Total U.S. strawberry (Fragaria ×ananassa) production was estimated to be 1.59 million t from 21,245 ha in 2016 [National Agricultural Statistics Service (NASS), 2017]. About 79% of the U.S. strawberry industry is concentrated in California, which predominately uses remontant/perpetual-flowering (i.e., day neutral) cultivars grown in annual plasticulture systems (California Strawberry Commission, 2017). Strawberry production in the Pacific Northwest (PNW), specifically Oregon and Washington, ranks fourth and fifth in national strawberry production, generating 5233 and 3810 t in 2016, respectively (NASS, 2017). The PNW strawberry industry traditionally produced fruit for processing and grew June-bearing cultivars in matted-row production systems without plastic mulch. This regional industry is currently undergoing a transition as acreage and production of processing strawberry declines because processors are increasingly buying cheaper strawberries from California. Consumption and value of fresh-market day-neutral strawberry is increasing, however, with the value of fresh market strawberry production in Washington and Oregon increasing 43% between the years 2000 and 2016 (NASS, 2001, 2017). Consequently, many PNW growers are exploring plasticulture production using day-neutral cultivars targeting the fresh market.
Black PE mulch is extensively used in plasticulture because of its low cost and ability to manage weeds, conserve soil moisture, modify soil temperatures, increase crop yields and quality, and promote on-farm profitability (Fernandez et al., 2001; Freeman and Gnayem, 2005; Garwood, 1998; Lament, 1993; Miles et al., 2012). These benefits extend to both conventional and organic production systems, as PE mulches may be used for weed management in organic agriculture as long as the mulch is completely removed from the field once the growing or harvest season is complete [§ 205.206 (United States Department of Agriculture; USDA, 2014a) and § 205.601 (b)(2)(i–ii) (USDA, 2014b)]. Presently, plastic BDMs are not allowed in certified organic production, but may be a tool to enhance sustainability in nonorganic production systems (Miles et al., 2017).
Despite the horticultural and economic benefits of PE mulch, removal, and disposal imposes both financial and environmental problems. Removal and disposal of PE mulch can be costly (Galinato and Walters, 2012; Galinato et al., 2012; Ghimire and Miles, 2016; Lucas et al., 2008) and was estimated to be ≈$1100 per hectare in strawberry systems in western Washington. These costs are expected to increase as the cost of labor increases (R. Sakuma, personal communication). To avoid these costs, some growers resort to stockpiling, landfilling, burying, or burning removed mulches, which causes hazards to the environment and human-health (Garthe and Kowal, 1993; Hakkarainen and Albertsson, 2004; Levitan, 2005). While mulch recycling is available in some regions, it is limited in the PNW and this adds to growers’ disposal costs for transport and cleaning of plastic mulch (G. Jones, personal communication). The significant transportation and labor costs needed to recycle PE mulch impede the adoption of plastic mulch recycling and the overall sustainability of plasticulture specialty crop production.
BDMs may minimize some of the economic, environmental, and human health impacts associated with PE mulches and their associated disposal (Kasirajan and Ngouajio, 2012; Miles et al., 2017). These materials are manufactured from feedstocks derived from fossil fuels plus natural materials (e.g., starch polysaccharides and cellulose, up to 20% of the BDM) (Jamshidian et al., 2010; Miles et al., 2017). BDMs are engineered to completely biodegrade within 2 years, with 90% of their mass released as CO2 and water and the remaining 10% residing in the soil as microbial biomass (according to International Organization for Standardization 17556 and ASTM D5988). BDMs are applied using the same field equipment as PE mulch and are designed to be functionally similar to PE mulch. BDMs have undergone extensive testing in vegetable production systems. Depending on the specific product, BDMs have been found to completely deteriorate within soils after 13 months of incorporation and produce yields comparable to crops grown with PE mulch (Cowan et al., 2013; Haapala et al., 2014; Li et al., 2014; Miles et al., 2012).
BDMs have not been tested widely in strawberry and could be a suitable alternative to PE mulch in expanding plasticulture production systems. Bilck et al. (2010) found white and black BDMs made from blends of cassava (Manihot esculenta) starch and polybutylene adipate-co-terephthalate (PBAT) maintained yield and berry quality relative to PE mulch in short-day ‘Ventana’ strawberry grown in Brazil. Mechanical properties measured 8 weeks after application showed BDMs had reduced tensile strength and elongation at break, whereas film rigidity was higher relative to PE mulch. However, the BDM films were found to provide adequate mulch functionality in terms of groundcover and maintenance of yield in this production system. Yield and fruit quality were similar to PE mulch in short-day ‘Honor’ and ‘Camarosa’ strawberry grown with five BDMs made from Mater-Bi (Novamont S.p.A, Novara, Italy) in Portugal (Costa et al., 2014). BDMs have also been studied as a tool to suppress weeds and enhance establishment of short-day ‘Jewel’ and ‘Honeoye’ strawberry grown in a perennial matted-row system (Weber, 2003). Black polymer (IP40 Black) and paper mulch (Planters paper; Ken-Bar, Inc., Reading, MA) were effective at reducing weeds, but limited runner production necessary for matted-row establishment.
Modification of soil temperature by mulches is an important aspect of strawberry production systems. White-on-black BDMs M2 and M3 (Mater-Bi) and M1 (Biomind; Polivouga, Albergaria-a-Velha, Portugal) in autumn–winter strawberry production showed 70%, 86%, and 20% soil coverage, respectively, at the end of the crop cycle, whereas PE mulch had 100% soil coverage (Andrade et al., 2014). Soil covered with these BDMs had 0.02 to 2.78 °C higher soil temperatures in the summer period at 15 cm depth than soils covered with PE mulch, which the authors of the study inferred was a key contributing factor to the reduced yields observed across all BDM-treated plots relative to PE. In other studies, soil treated with black BDMs (Ecoflex, BASF, Florham Park, NJ) overall showed a slightly lower soil temperature than low-density PE (LDPE, Pliant Corp., Schaumburg, IL) mulch at a depth of 1 cm in the soil (Ngouajio et al., 2008). These studies show that different BDMs have different effects on soil temperature; the impact of BDMs on soil temperature will be an important factor in how well BDMs fit in strawberry production.
The objectives of this research were to evaluate several commercial plastic and paper BDM products and to compare them with standard black PE mulch and bare ground cultivation in day-neutral strawberry grown in an annual system in western Washington. Mulch performance, including deterioration and weed suppression ability, as well as impacts on plant growth, yield, and fruit quality were measured to assess mulch performance and suitability for commercial production systems.
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