Organic Research Database

Weed control is a primary concern in organic farming, and black plastic mulch has become a valuable tool. Though very effective and affordable, plastic mulch has become an environmental management concern due to disposal issues. From 2003 to 2006, a series of trials was conducted at WSU Vancouver Research and Extension Unit to identify degradable mulches that can be effective and affordable alternatives to black plastic.  The field study tested 5 alternative mulches in 2003 and 2004, 8 in 2005, and 9 in 2006, including a total of 6 paper products, 4 cornstarch products, and 2 thermal/photo-degradable plastic products.  Factors evaluated were mulch durability, measured effect on soil temperature, and crop yield.  Crops were lettuce, broccoli, bell pepper, and icebox watermelon.  The mulch products evaluated in this study showed significant differences in durability, with standard black plastic (control) being the most durable, followed by Envirocare mulches.  In 2003 and 2007, paper mulches were significantly less durable than black plastic.  In 2005, 5 new paper mulch products were tested, but all degraded relatively quickly, with weed growth under the mulch being the major cause.  In 2006, one paper mulch (LF5) was almost as durable as black plastic, and a second paper mulch (Planters Paper) was significantly more durable than in 2005.  Garden BioFilm was the least durable in 2004, and similar to papers in 2005.  In 2006 Garden Biofilm NF01U/P 15  was somewhat durable in the field and resulted in higher crop yields.  Effect of mulches on days to first harvest were significant only with broccoli, which was harvested earliest from plots treated with Garden BioFilm and latest from plots with black plastic.  Yields of broccoli and watermelon were significantly different in 2004, and black plastic and Envirocare 1 tended to produce the highest yields. Yield of all crops were significantly different in 2005, and were significantly lower with the paper mulch products and Garden BioFilm.  Yield of lettuce was least impacted by mulch product due to its short time to harvest, and paper or cornstarch products may be most suitable for similar short season crops.  All mulch products except for Kraft 81-lb. paper showed an insulating effect on underlying soil temperature, i.e. temperature highs and lows beneath the mulch were less extreme than bare soil.   In this study Envirocare products did not degrade when they were incorporated into the field or into on-farm compost.  Ideally, a degradable mulch would degrade in the soil, eliminating removal and disposal costs.

From 2003 to 2006 a series of studies on alternatives to plastic mulches were conducted at WSU Vancouver Research and Extension Unit.  The experimental design was a randomized complete block with 4 replications.  Plots were 50 ft. long x 3 ft. wide, each including 4 subplots (lettuce, broccoli, bell pepper, and watermelon).  Plants were seeded in the greenhouse and transplanted to the field in mid-June.  Mulches were laid using a tractor attachment, except for the Garden Biofilm which was laid by hand.  Drip tape was laid at the same time and plots were drip irrigated.  The field study was managed organically, and plants were fertigated at transplanting and every 3 weeks thereafter.  Temperature was measured at the soil surface and at a 2-inch depth.  Vegetables in each plot were harvested at maturity, and data collected on total yield, marketable yield, number of marketable fruits/heads, and number of days to harvest.

     In 2003 the study included six mulch treatments: Garden Bio-Film, 81-lb Kraft paper, Kraft paper + linseed oil, Kraft paper + tung oil, Kraft paper + soybean oil, and black plastic (control). Oil was sprayed onto the paper prior to laying the paper in the field, and its purpose was to reduce the rate of paper degradation in the field.

     In 2004 the study included five mulches and black plastic: 81-lb Kraft brown paper, 42-lb Kraft brown paper with polyethylene coating, Garden BioFilm, Envirocare 1 (XP-4611W), Envirocare 2 (XP-4611J), black plastic (control).

     In 2005 the study included eight degradable mulches: Garden Biofilm, Envirocare 1, Envirocare 2, Longview Fibre Paper (LF) 1, LF 2, LF 3, LF 4, Planters Paper and black plastic (control).

     In 2006 the study included 9 degradable mulches: Garden Biofilm, Garden Biofilm NF01U/P 15 mic, Garden Biofilm NF803/P 12 mic, Garden Biofilm NF803/P 15 mic, Envirocare 1, Envirocare 2, Longview Fibre Paper (LF) 4, LF 5, Planters Paper and black plastic (control).