The type of soil noted for its ability to retain moisture effectively for irrigation is clay soil. Clay has very small particles and a compact structure which results in a high surface area. This allows clay soil to hold onto water effectively, preventing it from draining quickly. Consequently, when using clay soil for irrigation, it is beneficial because it can maintain moisture levels for a longer period, which is crucial in ensuring that plants have access to water without frequent irrigating.
However, it's also worth noting that while clay soil retains moisture well, it can have drainage issues if not managed properly. In comparison, sand soil tends to drain quickly, making it less effective for retaining moisture. Silt soil strikes a balance between sand and clay but does not retain water as effectively as clay. Loamy soil, being a mix of sand, silt, and clay, has good moisture retention but is generally considered ideal for a wide range of plants due to its balanced properties. Thus, while loamy soil is excellent for plant growth, clay soil is the standout in terms of moisture retention alone.