LONG TERM LARGE SCALE SOIL SOLARIZATION AS A LOW-INPUT PRODUCTION SYSTEM FOR FLORIDA VEGETABLES

Profound changes will occur from the loss of methyl bromide by the vegetable industry, since it is a key component in production systems. Many growers have relied only on methyl bromide to manage soil pathogens, nematodes, and weeds. This system combined with raised beds, plastic mulch, and drip irrigation has been very effective to produce high vegetable yields. Non-chemical alternatives like solarization and organic amendments are as yet largely unproven but do offer promise of sustainable solutions free of government regulation. The objective of this research was to study the effects of long-term, large-scale use of sustainable methods utilizing soil solarization and organic amendments on weed populations, nematodes, yields and soil fertility on peppers (Capsicum annuum L.) and cucumbers (Cucumis sativus L.). The field experiment was conducted during 1998 and 1999 season in a commercial vegetable farm in Boynton Beach, FL. There were five large plots consisting of 10 beds, 610 m long (1.3 ha). Treatments consisted of: 3 years of soil solarization and organic amendment; 2 years of soil solarization and organic amendment; 2 years of soil solarization and non-organic amendment; and methyl bromide as a control. At the end of the second crop, solarized treatments had higher % weed cover and were populated primally by bermudagras (Cynodon dactylon L. Pers.) a warm weather spreading perennial weed as compared with the methyl bromide production system, dominated by redroot pigweed (Amaranthus retroflexus L.) an annual weed easier to control than bermudagrass illustrating, a weak point of a long term solarization system. Population levels of the root-knot nematode [Meloidogyne incognita (kofoid and white) chitwood] fluctuated throughout the experiment. During 1999 and 2000, the lowest numbers occurred in the conventional system with methyl bromide. However on each sampling date, numbers in at least one of the sustainable systems were statistically similar to those in the methyl bromide-treated plots. Marketable yields of peppers appeared to be similar within the production systems for the 1998-1999 season. On all testing dates, organic matter, pH, and Mehlich 1-extractable P, K, Ca, Mg, and Zn were higher in systems where compost was applied than in systems without compost. Manganese was not 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) 178 affected, and Cu and Fe varied by year. The results suggest that large-scale soil solarization and organic amendment can be an attractive alternative to methyl bromide. However, methyl bromide produce the more consistent results. INTRODUCTION Profound changes will occur from the loss of methyl bromide by the vegetable industry, since it is a key component in U.S. production systems. In most cases, growers have relied only on methyl bromide to manage soil pathogens, nematodes, and weeds. This fumigation system combined with raised beds, plastic mulch and drip irrigation has been very effective to produce high vegetable yields. Chemical alternatives are the more desirable methyl bromide alternative by vegetable grower, but none of the products available now can completely replace methyl bromide as a soil fumigant, and these products are more expensive and may also be subject to future restrictions (Spreen et al., 1995). Non-chemical alternatives like solarization and organic amendments are as yet largely unproven but do offer promise of sustainable solutions free of government regulation. Long-term, large-scale soil solarization can offer the opportunity to evaluate the effectiveness of systems in controlling the most difficult soil pest problems. Weed seed germination and seedling growth is suppressed by high soil temperature (Horowitz, 1980). Clear polyethylene plastic under solar radiation can raise soil temperature above the thermal death point for most weed seedlings and seeds. Soil moisture increases soil heat conductivity and sensitizes seeds to high temperatures. Depending on the type of plastic used, soil temperature can exceed 40°C (clear plastic and UV-absorbing clear plastic can raise temperature to 45 and 50°C, respectively). Clear plastic mulch decreased pigweed (Amaranthus spp.) populations within two weeks to less than 10% for one year (Horowitz et al., 1983), demonstrating the sensitivity of annual weeds to solarization. Yellow (Cyperus esculenthus L.) and purple (Cyperus rotundus L.) nutsedge, which are difficult to manage with conventional methods, have also been controlled (Chellemi et al., 1996). Compost is not considered fertilizer; however, significant quantities of nutrients (particularly N, P, and micronutrients) become bio-available with time as the compost decomposes in the soil. Amending soil with compost provides a slow-release source of nutrients, whereas mineral fertilizer is usually water-soluble and is immediately available to plants (Ozores-Hampton et al., 1998). Compost usually contains large quantities of plant-available micronutrients The objective of this research was to determine the effects of large-scale, longterm use of sustainable methods on weed populations, nematodes, yields, and soil fertility on peppers and cucumbers utilizing soil solarization and organic amendments. MATERIALS AND METHODS A large-scale soil solarization field experiment was conducted during 1998 and 1999 season at Boynton Beach, FL (Table 1). The experiment used five large plots consisting of 10 beds, 610 m long (1.3 ha). All beds were 20 cm high, 92 cm wide, and spaced 1.7 m center to center. Bell pepper (Capsicum annuum L.) plants were spaced 25 cm apart and two offset rows per beds space 45 cm apart giving a plant population of 43,055 plants.ha-1. Clear solarization polyethylene used in both years in this experiment was low-density 1.2-mil containing UV light inhibitors (Sonoco Products Co., Orlando, FL). Subsurface irrigation was used throughout the growing season. The plants were monitored for insects and diseases and pesticide were applied as needed according to Univ. of Florida Extension guidelines (Maynard and Olson, 2000). Compost made from a mixture of yard trimmings and biosolids in a 4:1 ratio and composted using an in-vessel composting method for 21 days (Palm Beach Solid Waste Authority, Palm Beach Co., FL) was utilized in this experiment. Chemical and physical properties were analyzed by the Soil and Water Science Department, Univ. of Florida, Gainesville (Table 2). Fertilizer was applied in all plots at 71N-39P-44K kg.ha-1 broadcast application and 283N-0P-279K kg.ha-1 was bedded in the bed centers.