What is considered the finest soil type with a negatively charged surface and many adsorb sites?

The finest soil type with a negatively charged surface and many adsorb sites is clay. Clay particles are exceptionally small and have a high surface area compared to other soil types. This high surface area allows for a greater number of adsorption sites, which are essential for retaining nutrients and water. The negative charge of clay particles attracts positively charged nutrients (cations), such as calcium, magnesium, and potassium, allowing them to be held in the soil and made available to plants.

In contrast, sand, silt, and gravel have different characteristics. Sand has larger particles and a much lower surface area, leading to less ability to retain nutrients and water. Silt, while finer than sand, does not possess the same high cation exchange capacity as clay. Gravel, being coarse and largely inert, lacks the adsorbent properties that clay offers and does not contribute significantly to nutrient retention in the soil. Therefore, clay is recognized as the superior soil type for its ability to hold and supply nutrients due to its unique properties.