When the soil is too basic, plants do not grow in it. To improve the quality,…

Concept

Soil pH controls nutrient availability and root function. When soil is excessively alkaline, a suitable amendment should lower the pH rather than add more base.

Decomposing organic material forms humus and releases organic acids through microbial activity; these processes can gradually reduce alkalinity and improve soil structure.

Application

Here the soil is too basic. Adding organic matter supplies decomposable material whose acidic products help neutralize excess alkalinity while also improving aeration and water retention.

Contrast

• Calcium oxide is a strongly basic amendment used to raise the pH of acidic soil.

• A topical zinc-oxide skin preparation is not a standard soil pH amendment.

• The claim that at least two listed materials lower soil pH fails because only the decomposable organic material has that role.

• The claim that no listed material qualifies conflicts with the established acid-releasing effect of decomposable organic material.

Result

Therefore, organic matter should be added to the overly alkaline soil.