D. Castronuovo, C. Manera and S. Margiotta. Università degli Studi della Basilicata. Dipartimento Tecnico Economico per la. Gestione del Territorio Agricolo e ...
Mulching Studies in Greenhouse by Using Eco-Compatible Plastic Films on Fresh Tomato Crop V. Candido and V. Miccolis Università degli Studi della Basilicata Dipartimento di Produzione Vegetale Viale dell’Ateneo Lucano, 10 85100 Potenza Italy
D. Castronuovo, C. Manera and S. Margiotta Università degli Studi della Basilicata Dipartimento Tecnico Economico per la Gestione del Territorio Agricolo e Forestale Viale dell’Ateneo Lucano, 10 85100 Potenza Italy
Keywords: ultra-thin, co-extrused, biodegradable, plastic-greenhouse, tomato, weeds Abstract A high employment of plastics in agriculture causes the production of enormous quantities of waste, whose inappropriate management might have negative effects on the whole agro-ecosystem. In order to determine a reduction of the charge of plastic waste and to facilitate the waste disposal, one of the most interesting approaches, from an environmental point of view, lies in the location of innovatory materials for crop mulching materials such as co-extrused ultrathin films, which are able to reduce the plastic quantity to be managed; and biodegradable laminates, which after a first usage, will spontaneously start up a degradation process that avoids their collection and their consequent disposal. This paper reports the results of a research carried out in 2002, from March to July, close to Experimental Farm “Pantanello” (Lat. 40°09’; Long. 16°38’) in Southern Italy (Basilicata Region), with the aim to study tomato (Lycopersicon esculentum Mill. cv. Tomito F1) mulching in plastic-greenhouse. Several new mulching films were compared: two co-extrused ultrathin ones, two biodegradable ones and a traditional film (LDPE). The research has shown that coextrused films have spectroradio-metrics and mechanical characteristics able to ensure an anti-weed barrier, allowing a good thermal level in the soil too. They also gave better yield results than black LDPE. Besides, biodegradable films showed an agronomic behaviour equal to LDPE and their degradation times were compatible with the protected tomato crop cycle. INTRODUCTION The growing use of plastics in agriculture, annually consuming about 2.9 million tons around the world, constitutes a problem more and more evident in terms of environment and economy as far as management and disposal of post-consumption materials are concerned (Jouёt, 2001). On the other hand, one of the priorities of a sustainable agriculture, respectful of the environment, is that of using alternative techniques, other than chemical means. Amongst the different agronomic techniques, mulching by using plastic films, represents for vegetable crops, even in greenhouse cultivation, one useful practice to improve soil temperature, and at the same time, to set up better alternatives to the use of chemical compounds in weed control programs. These facts have encouraged industries and researchers to individualize and produce plastic films that present more eco-compatible requirements, while at the same time, maintaining mechanical and spectroradiometrics characteristics analogous to those of traditional types of plastics already in use. Among these innovative materials, coextrusive ultra-thin and degradable plastics were studied by Manera et al. (2003). In the present study we report results from tomato mulching trials in protected cultivation by using biodegradable films, having a maize starch base, and co-extrused ultrathin ones, previously undergone to mechanical and spectroradiometrics characterization and compared to a traditional plastic film in LDPE. Proc. IS on Greenhouses, Environmental Controls & In-house Mechanization for Crop Production in the Tropics and Sub-tropics Eds. Rezuwan Kamaruddin, Ibni Hajar Rukunuddin & Nor Raizan Abdul Hamid Acta Hort. 710, ISHS 2006
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MATERIALS AND METHODS Two co-extrused ultra-thin mulching films, 25 and 30 µm thick, silver and yellow in colour respectively; 2 black biodegradable films, 12 and 15 µm thick; and a black traditional film in LDPE, 50 µm thick, functioning as a control, have been studied. The mechanical and spectroradiometrics characterization of the films, both new and some periodically taken from the greenhouse, have been carried out using a computerized press Galdabini PMA 10 and two spectrophotometers, one operating in UVVIS-NIR [190 ÷ 2,500 nm] (Jasco V-570) and the other in IR [2,500 ÷ 12,500 nm] (Jasco FT/IR-430). Mechanical measurements were conducted for tensile strength, as according to Norm UNI 8422, and for tearing strength, as according to the Norm UNI 9563. From the first measurements, values of ultimate tensile strength and percentage strength at break have been acquired and from the second measurements, values of tearing strength resistance have been found. For each film, as required by the Norm UNI 5309, for traction and laceration tests, ten samples obtained respectively according to the previsions of the Norm UNI 5819 and UNI 9563, have been brought to their breakage point, which then consented us to express results in terms of average value and trustworthy bilateral intervals with 95% probability. The mulching-crop test was carried out at the “Pantanello” experimental farm (40°20’N; 16°48’E) in Metaponto area (Southern Italy), using an unheated plasticgreenhouse having a metallic structure, covered by a LDPE film, 200 µm thick and with a volume/surface index of 3.0 m3 m-2. The greenhouse soil is sandy type (82.7% sand, 8.9% limestone and 8.4% clay), with a pH of 8.4, poor in total nitrogen (0.5 g kg-1), very poor in organic matter content (3.3 g kg-1) and well-supplied with phosphorus (28.4 mg kg-1) and with exchangeable potassium (307.0 mg kg-1). The film lay-out was performed by hand on soil strips (0.8 m wide) after correctly ploughing it down to a depth of 0.3 m and successively milled. The experimental soil surface was subdivided in 18 plots of 30 m2, each of them hosting a mulching film other than an uncovered soil as a control; the 6 treatments were arranged in a randomized block design with 3 reps. Before laying the film down, PT 100 probes were placed at the center of each plot at 0.1 and 0.3 m deep, under the mulching films, in order to register soil temperatures. The data were recorded by a Campbell CR 10X data-logger with a scan every 30 minutes. The transplant took place on March 20th 2002 by using seedlings of tomato with determined growth (Lycopersicon esculentum Mill. cv. Tomito F1) at the stage of the 3rd4th true leaf; the row distance was 1.80 m, while the distance between plants on the rows was 0.30 m, in order to obtain a density of 1.85 plants per m2. A drip irrigation system was applied by means of drippers of 2.5 l h-1 placed under the mulching films at 0.20 m on the rows. During the whole crop cycle, 13 irrigations were made involving a seasonal irrigation volume equal to 1,500 m3 ha-1. Fertilization was carried out by incorporating, before transplanting, into the soil 50 kg ha-1 N, 50 of P2O5 and 100 of K2O; while, after the plant establishment, 60 kg ha-1 of N, 40 of P2O5 and 100 of K2O were added by fertigation. The harvesting, performed on two different dates, the 17th and 27th of June 2002, was carried out by picking all the tomato clusters which had at least 80% of their berries red in color. Considering a 8.1 m2 sample area for each plot, at every harvest number and weight of the picked clusters, both marketable and waste, were determined. Successively, for the berries of 10 marketable clusters were determined the following traits: number, mean weight, diameter, consistence (kg cm-2), soluble solid (°Brix), and also, the dry matter content after drying them in a ventilated heater. Furthermore, at the end of the crop cycle, all the weeds of each plot, emerging on the soil mulched samples (2 m2), were botanically classified, counted and weighed; then, weed dry biomass was calculated after drying a sample of epigeous organs of each species. Collected data, both related to yield traits and weeds, underwent analysis of variance and the statistically different mean values were ranked using the Duncan’s test.
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RESULTS AND DISCUSSION From the mechanical trials carried out on the concerned films, the following information was obtained: - The ultimate tensile strength for the biodegradable films, which resulted high for the new material (about 38 N mm-2 for 12 µm film thickness and about 36 N mm-2 for 15 µm film thickness), degraded in a significant way during the first month. The values of tearing strength resistance of the two co-extrused laminates remained almost unaltered during the period showing average values of about 30 N mm-2. The tearing strength resistance of the LDPE remained almost constant during the period even though its average values were equal to about 22 N mm-2, inferior to other tested films (Fig. 1). - The biodegradable films registered an inferior value of percentage stretch at break compared to the other laminates tested, decreasing over time equal to about 250% for the new films and about 150% for films tested after 70 days of layout. The two coextrused films demonstrated different behaviours in that the silver film constantly maintained its percentage stretch at break value over time, equal to about 380%, vice versa the yellow film was characterized by a percentage stretch at break value oscillating around an average value equal to about 350%, with its highest values at 420%. The stretch values of the LDPE presented tendencies similar to those found for the biodegradable films, although it presented superior values, equal to about 300% (Fig. 1). - The biodegradable laminates were characterized by low tearing strength resistance values averaging about 80 N mm-1, although, above all for the 12 µm thickness film, an increase of the resistance over time was found. The two co-extrused films showed identical tearing strength resistance values, equal to about 180 N mm-1, that nonetheless, over time separated from one another. Finally, the LDPE demonstrated decreasing values almost linear over time, around 100 N mm-1 (Fig. 1). The spectroradiometric trials made it possible detect that: - In the UV-VIS-NIR [190 ÷ 2,500 nm] the biodegradable laminates present similar transmittance values, even though a slightly higher value was found for the film with 12 µm thickness. Between co-extrused laminates, the yellow film registered a higher transmittance than the silver one. Finally, the LDPE film demonstrated transmittance values typical of this type of material. - In the interval between 2,500 and 12,500 nm, the two biodegradable films registered a slight leveling off in transmittance values (especially between 8,000 and 10,000 nm). On the contrary, the silver co-extrused and LDPE films showed transmittance values that tend to increase as the wavelength increases. The yellow co-extrused film was characterized by a transmittance value which was more or less constant between 7,500 and 10,000 nm which then tends to decrease in the range between 10,000 and 12,500 nm (Fig. 1). For the whole cycle, the analysis of thermal tendencies of the soil at 10 and 30 cm of depth have permitted to find the following: - At 10 cm of depth, the co-extrused ultra-thin films showed analogous thermal performance values with temperatures between 23.4°C (the lowest temperature registered by the yellow film) and 25.5°C (the highest temperature registered by the silver film); the biodegradable films, characterized by similar thermal tendencies among themselves as well, registered minimum temperatures equal to 22.8°C (12 µm thickness film), while the maximum temperatures were both equal to 25.0°C; the LDPE film registered higher maximum and minimum temperatures compared to both biodegradable films showing values on average superior to about 1°C. Lastly, the non-mulched soil presented minimum temperature with minor values of about 0.7°C and 1.2°C with respect to the biodegradable and to the co-extrused ultra-thin films (Table 1); at 30 cm of depth there have been similar thermal trends with respect to the values registered at 10 cm of depth, with minor values of maximum temperatures (Table 1). From Table 2, it is possible to observe that the mulching carried out with the coextrused films, thanks to a superior number and average weight of clusters produced by 417
the plants, significantly increased the production of marketable cluster compared to the control. The biodegradable films manifested similar productive behaviors not statistically different from those seen for the LDPE film and for the non-mulched control area. Furthermore, the quality of the berries, generally, was not much influenced by the mulching: the co-extrused ultra-thin films showed a slight increase in soluble solid content (°Brix), compared to both the control and the other mulching films, while fruit consistency resulted inferior with the LDPE (Table 2). Concerning weed control, as can be seen in Table 2, mulching reduced on average 71% and 60%, compared to the number and dry biomass of weeds of the non-mulched control, without substantial differences found among the different plastic materials. Finally, considering the different weed species, it has been noted that the mulching carried out using the co-extrused films wiped out the Portulaca oleracea and Digitaria sanguinalis emergencies, something that did not happen with the biodegradable films (Table 3). CONCLUSIONS It can be established from the results obtained that the innovative co-extrused ultra-thin films can be used for tomato mulching, in that they present mechanical characteristics superior to those of films commonly used (Castronuovo, 2003); their spectroradiometrics and thermal characteristics ensure an effective emergency and antiweed barrier and they allow for the reaching of good thermal levels in the soil. Furthermore, their reduction in thickness reduces their impact on the environment thanks to lower quantities of plastic used for each surface unit. As for tomato cultivation, among the different mulching materials under comparison, the two co-extrused films provided the best productive results. The biodegradable films, confirmed as well by observations in the melon cultivation (Candido et al., 2003), demonstrated degradation times which are compatible with the cultivation cycle of the tomato in greenhouse, manifesting similar productive behaviors which were not diverse from those found for LDPE and for the nonmulched soil, although they do not always seem to be effective against weed growth. At the end, the consequences that the residuals of degradation can cause in agricultural soil and in the ecosystem still need to be studied more profoundly. 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. Literature Cited Candido, V., Miccolis, V., Gatta, G., Margiotta, S. and Manera, C. 2003. Innovative films for melon mulching in protected cultivation. Acta Hort. 614:379-386. Castronuovo, D. 2003. 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. p.1-284. Jouët, J.P. 2001. Plastics in the world. Plasticulture 120:108-126. Manera, C., Margiotta, S. and Castronuovo, D. 2003. Soil solarization tests in greenhouses using up-to-date material. Atti Convegno internazionale di Ing. Agraria “XXX CIOSTA”. 2:786-799.
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Tables
Table 1. Soil temperatures under mulching films at 10 and 30 cm depth. Mulching films Biodegradable (12 µm) Biodegradable (15 µm) Co-extrused ultrathin yellow (30 µm) Co-extrused ultrathin silver (25 µm) LDPE (50 µm) No film
Temperatures (°C) at 10 cm depth Min Mean Max 22.8 21.0 25.0 22.9 21.0 25.0 23.4 21.4 25.2 23.5 21.4 25.5 23.7 21.5 25.9 22.2 20.3 24.3
Temperatures (°C) at 30 cm depth Min Mean Max 23.0 22.5 23.6 22.8 22.3 23.3 22.9 22.4 23.5 23.2 22.7 23.7 23.4 22.8 24.0 22.7 22.0 23.6
Table 2. Mulching effects on yield and some qualitative traits of tomato. Traits
No film -1
Marketable yield (t ha ) 23.5 B Clusters per plant (n.) 18.7 A Clusters mean weight (g) 88.0 A Berries per plant (n.) 130.8 B Berries mean weight (g) 17.8 bc Berries diameter (mm) 32.9 a Berries soluble solids (°Brix) 6.8 b Berries consistency (kg cm-2) 5.1 a Berries dry matter (%) 7.4 A 1
Mulching films1 Biodegradable Co-extrused ultrathin LDPE 12 µm 15 µm Silver Yellow 24.2 B 21.3 B 29.5 A 28.1 A 22.8 B 18.2 A 15.5 B 17.8 AB 18.5 A 16.2 B 74.7 B 82.3 AB 91.7 A 83.9 AB 81.4 AB 124.6 AB 109.3 B 126.6 AB 135.1 A 115.9 B 16.0 c 16.9 c 20.3 a 18.5 ab 18.1 b 31.8 ab 31.9 ab 32.5 a 32.2 a 31.5 b 7.0 ab 7.0 ab 7.3 a 7.1 ab 7.0 ab 5.0 a 4.9 ab 5.1 a 5.1 a 4.8 b 7.7 A 7.5 A 7.7 A 7.8 A 7.8 A
Values within each trait are statistically different at the 0.05 P level (small letters) and at the 0.01 P level (capital letters).
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Table 3. Mulching effects on number and dry weight of weeds in the tomato protected crop. No film
Weed species
Mulching films1 Co-extrused Biodegradable ultrathin 12 µm 15 µm Silver Yellow
LDPE
Digitaria sanguinalis (n.m-2) (L.) Scop. d.w. (g m-2)
6.0 a 11.3 a
3.3 b 9.6 a
2.3 b 11.9 a
0.0 c 0.0 b
0.0 c 0.0 b
0.7 c 11.3 a
Setaria viridis (L.) Beauv.
(n.m-2) d.w. (g m-2)
0.0 b 0.0 b
0.0 b 0.0 b
2.0 a 13.5 a
0.3 b 7.2 ab
0.0 b 0.0 b
0.0 b 0.0 b
Melilotus sulcatus L.
(n. m-2) d.w. (g m-2)
10.7 A 27.0 A
1.3 B 8.5 B
1.0 B 6.9 B
1.0 B 3.6 B
0.7 B 3.1 B
0.3 B 1.3 B
Portulaca oleracea L.
(n. m-2) d.w. (g m-2)
1.0 a 4.0 a
0.3 ab 1.8 ab
0.7 ab 2.6 ab
0.0 b 0.0 b
0.0 b 0.0 b
0.0 b 0.0 b
Total weeds2
(n. m-2) d.w. (g m-2)
19.3 A 50.9 A
6.3 B 9.7 B 20.6 BC 40.8 AB
3.3 B 15.0 C
3.7 B 5.1 C
5.0 B 16.2 C
1
Values within each trait are statistically different at the 0.05 P level (small letters) and at the 0.01 P level (capital letters). 2 The following other species are also comprised: Cyperus rotundus L., Echinochloa crus-galli (L.) Beauv., Chenopodium album L., Solanum nigrum L. and Sonchus oleraceus L.
Figurese Ultimate tensile strength
Percentage stretch at break
IR Spectrum
Tearing strength resistance
Fig. 1. Mechanical and spectroradiometrical characteristics of employed plastic films. 420
