Which feature best describes subsurface irrigation systems?

Subsurface irrigation systems are specifically designed to deliver water directly to the root zone of plants located beneath the soil surface. This method allows for efficient moisture management, as it minimizes evaporation and runoff, while maximizing the use of water by targeting the areas where it is most needed. By placing the irrigation elements underground, the roots are provided with a consistent supply of water without saturating the soil surface, which can create issues such as weed growth or waterlogging.

The features described in the other options do not align with the principles of subsurface irrigation. For instance, applying water above the soil surface is characteristic of surface or overhead irrigation methods, while the use of overhead sprinklers is also indicative of a different irrigation approach. Additionally, subsurface systems do not necessarily require tilled land; they can be integrated into various types of soil management practices. Thus, option B correctly captures the essence of subsurface irrigation, highlighting its method of water delivery directly to the plant roots below the surface.