1. Basic Soil Plant Relationships Fundamentals of Nutrient Management Training Course Dec. 14, 2005 Jim Gorman West Virginia University

2. Nutrient Availability Plant availability of nutrients is controlled by: Physical Chemical Biological properties of soils

3. Reactions Controlling Nutrient Availability Nutrient uptake by plants Adsorption and exchange reactions Precipitation and dissolution reactions Nutrient additions –Fertilizers, Manure, Crop residues –Atmospheric additions Organic Decomposition Oxidation and Reduction reactions

4. Arnon’s Criteria for Essential Plant Nutrients Plant cannot complete its life without that element An element cannot be substituted by another element It is required for a specific metabolic function

5. Essential Plant Nutrients Sixteen Mineral Nutrients (13) Carbon, Hydrogen, and Oxygen from Air or Water Macronutrients (6) Micronutrients (7)

6. Macronutrients Fertilizer Elements –Nitrogen (NH 4 +, NO 3 - ) –Phosphorus (H 2 PO 4 -, HPO 4 2- ) Potassium (K + ) Secondary Nutrients –Calcium (Ca 2+ ) –Magnesium (Mg 2+) –Sulfur (SO 4 2- )

7. Micronutrients Cations –Iron(Fe 2+, Fe 3+ ) –Copper (Cu 2+) –Manganese(Mn 2+ ) –Zinc(Zn 2+ )

8. Micronutrient Anions Molybdenum(MoO 4 2- ) Boron(H 3 BO 3 ) Chlorine(Cl - )

9. Elements Required by Some Plants Sodium(Na) Cobalt(Co) Vanadium(V) Nickel(Ni) Selenium(Se)

10. Plant Nutrient Concentrations

11. Nutrient Concentrations

13. Leibig’s Law of Minimum Production can never be more than that allowed by the most limiting plant nutrient

14. Essential Nutrients Both macro and micronutrients are equally important

15. Ion Exchange in Soils Ion are concentrated on the surfaces of clays Mostly cations are concentrated on negatively charged clay surfaces Exchange is reversible Ion exchange replenishes soil solution when nutrients are taken up by plants

16. Reversible Reactions Clay-2Al +3 + 3Ca 2+ => Clay-3Ca 2+ +2Al 3+

17. Cation Exchange Capacity The total amount of exchangeable cations that can be held on the surfaces of soil particles. Cation exchange capacity of soils is expressed as milliequivalent per 100 g of soil at neutral pH.

18. Milliequivalent An equivalent is a mole of charge and a mole is = 6.023 X 10 23 A milliequivalent is 1/1,000 th of an equivalent

19. Anion Exchange Capacity Source of AEC –Oxides and Hydroxides of Iron and Aluminum –Kaolinite Clay AEC increase as pH decreases Strength of adsorption –H 2 PO 4 - >SO 4 2- >NO 3 - >Cl -

20. Basic Cations Ca 2+ Mg 2+ Na + K +

21. Base Saturation Base Saturation % = (Total Bases/CEC) X 100 Or [(Ca + Mg + Na + K)/ CEC] X 100

22. Sources of Negative Charge on Clays Isomorphic substitution --Si replaced by Al e.g., Mica Vermiculite --Al replaced by Mg e.g., Montmorillonite pH Dependent Charge --Oxides of Iron and Aluminum --Kaolinite --Organic Matter

23. Structure of Clay Minerals Basic Units Are: Silicon Tetrahedron: A single cation (Si) bonded to four oxygen --Tetrahedron sheets are formed by sharing of Oxygen Aluminum Octahedron: A single cation (Al or Mg) bonded to 6 oxygens

24. Silica Tetrahedron

25. Tetrahedrons Sharing oxygens

26. Aluminum Octahedron

27. Sharing Octahedrons

28. Tetra Sharing Octahedron

29. Types of Clay Minerals Kaolinite (1:1) Mica (2:1) Illite (2:1) Vermiculite (2:1) Montmorillonite/ Smectite(2:1) Chlorite (Mg in the interlayer) (2:1:1)

30. Kaolinite 1:1 Clay Mineral No Isomorphic substitution All charge is pH dependent No internal surface for adsorption CEC is 1 - 10 meq/100 g AEC (40 meq/100g at pH 4.7)

31. Kaolinite

32. Mica/Illite 2:1 clay mineral Isomorphic substitution in tetrahedral layer Charge balanced by potassium No internal surfaces Low pH dependent charge CEC 20 to 40 meq/100g AEC less than 5 meq/100g

33. Mica

34. Vermiculite 2:1 Clay mineral Isomorphic substitution in both tetrahedral and octahedral layers Low pH dependent charge Large internal surface area CEC 120 to 150 meq/100g AEC is less than 5 meq/100g Expanding clay minerals

35. Montmorillonite/smectites 2:1 Clay Minerals Large internal areas Substitution in the Al octahedral layer No K fixation Expanding type clays Low pH dependent charge CEC 80 to 120 meq/100g AEC less than 5 meq/100g

36. Chlorite 2:1:1 Clay Mineral High pH dependent charge Interlayer has magnesium hydroxide CEC 20 to 40 meq/100g No internal surface for exchange No K fixation

37. Organic Matter All pH dependent charge COOH, OH, and NH2 groups responsible for charge CEC 100-300 meq/100g

38. CEC of Soils Sands3-5 meq/100g Sands (dark colored)10-20 meq/100g Loams10-15 meq/100g Silt Loams15-25 meq/100g Clay and clay loams20-50 meq/100g Organic Soils50-100 meq/100g

39. Lyotropic Series (Strength of Adsorption) Al 3+ >Ca 2 +>Mg 2+ >K + =NH 4 + >Na + --Charge of the ion --Size of the ion

40. Root CEC Grasses -- 10-30 meq/100g -- Prefer monovalent Ions e.g., K + Legumes -- 40-100 meq/100g -- Prefer divalent e.g., Ca 2+

41. Nutrients Levels in the Plants Deficient: When the concentrations of an essential element is low enough to severely limit yield and deficiency symptoms may or may not be visible. Critical Range: Concentration in the plant tissue below which response to added nutrients occurs.

42. Nutrients Levels in Plants Sufficient: The nutrients concentration range in which added nutrient will not increase yield but can increase concentration in the plant tissue. (Luxury Consumption). Excessive or Toxic: When the concentration of the essential nutrient is high enough to decrease yield.