Developing an Annual Day-Neutral Strawberry Planting System with Biodegradable Mulches

Strawberries growing on plasticulture. Photo: Nathan Hecht

Author: Steve Poppe, WCROC Horticulture Scientist. Despite growing consumer interest in local foods, the supply of Minnesota-grown strawberries is extremely limited due to the short growing season and perishability of traditional varieties. While the traditional June-bearing varieties produce fruit from early June through early July, the U of MN West Central Research and Outreach Center (WCROC) has developed a day-neutral low tunnel system, which offers high quality fruit from late July to October.

The low tunnel system requires hoop-like structures that go over the rows of strawberry plants. In addition, the strawberry plants must be planted into some type of mulch for adequate weed control and to maximize plant growth. In initial studies, we used white-on-black plastic mulch in the row which is a very effective weed control strategy. However, farmers expressed concern over the amount of plastic used, especially since the plastic mulch is not reusable.

This concern led us to our current project of evaluating the effectiveness of biodegradable mulch in the low tunnel system. Our experimental objective was to determine if there is a more environmentally sustainable alternative to plastic mulch.

Our project consisted of the following objectives:

Low-tunnel strawberries in November, 2018.
Photo: Annie Klodd.

1. Determine the performance of biodegradable mulches in an extended season annual strawberry production system as compared to our standard white-on-black plastic mulch.
2. Improve understanding of the effectiveness of sustainable mulches between crop rows in an extended season annual strawberry system as compared to landscape fabric used between crop rows.
3. Increase the awareness of the benefits of the extended season annual strawberry system.
4. Increase awareness among farmers to help them establish extended season annual strawberry systems on their farms.

White-on-Black Plastic vs. Biodegradable Plastic

In 2017, we established trial plantings at the WCROC. Two varieties of day-neutral strawberries were grown under low tunnels – half using white-on-black plastic, and the other half using biodegradable plastic to compare the performance of the biodegradable plastic mulch to traditional plastic mulch.

The two varieties produced an average of 10,065 lbs/acre when grown on white-on-black plastic mulch and 7,205 lbs/acre when grown on biodegradable mulch (Table 1). The study was repeated in 2018, and the white-on-black plastic mulch planting averaged 15,380 lbs/acre while the biodegradable mulch planting averaged 12,353 lbs/acre (Table 2).

Table 1: 2017.  Comparing two within-row treatments, white-on-black plastic and biodegradable plastic, and two strawberry varieties with average yield per plant, cumulative yield, and average berry size for two day-neutral strawberry varieties Portola and Albion.

Table 1 2017	Yield (lb/plant)		Cumulative Yield (lb/ac)		Berry Weight (g)
	White-on-black Plastic	Biodegradable	White-on-black Plastic	Biodegradable	White-on-black Plastic	Biodegradable
Portola	0.69	0.42	12628	7580	18.1	14.6
Albion	0.41	0.37	7502	6829	16.1	15.7

In 2017, on average, white-on-black plastic mulch produced higher yields of larger fruit regardless of variety, but this difference was especially prominent in Portola. When examining within mulch treatments, Portola showed significantly higher yields and larger fruit than Albion in traditional plastic mulch, but these differences did not appear in biodegradable mulch.

Table 2: 2018.  Comparing two within-row treatments, white-on-black plastic and biodegradable plastic, and two strawberry varieties with average yield per plant, cumulative yield, and average berry size for two day-neutral strawberry varieties Portola and Albion.

Table 2 2018	Yield (lb/plant)		Cumulative Yield (lb/ac)		Berry Weight (g)
	White-on-black Plastic	Biodegradable	White-on-black Plastic	Biodegradable	White-on-black Plastic	Biodegradable
Portola	0.96	0.76	17518	13832	14.7	14.2
Albion	0.73	0.60	13241	10875	13.1	13.2

In 2018, the data suggests a significant difference between varieties and a barely significant difference between mulches.  In general, white-on-black plastic mulch yields had more strawberries over the course of the season when compared with biodegradable plastic mulches. Portola produces significantly more than Albion, even when using the biodegradable plastic mulch.

Cover Crops vs. Landscape Fabric

To further reduce plastic in the system, we also evaluated the use of cover crops in place of landscape fabric for weed suppression between the rows of strawberry plants. We planted winter rye in May 2017 and again in 2018 as a cover crop in between the strawberry rows, but it failed to provide adequate cover to suppress weeds for the entire growing season. By mid-August, the winter rye had died off, which allowed weeds to take over between the rows.

Our best guess is that the winter rye had met its reasonable life expectancy and died off naturally. Even though fruit quality and quantity were not affected by the weeds between the rows, we are reevaluating the use of winter rye as a weed suppressant.

For more information about our low tunnel day-neutral strawberry project, visit https://wcroc.cfans.umn.edu/research-programs/horticulture

Author: Steve Poppe, West Central Research and Outreach Center (WCROC) Horticulture Scientist