Potential of a Corn Starch-Based Biodegradable Plastic Film for Soil Solarization

Transcription

1 Potential of a Corn Starch-Based Biodegradable Plastic Film for Soil Solarization D. Castronuovo, V. Candido 1, S. Margiotta, C. Manera and V. Miccolis 1 Università degli Studi della Basilicata Dipartimento Tecnico Economico, 1 Dipartimento di Scienze dei Sistemi Colturali, Forestali e dell Ambiente Via dell Ateneo Lucano, Potenza Italy M. Basile and T. D Addabbo Consiglio Nazionale delle Ricerche Istituto per la Protezione delle Piante Via G. Amendola 165/A Bari Italy Keywords: mechanical and spectroradiometrical characterization, melon, plastic greenhouse, open field, root-knot nematodes, weeds Abstract 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 th IS on Chemical and Non-Chemical Soil and Substrate Disinfestation Ed. A. Vanachter Acta Hort. 698, ISHS

2 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; E; 10 m a.s.l.). In both years, solarization treatment was applied from July 13 rd to September 13 rd on 30 m 2 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 F 1 ) 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 2 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 2 sample area were counted and weighed. Data were subjected to analysis of variance and means separated by Duncan s Multiple Range Test. RESULTS Mechanical Characterization and Spectroradiometrical Characterization 1. Ultimate Tensile Strength. In both years fresh (before application) biodegradable film presented a good ultimate tensile strength, about 26 N mm -2, comparable to EVA film. However this value was reduced to the half just 15 days after application, either in samples from greenhouse and from open field. Traditional films gave normal values of ultimate tensile strength, about 30 N mm -2 for EVA and 27 N mm -2 for LDPE (Fig. 1). 2. Percentage Stretch at Break. Percentage stretch at break of fresh degradable film was similar to the other films, about 420%, but decreased rapidly, especially in open field, to about 25%, in 2002 and 15%, in A consistent reduction of percentage stretch at break was recorded for EVA film in open field. A peak after 30 days, more evident in open field, followed by a slight decrease was found for LDPE film (unreported data). 3. Tearing Strength Resistance. In both years tearing strength resistance measurements were possible only on the biodegradable films, as erratic values were found for the other films; tearing strength resistance of biodegradable film decreased during the first 15 days after application (from 180 N mm -1 to a 20 N mm -1 ), more evidently in open field, and then remained constant until the end of the experiment (unreported data). 4. Spectroradiometrical Characterization. Spectroradiometrical measurements before the application on the soil showed that the lowest transmittance of biodegradable film was in the UV-VIS-NI (190 2,500 nm), probably because of its opaque lactescent colour, whereas in the IR (2,500 12,500 nm) it was the film that reduced better the soil heat loss, with no transmittance in the range 8,000 10,000 nm (Fig. 1). Transmittance of EVA film was high in the UV-VIS-NIR, whereas in the IR it was lower than LDPE and higher than biodegradable film. The highest transmittance in the UV-VIS-NIR was found in LDPE film, that presented average values in the IR. During solarization transmittance of all the plastic films decreased in the UV-VIS-NIR, more evidently in the range nm; a progressive reduction of total transmittance of the films, related to the length of the application period, was found in the long IR. Agronomical Characterization 1. Soil Temperature during Solarization. As 40 C is considered as the minimum temperature level for the positive effects of solarization on pathogens, it has been calculated the number of hours for each film and for each depth where this thermal limit was exceeded. 202

3 In the 2002 experiment no significant differences among the tested films were found in greenhouse at 10 cm depth in the C temperature range (Table 1); at 30 cm depth LDPE was the most effective, followed by biodegradable and EVA. In open field at 10 cm depth LDPE gave the best performances followed by biodegradable and EVA, whereas no film exceeded the 40 C limit at 30 cm depth. In the range C at 10 cm depth, greenhouse trials showed that the best performance was given by LDPE, followed by EVA and biodegradable, whereas in open field trials the highest number of hours was reached by LDPE followed by biodegradable. At 30 cm depth no film exceeded 46 C, either in greenhouse and in open field. At 10 cm depth, only LDPE and biodegradable films reached C temperatures. The 2003 greenhouse experiments showed that, in the range C at 10 cm depth, the best soil temperature performance was given by EVA, followed by LDPE and biodegradable; at 30 cm depth, EVA, followed by biodegradable and LDPE, totalized the highest numbers of hours. In open field conditions, EVA resulted the most effective film at 10 cm, and the only film over the 40 C at 30 cm depth. In greenhouse at 10 cm depth, in the interval C, the best performance was given by EVA, followed by LDPE and biodegradable, whereas only soil covered with LDPE and EVA exceeded 46 C in open field; at 30 cm only LDPE and EVA overcame 46 C in greenhouse, whereas it was never reached in open field. In the range C, solarized soil exceeded 51 C temperature only in greenhouse at 10 cm and highest number of hours was recorded respectively for EVA, LDPE and biodegradable. 2. Melon Yield and Disease Control. Soil solarization positively influenced melon yield and fruit quality ( Brix and dry matter) either in greenhouse and in open field (Table 2). Solar heating was more effective in greenhouse, as number and weight of marketable fruits were doubled compared to the non solarized control, without significant differences among the films. On the contrary a 37% yield increase was found in open field conditions. The gall index on melon roots was always significantly higher in the control than in solarized plots, without no statistical difference among the films. Greenhouse solarization resulted in a 72% and 99% reduction of weeds number and weight, respectively (Table 3), only Ciperus rotundus was not controlled (unreported data). In open field emergence of weeds was not affected by solarization treatment. DISCUSSION AND CONCLUSIONS Mechanichal properties of biodegradable film resulted in a fast decay; however thermic performance of the film was not reduced being, particularly in greenhouse, always similar to the plastic films. This decay of mechanical properties was expected and could be attributed to the degradation process starting during its application. Spectroradiometrical characterization evidenciated that in the UV-VIS-NIR traditional films resulted in average transmittance values higher than biodegradable film, probably because of its opaque colour. In the IR, biodegradable film showed the best optical performances, as its transmittance was almost nil in the nm range. As previously observed (Candido et al., 2001), the results from these experiments confirmed the effectiveness of solarization, particularly in greenhouse, for the improvement of yield and quality of spring melon crop in Metaponto area conditions, due to the control of root-knot nematodes and weeds. Moreover, the reduction of plastic wastes by the use of biodegradable films makes soil solarization an environmentally sound alternative to methyl bromide. ACKNOWLEDGEMENTS This research has been co-financed with funds from MIUR Cofin 2001, project head Prof. Ing. Carlo Manera. The work carried out is equally attributed to all authors involved. 203

4 Literature Cited Candido, V., Miccolis, V., Gatta, G., Margiotta, S., Picuno, P. and Manera, C The effect of soil solarization and protection techniques on yield traits of melon in unheated greenhouse. Acta Hort. 559: Castronuovo, D Caratterizzazione meccanica, radiometrica ed agronomica di materiali plastici innovativi per la pacciamatura delle colture ortive e per la solarizzazione del terreno. PhD Thesis on Rural Engineering XVI cycle University of Basilicata (Italy). Di Vito, M., Lamberti, F. and Carella, A La resistenza del pomodoro nei confronti dei nematodi galligeni: prospettive e possibilità. Riv. Agron. 13: Katan, J Solar heating of soil for control of soil borne pests. Annu. Rev. Phytopathol. 19: Manera, C., Margiotta, S. and Castronuovo, D Soil solarization tests in greenhouses using up-to-date material. Atti Convegno Internazionale di Ingegneria Agraria XXX CIOSTA 2: Tables Table 1. Number of hours of different ranges of soil temperatures during solarization treatments. Solarizing films Biodegrad EVA LDPE Control Soil depth (cm) (1) greenhouse; (2) open field Hours number per temperature interval C C C C C C In (1) Out (2) In Out In Out In (1) Out (2) In Out In Out Table 2. Yield and quality of melon fruits as affected by soil solarization. TRAITS (1) SOLARIZING FILMS Biodegradable EVA LDPE Control GREENHOUSE Yield (t ha -1 ) 37.8 A 37.9 A 40.8 A 17.8 B Fruits per plant (n.) 4.9 A 4.7 A 5.5 A 2.5 B Fruit soluble solids ( Brix) 11.4 a 11.5 a 10.9 a 9.7 b Fruit dry matter (%) 8.6 a 8.5 a 8.4 a 7.4 b OPEN FIELD Yield (t ha -1 ) 18.9 A 18.6 A 18.2 A 13.5 B Fruits per plant (n.) 2.4 A 2.5 A 2.3 A 1.8 B Fruit soluble solids ( Brix) 13.0 a 12.6 a 13.0 a 12.0 b Fruit dry matter (%) 10.7 A 11.0 A 10.9 A 9.9 B (1) Means within each character followed by different letters are statistically different at the 0.05 P level (small letters) and at 0.01 P level (capital letters) according to Duncan test. 204

5 Table 3. Root gall index of melon plants and weed emergence as affected by soil solarization. TRAITS (1) SOLARIZING FILMS Biodegradable EVA LDPE Control Root-knot Nematodes Greenhouse 0.3 B 0.1 B 0.3 B 3.6 A Gall Index (0-5) Open field 1.0 B 1.6 B 1.4 B 3.5 A Total weeds (2) (n. m -2 ) 9 B 7 B 6 B 26 A Greenhouse (g m -2 ) 13 B 12 B 11 B 1358 A Total weeds (3) (n. m -2 ) 45 A 28 A 52 A 39 A Open field (g m -2 ) 562 A 700 A 528 A 703 A (1) Means within each character followed by different letters are statistically different at the 0.01 P level according to Duncan test. (2) The following weed species are included: Cyperus rotundus L., Portulaca oleracea L., Setaria viridis (L.) Beauv., Digitaria sanguinalis (L.) Scop.; (3) Portulaca oleracea (L.), Echinochloa crus-galli (L.) Beauv., Convolvulus spp. and Melilotus sulcatus L. 205

6 Figurese N mm -2 Ultimate tensile strength Days N mm -2 Ultimate tensile strength Days EVA IR Spectrum LDPE T % Biodegradable Wavelength [nm] Fig. 1. Mechanical and spectroradiometrical characteristics of employed plastic films. 206