Which factor is crucial for enhancing nutrient retention in soil?

Humus content plays a critical role in enhancing nutrient retention in soil due to its ability to improve soil structure and increase the soil's cation exchange capacity (CEC). Humus is the organic component of soil formed from decomposed plant and animal matter, and it contributes significantly to soil fertility.

The presence of humus increases the soil's ability to hold nutrients and retain moisture. It does so because humus has a high surface area with negatively charged sites that attract positively charged ions, or cations, which include essential nutrients like potassium, calcium, and magnesium. By holding these nutrients in the soil, humus ensures they are available for plant uptake. Additionally, the presence of humus can enhance microbial activity, further promoting nutrient availability.

Other factors listed, such as soil salinity, temperature, and pore size, while they may influence other aspects of soil health and plant growth, do not have the same direct and powerful impact on nutrient retention as humus content does. For example, high soil salinity can lead to nutrient leaching and loss, which diminishes nutrient availability to plants. Soil temperature affects microbial activity and nutrient cycling but does not directly influence nutrient retention capacities in the same way that humus does. Pore size primarily impacts drainage and