FFA Agronomy CDE Practice Exam 2025 – The All-in-One Guide to Excelling in Your Agronomy Career Development!

The primary contributors to the negative charge in soil are clay and organic matter. This is because both clay particles and organic matter have a higher surface area relative to their volume, which allows them to hold onto more charged particles. Clay, especially, is composed of very tiny mineral particles that have specific properties leading to an inherent negative charge.

Organic matter, which primarily comes from the decomposition of plant and animal materials, also carries a significant negative charge due to its complex molecular structure. This negative charge plays a crucial role in soil fertility, as it allows the soil to attract and hold onto positively charged ions (cations) such as calcium, magnesium, and potassium, which are vital for plant nutrition.

In contrast, sand is typically neutral or slightly positive and does not contribute significantly to the soil's overall charge due to its larger particle size and lower surface area. Silt, while it has some interaction with cations, does not contribute as effectively as clay and organic matter in developing a negative charge. Additionally, water content affects the movement and availability of nutrients in the soil but does not contribute directly to the charge itself.