Working on ways to reduce ag waste

If you grow strawberries, there’s a good chance you have used plastic mulch in the past (or are thinking about trying it in the future). However, the most commonly used mulch is anything but green for the horticulture industry.

Polyethylene (PE) mulch suppresses weeds, optimizes the soil and canopy microclimate and enhances efficient production of quality fruits and vegetables as well as their yields. PE mulch is not biodegradable, though, and limited cost-effective waste management options lead to large amounts of used PE mulch being sent to landfills, stockpiled on farms, burned and sometimes buried in soil.

Looking at mulch technologies to reduce agriculture plastic waste generation in strawberry cultivation are Givemore Munashe Makonya, research fellow at Washington State, along with researchers from Montana State; North Dakota State; and University of Wisconsin-Madison. He presented their work at the most recent American Society for Horticultural Science conference.

PE mulch was introduced in the 1950s, so it is a tried-and-true product. Its biggest problem is its end-of-life management – very little recycling of PE mulch is occurring. And it is not biodegradable.

As its name suggests, soil biodegradable plastic mulch (BDM), which has been around since the 1990s as an alternative to PE mulch, is. It’s been engineered to break down in soils upon incorporation. It is made using a blend of fossil fuel-derived and biobased ingredients. BDM achieved greater than 90% biodegradation in lab-based soil tests within two years or less, thanks to soil microbial activity. At end-of-life, it’s simply tilled into the soil.

A separate study showed a 3.8% to 20.6% better environmental impact of BDM over PE.

Makonya noted there is a difference in BDM colors, though. Trials conducted at Washington State found that strawberry yield and fruit quality are comparable when plants are grown with either black PE mulch or black BDM. Green BDM, however, deteriorates rapidly, depending on environmental conditions, and that deterioration may lead to increased weed pressure and reduced production – similar to basic bare ground cultivation.

BDM use is still limited today, largely due to a lack of knowledge about BDM, according to Makonya.

“Black BDM is a good alternative to black PE mulch where recycling is not feasible – and for short-lived strawberry plantings (shorter than 18 months),” he noted.

But be aware of its limitations: BDM is not a fumigation tarp. BDM is not allowed in certified organic production. BDM can rip and tear under windy conditions. And BDM fragments may be a harvest contaminant for low-growing crops in certain mixed-crop rotations (such as lettuce).

Another alternative to PE mulch is hydromulch, a sprayable mulch alternative that can be made with ingredients that meet certified organic production requirements. It consists of cellulose (recycled paper), water and a tackifier (guar gum). It is both biobased and biodegradable.

Trials undertaken at Washington State and North Dakota State demonstrated hydromulch maintains strawberry yield and fruit quality – but with reduced weed suppression.

The biggest drawback for hydromulches currently is that they are costly due to the logistics of sourcing quality hydromulch feedstock and the lack of specialized application equipment.

Lignocellulose film is a third fully biodegradable and emerging alternative to PE mulch. It can be made with ingredients suitable for certified organic production as well. Makonya said field trials with cellulose-based film are limited, but current findings show high levels of biodegradability and maintenance of crop growth.

The film is developed using low-cost, abundant and renewable woody biomass and molten salt hydrate. However, it is not yet commercially available, nor has it been tested in strawberry. Makonya reported there were promising greenhouse trials using it for raspberry, though.

His concluded his presentation by stating, “Growers, crop consultants and marketers should consider biodegradable mulch alternatives to reduce plastic waste generation and persistent plastic pollution in agricultural and environmental settings, particularly if recycling is not available or a cost-effective option.”

Want to learn more? Check out the “Mulch Matters” podcast, which covers the latest research about BDM and recycling options for PE mulch.

by Courtney Llewellyn