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Nutrient Availability

Nutrient Availability. Section I Soil Fertility and Plant Nutrition. Nutrient Availability Defined. Available nutrients are those that are present in the correct chemical form for uptake by a plant during its life cycle.

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Nutrient Availability

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  1. Nutrient Availability Section I Soil Fertility and Plant Nutrition

  2. Nutrient Availability Defined • Available nutrients are those that are present in the correct chemical form for uptake by a plant during its life cycle. • Available nutrients may be derived from the solid portion of the soil or the atmosphere. • Nutrients must be taken up as ions or molecules from soil solution or through the leaf from the atmosphere.

  3. Nutrient Availability and Soil Fertility • Much of the science of soil fertility is concerned with the:Measurement and Adjustmentof Nutrient Availability

  4. Nutrient Availability • Chemical Availability • Is the nutrient in the proper chemical form and concentration for plant needs? • Positional Availability • Is the nutrient accessible by the plant? • Relates to fertilizer placement • Physiological Availability • Is the plant able to take up the nutrient? • Other growth-limiting factors can intervene

  5. Measuring Nutrient Availability • What should a soil test measure? • Soluble nutrient only? • Other forms? • What are “available” nutrients anyway?

  6. Chemical Availability • Available Nutrient forms (macronutrients) N NO3-, NH4+ P H2PO4-, HPO42- K K+ S SO42- Ca Ca2+ Mg Mg2+

  7. Chemical Availability • Available Nutrient forms (micronutrients) Cl Cl- Mo MoO42- Fe Fe2+, Fe3+ Mn Mn2+, Mn3+ Zn Zn2+ Cu Cu2+, Cu+ Ni Ni2+ BH3BO3

  8. Minerals and Soil Nutrients (1) Common Soil MineralsNutrients provided Feldspars Ca, Mg, Fe, Na, K Apatite P Iron oxides Fe Carbonates Ca, Mg Clay Minerals Si, Ca, Mg, Fe, K,Mn, Zn, Cu

  9. Minerals and Soil Nutrients (2) • Clays are important sources of several nutrients, through the mechanism of cation exchange. • Exchangeable Ca, K, and Mg are important sources of these nutrients in soils

  10. Organic Matter and Soil Nutrients • Soil organic matter is an important source of the plant nutrients • N, P,S • SOM must be ___________________ before these nutrients are available for plant uptake. decomposed

  11. Nutrient Availability - Positional • In addition to being in the proper form, nutrients must be in the proper location for plant uptake to occur. • Depth of plant root zone affects where the plant can extract nutrients • Fertilization methods, irrigation methods can affect nutrient distribution.

  12. Nutrient Mobility in Soil Soil volume exploited for “immobile” nutrients: Most others Soil volume exploited for “mobile” nutrients: N, S

  13. Consequences of Nutrient Mobility • Interpretation of soil test values • Mobile • “total” available nutrient within the root zone is available for uptake • Immobile • Only a small fraction of available nutrient within the root zone is available for uptake • Placement of fertilizers

  14. Soil Tests Courtesy IAS Laboratories, Phoenix, AZ

  15. Positional Nutrient Availability Fluid Journal, Fall 2001, used without permission

  16. Apply immobile nutrients here

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