins and leaf tips

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Deficiency symptoms

• Magnesium Interveinal chlorosis and necrosis.
  Deficiency causes hypomagnasaemia in animals

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• Lower leaf interveinal chlorosis in Gerbera.
• Geranium - lower leaf interveinal chlorosis.
  Notice the initial (left) versus advanced (right)
  interveinal chlorosis.

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Fertilizers

• N urea (contains 46 N)
• P Triple Superphosphate (TSP) contains 21 P
• Rock phosphate (about 15 P)
• K Muriate of Potash (contains 50 K)

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Basal Fertilization

• During Planting
• N 50 kg/ha
• P 50 kg/ha
• K 50 kg/ha

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How much fertilizer?

• 50 kg N 100/46 x 50 kg urea
• 50 kg P 100/21 x 50 kg TSP
• 50 kg K 100/50 x 50 kg MOP

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Maintenance FertilizerPure grass pastures -
grazed

• N 200 to 400 kg/ha per year
• Applied 4-6 times per year
• P 40-80 kg/ha
• K 75-100 kg/ha
• Applied 1-2 times a year

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Maintenance FertilizerGrass Legume Pasture

• N 0
• P 40 80 kg/ha
• K 35 60 kg/ha
• Applied 1-2 times a year
• Micronutrients
• 5-8 kg/ha Copper sulphate
• 5-6 kg Zinc sulphate
• 200 g/ha molybdenum

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Cut Fodder Grasses

• N 50 kg/ha (after every cut)
• P 40 kg/ha (after 3 cuts)
• K 50 kg/ha (after 3 cuts)

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NITROGEN
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Importance of N in pastures

• Needed in large quantities for maximum growth
  up to 800 kg/ha per year
• Most soils cannot supply the required rate
• N from fertilizers are soluble and easily leached
• N supply also affects protein content

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N effects on dry matter yield
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N effects on crude protein content
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Sources of N

• Organic matter in soils
• N fertilizers
• N fixation by legumes
• N fixation by bacteria and algae
• In rain water

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Nitrogen in Soils

• Stored in organic matter to depth of 90 cm from
  surface

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Biological N fixation (Bionif)

• Legumes as host in symbiotic association with
  Rhizobium
• Rhizobium forms nodules in roots
• Effective nodules are large and pink in colour
  (leghaemoglobin)
• Ineffective nodules are small in size and pale in
  colour

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Biological N fixation
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• Rhizobium converts N from atmosphere into nitrite
  and nitrate
• Rhizobium requires supply of micronutrients such
  as Mo, Cu, B for this process
• Rhizobium is inhibited by presence of nitrates in
  soils

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Amount of N fixed by legumes

• Varies with types of legumes and Rhizobium
  strains
• Temperate legumes (e.g. in NZ) 280-400 kg N/ha
  per year
• Good tropical legumes 170 280 kg N/ha per
  year
• Moderate tropical legumes 55-170 kg N/ha per
  year

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Rhizobium inoculation

• Inoculation necessary only when soils have never
  had legumes grown on it
• Rhizobium is cultured in peat
• Seeds of legumes are mixed with peat culture
  before sowing
• Use of sticker and pelleting with TSP helps in
  inoculation

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Recycling of N

• 75 of N ingested by animals are returned through
  urine, but 45 is lost through volatilization or
  leaching
• 17 of N ingested by animals are returned through
  faeces and 6 lost through volatilization and
  leaching

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N Cycle
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Transfer of N from legumes to grass

• Direct transfer (amino acids from roots of
  legumes to grass)
• Decomposition of roots and rhizobium (1-5 kg N/ha
  per year)
• Decomposition of leaves and stems of legumes
• Through grazing animals (85 of N is returned)

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Problems in maintaining legume-grass pastures

• Legumes are intolerant of heavy grazing
• Many pasture grasses dominate legumes when soil
  fertility is high
• Animals sometimes select for legumes
• Legumes are sensitive to nutrient deficiencies

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Grass-legume vs Grass-N

• Low cost
• Limited yield
• High nutritive quality
• Not tolerant to heavy grazing
• Not suitable for cut and carry

• High cost of fertilizer
• High yields
• Moderate nutritive quality
• Tolerant to heavy grazing
• Suitable for cut and carry

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END