| Over the past few decades, the use of traditional mulch film made of poly-ethylene enhanced agriculture production worldwide, and meanwhile caused a range of agricultural and ecological concerns, mainly degradation of soil fertility due to residue accumulation, which have become an increasingly challenging issue for agricultural sustainability. As a consequence, biodegradable films are proposed as one of effective solutions to alleviate this issue. Among them, Poly (butyleneadipate-co-terephthalate)(PBAT), a biodegradable aliphatic-aromatic polyester, possesses similar mechanical properties to polyethylene and therefore is generally considered an ideal substitute for conventional films. This study aims at making a comprehensive evaluation of some recently developed biodegradable films by comparing their biological effects and field degradation properties. Meanwhile, field demonstration in four ecological areas of China were conducted in order to investigate the practical performance. The main findings are summarized as follows:1. The Biological effect of biodegradable mulch film and degradation performanceFive biodegradable films with a main component of PBAT were applied to cover the beds of maize in the experimental field. Soil temperature, plant growth indices, yield components and field biodegradation were investigated and compared. The field degradation of both biodegradable and conventional films was assessed by a standard of degradation degree. Biodegradable films, compared to bare plot, markedly raised soil temperatures at three observed soil depths (5cm,10cm&15cm) and this heat capturing effect is as pronounced as the conventional polyethylene film. The growth of maize was significantly stimulated in all mulched plots, with the occurrence of seedling emergence and of silking stage being3-5days and10-13days earlier than bare plots, respectively. A minor advantage of biodegradable film over conventional film was also observed. The highest chlorophyll content (indicated by SPAD) was found in the bare plot, followed by M2and M1, yet there were no significant differences among mulching treatments. By contrast, leaf area indices (LAI) of biodegradable films were significantly higher than non-mulched plot, with the highest in M2. At jointing stage, the plant height under all mulched plots were greater than that under the bare plot; While at maturity stage, plants in the bare plot had the highest height, and there was no significant difference among the five biodegradable films. The largest accumulation of nitrogen, phosphate and potassium in plants occurred in the bare plot, being significantly higher than mulched plots. The fresh yield, kernels per ear and100kernel weights were significantly larger in all mulched plots than those in the bare plot. The yield per plot of biodegradable films was higher than that of the conventional film, and no difference exists between biodegradable films and polyethylene film in terms of kernels per ear and100kernel weight.Field observation revealed that biodegradable film started losing integrity at approximately20days after application on the ground. The earliest clear disappearance of film started at90days after application for M2, while a relatively slow degradation were found in M1and M4, which reached the4th period of degradation after100days of field exposure.2. Environmental and yield effect of biological mulches in different growing zonesField demonstration were conducted in Huzhou, Zhejiang Province (2spots with maize and vegetable demonstrations, respectively), Harbin, Heilongjiang Province (maize) and Qitai, Xinjiang Autonomous Region. Extent of film degradation was observed at predetermined time intervals as well as crop growth and economic yield. Around7ha of maize in Huzhou, Zhejiang Province revealed that the experimental biodegradable mulch film showed a comparable performance in boosting maize growth and achieving earlier maturity compared with bare plot. In the plots growing maize cultivar Zhefengnuo3, biodegradable films achieved a yield of10875kg/ha,3.33%lower than that of conventional PE film; in the plots growing Huziheinuo1, fresh maize yield under biodegradable films reached10650kg/ha,4.70%lower than that of conventional PE film. Visual observation discovered that biodegradable film started developing cracks15days after application, mainly due to bird landing and wind blowing. The loss of integrity led to the film being more brittle to be penetrated by weeds under the film surface. Biodegradable films were also applied on the beds in high tunnels in Huzhou, Zhejiang Province. Biodegradable films proved relatively stable even after the vegetables were harvested, suggesting that the environmental conditions under high tunnel may not have been ideal enough to meet the needs of polymer degradation.Biodegradable films covering maize field in Harbin, Heilongjiang Province also exhibit similar results. Biodegradable film significantly raised topsoil temperature5cm deep. During maize early growth stage, there was no difference between biodegradable film and its conventional counterpart. During the final maize growth stage, temperature of all plots under biodegradable films were remarkably higher than conventional films at each observation hour and this gap widens with diurnal time. Compared with conventional polyethylene film, biodegradable film covering the beds of Demeiya3improved maize yield by15.5%and fresh grain weight per plot by16.0%; while the yield of Xingxingl and Jidan27under biodegradable film were15.4%and13.5%lower than that under conventional film, respectively and fresh grain weight18.9%and13.8%lower, respectively.Field degradation of biodegradable films was also characterized in Xinjiang, northwest China. Large cracks developed on the film surface60days after application and biodegradable film broke into pieces. Minor strip and net-like pieces occurred120days after application, leaving less film residue on the soil surface. |
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