Soil Fertility Quiz #1

Organic Matter has a CEC of

200 cmol/kg

Which clay mineral has the highest cation exchange capacity per unit mass?

montmorillonite

Which of the following is the most direct consequence of leaching in humid regions with respect to soil acidity?

loss of base cations from the soil profile and replacement by H and Al on exchange sites

Copper deficiency frequently occurs in peat and muck soils primarily because:

Cu2+ is strongle bound to organic functional groups such as carboxyl and phenolic groups, forming largely unavailable insoluble complexes

A soil scientist evaluates a molybdenum-deficient legume field showing symptoms that closely resemble nitrogen deficiency - pale green leaves, stunting, and poor nodulation - even though soil N is adequate. What is the mechanistic explanation linking Mo deficiency to these nitrogen-related symptoms?

Mo is a structural component of both nitrate reductase and nitrogenase; without adequate Mo, NO3 reduction and biological N2 fixation are impaired, limiting plant-available N regardless of soil N supply

A soil test reveals a high “quantity” of phosphorus but a very low “intensity”. How is this soil’s phosphorus status best described?

the soil has significant P reserves, but the current concentration of P in the soil solution is insufficient for plant needs

How does soil pH affect microbial activity?

most beneficial bacteria prefer neutral to slightly basic conditions

Why are primary macronutrients most likely to limit crop growth?

They are required in large quantities and frequently removed or lost from soils

An agronomist is managing a corn field in a region with cool, wet spring soils and a soil pH of 7.8. Which fertilizer strategy would be most effective to ensure early-season phosphorus availability?

Applying a 2×2 starter band of ammonium polyphosphate (10-34-0).

Two soils have the following properties: Soil A - CEC = 5meq/100g, Ca2+ saturation = 60%; Soil B - CEC = 20 meq/100g, Ca2+ saturation = 25%. Which soil supplies more plant-available Ca2+, and what principle explains this?

Soil A; because a higher percentage Ca2+ saturation drives greater Ca2+ desorption into the soil solution, even though total exchangeable Ca2+ may be lower.