The primary justification for using this system is that strawberry crops canbe produced without fumigation ; although if the soilless media could be disinfested and recycled, instead of discarded at the end of each cropping cycle, it would, in theory, represent a more sustainable system. Additional advantages include the ease of attracting harvest labor due to the high fruit yield per linear foot of bed row, and the ability to leave the beds in place for several crop cycles. One of the disadvantages is that coir and peat substrates are expensive and of limited quantity. However, composted wood fiber and composted pine bark have shown good results as substrates and are available locally and are generally less expensive . Logistical issues such as substrate costs and the delivery and installation of large amounts of substrate material have yet to be addressed in U.S. systems. Field trials of a raised bed trough system were carried out at Monterey Bay Academy, near Watsonville, and at Mar Vista Berry, near Santa Maria, from fall 2010 to summer 2011. The studies were set up in randomized complete block designs consisting of five treatments replicated four times. The treatments were 100% coir , a 70:30 peat and perlite mixture, an amended soil mix of 50% steamed soil plus 25% rice hulls and 25% coir, a standard fumigation treatment , and an untreated, non-fumigated control. Harvesting was done from April 28 to Sept. 15, 2011 , and April 13 to Oct. 4, 2011 . The fruit was sorted into marketable berries and cull . Periodic collection of substrate samples was done to monitor pH, electrical conductivity , nitrate nitrogen , ammonium nitrogen and available phosphorus . All data were subjected to analysis of variance ,macetas de plastico 30 litros and Fisher’s protected LSD at 0.05 was used to compare means. Table 1 shows the plant diameters and yields of strawberry crops grown in the plots at Monterey Bay Academy and Mar Vista Berry.

There were highly significant differences in plant diameter and yield of strawberries grown at Monterey Bay Academy.The three substrate treatments did not significantly differ in marketable yield. The untreated, non-fumigated control treatment had the smallest plant diameter and lowest marketable yield. The marketable yield of the coir, peat and perlite, and steamed soil with amendments treatments was 27%, 29% and 13% higher, respectively, than the yield from the standard fumigated treatment. At Mar Vista Berry , the widest plant diameters were in the steamed soil with amendments plots and the peat and perlite substrate plots . However, the substrate treatments did not affect the marketable fruit yield. Significant differences were noted only on the cull yield. The highest cull yield was observed in the steamed soil with amendments; this was the case at both Mar Vista Berry and Monterey Bay Academy, and it could be attributed to the very low pH and high EC of this substrate. One of the main concerns in soilless strawberry production is the maintenance of a favorable pH, EC and nutrient supply to the growing plants. For most of the sampling periods at the experimental sites, different substrate and soil treatments had significantly different levels of pH, EC, nitrate nitrogen, ammonium nitrogen and available phosphorus. At both sites, the pH of the coir and the peat and perlite treatments was lower in the early sampling periods but increased with time, reaching the targeted value of 5.7 after 3 to 4 months ; this slow rise in pH to the target value was attributed to the high nutrient adsorptive capacity of the soilless substrates. The pH of the amended soil treatments at both sites was generally low at all sampling periods, and the target value was not reached during the production cycle. With the exception of the initial sampling period, the EC of the substrate treatments at Monterey Bay Academy was generally low . In contrast, the EC in the Mar Vista Berry beds was consistently high, which could be due to the higher amount of salts in the irrigation water.

The EC of the steamed soil with amendments treatment at Mar Vista Berry was also consistently high throughout the growing season. The soilless substrates are low in nutrients; thus, fertilization is one of the key issues in these systems. Surprisingly, the initial nitrate nitrogen of the coir and the peat and perlite mixture was higher at both sites, and the target value of 100 ppm was maintained in the beds through the season except for the latter stages of plant growth . The standard fumigated beds had generally low nitrate nitrogen. At all sampling periods, the ammonium nitrate was lower than the RABETS target value of 14 ppm . The RABETS target of 30 ppm available phosphorus was maintained in all of the media treatments at both sites .Anaerobic soil disinfestation , a nonchemical alternative to methyl bromide, was developed in Japan and the Netherlands to control soil borne pathogens and nematodes in strawberries and vegetables. Anaerobic soil disinfestation integrates the principles of solarization and flooding in situations where neither method alone is effective or feasible. Anaerobic soil conditions are created by incorporating readily available carbon sources into topsoil, covering the soil with plastic tarp and irrigating to field capacity. The tarp is left in place to maintain soil moisture above field capacity and to sustain anaerobic conditions. Anaerobic decomposers respire using the added carbon, which results in a buildup of anaerobic byproducts that are toxic to pathogens . These byproducts degrade rapidly once the tarp is removed or holes are punched through the tarp for planting. Studies were conducted during 2008 to 2011 in an attempt to optimize anaerobic soil disinfestation for California strawberry and Florida vegetable production systems. Overall, it was very effective in suppressing Verticillium dahliae in soils, and it resulted in 85% to 100% of the marketable fruit yield observed with fumigated controls in coastal California strawberries when 9 tons per acre of rice bran was preplant incorporated and 3 to 4 acre-inches of irrigation was applied in sandy loam to clay loam soils . In the semitropical climate of Florida, when composted broiler litter and heavy black strap molasses were incorporated as substrate, anaerobic soil disinfestation treatments provided good control of nutsedge and excellent control of grasses, broad leaf weeds, Phytophthora capsici and Fusarium oxysporum f. sp. lycopersici .

In the cooler conditions of the Central Coast, however, anaerobic soil disinfestation may not provide effective control of many weed species . To ensure consistency of pest suppression across varying locations, the effects of soil temperatures and treatment length and the mechanisms of pest suppression by anaerobic soil disinfestation are being further elucidated. Its integration with other non-fumigant approaches may also have promise. For example, a combination of anaerobic soil disinfestation and mustard seed meal application is currently being tested .Heat treatment with steam can be used for soil sterilization or pasteurization . Studies have shown that most plant pathogens, insects and weeds will die when moist soils are heated to temperatures higher than 150°F for 30 minutes . The duration and amount of steam needed to raise the soil temperature to 150°F depend on various soil factors, including texture,cultivo hidroponico type and moisture content. Minuto et al. found that soil could be heated most rapidly at a moisture content between 8.5% and 12% in a sandy loam and between 6% and 7% in a sandy soil. Steam applied to field soil that raised the temperature to 158°F for 20 minutes resulted in weed control comparable to methyl bromide . In addition to pest control, an advantage of steaming is that it lacks the negative environmental and worker health issues associated with chemical fumigants. Some have reported that steaming has little or no lasting negative impact on soil quality or soil microbial communities as opposed to the known potential impact of methyl bromide fumigation on both soil quality and microbes . Other studies have reported a more significant change in soil microbial activity due to steam sterilization . Differences among steam studies may be related to duration of steam application and soil temperatures attained during steam treatments as well as the soil organic matter content. Steam has also been shown to increase crop growth and yields . Previous work found that strawberry fruit yields from steam-treated soils were similar to those from soils fumigated with methyl bromide plus chloropicrin .Natural products such as mustard seed are being evaluated as biofumigants. Recent studies found that mustard seed meal amendment can suppress root infection by Rhizoctonia solani . We have been testing mustard seed meal in strawberry beds at rates of 500 to 4,000 pounds per acre incorporated into the soil. Mustard meal alone does not consistently produce high fruit yields or control weeds . One possible method to enhance solarization is to use combinations of mustard meal, chloropicrin, and metam sodium treatments . By heating the soil with solarization or steam, the pest control activity of metam sodium, chloropicrin or mustard meal may be higher than at ambient soil temperatures.

A field study was conducted at Monterey Bay Academy from October 2010 to September 2011 to evaluate anaerobic soil disinfestation and steam with and without mustard seed meal application prior to planting strawberry beds. Treatments included a control; Pic-Clor 60 at 300 pounds per acre as a standard; mustard seed meal at 3,000 pounds per acre; anaerobic soil disinfestation with rice bran at 9 tons per acre; anaerobic soil disinfestation with rice bran at 7.5 tons per acre and mustard seed meal at 3,000 pounds per acre; steam; and steam plus mustard seed meal at 3,000 pounds per acre. The trial was arranged in a randomized complete block design with four replicates. Anaerobic soil disinfestation was initiated Oct. 7 to create a saturated condition. The plots were maintained above field capacity with intermittently applied irrigation water from Oct. 8 to Nov. 3, 2010. Steam was applied via spike injection from a stationary steam generator for a sufficient time to raise the soil temperature to 158˚F for 20 minutes on Oct. 13 and 14, 2010. Weed densities were measured in 25-square-foot sample areas covered with clear tarp, on Dec. 15, 2010, Jan. 21, Feb. 23 and April 6, 2011. Strawberry fruit was harvested weekly from April 28 to Sept. 15, 2011. Fruit was sorted as marketable and cull at each harvest date. Data were subjected to analysis of variance and means were separated using Fisher’s protected LSD.Overall, the steam treatment and the steam treatment with mustard seed meal were as effective as Pic-Clor 60 in providing weed control . Anaerobic soil disinfestation plus rice bran suppressed weed densities, but it was less effective than Pic-Clor 60. No strawberry plant injury was observed in any of the treatments . Marketable yields data collected from April 28 to Sept. 15, 2011, indicate that strawberry fruit yields in the steam treatments and the anaerobic soil disinfestation treatments were comparable to those in the Pic-Clor 60 application . These data, along with data from our prior studies, show that steam is as effective as chemical fumigation; and that anaerobic soil disinfestation also produces yields equivalent to Pic-Clor 60 but may need to be combined with herbicide use in severely weed-infested sites. The costs of the anaerobic soil disinfestation treatments with rice bran, and with rice bran plus mustard seed meal, were $1,632 and $3,093 per acre, respectively, including material, spreading, incorporation and irrigation . The cost of steam was $10,440 per acre, compared to $1900 per acre for Pic-Clor 60. Therefore, although the yields and gross revenues were comparable across treatments, the net returns after treatment and harvest costs were highest for the Pic-Clor treatment, followed by the anaerobic soil disinfestation with rice bran. The lowest net revenue was for the steam plus mustard seed meal treatments due to the high cost of the steam treatment. The cost data showed a critical need for more-efficient steam injection systems before steam can be adopted commercially. Recent advances with steam application equipment can reduce the cost of steam treatment to less than $5,500 per acre with the potential for further cost reductions . Since 2011 we have used an automatic mobile steam applicator in our research, which lowers the labor costs relative to those reported here by approximately 50% to 70%. It mixes steam with soil, allowing soil to be heated from 60˚F to 160˚F in 90 seconds — much more rapidly than the steam application system used here .