Polyethylene mulch has been used in agriculture for more than 60 years and contributes to crop yield and quality by reducing weed pressure and herbicide use, moderating soil temperature, and conserving soil moisture (Emmert, 1957; Ibarra-Jimenez et al., 2006; Kasirajan and Ngouajio, 2012; Lamont, 2005). In 2011, PE mulch was applied on nearly 20 million ha in China with use projected to grow 7% or more annually (Liu et al., 2014). At nearly the same time, in 2012, an estimated 89.2 thousand t of PE mulch was used in North America, and the projected use is estimated to be ≈106 thousand t in 2017 (MarketsandMarkets, 2012).
Despite its many benefits, used PE mulch is difficult to recycle as it is contaminated with soil and/or vegetation (up to 50% by weight) (Kasirajan and Ngouajio, 2012). Currently, only 10% of agricultural plastics are recycled (Grossman, 2015; Levitan and Barros, 2003), mostly because not all facilities will accept used PE mulch because of the difficulty of removing adhering soil and plant debris (Levitan and Barros, 2003). PE mulch removal and disposal in a landfill is costly, up to $584/ha (Galinato and Walters, 2012; Galinato et al., 2012). The lack of affordable recycling and disposal choices has left farmers with few end-of-life options for PE mulch at the end of the growing season. Thus, many farmers dispose used PE mulches in landfills, or stockpile it on-site, whereas others till it into the soil or burn it on-site (Kasirajan and Ngouajio, 2012).
Mulch that can be tilled into the soil after crop harvest and thereafter biodegrades in the soil may provide farmers with an environmentally beneficial and low-cost disposal option. Several BDM alternatives to PE mulch have been developed, including paper and plastic BDMs. Although paper mulch has been shown to fully biodegrade in soil (Haapala et al., 2014; Li et al., 2014), it tends to breakdown too rapidly during the growing season, especially along the sides of the bed where there is direct soil contact (Merfield, 2000; Miles et al., 2012). Also, brown paper mulch (WeedGuardPlus; Sunshine Paper Co., Aurora, CO) has been shown to lower soil temperature by 0.5 and 1 °C compared with bare ground in open field and high tunnel tomato production systems, respectively, resulting in lower yields compared with black PE mulch (Cowan et al., 2014). Plastic BDM has been reported to perform similarly to PE mulch with regard to soil temperature and yield. Studies in Spain (Anzalone et al., 2010; Martin-Closas et al., 2008) and the United States (Cowan et al., 2014) found that tomato yield is similar when plants are grown with black plastic and brown paper BDMs compared with black PE mulch in most years. In one study, the percentage of ripe fruit was lower for brown paper and black plastic BDMs compared with black PE mulch only in 1 year of a 3-year study (Anzalone et al., 2010). Waterer (2010) compared the field performance of black and clear BioTelo (consisting of Mater-Bi polymeric resin; Novamont, Novara, Italy) and black and clear PE mulch for the production of five warm season vegetable crops [‘Navajo’ sweet corn (Zea mays L.), ‘Goldrush’ zucchini (C. pepo), ‘Fastbreak’ muskmelon (Cucumis melo L. var. reticulatus), ‘Redstart’ pepper, and ‘Dusky’ eggplant (Solanum melongena L.)] over three cropping seasons in Saskatchewan, Canada. No significant differences in soil temperature, crop growth, or yield responses were found for the BDMs as compared with the same color of PE mulch, whereas mulch adhesion on fruit was not mentioned.
Weed control is the primary function of mulch; thus, a BDM must remain intact on the soil surface long enough to provide a barrier to weed seed germination and growth. The critical period of weed control for tomato is 4–5 weeks after transplanting (Weaver and Tan, 1983). During this time, competition with weeds may decrease plant size and the number of marketable fruit. PE mulch and two plastic BDMs (both Mater-Bi based) gave similar weed suppression throughout the tomato production season, despite 15% of the bed becoming exposed because of mulch deterioration for BDMs (Minuto et al., 2008). Cowan et al. (2014) likewise found that tomato yield was not reduced by weed growth that occurred when soil was exposed over the course of the growing season because of mulch deterioration. Pumpkin has a relatively long growing season, and the critical period for weed control has been estimated to last until 4–6 weeks after planting (Schonbeck, 2015).
When growing fruit rest on BDMs, problems can arise with the durability of the mulch because of the weight and pressure imposed by the fruit, and the quality of the fruit because of adhering mulch fragments. Limpus (2012) reported that melon, tomato, pepper, and eggplant fruit resting on the surface of plastic BDMs can cause the mulch to split, although growers did not indicate the splitting to be widespread. BDM fragments did adhere to the surface of the tomato and pepper fruit, but the adhering mulch was easily removed. However, C.A. Miles (unpublished data) reported BDM fragments adhering to the surface of watermelon (Citrullus lanatus) fruit that could not be wiped off.
Fruit quality is another important consideration for crops grown with BDM. There was no difference in fruit TSS because of mulch when Rangarajan and Ingall (2006) measured the quality of ‘Athena’ muskmelon grown with four plastic BDMs and a PE mulch. Filippi et al. (2011) evaluated melon grown with two BDMs (black and green, both Mater-Bi based) and a PE mulch in Italy in 2004, and then again with three plastic BDMs (two green and one black) and a PE mulch in 2005. BDMs produced higher yield than PE mulch, whereas fruit TSS and percent dry matter (DM) content were higher with BDMs in 2004, but not in 2005.
Although several studies have evaluated BDM deterioration, weed pressure, and crop yield and quality, no studies have used pie pumpkin as a test crop. Pie pumpkin and similar cucurbit crops are economically important crops and are grown worldwide. The selection of pie pumpkin as the test crop in this study allowed for nearly identical planting and harvest dates at Mount Vernon and Knoxville test sites, despite their major climate differences. Pumpkin leaves and stems have enlarged, rigid and sharp trichomes that are abrasive and could contribute to mulch tearing. As pumpkin fruit mature and become heavier, there can be substantial fruit-to-mulch contact that might accelerate mulch deterioration through splitting, and/or lead to mulch adhesion on fruit and fruit quality losses. The fruit is often stored for several months, especially by fresh-market growers, and it is uncertain if a BDM has an impact on the quality of stored fruit. The objectives of the current study were to evaluate the deterioration of five BDMs throughout two pie pumpkin growing seasons (June–September in 2015 and 2016) in two diverse regions of the United States (Mount Vernon, WA and Knoxville, TN), and to compare these BDMs with PE mulch and bare ground for weed control and impact on pie pumpkin total fruit yield, marketable yield, and fruit quality at harvest and during 8-week storage.
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