Final answer:
Clay soils have a higher cation exchange capacity than sandy soils due to their finer particles, larger surface area, and higher amount of negatively charged ion exchange surfaces, which hold onto positively charged ions critical for plant nutrition.
Step-by-step explanation:
Clay soils usually have a higher cation exchange capacity than sandy soils because they contain more ion exchange surfaces due to the breakdown of soil minerals and organic matter over time. These ion exchange surfaces are negatively charged and can attract and hold positively charged ions (cations) such as potassium (K+), magnesium (Mg2+), and calcium (Ca2+). The composition of clay, with its fine particles, large surface area, and negative charge, allows for a greater capacity to retain cations than the coarser and less chemically active sandy soils.
The texture of the soil has a significant role in its capacity to hold water and nutrients. Clay soils, characterized by small particle size and high surface area, result in many small pore spaces where water and nutrients can be held tightly. On the other hand, sandy soils have larger but fewer pore spaces, making them less able to retain water and nutrients. This is crucial for plant growth, as it affects both the water available to plants and the nutrients present in the soil solution.
The cation exchange capacity is vital for agriculture as it impacts the soil's ability to supply nutrients to crops. Clay soils are better at providing a consistent supply of essential nutrients to plants, which is why they are often considered better agricultural soils compared to sandy soils, despite clay's slower water movement.