SHW 3002 ANIMAL AGRICULTURE1 NUTRIENT REQUIREMENTS OF PASTURES

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) SpeciesYieldt/haNPKCaMg Brachiaria ruziziensis Pennisetum purpureum Panicum maximum

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 riceK deficiency in alfalfa K deficiency in maize

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 = kg/ha K = 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) – kg N/ha per year Good tropical legumes : 170 – 280 kg N/ha per year Moderate tropical legumes : 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 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

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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