The effect of organic supplementation of solarized soil on the quality of tomato fruit

Soil solarization, used to control weeds and soil-borne pathogens in hot climates, has not yet been widely adapted as a commercial practice because of its lack of efficacy. Experiments were carried out in southern Italy over two growing seasons to study the effect of three levels (0, 0.35 and 0.7 kg m⁻²) of organic supplementation of the soil prior to solarization on soil mineral availability and fruit quality attributes. Soil temperature and chemical properties were monitored, together with changes in the physical characteristics and chemical composition of tomato fruits grown under commercial greenhouse conditions. Organic supplementation increased the soil temperature achieved through solarization by 3.9 to 5.5 °C. Organic supplementation increased (P ≤ 0.05) the soil concentration of NO₃⁻-N, exchangeable K₂O, Ca²⁺, Na⁺ and Mg²⁺ and the level of electrical conductivity in the soil extract. Physical characteristics of tomato fruits were improved by supplementation, with fresh and dry weight enhanced up to 11 and 21%, respectively, mesocarp thickness up to 19%, firmness up to 36% and skin redness (a^*/b^* ratio) up to 24%. As the supplementation rate was raised from 0 to 0.7 kg m⁻², the fruit content of reducing sugars increased (P ≤ 0.01) from 1.75 to 2.14 g per 100 g f.w., ash from 0.49 to 0.62%, soluble solid from 5.12 to 6.18 °Brix, titratable acidity from 0.16 to 0.19%, and ascorbic acid from 25.1 to 32.5 mg 100 mL⁻¹. We concluded that organic supplementation appears to be a valuable and environmentally friendly way to improve the mineral availability in the soil and improve fruit quality of tomato.