Which component is primarily improved by adding organic matter to soil?

Adding organic matter to soil primarily improves nutrient retention, making it a crucial aspect of soil health and fertility. Organic matter, such as decomposed plant and animal materials, enhances the soil's structure and promotes the formation of stable aggregates. This process increases the soil's overall surface area and creates more sites for nutrient exchange.

Specifically, organic matter has a high cation exchange capacity (CEC), which allows it to hold onto essential nutrients like potassium, calcium, and magnesium. This means that nutrients are less likely to leach away with water movement and remain available to plants for a longer period. Furthermore, organic matter can also improve microbial activity in the soil, which aids in the breakdown of nutrients into forms that plants can absorb.

While improvements in soil color, soil aeration, and soil salinity can also occur with the addition of organic matter, these changes are secondary effects. Soil color may deepen due to the presence of organic materials, and soil aeration can be enhanced as organic matter improves soil structure. However, the most significant and direct impact from adding organic matter is on the soil's ability to retain and supply nutrients, which is vital for supporting plant growth.