Improved efficiency of soil solarization for growth and yield of greenhouse tomatoes

Soil solarization is a pre-planting treatment not based on chemicals, used in hot climates to control weeds and soil-borne pathogens. Its effectiveness has been widely demonstrated, for example, in the USA, Spain, Portugal, Egypt, Italy, Mexico, India and Iraq. However, an improvement in efficacy is needed before it can be widely adapted as a commercial practice. Supplementation of the soil with organic matter prior to solarization has been proposed as a management option, but its effectiveness has yet to be confirmed by any systematic study. Therefore, here we carried out a set of experiments in southern Italy over two seasons to study the effect of four levels of organic supplementation of 0, 0.35, 0.70 and 1.05 kg m−2 prior to solarization. Soil temperature and its chemical properties, as well as plant vegetation growth and fruit production were monitored for tomato plants grown under commercial greenhouse conditions. Organic supplementation increased the maximum soil temperature achieved through solarization by 3.9 °C to 4.7 °C. At 5 cm below the soil surface, a temperature of over 52 °C prevailed for 22 to 23 days when 0.70 kg m−2 organic supplement was incorporated, and for 14 to 13 days in the presence of 0.35 kg m−2 supplement, but this temperature was attained only for one day in the absence of any supplement. Organic supplementation significantly increased the soil concentration of ${\rm NO}_3^{-}-{\rm N}$, exchangeable K2O, Ca2+ and Mg2+ and electrical conductivity. Increased available P2O5 and total N at the end of the crop cycle were also associated with supplementation of solarized soil. Plant vegetative growth was improved by supplementation, with crop plant stem diameter enhanced by up to 18%, above-ground vegetative fresh and dry weight by up to, respectively, 53 and 44%, and the number of leaves per plant by up to 16%. As the supplementation rate was raised from 0 to 0.70 kg m−2, fruit yield was increased by about 70% (from 4.9 to 8.3 kg plant−1). Organic matter supplementation may provide the basis for a more favorable sink/source balance for tomato cropping. We conclude that organic supplementation represents a beneficial management measure to increase the effectiveness of soil solarization, and that these results provide encouragement for the future commercial application of this environmentally-friendly technique