Solarization working like a “solar hot panel” after compost addition sanitizes soil in thirty days and preserves soil fertility

An innovative soil solarization method working like a solar hot panel, was applied on a soil previously amended with compost, to test for sanitation efficiency in controlling soil-borne fungi and preserving soil chemical and biological fertility. Soil was sprayed on surface with biodegradable black liquid consisting in a polysaccharide gel-carbon black mixture then covered with a clear plastic film. Two concurrent experiments were carried out under tunnel. In the first one, thirty-days long solarization cycles were carried out with the aim to measure thermal efficacy and survival of three fungal pathogens by comparing the innovative to the conventional solarisation. The innovative solarization improved sanitation with respect to Sclerotinia sclerotiorum, Fusarium oxysporum f. sp. melonis and Plectosphaerella cucumerina, it increased soil maximum and minimum temperatures, as well as the sum of hours conventionally considered effective for fungi disinfection (>37 °C). In the second experiment, carried out in 2014-2016, the innovative solarization was scheduled insight a crop sequence of leafy vegetables for the ready-to eat salads sector and the efficacy of organic amendment for soil fertility preservation was tested too. A yearly organic amendment by olive husk compost at rate of 15 t ha−1 was applied before innovative solarization. This approach was compared to i) soil disinfection by standard farm solarization plus mineral fertilization; ii) control consisting in soil not solarized nor fertilized. K2SO4-extractable C and N, microbial biomass and enzymatic activities associated with biogeochemical cycles of C, N, P, S, were monitored before and after solarization. Results showed that soil amendment associated to innovative solarization almost cancelled detrimental effects of solarization on biochemical activities, increased soil organic C content of 2 g kg−1 and increased the yield of leafy vegetables by 30% compared to both control not treated and standard solarization.