作物的营养

1. 作物的营养

2. Reading for class • Mineral Nutrition • Nitrogen and minerals • Crop residues

3. Essential Plant Minerals • 16 essential elements • C, H, O – air and water, photosynthesis • P, K, S, -- major elements • Ca, Mg – lime elements • Fe, Mn, B, Mo, Zn, Cu, Cl, Na – micro or minor elements • I and Co important for animals

4. Nitrogen • Sources: • Soil Organic Matter (5% N) – soil supplying capacity SOM • Fertilizers – • urea 46-0-0 • Ammonium sulphate – 20-0-0 + sulphur • Manures (compost) – external inputs SOM NH4+ NO2- NO3- N2O N2 Roots Roots Nitrification Denitrification Mineralization

5. Hydrolysis = 1 Volatalization = 2; Immobilization and Mineralization = 3; Runoff = 4; Fixation = 5; Denitrification = 6; Leaching = 7 Nitrogen transformations N20 N20 N2 Fertilizer 2 NH3 1 4 6 Runoff NO3- NH4+ 3 6 Organic N Plant Roots 5 3 6 Soil minerals Organic N 6 NO3- N20 N2 3 7 7

6. Nitrogen • 78% in the air • Rhizobial bacteria associations with roots – legumes and greenmanures • Mobile element – easily leached • Important for amino acids, proteins and many enzymes, hormones and other biochemicals Nitrogen deficiency -- yellowing older leaves -- stunted, poor tillering -- earlier maturity

7. Phosphorus • Source: • Soil minerals to soluble phosphatic acids • External inputs • Triple super phosphate 0-46-0 • Diammonium phosphate 16-46-0 • Nitrophos – 20-20-0 • Rock phosphate – slow release • Organic phosphates released from SOM

8. Phosphorus • P - Fixation in soils – an immobile element • P - placement and banding • Important in nucleic acids (RNA and DNA), proteins, phospholipids, ATP (energy) Phosphorus deficiency -- dark green to red -- late, irregular maturity

9. Potassium • Source: • Clay minerals – NYS soils high illite, so rarely deficient • External inputs • Potassium Chloride – 0-0-60 • Complex or complete 10-10-10 etc. • Manures and composts

10. Potassium • Partly mobile and can be leached • Accumulates in growing tissue • Activates enzyme systems • Important in translocation sugars but role not precisely known • Mobile in the plant • Luxury accumulation Potassium deficiency -- leaf tip burning, necrosis -- shrivelled seeds -- poor growth

11. Sulphur • Source: • Contaminant in air and fertilizers • Sulphates – ammonium sulphate • Organic matter • Soil minerals • Not very mobile in the plant • Important some AA’s, proteins, enzymes Sulphur deficiency -- older leaves yellow -- poor growth and tillering

12. Other elements • Calcium – cell wall, membranes, cell division, enzymes, pH adjustment • Magnesium – chorophyll, catalyst for enzymes • Iron – enzymes, Photosynthesis, heme proteins • Boron – carbohydrate translocation, sterility • Manganese -- enzymes • Copper -- enzymes • Zinc -- enzymes • Molybdenum – nitrogen fixation, enzymes

13. Critical levels • Important concept to understand micro-nutrient deficiencies • Critical levels for micro-nutrients relatively at low concentrations

14. Nutrient deficiencies

15. Liebig’s Law of the minimum Justus Von Liebig – 1803-1873 Two books, Organic Chemistry an its Application to Agriculture and Physiology, and Organic Chemistry in its Application to Physiology and Pathology, published in 1840 and 1842 respectively, revolutionized food production.

16. Fertilizer • Means to supply plants with essential nutrients in addition to that supplied by the soil • Organic – manure, composts, greenmanures • Inorganic – many different types available • Plant really doesn’t distinguish between organic or inorganic. • Inorganic are usually more concentrated so can provide is less bulk

17. Fertilizer Definitions • Complete fertilizer – usually contains N-P and K • Compound fertilizer – one formulated to give a ratio N-P-K eg. 10-10-10 • Fertilizer ratio – ratio N, P205, and K20 so 10-10-10 would have 10% of these elements • Premium fertilizer – a fertilizer usually containing micro-nutrients

18. Fertilizer Calculations • How much 6-24-24 and ammonium nitrate (33.5%N) is needed to fertilize a corn crop at 120-60-60 kg / ha. 50 kg bags • Answer: • 100 kg bag of fertilizer provides 6-24-24 kg of the three elements. Or 33.5 kg N if ammonium nitrate • To get 60 kg P205 and K20 you need 60/24 bags = 2.5 of 6-24-24 or 250 kg of fertilizer • That provides 2.5*6 = 15 units of N • So need (120-15)/33.5 = 3.13 bags or 313 kg of ammonium nitrate • Apply all this evenly over 1 hectare of land

19. Fertilizer issues • Cost and availability • Cost of application • Need to include energy costs to produce • Problems of groundwater pollution • Need to improve efficiency of use • In developing nations a lot of organic fertilizer is burnt to cook food.

20. Kg N for above ground biomass 0.4 0.5 0.3 1 t / ha is about 15-16 bushels per acre

21. Extra Nitrogen needed for high yields Assumes the soil provides enough nitrogen for a 2,000 kg/ha yield or 42 kgN/ha Plus a harvest index of 0.4

22. Nitrogen contents in above ground parts of wheat by yield

23. N-use efficiency • Need to improve the efficiency of external nitrogen applied • Splitting • Placement • Slow release • Nitrification inhibitors • Increase the soil supplying capacity • Microbial activity • Increase SOM -- compost, greenmanures, residues

24. Nutrients and pH • Each element has an optimum pH for availability and non-availability • Most elements available between pH 6 to 7 • Liming can be used to adjust pH if soil is acidic

25. Plant sensitivity to soil pH

26. Lime requirement(pages 30-42 in CFCSH) • A means to adjust soil pH when soil is acid – below pH 6.3. Plants prefer pH 6.4-7.5 – most nutrients available at that pH • Lime requirement based on soil tests • Plants differ in their sensitivity to pH – some prefer acidic, others alkaline and most prefer neutral • Lime materials vary from limestones to hydrated lime. Compared using the term total neutralizing value or the ability of the lime to neutralize acids. • Limestone not only supplies calcium but also some magnesium and neutralizes acids

27. Lime requirement • TNV of 78% means 100 pounds of limestone can neutralize the same amount of acid as 78 pounds of pure calcium carbonate. • Lime must first dissolve in soil solution before it can react – affected by particle size – the finer the faster to dissolve • The term effective neutralizing value (ENV) is related to TNV and particle size. • It is the fraction of the limestone, expressed as pure calcium carbonate, that is expected to react in the first year of application

28. Lime • Takes time to react • Must be incorporated into the root zone – assumes an 8 inch plow layer • Soil test will determine how much to apply • Depends on soil texture

29. Nitrogen fixing bacteria • Symbiotic association with rhizobium bacteria • Species specific – need to innoculate • Soil pH, drainage, temperature important

30. Nitrogen fixation • Mainly found in the legume family • Can result in a positive addition to soil nitrogen but… • Not if you remove all the seed and above ground parts – then it will be negative • Greenmanures an effective way to supply nitrogen but.. • Break down very fast and results in a flush of nitrate that can be leached

31. Thank you!