Evaluation of Recycled Paper Mulch as an Alternative to Black Plastic Mulch in Vegetable Horticulture

View the project final report

• 1993 annual report

Commodities

• Vegetables: cucurbits, tomatoes

Practices

• Pest Management: mulches - general, mulching - plastic

Many vegetable farmers use black plastic film mulch on tomatoes, cucumbers and other warm-season vegetables because plastic blocks weed growth, conserves soil moisture and warms the soil thereby promoting early crop maturity. However, plastic does not add organic matter or nutrients to the soil, its manufacture consumes considerable fossil fuel, and its disposal adds to the nation's solid waste burden. Some growers use paper mulches, including a commercially available black paper mulch, newsprint end rolls and other paper wastes as biodegradable alternatives to plastic. However, these materials do not warm the soil as effectively as plastic, and the often break down too fast, with resulting loss of weed control.

On many small, biologically managed farms, organic mulches such as hay, straw or leaves are used to provide organic matter and nutrients, protect and improve the soil, and suppress weeds. However, these materials cool the soil, which may delay ripening in tomatoes and other summer vegetables. Also, they may be too expensive and labor-intensive to apply on larger farms. Growers and researchers have experimented for the past several years with winter cover crops that are killed by mowing in spring and left in place as a mulch. Results have varied from disappointing due to inadequate weed control, to excellent with tomato or squash yields exceeding those with plastic mulch. This approach merits further development.

The overall goal of this project is to assist vegetable growers in developing optimal mulching strategies for their farms. Specific objectives include:

1. To identify advantages and problems of different mulches used by vegetable growers, establish research priorities, and engage growers in the process of developing and disseminating information on mulching systems.

2. To evaluate recycled paper, vegetable oil-impregnated paper, and organic mulches as sustainable alternatives to plastic film mulch.

3. To disseminate information on horticultural, soil, economic and ecological merits of different mulches so growers can make informed choices appropriate to their specific sites and operations.

4. To identify safe and cost-effective means to utilize waste paper as a mulching material.

Field experiments were conducted at five biologically managed working farms in Virginia in 1993-94 to evaluate recycled kraft paper, oiled paper, hay and other organic mulches as alternatives to black plastic mulch for tomatoes. None of these alternative duplicated the early yields and superior weed control obtained with plastic. Organic mulches cooled the soil and somewhat delayed maturity, although total yields equaled those for plastic-mulched tomatoes. Paper treated with waste cooking oil dramatically warmed the soil early in the season, but weeds broke through this mulch. However, results indicated that plastic may not always be the best choice for tomatoes, especially in hot dry weather, when crops growing in the cooler organic mulches suffered less stress and gave more sustained production.

During 1993-94, seventy-two vegetable growers were interviewed to learn about existing mulching practices and innovations, and to engage growers in the process of proposing, testing and implementing new mulching strategies. A majority of participants prefer hay and straw mulches because they conserve soil moisture, add organic matter, reduce weeds and support good crop yields. Although growers noted the advantages of plastic, many raised environmental and waste-disposal concerns, and some have stopped using plastic for these reasons. Some growers reported using paper or killed cover crop mulches, and others expressed interest in experimenting with these materials.

Interview participants received reports on the findings of this survey and of field trials conducted in 1993-94, and were invited to participate in designing and conducting mulch experiments during the 1995 season. Seven growers responded to this invitation, and worked with the project coordinator to design and conduct on-farm experiments to address questions of particular interest to each grower.

Several growers in the survey suggested using two to four layers of newspaper under an organic mulch to enhance weed control or soil moisture conservation, and one recommended newsprint end rolls (available free at newspaper printing presses) because they are easier to apply and are free of inks. Experiments were conducted on five farms to evaluate this strategy, and the paper substantially improved weed control at four of these sites. Five tons per acre of hay (~ one 35-lb square bale per 150 square feet) laid over two thicknesses of newsprint controlled weeds as effectively as ten tons hay per acre without paper. Heavy applications of hay or straw can be expensive, and may upset the mineral balance of certain soils. Thus the use of paper to improve weed control by light applications of organic mulch is a significant grower innovation that has now shown promise in replicated trials.
Four growers hosted on-farm experiments with oiled paper mulch as an alternative to plastic. One participant successfully laid a small roll of oiled, heavy-duty kraft paper with a tractor-drawn plastic mulch layer, a key step toward implementing paper mulching on larger farms. Oiled kraft paper and a double layer of oiled newsprint warmed the soil early in the season, whereas a commercial black paper mulch did not. Both oiled paper mulches lasted longer than the black paper, and controlled weeds adequately, though not as completely as plastic. Participating growers expressed interest in further exploring oiled paper mulch.
In the course of conducting this project, it became apparent that choosing the "best" mulch is inherently a site-specific process. Crop, soil, climate, availability of mulching materials, and the farm's scale, machinery, financial and other resources must all be taken into account. The question, "what is the best mulching practice for this crop?" can best be answered through an integration of relevant research information with the grower's own ingenuity, knowledge and experience with his/her farm. Our objective for the remainder of this project is to develop and disseminate information on various mulching materials and their interaction with crop and soil, that will assist vegetable growers in developing ecologically and economically sound, site-specific mulching strategies.

The goal of this study is to conduct a holistic evaluation of plastic, paper and organic mulches, and communicate our findings to growers so that they can make informed choices of mulching system. Four groups of factors are considered: horticultural performance, effects on soil conditions and quality, environmental impacts, and economic feasibility, especially for the small-scale grower. Research was initiated in 1993 and continued through the 1995 growing season, with the specific objectives listed below. During 1994, objectives were modified slightly (modifications in italics) to better reflect growers' research needs within the study area.

1. To identify advantages and problems of mulching systems used by vegetable growers at different scales and degrees of mechanization, identify research priorities, and engage growers in the process of developing and disseminating information on mulching systems.

2. To evaluate recycled paper film and organic mulches as sustainable alternatives to plastic film mulch, considering horticultural performance, effects on soil conditions, costs and benefits to the grower, resource consumption, solid waste reduction and other environmental impacts.

3. To disseminate information on horticultural, soil, economic and ecological merits of different mulches so growers can make informed choices appropriate to their specific sites and operations.

4. To evaluate treatment of paper mulch with waste cooking oil to increase early-season soil temperature and to delay breakdown of paper mulch under field conditions.

5. To identify safe and cost-effective means to utilize waste paper as mulch, and explore feasibility of manufacturing a recycled paper mulch using environmentally benign processes with potential as a small business venture.

Field studies during 1993-94 showed that neither paper nor organic mulches can fully duplicate the benefits of plastic film mulches (Objective 2), but also that plastic is not always the best choice for tomato production (Schonbeck, 1995b). Objective 4 was essentially completed in the 1994 season. Oiled paper provided greater early-season soil warming than plastic, but sometimes broke down too soon, resulting in a partial loss of weed control (Ibid.).

In the course of conducting this project, it became apparent that choosing an optimal mulching system is inherently a site-specific process, depending on crops grown, soil and climatic conditions, mulching materials available on-farm or nearby, and the farm's scale, level of mechanization, and financial and other resources. Also, there exists a large body of research information on mulch interactions with soil, crop, weeds and other pest and beneficial organisms, but much of this information is not accessible to most growers. The question, "what is the best mulching practice for this crop?" can best be answered through an integration of relevant research information with the grower's own ingenuity, knowledge and experience with his/her farm. The greatest service this project can do is to provide information in such a way as to help growers make such decisions. Therefore, the focus for the current stage of this study has shifted largely to Objectives 1 and 3.

No further work was done on Objective 5 since the 1994 annual report for two reasons. First, the steam explosion process for recycling mixed paper waste into a mulch paper, explored during 1993-94, appears to entail high direct and environmental costs. Second, in 1993-94 field trials, neither untreated nor oiled paper mulches showed any horticultural advantages over plastic or organic mulches for tomato production. However, a number of growers expressed interest in exploring paper mulches for specific applications on their farms. Several indicated a strong preference for not using plastic and felt that initial results with oiled paper were promising enough to merit further evaluation. Also, several others indicated that laying paper under organic mulches may enhance weed control and/or soil conditions (Schonbeck, 1995a). Therefore, practical and logistical aspects of utilizing waste paper as agricultural mulch will be explored.