Effects of agrochemicals, ultra violet stabilisers and solar radiation on the radiometric properties of greenhouse films

Abstract

Agrochemicals, based on iron, sulphur and chlorine, generate by products that lead to a degradation of greenhouse films together with a decrease in their mechanical and physical properties. The degradation due to agrochemicals depends on their active principles, method and frequency of application, and greenhouse ventilation. The aim of the research was to evaluate how agrochemical contamination and solar radiation influence the radiometric properties of ethylene-vinyl acetate copolymer greenhouse films by means of laboratory and field tests. The films, manufactured on purpose with the addition of different light stabiliser systems, were exposed to natural outdoor weathering at the experimental farm of the University of Bari (Italy; 41° 05' N) in the period from 2006 to 2008. Each film was tested for two low tunnels: one low tunnel was sprayed from inside with the agrochemicals containing iron, chlorine and sulphur while the other one was not sprayed and served as control. Radiometric laboratory tests were carried out on the new films and on samples taken at the end of the trials. The experimental tests showed that both the natural weathering together with the agrochemicals did not modify significantly the radiometric properties of the films in the solar and in the photosynthetically active radiation wavelength range. Within six months of experimental field tests the variations in these radiometric characteristics were at most 10%. Significant variations, up to 70% of the initial value, were recorded for the stabilised films in the long-wave infrared radiation wavelength range. IntroductionThe radiometric properties of covering greenhouse films influence both the energy balance of the greenhouse and the crop behaviour (Kittas and Baille, 1998;Papadakis et al., 2000;Vox et al., 2010). The microclimate of the protected volume modifies the growing conditions of the crop in comparison with the external climatic conditions according to the quantity and quality of the solar radiation passing through the covering. The stability over time of the radiometric properties of the film during the crop cultivation cycle is an important goal for growers.Physical and mechanical properties decrease when the plastic film covering degrades in the field by discolouration, cracking of the surface, and stiffening. The average service life of plastic greenhouse films depends on parameters related both to the film itself and to the environment in which the film is used (Briassoulis, 2005;Briassoulis and Schettini, 2003;Desriac, 1991; Briassoulis, 1998, 2000;Khan and Hamid, 1995;Martin-Closas et al., 2008;Ruiz et al., 2006), varying from 3-6 months, for one cultivation season, to a maximum of 3-4 years in the Mediterranean area. The ultra violet (UV) radiation in the solar spectrum absorbed by the plastic films is one of the factors that have the biggest influence on the ageing and degradation process (Nijskens et al., 1990;Dilara and Briassoulis, 1998). The UV radiation, especially the UV-B and UV-A radiation that occurs in the ...

Vineyard microclimate and yield under different plastic covers

“…According to Serrano et al (2001), higher SR attenuation over time is caused by higher plastic degradation and dust accumulation, which was also observed by Chavarria et al (2009) in vineyards under plastic covers. When exposed to natural weathering and agrochemicals commonly sprayed by growers, the plastic films are subjected to degradation of their mechanical and physical properties, causing discoloration, surface cracking, and stiffening (Vox and Schettini 2013), depending on their active principles, application method and frequency, ventilation, and greenhouse structure (Dilara and Briassoulis 2000). Ultra violet radiation (UV) absorbed by plastic films is the factors that For each main factor separately, averages followed by different letters in the same line differ statistically from each other by Kruskal-Wallis test (P < 0.05) *PAR at AWS estimated from incoming solar radiation (Assis and Mendez 1989) most influences aging and photo-degradation processes, especially UV-B and UV-A radiation, which lead to bond cleavage and depolymerization and radical oxidation reactions (Sanchez-Lopez et al 1991).…”

“…3) was probably caused by plastic aging, which caused changes in optical characteristics and, consequently, higher short-and long-wave retention in the environments. According to Vox and Schettini (2013), inside the plastic cover exposed to climatic agents and agrochemicals, the highest retention occurs for long-wave infrared radiation (LWIR), ranging from 7500 to 12.500 nm. The analysis of the daytime Rn (Fig.…”