Transcript NITROGEN

NUTRIENT REQUIREMENTS
OF PASTURES
SHW 3002 ANIMAL AGRICULTURE
1
Why pastures have to be fertilized
Nutrients are removed from soil by
pastures
Soil is not able to completely supply
the required nutrients
Nutrient uptake per year (kg/ha)
Species Yield N
t/ha
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
Deficiency Symptoms
NITROGEN : General chlorosis of
leaves with older leaves first showing
symptoms
NITROGEN DEFICIENCY
Potato leaves:
Left : normal green leaf
with sufficient nitrogen
supply
Right : nitrogen deficient
leaf, pale green and
yellow tinted
Deficiency symptoms
Phosphorus – Leaves become purple
or red in the veins. Early symptoms,
leaves dark green in colour
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.
Deficiency Symptoms
Potassium (K) – yellow spots leaves
scorching on leaf margins and leaf
tips
K deficiency in maize
K deficiency in alfalfa
K deficiency in maize
K deficiency in rice
Deficiency symptoms
Magnesium – Interveinal chlorosis
and necrosis. Deficiency causes
hypomagnasaemia in animals
Lower leaf
interveinal
chlorosis in
Gerbera.
Geranium - lower
leaf interveinal
chlorosis. Notice
the initial (left)
versus advanced
(right) interveinal
chlorosis.
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)
Basal Fertilization
During Planting –
N – 50 kg/ha
P – 50 kg/ha
K – 50 kg/ha
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
Maintenance Fertilizer
Pure 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
Maintenance Fertilizer
Grass 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
Cut Fodder Grasses
N – 50 kg/ha (after every cut)
P – 40 kg/ha (after 3 cuts)
K – 50 kg/ha (after 3 cuts)
NITROGEN
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
N effects on dry matter yield
N effects on crude protein content
Sources of N
Organic matter in soils
N fertilizers
N fixation by legumes
N fixation by bacteria and algae
In rain water
Nitrogen in Soils
Stored in organic matter to depth of
90 cm from surface
decomposition
Nitrate
35 – 50 kg/ha per year
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
Biological N fixation
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
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
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
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
N Cycle
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)
Problems in maintaining legumegrass 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
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
END