Since the early 1950s, commercial fresh market vegetable production has transitioned from bare ground systems to plasticulture in many regions practicing intensive production (Lamont, 2005). Today, production of fresh market vegetables on raised beds covered with plastic mulch and drip irrigated has become a standard for most growers worldwide. In 1999, for example, over 30 million acres of agricultural land (over 185,000 acres in the United States) were covered with plastic mulch and the figure has increased significantly since (Miles et al., 2005). It is estimated that ≈1 million tons of mulch film are used worldwide every year in agriculture (Halley et al., 2001). In the United States alone, 130,000 tons of mulch film was used in 2004 (Warnick et al., 2006). Fresh market vegetables that are grown mainly on plastic mulch include bell pepper (Capsicum annuum), muskmelon (Cucumis melo), eggplant (Solanum melongena), slicing cucumber (Cucumis sativus), summer squash (Cucurbita pepo), tomato (Solanum lycopersicum), and watermelon (Citrullus lanatus). The success of plasticulture vegetable production is due to multiple benefits, including early crop maturity, improved yields, high produce quality, reduced weed infestation, better insect management, potential decrease in disease incidence, and efficient use of water and fertilizers. However, one major drawback of plasticulture in vegetable production is the cost and environmental concern associated with the removal and disposal of used plastic. Removal and disposal of used plastic can cost $250/ha (Shogren, 2000). Several alternatives to reduce this cost have been evaluated by research teams throughout the world. Strategies have varied from the development of biodegradable or degradable mulches to technologies that allow a more efficient recycling or disposal of the used plastic mulch (Feuilloley et al., 2005; Gross and Kalra, 2002; Halley et al., 2001; Ngouajio and Ernest, 2005; Olsen and Gounder, 2001; Sanchez et al., 2008; Shogren, 2000; Vert et al., 2002; Warnick et al., 2006).
Early attempts to develop plastic mulches that breakdown in the field after crop harvest have shown that degradable polymers may produce microfragments that remain in the soil for a long period of time (Feuilloley et al., 2005). A truly biodegradable material should be destroyed by soil microorganisms, bioassimilated, or mineralized (Feuilloley et al., 2005; Gross and Kalra, 2002; Vert et al., 2002). Starch-based polymers have shown enhanced biodegradability, but remain too expensive and sometimes too heavy for agricultural applications (Feuilloley et al., 2005; Halley et al., 2001; Olsen and Gounder, 2001). Paper mulches have also been tested (Sanchez et al., 2008; Shogren, 2000). However, their high costs, heavy weight, and low field performance, especially under adverse conditions (rainfall, high winds, etc.), have limited adoption of those technologies by growers, especially large-scale commercial farmers (Sanchez et al., 2008; Shogren, 2000). More recently, studies have tested the performance of biodegradable materials applied as slurries. These include foam mulches, hydraulic mulches, and hydramulch (Warnick et al., 2006). Those materials are fully degradable, but are expensive, difficult to handle, and require specialized equipment for application. Also, they do not provide the level of weed suppression and soil warming generally achieved with plastic mulch (Warnick et al., 2006).
In the area of new technologies, preliminary studies have shown that baling used plastic may allow growers to reduce the volume and therefore the cost of disposal. Although this technique may allow savings by growers, this does not resolve the environmental issue related to landfilling used plastic and can still cost $125 to $175 per hectare (Olsen and Gounder, 2001). Another strategy has been double cropping, which allows growing two (or more) crops on the same mulch (Ngouajio and Ernest, 2005). One of the advantages of double cropping is the reduction of the total volume of used agricultural plastic. Unfortunately, this technique cannot be used efficiently in all crops and environments. The possibility of generating energy from used agricultural films is currently being studied; however, this technology is not yet fully developed (Garthe et al., 2006; Lawrence et al., 2006).
The need to develop a plastic mulch with physical, mechanical, and optical performances equivalent to the conventional polyethylene mulch and yet biodegradable over a specific time frame would represent a significant tool to vegetable growers. In previous studies, polybutylene adipate-co-terephthalate (PBAT), an aliphatic-aromatic copolyester polymer, was used to produce biodegradable mulch films with various colors and thicknesses (Kijchavengkul et al., 2006, 2008a, 2008b). The PBAT polymer is known under the commercial name Ecoflex® (BASF, Florham Park, NJ) and its basic chemical structure is shown in Fig. 1. Laboratory tests with corn starch as a control have confirmed the biodegradability of the films (Kijchavengkul et al., 2006, 2008a). However, field testing of the films is necessary to assess their performance in a production system. Therefore, this study was conducted to evaluate the performance of the new PBAT biodegradable mulch films under field conditions using fresh market tomato as a model system.
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