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POTENTIAL OF A CORN STARCH-BASED BIODEGRADABLE PLASTIC FILM FOR SOIL SOLARIZATION

In temperate regions soil solarization with plastic films represents a valuable alternative to the use of methyl bromide for the control of soil borne diseases. However, large quantities of wastes are derived by plastic materials used for solar heating, whose inappropriate management could affect negatively the whole agro-ecosystem. Use of biodegradable films, which spontaneously start up a degradation process after their soil application, could represent a potential solution to these disposal problems. Greenhouse and open field experiments were undertaken in 2002 and 2003 in Southern Italy with the aim to assess the effect of soil solarization with a corn starch-based biodegradable plastic film on soil temperature, root-knot nematode (Melodogyne spp.) and weed control and crop yield, in comparison with EVA and LDPE plastic films. Mechanical and spectroradiometrical properties of the films were also studied. Use of biodegradable films resulted effective, particularly in greenhouse, for the control of nematodes and weeds improving yield and quality of melon fruits. INTRODUCTION Soil solarization is widely applied as an effective alternative to the use of chemicals for the control of soil phytoparasitic nematodes and weeds (Katan, 1981). However, the disposal of the large amounts of wastes deriving by the massive application of plastic materials in agriculture is more and more a serious environmental problem to solve. A possible solution could be represented by the use of innovative materials, such as biodegradable films, that spontaneously start up a degradation process after their application (Castronuovo, 2003). Nevertheless, technical performances of these films should be verified, more specifically if their mechanical and spectroradiometrical properties are comparable to those of traditional materials. Therefore, greenhouse and open field experiments were undertaken in southern Italy in 2002 and 2003 in order to verify the effectiveness of a corn starch based biodegradable film for solarization against phytoparasitic nematodes and weeds, in relation to its mechanical and spectroradiometrical properties. MATERIALS AND METHODS Three solarizing films, a corn starch-based biodegradable milky coloured film (40 μm thick) and two traditional transparent films (LDPE 50 μm; EVA 35 μm) were examined. Mechanical and spectroradiometrical characteristics of the films were determined at 15 days intervals during solarization using a computerized press (Galdabini PMA 10) and two spectrophotometer, working in UV-VIS-NIR (Jasco V-570) and IR (Jasco FT/IR-430), respectively. Mechanical measurements were determined by tensile (UNI 8422) and tearing (UNI 9563) strength tests, in order to obtain values of ultimate tensile strength, percentage stretch at break and tearing strength resistance (Manera et al., 2003). Proc. VI IS on Chemical and Non-Chemical Soil and Substrate Disinfestation Ed. A. Vanachter Acta Hort. 698, ISHS 2005 202 After laboratory tests the plastic films were used in two solarization trials in 2002 and 2003, either in metal and plastic tunnel greenhouse (LDPE 200 μm) and in open field in the Experimental Farm Pantanello at Metaponto (40°20’N; 16°48’E; 10 m a.s.l.). In both years, solarization treatment was applied from July 13 to September 13 on 30 m plots, after rotavation and irrigation of the soil. Plots were arranged according to a randomized block design with three replications for each treatment. During solarization soil temperatures were monitored at 10 and 30 cm depth every 30 min by precision probes (PT 100) and a CR10x data logger. Moreover, for each film the number of hours above 40°C, assumed as the minimum effective temperature on soil pathogens, was also calculated. Melon (Cucumis melo L. var. reticulatus Naud. cv. ‘Drake F1’) was cultivated in experimental plots in spring (March – July) 2003, either in greenhouse and in open field, with the aim to verify the yield response of a vegetable crop to the solarization treatment. In each plot, number and weight of marketable fruit were recorded on a 16 m area (eight plants) and soluble solids (°Brix) and pulp dry matter content were determined on ten fruits. Moreover, root-knot nematode M. javanica gall index was determined on eight plants of each plot, according to a 0-5 scale (Di Vito et al., 1979) and weeds from a 2 m sample area were counted and weighed. Data were subjected to analysis of variance and means separated by Duncan’s Multiple Range Test.