Plastic mulch is commonly used to produce many vegetable crops because of its potential to decrease days to harvest, control weeds, and improve soil moisture conservation. However, use of plastic mulch is relatively new for sweet corn (Zea mays L.) in North America. We compared five plastic soil-biodegradable mulches [BDMs; Bio360, Organix AG, Clear Organix AG, Naturecycle, and Experimental polylactic acid/polyhydroxyalkanoates (Metabolix, Inc., Cambridge, MA)] and a paper mulch (WeedGuardPlus) against standard black polyethylene (PE; nonbiodegradable) mulch and bare ground cultivation for growth, yield, and quality of sweet corn cultivar Xtra Tender 2171. This field experiment was carried out in Mount Vernon, WA, which has a Mediterranean-type climate with an average air temperature of 16.1 °C during the 2017 and 2018 growing seasons. The experiment was drip irrigated; and in both years, preemergence herbicides were applied to the entire experimental area 1 to 2 days after seeding, and post-emergence herbicides were applied to alleys. While most mulches remained intact until the end of the growing season, Clear Organix AG started to split shortly after laying, resulting in significant weed pressure by midseason in both 2017 and 2018. Plant height toward the end of the season was lowest for plants grown on bare ground, intermediate for Clear Organix AG and WeedGuardPlus, and highest for the black plastic BDM and PE mulch treatments both years, except for Bio360 in 2018 where plant height was intermediate. Days to 50% tasseling and 50% silking were delayed 9 and 13 days, respectively, for bare ground and WeedGuardPlus compared with all other treatments in both years. Marketable ear yield was highest with the black plastic BDMs and PE mulch and lowest with bare ground, WeedGuardPlus, and Clear Organix AG treatments in both years. Total soluble solid content of kernels, and length and diameter of ears grown on the plastic BDM and PE mulch treatments were equal to or greater than, but never lower than, bare ground and WeedGuardPlus. These results indicate that growth, yield, and quality of sweet corn grown with black plastic BDMs are comparable to PE mulch, making black plastic BDMs an effective alternative to black PE mulch for sweet corn production in a Mediterranean-type climate.
Shuresh Ghimire, Edward Scheenstra, and Carol A. Miles
Carol Miles, Lisa DeVetter, Shuresh Ghimire, and Douglas G. Hayes
Biodegradable plastic mulch has the potential to be a sustainable technology in agricultural production systems if the mulch performs equally to polyethylene (PE) mulch and biodegrades completely into constituents that do not harm the soil ecology or environment. Reduced labor costs for removal and disposal, and reduced landfill waste add further appeal to the sustainability of biodegradable plastic mulch. Biodegradable paper mulch has been allowed in certified organic production systems in the United States for many years, while the National Organic Program (NOP) added biodegradable biobased plastic mulch to the list of allowed synthetic substances for organic crop production in Oct. 2014. Although biodegradable plastic mulch may meet the NOP biodegradability requirements (90% biodegradation within 2 years), currently no products have been approved for use in certified organic production because, so far, none meet the requirement of being completely biobased. Additionally, while the synthetic manufacturing processes that are used to make biodegradable plastic mulch are allowed by the NOP, the use of genetically modified organisms (GMOs) in the feedstocks, including their fermentation, is not allowed. Organic growers are advised always to check with their certifier before applying a product as some biodegradable mulch manufacturers and marketers erroneously advertise their product as “organic.” Looking forward, if biodegradable plastic mulch meets the NOP requirement of 90% biodegradation after 2 years, there is a possibility that 10% of plastic mulch residuals will persist (if the mulch contains nonbiodegradable ingredients); in this case, after 8 years of annual biodegradable mulch application, plastic residuals in the soil would exceed twice the amount of mulch applied per year. The current methods used by the NOP to test mulch biodegradation are laboratory based and it is uncertain if the results accurately represent field conditions. Reliable field sampling methods to measure residual mulch fragments in the soil need to be developed; however, it is unlikely such field tests will measure CO2 evolution, and thus will not be a true measure of biodegradation. Additional testing is needed under diverse field conditions to accurately quantify the rate and extent of biodegradation of mulch products that are marketed as biodegradable.
Shuresh Ghimire, Arnold M. Saxton, Annette L. Wszelaki, Jenny C. Moore, and Carol A. Miles
Biodegradable mulches (BDMs) provide a unique advantage to growers in that they can be tilled into the soil after use, eliminating disposal costs that include time, labor, and equipment needs. Biodegradation of BDMs in the soil can be assessed by the presence of visible mulch fragments; although this is not a direct measure of biodegradation, it provides an initial estimation of mulch biodegradation. We carried out three field experiments to develop a protocol for quantifying BDM fragments in the soil after soil incorporation of mulch. Expt. 1 was done at Mount Vernon, WA, and Knoxville, TN, using five BDMs in four replications, including a polyethylene (PE) mulch reference treatment (three replications and at Mount Vernon only), and a ʽCinnamon Girl’ pumpkin (Cucurbita pepo) test crop. At the end of the growing season, mulches were tilled into the soil to a depth of 6 inches and within 16 days, five soil samples were collected with a golf hole cutter (4 inches diameter and 6 inches deep). Fifty-nine percent of the PE mulch fragments were recovered from the reference treatment. Among the remaining treatments, there was a high plot-to-plot variation as to the percent of the BDM recovered (3% to 95% at Mount Vernon, 2% to 88% at Knoxville). To exclude the possibility of mulch degradation impacting mulch recovery, in Expts. 2 and 3 (at Mount Vernon only), one BDM was laid, then tilled into the soil and sampled using the same sampling core as in Expt. 1, but all in 1 day. In Expt. 2, 15 soil samples were collected per plot, which recovered 70% of the mulch, and in Expt. 3, the entire plot was sampled by collecting 128 soil samples per plot, which recovered 62% of the mulch. In summary, sampling with a relatively large core recovered less than 70% of tilled-in mulch, there was high variability between plots within each treatment because of uneven distribution of the mulch fragments in the plot, and even 50 samples per plot did not provide an accurate estimate of the amount of mulch remaining in the field. Thus, soil sampling with a large core was ineffective, and new sampling methods are needed to assess the amount of BDM remaining in the field after soil incorporation.
Shuresh Ghimire, Annette L. Wszelaki, Jenny C. Moore, Debra Ann Inglis, and Carol Miles
The use of plastic biodegradable mulch (BDM) in many vegetable crops such as tomato (Solanum lycopersicum L.), broccoli (Brassica oleracea L. var. italica), and pepper (Capsicum annuum L.) has been proven to be of equal benefit as polyethylene (PE) mulch. However, there are limited research findings on the performance of BDM with a large fruited crop such as pumpkin (Cucurbita pepo L.) where the fruit can rest directly on the mulch for an extended period. To investigate whether heavy fruit might cause the mulch to degrade more quickly than expected, thereby, influencing weed control, fruit yield, and fruit quality including mulch adhesion on fruit, we carried out a field experiment in 2015 and 2016 at two locations in the United States with distinctive climates, Mount Vernon, WA and Knoxville, TN. Three plastic mulches marketed as biodegradable (BioAgri, Organix, and Naturecycle), one fully biodegradable paper mulch (WeedGuardPlus), and one experimental plastic BDM consisting of polylactic acid and polyhydroxyalkanoates (Exp. PLA/PHA) were evaluated against PE mulch and bare ground where ‘Cinnamon Girl’ pie pumpkin was the test crop. There was significant weed pressure in the bare ground plots at both locations over both years, indicating viable weed seed banks at the field sites. Even so, weed pressure was minimal across mulch treatments at both locations over both years because the mulches remained sufficiently intact during the growing season. The exceptions were Naturecycle in 2015 at both locations because of the splitting of the mulch and consequently higher percent soil exposure (PSE), and the penetration of all the plastic mulches at Knoxville by nutsedge (Cyperus sp. L.); nutsedge did not penetrate WeedGuardPlus. At Mount Vernon, overall pumpkin yield across both years averaged 18.1 t·ha−1, and pumpkin yield was the greatest with PE, Exp. PLA/PHA, BioAgri, and Naturecycle (19.9–22.8 t·ha−1), intermediate with Organix and WeedGuardPlus (15.3–18.4 t·ha−1), and the lowest for bare ground (8.7 t·ha−1). At Knoxville, overall pumpkin yield across both years averaged 17.7 t·ha−1, and pumpkin yield did not differ because of treatment (15.3–20.4 t·ha−1). The differences in yield between treatments at Mount Vernon were likely because of differences in the soil temperature. At 10 cm depth, the average soil temperature was 1 °C lower for bare ground and WeedGuardPlus as compared with PE mulch and plastic BDMs (20.8 °C). In contrast, soil temperatures were generally higher (25.2 to 28.3 °C) for all treatments at Knoxville and more favorable to crop yield compared with Mount Vernon. Forty-two percent to 59% of pumpkin fruit had mulch adhesion at harvest at Mount Vernon, whereas only 3% to 12% of fruit had mulch adhesion at Knoxville. This difference was because of the location of fruit set—at Mount Vernon, most of the fruit set was on the mulch whereas at Knoxville, vine growth was more extensive and fruit set was mostly in row alleys. Fruit quality differences among treatments were minimal during storage across both locations and years except for total soluble solids (TSS) in 2016, which was lower for bare ground and WeedGuardPlus compared with all the plastic mulches. Taken overall, these results indicate that pie pumpkin grown with BDM has fruit yield and quality comparable to PE mulch; however, adhesion of some BDMs on fruit could affect marketable yield. Furthermore, paper mulch appears to prevent nutsedge penetration.
Huan Zhang, Carol Miles, Shuresh Ghimire, Chris Benedict, Inga Zasada, Hang Liu, and Lisa DeVetter
Planting floricane-fruiting red raspberry (Rubus ideaus L.) propagated through tissue culture (TC) is becoming increasingly popular in the Pacific Northwest. However, there is a challenge associated with their establishment compared with traditional planting materials (dormant roots and canes), especially regarding weed management due to their sensitivity to herbicides. In addition, there has been an increased interest in late summer planting compared with traditional spring planting because growers find improved establishment in late summer planting. Although polyethylene (PE) and biodegradable plastic mulches (BDMs) have demonstrated excellent weed control and increased plant growth and yield in spring-planted TC raspberry, their impacts in late summer plantings are still unknown. The overall objective of this study was to investigate whether PE mulch and BDMs have similar effects on weed management and raspberry growth and yield in late summer plantings as in spring plantings. One PE mulch, four BDMs (BASF 0.5, BASF 0.6, Novamont 0.5, and Novamont 0.6), and a bare ground (BG) control were evaluated in a commercial ‘WakeHaven’ raspberry field planted in Aug. 2017. Mulch performance [percent soil exposure (PSE)], mulch mechanical properties (elongation and breaking force), soil temperature and moisture, plant growth, fruit yield and quality, and weed suppression were measured from 2017 to 2019. Average PSE was 1.4% and 2.0% to 15.0% by Dec. 2017 in the PE and BDM treatments, respectively. PE mulch generally had greater elongation and breaking force than BDMs. All BDMs were removed by Mar. 2018 because of the damage caused by on-farm activities and strong winds. Although average primocane height was greater for plants grown with PE mulch compared with all the other treatments except BASF 0.5 in Sept. 2018, there was no difference in yield between PE and the BG treatments, potentially because of cold damage on the buds in PE plots. There were no weeds in any of the mulched treatments in Sept. and Oct. 2017 and in PE mulch in Sept. 2018. In contrast, the BG plots had 51, 51, and 266 weeds/m2, respectively, and required handweeding and herbicide applications. In addition, early season application of herbicides to suppress primocane emergence was not required in the PE plots. Overall, PE mulch could be a viable tool for growers planting raspberry in late summer. The suitability of BDMs with similar thicknesses and formulations as used in this experiment is uncertain for late summer plantings because of the damage caused by on-farm activities and strong winds.
Lisa W. DeVetter, Huan Zhang, Shuresh Ghimire, Sean Watkinson, and Carol A. Miles
Day-neutral strawberry (Fragaria ×ananassa) is typically grown in plasticulture production systems that use black polyethylene (PE) mulch for weed management and promotion of crop growth and yield. The objectives of this research were to evaluate several commercial plastic and paper biodegradable mulch (BDM) products [Bio360, Experimental Prototype (Exp. Prototype), and WeedGuardPlus] in comparison with standard black PE mulch and bare ground cultivation in day-neutral strawberry grown in an annual system in northwestern Washington. Mulch performance [as percent visual cover (PVC)], weed suppression, marketable yield, plant biomass, and fruit quality were evaluated in ‘Albion’ and ‘Seascape’ strawberry grown in 2014 and 2015. PVC measured at the end of the production season was lowest for the Exp. Prototype (8%) in 2014 and was greatest for Bio360 (90%), WeedGuardPlus (90%), and PE (98%). In 2015, PVC at the end of the production season was again lowest for Exp. Prototype (62%), followed by WeedGuardPlus (64%), Bio360 (93%), and PE mulch (97%). Overall, weed pressure was higher in 2015 relative to 2014 and was greatest in the bare ground treatment in both years of the study. By the end of the 2015 season, weed cover in the bare ground treatment was 95%, followed by WeedGuardPlus (50%), Exp. Prototype (34%), PE (25%), and Bio360 (15%). Yield showed year and cultivar effects and was higher in mulched treatments. Plant biomass showed varying effects; root biomass was lowest in ‘Seascape’ in 2015 under the bare ground treatment and greatest under Bio360, which was similar to PE mulch and WeedGuardPlus. Leaf biomass was lowest in the bare ground treatment and highest in mulched treatments (except in 2015, when leaf biomass was intermediate for plants grown with WeedGuardPlus). Crown biomass showed a similar trend and was overall greater for plants grown in mulched treatments except for Bio360 in 2014, which was the same as the bare ground treatment. Overall, fruit quality was maintained among strawberry grown with BDMs, with soluble solids concentration (SSC, %) and titratable acidity (TA) being the only variables to show treatment effects. SCC tended to be lower in fruit from bare ground plots. TA was different for ‘Seascape’ in 2015 with fruit from bare ground and Exp. Prototype treatments having higher TA than the PE treatment. This study demonstrates that BDMs can be comparable to PE mulch in terms of performance and impacts on crop productivity in day-neutral strawberry, suggesting that BDMs could be a viable alternative to PE mulch for strawberry growers in the Pacific Northwest.
Marife B. Anunciado, Larry C. Wadsworth, Shuresh Ghimire, Carol Miles, Jenny C. Moore, Annette L. Wszelaki, and Douglas G. Hayes
Plastic mulch films contribute to improved crop yield and quality for vegetable and small fruit cropping systems. Although the single-season agronomic performance of conventional polyethylene mulches and soil-biodegradable mulches (BDMs) are similar, over time BDMs can begin to break down during storage and subsequently not provide season-long soil coverage. In this study, the changes in physicochemical properties of BDMs were investigated over 3 years of indoor storage (2015–18) under ideal environmental conditions in two laboratories. Mulches evaluated were black, 20–40 µm thick, suitable for annual vegetable production, and included three BDMs: two polybutylene adipate terephthalate (PBAT)-enriched mulches that are commercially available in North America, an experimental polylactic acid (PLA) and polyhydroxyalkanote-based film, and a conventional polyethylene mulch as a control. Tensile properties, specifically peak load and elongation at maximum tensile stress, decreased during storage, particularly for the PBAT-based BDMs, indicating a loss of strength. During year 3 of storage, the tensile properties declined extensively, suggesting embrittlement. The average molecular weight of PLA and PBAT slightly increased during year 1, perhaps due to release of monomers or oligomers, and then decreased extensively during years 2 and 3 due to hydrolysis of ester bonds (confirmed by Fourier transform infrared spectroscopic analysis). The structural integrity of BDMs was assessed during years 2 and 3 of the study (2017–18) in field trials at the locations where they were stored, Knoxville, TN, and Mount Vernon, WA, for vegetable production. The degradation of the BDMs during the cropping season was higher in 2018 compared with 2017, suggesting that degradation of mechanical and chemical properties while in storage may have contributed to rapid degradation of mulches in the field. In summary, BDMs undergo degradation even under ideal storage conditions and may perform best if deployed within 2 years of their receipt date. The farmer should verify that proper storage conditions have been used before receipt and that manufacturing date precedes the receipt date by no more than 6 months.