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Nutrient Mobility

Nutrient Mobility. Nutrient Movement to Roots Root Volume in 0-15 cm surface horizon of a soil: 0.5 to 1% Therefore, movement of available nutrients to the plant roots is critical. Mechanisms of nutrient movement to roots:. Nutrient Mobility. Estimating Nutrient Movement by Mass Flow

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Nutrient Mobility

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  1. Nutrient Mobility • Nutrient Movement to Roots • Root Volume in 0-15 cm surface horizon of a soil: 0.5 to 1% • Therefore, movement of available nutrients to the plant roots is critical. • Mechanisms of nutrient movement to roots:

  2. Nutrient Mobility • Estimating Nutrient Movement by Mass Flow Concentration of nutrients in soil solution X Volume of water transpired by the plant • Avg. Soln. Nutr. Conc. • Ca = 30 mg/L • Mg = 25 mg/L • K = 4 mg/L • P = 0.04 mg/L • Avg. Crop Transpiration: 2 - 4 million L/ha/yr

  3. Nutrient Mobility • Estimating Nutrient Movement by Mass Flow • Avg. amount of nutrient carried by mass flow • Ca = 60 - 120 kg/ha • Mg = 50 – 100 kg/ha • K = 8 – 16 kg/ha • P = 0.08 - 0.16 kg/ha • Typical crop nutrient removal (kg/ha) • Crop Ca Mg K P • Corn 5 10 40 25 • Soybeans 10 10 50 15 • Alfalfa 112 20 200 25

  4. Nutrient Mobility • Diffusion • Nutrients will diffuse from a high to a lower concentration • Fick's Law F = -DA dC/dx • F = flux • A = area • D = Diffusioncoefficient • dC/dx = concentrationgradient Soil Solution Concentration Distance from Root

  5. Nutrient Mobility • Diffusion • Diffusion coefficient • NO3-, Cl- D = 10-6 cm2/sec • NH4+, K+, Ca2+, Mg2+ D = 10-7 cm2/sec • Zn2+, Mn2+ D = 10-8 cm2/sec • H2PO4- D = 10-10 cm2/sec • Diffusion distances • N 1 cm • K 0.2 cm • P 0.02 cm Mean distance between Corn roots ~ 0.7cm

  6. Nutrient Mobility

  7. Nutrient Mobility • Nutrient Mobility and Management • Immobile nutrients (Ex. P) • Mobile nutrients (Ex. NO3-)

  8. Nutrient Uptake • Uptake is dependent on energy relationships • Ion activities in solution relative to root • Metabolic energy Root Soil Solution

  9. Nutrient Uptake • Passive vs Active uptake • Passive uptake • Ions move into the plant down an energy gradient • Non-specific Soil Solution Root

  10. Nutrient Uptake • Passive vs Active uptake • Active uptake • Biochemical energy used to transport ions into the cell against the energy gradient • May be nutrient specific Cell Membrane Soil Solution Root Carrier Carrier ATP P P ADP

  11. Nutrient Uptake • Passive vs Active uptake • Charge Balance • If cations are taken up, then other cations must be released into the soil solution – Usually H+ • If anions are taken up, then other anions must be released into the soil solution – Usually OH- • Major changes in Rhizosphere pH

  12. Nutrient Uptake NH4+ Fertilizer + N03- Fertilizer % P In plants + + + + + + 4 5 6 7 8 Rhizosphere pH

  13. Cation and Anion Uptake Interactions

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