Cover crops under orchards act similarly to mulches and thus can increase the risk of frost. They may have other beneficial effects, however, such as reducing soil erosion, which outweigh the freeze risk factor. Covering of plant parts beneath the soil surface with a layer of soil is a way of protecting against frost.
The idea of using irrigation to help prevent frost is that the water that is sprayed in the fields freezes and releases heat to the air as the liquid water changes to ice. The goal is to keep the air temperature in the area at 32 F by adding heat in this process.
Water acts as an insulator. Plant cells that are plump with water will be stronger against cold damage. Likewise, moist soil will tend to stay warmer than dry soil, so a regular watering schedule in dry, cold weather can help protect plants from freezing temperatures
For frost protection, specially designed springs are often used, which are protected by an enclosure to prevent icing of the heads. Clean filters are needed to be sure that the system operates properly, especially when river or lagoon water is used.