Some of the best things in life are free, and the abundant energy of the sun is one of them. This is very good news for those of us who work with garden and agricultural soils, which are home to hundreds of thousands of crop pests: insects, nematodes, termites, arthropods, rodents and weeds, as well as fungal, bacterial and viral pathogens. The power of the sun can be used in a passive way to defeat a number of these barriers to productivity, using a process called soil solarization.
Conventionally, since at least the 1930s, soil sterilants, like methyl bromide, have been used to fumigate agricultural soils and kill all sorts of organisms, whether or not they are harmful to the crop. Because this chemical depletes the ozone layer, its use has been steadily declining in most of the world since the Montreal Protocol on Substances that Deplete the Ozone Layer. The United States is one of the only nations that has lobbied for significant exceptions, despite having more than 1,000 documented cases of poisoning among agricultural workers using the stuff.
Although a solar alternative to using dangerous chemical fumigants has been documented as being used in ancient times by farmers on the Indian subcontinent, it didn’t really catch on here until the mid-1970s.
Soil solarization—also called solar soil heating—is accomplished by mulching and covering agricultural soils during the hot season, usually using a transparent or translucent polyethylene tarp. This is different from plasticulture, in which a polyethylene mulch is used during the growing season to suppress weeds and increase the efficiency of drip irrigation.
Image: California Agriculture