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NUTRIENT REQUIREMENTS OF PASTURES

This article discusses the importance of fertilizing pastures to meet the nutrient requirements of plants. Nutrient deficiencies and symptoms are outlined, along with recommended fertilizers and application rates. The role of nitrogen in pastures, sources of nitrogen, and biological nitrogen fixation is explained. The benefits and challenges of grass-legume pastures are also discussed.

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NUTRIENT REQUIREMENTS OF PASTURES

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  1. NUTRIENT REQUIREMENTS OF PASTURES SHW 3002 ANIMAL AGRICULTURE

  2. Why pastures have to be fertilized • Nutrients are removed from soil by pastures • Soil is not able to completely supply the required nutrients

  3. Nutrient uptake per year (kg/ha)

  4. Deficiency Symptoms • NITROGEN : General chlorosis of leaves with older leaves first showing symptoms

  5. NITROGEN DEFICIENCY Potato leaves: • Left : normal green leaf with sufficient nitrogen supply • Right : nitrogen deficient leaf, pale green and yellow tinted

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

  7. 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.

  8. Deficiency Symptoms • Potassium (K) – yellow spots leaves scorching on leaf margins and leaf tips

  9. K deficiency in maize K deficiency in maize K deficiency in alfalfa K deficiency in rice

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

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

  12. 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)

  13. Basal Fertilization • During Planting – • N – 50 kg/ha • P – 50 kg/ha • K – 50 kg/ha

  14. 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

  15. 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

  16. 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

  17. Cut Fodder Grasses • N – 50 kg/ha (after every cut) • P – 40 kg/ha (after 3 cuts) • K – 50 kg/ha (after 3 cuts)

  18. NITROGEN

  19. 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

  20. N effects on dry matter yield

  21. N effects on crude protein content

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

  23. decomposition Nitrate 35 – 50 kg/ha per year Nitrogen in Soils • Stored in organic matter to depth of 90 cm from surface

  24. 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

  25. Biological N fixation

  26. 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

  27. 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

  28. 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

  29. 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

  30. N Cycle

  31. 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)

  32. 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

  33. 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 Grass-legume vs Grass-N

  34. END

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