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Understanding Nutrient Availability in Soil: Key Concepts and Measurement Methods

This section explores the importance of nutrient availability in soil fertility, covering chemical, positional, and physiological aspects. Learn about essential macronutrients and micronutrients, common soil minerals, and the role of organic matter in nutrient uptake by plants.

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Understanding Nutrient Availability in Soil: Key Concepts and Measurement Methods

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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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