- A Soil pH is sometimes reported to exert little measurable effect on the solubility or overall availability of soil nutrients in most cases in routine practice overall in most cases
- B Soil pH dramatically affects nutrient solubility: most nutrients are available at pH 6-7; iron and manganese become insoluble above pH 7; aluminum and manganese become toxic below pH 5
- C Soil pH is sometimes said to influence mainly the availability of nitrogen alone, with little effect on any other soil nutrient present under typical conditions according to standard textbooks
- D Mineral deficiencies are sometimes reported to arise mainly within acidic soils, and are said to rarely occur within alkaline soils generally in general practice as frequently described
Correct answer: B. Soil pH dramatically affects nutrient solubility: most nutrients are available at pH 6-7; iron and manganese become insoluble above pH 7; aluminum and manganese become toxic below pH 5
Explanation: Optimal nutrient availability is pH 6-7. Below pH 5: Al3+, Mn2+, and Fe2+ become soluble and toxic; P binds to Al and Fe. Above pH 7: Fe, Mn, Zn, Cu, B become insoluble (deficient). N-fixing bacteria prefer neutral pH. Liming raises acidic soil pH; sulfur applications lower alkaline soil pH.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.