What does soil pH measure?

Soil pH specifically measures the concentration of hydrogen ions (H+) present in the soil solution. This concentration determines how acidic or alkaline the soil is, which significantly influences nutrient availability, microbial activity, and overall soil health. When soil pH is low (acidic), it indicates a higher concentration of hydrogen ions, while a higher pH (alkaline) indicates a lower concentration of hydrogen ions.

Understanding soil pH is crucial for effective nutrient management, as it directly affects which nutrients are accessible to plants. Certain nutrients are more available at specific pH levels. For example, nutrients like iron and manganese become less available in alkaline conditions, which can lead to deficiencies in plants.

The other options relate to different aspects of soil characteristics. The amount of organic matter influences soil texture and nutrient content but is not directly measured by pH. Soil erosion resistance pertains to physical properties and environmental factors rather than chemical ones like pH. Nutrient retention relates to soil structure, cation exchange capacity, and organic matter, but this is affected by pH rather than being a direct measurement of it. Thus, recognizing that soil pH quantifies the concentration of hydrogen ions provides foundational knowledge for managing soil health and crop productivity effectively.