In locations where wind machines are not cost effective, management of the orchard floor is even more important. In the September October issue of California Agriculture , UC scientists show that cover crops or mulch can lower minimum nighttime temperatures by as much as 2.2 F in orchards, increasing the threat of frost damage. Cover crops are often planted in citrus orchards because of perceived beneficial effects on water infiltration, erosion and pest management. However, the benefits from using cover crops may be offset by the potential for freeze damage. Bare soil has a greater capacity to absorb the warmth of the sunlight during the day and transfer heat back to the surface at night.
Cover crops reflect more solar radiation, allowing less to reach the soil surface.
They also evaporate more water from the surface soil layer, reducing its thermal conductivity and heat capacity. Consequently, bare soil has better heat storage during the day and improved heat transfer during the day and night. If a cover crop is desirable, the scientists recommend planting late in the fall. California Agriculture is the University of California's journal of research in agricultural, human and natural resources.