Yield Response and Antioxidant Activity of Greenhouse Organic Pumpkin (Cucurbita moschata Duch.) as Affected by Soil Solarization and Biofumigation

Abstract

In intensive cropping systems, soil fumigation, i.e., the use of gas chemical pesticides applied to the soil covered with impermeable plastic film, represents an effective method to control most of the soilborne pests. However, its general non-selectivity to the useful soil microflora and microfauna together with their significant environmental problems has limited their use. Numerous studies have concerned the application of less impactful but, at the same time, equally effective disinfection methods. These are techniques with a low environmental impact that are particularly suitable for horticultural systems. Among these, both soil solarization and biofumigation are popular techniques, even in organic vegetable cropping systems. This paper reports the results of a study to evaluate the effects of soil solarization on the yield response and the antioxidant levels of organic pumpkin (Cucurbita moscata Duch.). Solarization was carried out alone and with the addition of some organic matrices, such as compost, manure and green manure species. The evaluation of the antioxidant activity was carried out with DPPH (1,1-diphenyl-2-picrylhydrazyl radical) assay: DPPH has a specific absorption band, which disappears in presence of an antiradical compound, showing its antioxidant capacity. Our results revealed that the pumpkins grown in solarized soil had IC50, i.e., the concentration of sample which reduced the initial DPPH of 50%, values ranging between 0.6 to 18.0 mg mL−1, lower than the values of IC50 of pumpkins grown in non-solarized soil, which ranged from 36.0 to 43.6 mg mL−1. The obtained results highlighted the validity and utility of solarization for the organic vegetable crops. Furthermore, this technique has also shown its effectiveness in the long term since yield increases concerned several crops in succession. Finally, our results highlighted that heat treatment solarization can influence the level of several compounds in the pumpkin, and, therefore, also of the polysaccharides.