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Assessing New Mulch Technologies for Washington Raspberry

Volume 11 Issue 2

 

Lisa W. DeVetter, Huan Zhang, Carol Miles, and Chris BenedictAcknowledgements:

We would like to acknowledge technical support provided by Sean Watkinson, Ed Scheenstra, Qianwen Lu, Emma Rogers, and Brenda Madrid.  Project funding was provided by the Washington Red Raspberry Commission and Washington State Department of Agriculture Specialty Crop Block Grant program.

Justification:

The use of plastic mulch films for raspberry production in northwest Washington has expanded. Plastic mulch adoption in northwest Washington raspberry systems is motivated by improved growth and establishment of tissue culture transplants and subsequent yield increases through soil temperature and moisture modification (Zhang et al., 2019, 2020, and 2021). Weed management is another benefit, as plastic mulch utilization can reduce the need for hand weeding and herbicide application while it is deployed. Black plastic mulch made from polyethylene (PE) and used for 9-18 months has been the most widely adopted mulch type among raspberry growers. However, other mulch technologies exist that could offer advantages to raspberry growers.Objectives:

The overarching objective of this project was to evaluate the suitability of other mulch technologies in northwest Washington raspberry with an emphasis on mulches that could be utilized for multiple years as well as new soil-biodegradable plastic mulches.

Study Location:

A randomized complete block design experiment with four replications was established at WSU NWREC in Mount Vernon in May 2019. Individual plots were 1 row wide and 58 ft long. Treatments as well as estimated costs for weed management for the 3-year study are provided in Table 1.

Table 1.  Treatment, manufacturer, material information, and estimated establishment (year 1) costs of treatments.

Treatment and abbreviation Manufacturer or Converter Width (in) Thickness (µm) Primary ingredient(s)z Estimated weed management costs for 3 years (extrapolated to per acre)y
Novamont perennial biodegradable mulch

(Novamont)

 Novamont S.p.A., Novara, Italy 60 18 –x –x
DayBlack Premium (“weedmat”) Extenday USA Inc., Union Gap, WA 45 85 g/m2 PE, woven $1,212
BIO360 0.6 biodegradable mulch (Bio360) Dubois Agrinovation, Saint Remi, Quebec, Canada 72 15.2 Starch based, PBAT copolyester $516
Polyethylene, non-degradable (PE) FilmTech, LLC., Stanley, WI, USA 70 22.7 PE film $251
Bare ground; herbicide + hand weeding (BG) NAw NA NA NA $88

z PE = Polyethylene; PLA=polylactic acid; PBAT = poly(butylene adipate-co-terephthalate).

y Purchase cost can vary based on feedstock ingredients, market conditions, manufacturer/supplier, and availability; year 2 and 3 costs for BIO360 0.6 and PE include herbicide costs, as these mulches were removed by year 2. Costs represented are just initial costs and does not factor in costs of removal and disposal.

x Experimental; information not provided by manufacturer.

 

Results:

  • Soil temperatures at a 4-inch depth averaged from May to Oct. 2019 and 2020: 56.4, 56.3, 57.7, 57.6, and 56.7 °F for the BG, Bio360, Novamont, PE, and weedmat plots, respectively. There were less soil temperature fluctuations under weedmat, while PE increased temperatures up to ~4 °F relative to bare ground in July.
  • Average volumetric water content (m3/m3) at a 4-inch depth averaged from May to Oct. 2019 and 2020: 0.31, 0.35, 0.33, 0.34, and 0.40 m3/m3 for the bare ground, Bio360, Novamont, PE, and weedmat plots, respectively. Soil moisture retention was greatest under weedmat.
  • Final mulch surface deterioration measurements recorded Sept. 2021 showed deterioration (i.e., rips, tears, holes; not a measure of biodegradation) was lowest in the weedmat plots (0.25%) followed by PE (11.25%). Biodegradable plastic mulch treatments (i.e., Novamont and Bio360) had >92% deterioration by the end of the assessment period in Sept. 2020 and were removed at this timepoint due to extensive deterioration.
  • Weed number and biomass were greatest in the bare ground plots. No differences in weed suppression were observed across mulching treatments while mulches were deployed.
  • Yield differed by treatment (P<0.0001) and year (P=0.006), but there was no yield by treatment interaction (P=0.37) (Fig. 1). Yield was greatest in plots grown with weedmat and PE. Yield was lowest in the bare ground plots and declined in 2021 due to the heat damage.
  • No consistent treatment effects were found for berry size and fruit quality, although berry size tended to be lower in bare ground plots.
  • Primocane number and height were consistently greatest in plots mulched with PE and weedmat (P<0.05), which attributed to the increase in yields in those treatments.
  • No voles were observed under the mulches throughout the study period. Bare-ground alleyways discourage vole activity, so mulching combined with alleyway tillage should minimize potential damage due to voles.
  • Based on results of this 3-year study, PE mulch is the most economical option for promotion of crop growth and weed suppression (Table 1). While weedmat had yields equivalent to PE-treated plots, it was ~5 times more expensive to install. Disposal fees are based on weight, so weedmat is also expected to be more costly to dispose of given its greater density than PE.
  • Soil-biodegradable mulches, Novamont and Bio360, had yields greater than bare ground treated plots, but lower than PE and weedmat treated plots. This contrasts with previous research (Zhang et al., 2019, 2020, and 2021; Tofanelli and Wortman, 2020), which shows yields from soil-biodegradable mulch treated plots are equivalent to PE mulch. Soil temperature, soil moisture, and weed suppression were similar between the soil-biodegradable mulch treatments and PE, so the cause of reduced yields among soil-biodegradable plastic mulch treated plots is unknown.
  • One advantage of soil-biodegradable plastic mulches is that they degrade in soils, which can remove ~$150/ton fees associated with PE and weedmat plastic mulch disposal (source: Recycling and Disposal Services, Inc., Ferndale, WA).

Figure 1: Machine harvested yield extrapolated to a per acre basis for plots mulched with weedmat, Novamont biodegradable plastic mulch, polyethylene black plastic mulch (PE), bare ground, and Bio360 soil-biodegradable plastic mulch. Soil-biodegradable plastic mulches were applied from 2019-2020. Remaining mulch treatments were applied from 2019-2021. Letters denote significant differences (α=0.05) for comparisons made combining 2020 and 2021 yield data due to a lack of a significant year x treatment interaction

 

More information about plastic mulch and biodegradable plastic mulch can be found at:

https://smallfruits.wsu.edu/plastic-mulches/

 

References:

Tofanelli, M. B., & Wortman, S. E. (2020). Benchmarking the agronomic performance of biodegradable mulches against polyethylene mulch film: a meta-analysis. Agronomy, 10(10), 1618.

Zhang, H., Miles, C., Gerdeman, B., LaHue, D. G., & DeVetter, L. (2021). Plastic mulch use in perennial fruit cropping systems–A review. Scientia Horticulturae, 281, 109975.

Zhang, H., Miles, C., Ghimire, S., Benedict, C., Zasada, I., & DeVetter, L. (2019). Polyethylene and biodegradable plastic mulches improve growth, yield, and weed management in floricane red raspberry. Scientia Horticulturae, 250, 371-379.

Zhang, H., Miles, C., Ghimire, S., Benedict, C., Zasada, I., Liu, H., & DeVetter, L. (2020). Plastic mulches improved plant growth and suppressed weeds in late summer-planted floricane-fruiting raspberry. HortScience, 55(4), 565-572.