COMPARISON OF ORGANIC AND INORGANIC MULCHES FOR HEIRLOOM TOMATO PRODUCTION

Abstract

Many tomato growers face challenges in producing their crops due to stricter environmental regulations and fewer chemicals available for weed control. There is a demand for cultural practices that reduce chemical inputs and synthetic materials. Heirloom tomato varieties are becoming more popular among commercial tomato growers due to increased demand from consumers. Since most heirloom tomatoes at present are grown on small acreage, the addition of organic mulches may be a practice feasible for reducing chemical inputs for weed suppression. Heirloom tomatoes were grown using organic mulches (shredded newspaper, wheat straw and composted landscape bark) and an inorganic mulch (black plastic) plus a bare ground control to evaluate their effectiveness on heirloom tomato marketable yield and weed suppression. All treatments were grown with pre-emergence herbicide (high input) and without pre-emergence herbicide (low input). Marketable yields for the 10 treatments ranged from 3.4 to 50 MT/ha and 11.5 to 35.6 MT/ha in 2000 and 2001, respectively. Mulch x herbicide interactions were not significant for yield in either year. Mulches with and without herbicide inputs produced higher yields than unmulched plots in both years. Bare ground control with no herbicide inputs resulted in the lowest yields and highest weed densities and biomass. In an attempt to reduce chemical inputs for weed control in tomato production, organic mulching materials may be a viable option for vegetable growers. INTRODUCTION Methyl bromide, used as a soil fumigant to control nematodes, soil-borne pathogens and weeds in fruit and vegetable production systems, will be banned in the United States by 2005, in compliance with the U.S. Clean Air Act (Charron and Sams, 1999; Holman, 1999). Public concerns with health and environmental effects of synthetic pesticides commonly used in commercial fruit and vegetable production is prompting researchers to look at alternative, non-chemical pest control measures (Charron and Sams, 1999). As a result of consumer health and safety issues, retail sales in the U.S. organic industry reached $7.8 billion in the year 2000 (Wood et al., 2002). There is a need for cultural practices that reduce chemical inputs and synthetic materials (Abdul-Baki and Teasdale, 1993; Abdul-Baki et al., 1996; Koike and Subbarao, 2000). Production practices for vegetable and fruit production need to focus on fewer synthetic inputs, disease and weed control, reducing soil erosion, and maintaining soil structure while producing high quality fruit and profitable yields. Fresh market tomatoes are grown for retail, wholesale and supermarket trade (Precheur et al, 2001). Fresh market tomatoes are the most frequently produced crop on small farms in the northeastern U.S. Small acreage farms are increasing in numbers across the United States and are predominately run by part-time operators (Teasdale and Colacicco, 1985). Small farms often grow and market unique or specialty produce, avoiding competition from most large-scale vegetable production operations. An increasingly popular sector of the produce industry is heirloom and ethnic vegetable crops. Heirloom varieties, particularly tomatoes, were traditionally grown in backyard gardens and are becoming more popular with small commercial growers. One alternative to pesticides for weed and disease suppression is the use of mulch. Proc. XXVI IHC – Sustainability of Horticultural Systems Eds. L. Bertschinger and J.D. Anderson Acta Hort. 638, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA) 172 Mulch is defined as any material used to cover the soil surface to prevent loss of moisture, reduce weed pressure, maintain consistent soil temperatures and promote soil productivity (Jacks et al., 1955; Carter and Johnson, 1988; Abdul-Baki and Teasdale, 1994). Mulches also aid in weed suppression (Davis, 1994). Organic mulches can be as effective as herbicides in suppressing weeds (Ozores-Hampton, 1998). Synthetic mulch such as black polyethylene film has been used in vegetable production since the early 1960’s to increase soil temperatures, conserve moisture, reduce weed pressure and increase yields (Lamont, 1991; Courter et al., 1969; Carter and Johnson, 1988; Abdul-Baki et al., 1996). However, there are disadvantages to using this synthetic material. Aside cost, which can be as high as $630/A, disposal of the material is a problem (Wiggen, 1995; Davis, 1994). Black plastic mulching materials are burned or disposed of in landfills. Since burning certain plastics give off toxic fumes such as hydrochloric acid, this mulching material is environmentally unfriendly while adding nothing to the soil structure or fertility. Use of cover crops and living mulches for weed control and soil fertility has produced mixed results (Paine and Harrison, 1993). One problem growers face with the use of cover crops and living mulches for vegetable production is that cover crop management may interfere with spring planting and/or fall harvest (Stivers-Young and Tucker, 1999). For cover crops to become well established and suppress weeds, the cover crop requires vigorous early growth and timely mowing to reduce its competition for water, nutrients and light (Costello and Altieri, 1994; Abdul-Baki and Teasdale, 1994; Wiles et al., 1989). The use of cover crops for weed suppression requires adequate biomass while controlling its competition with the crop to prevent yield losses (Hoffman et al., 1993). If uncontrolled, cover crop biomass may control weeds while reducing yields. In a cornhairy vetch system hairy vetch suppressed weeds effectively without reducing corn yield, but only when corn planting coincided with precise vetch bloom time (Hoffman et al., 1993). Vegetable crop growth and yield are affected by the use of cover crop systems (Masiunas, 1998). Crop yields are generally correlated to the amount of weed suppression supplied by the cover crop mulch (Smeda and Weller, 1996). Use of living mulches has shown that competition between the crop being produced and the living mulch may cause a reduction in yield in some crops (Wiles et al., 1989). Delay in silking in sweet corn and in harvest 5-7 days were observed when red fescue and colonial bentgrass were grown as living mulches (Nicholson and Wien, 1983). Use of organic surface mulches, which are plowed into the soil at the end of the growing season, may be a viable option for weed suppression and improving the soil structure without interfering with the crop being produced. This cultural practice would serve several purposes in the production scheme and could be an excellent addition to any IPM program for tomato production, particularly on small acreage farms (Davis, 1994). Fresh-market tomatoes which require multiple harvests may be better suited to the use of mulches than processing tomatoes which are commercially harvested with a once-over mechanical harvester (Creamer et al., 1996). The objective of this study was to test the effect of several mulches (shredded newspaper, straw mulch, composted bark, and traditional black plastic mulch along with a bare ground control) with and without pre-emergent herbicide on the marketable yield of heirloom tomato cultivar ‘Nebraska Wedding’ and to test their effectiveness in reducing weed density and biomass. MATERIALS AND METHODS Field experiments were conducted in 2000 and 2001 at The Ohio State University (OSU) Waterman Agricultural and Natural Resources Laboratory, Columbus, Ohio. Field plots were established on raised beds in a randomized complete block design with 4 replications in a 5X2 factorial using 4 mulches (composted landscape bark, wheat straw, shredded newspaper, black plastic mulch) and an unmulched bare ground control. All mulch treatments were tested with (high input) and without (low input) pre-emergence