Field Evaluation of ASD, Mustard Seed Meal and Steam
A field study was conducted at Monterey Bay Academy during October 2010 to September 2011 near Watsonville, CA to evaluate nonfumigant soil disinfestation with ASD and Steam with and without mustard seed meal (MSM) application prior to planting strawberry. Treatments included Pic-Clor 60 at 300 lbs/A as a standard, a control, MSM at 3,000 lbs/A, ASD with rice bran 9 t/A, ASD + MSM with rice bran 7.5 t/A + MSM 3,000 lbs/A, steam and steam + MSM (3,000 lb/A). ASD was initiated on Oct. 7 to create a saturated condition and then maintain above field capacity with intermittently applied irrigation water (total 2.5 acre-inches) from Oct. 8 to Nov. 3, 2010. Steam was applied via spike injection from a stationary steam generator for sufficient time to raise the soil temperature to 158°F for 20 min on Oct. 13 and 14, 2010. Weed densities were measured in 25 ft2 sample areas covered with clear tarp, on 15 Dec. 2010, 21 Jan., 23 Feb., and 6 Apr. 2011. Strawberry fruit were harvested weekly from 28 Apr. 2011 to 15 Sept. 2011. Fruits were sorted as marketable and cull (non-marketable) at each harvest date. Data were subjected to analysis of variance and means were separated using LSD.
Results for ASD and Steam. Overall, the steam treatment alone, or with MSM was as effective as Pic-Clor 60 in providing weed control. (Table 4). ASD alone suppressed weed densities, but was less effective than Pic-Clor 60 on weeds. No strawberry plant injury was observed in any of the treatments (not shown). Marketable yields collected from 28 Apr. to 15 Sept. 2011 indicate that strawberry fruit yields in steam and ASD treatments with rice bran and MSM were comparable to the Pic-Clor 60 application (Table 4). This data along with data from our prior studies show that steam is as effective as chemical fumigation. From this and other data ASD also produces yields equivalent to Pic-Clor 60, but may need to be combined with herbicide use in severely weed infested sites.
The cost of the ASD treatment with rice bran and with mustard seed meal were similar, $1,632 and $1,693 per acre respectively including the material, spreading, incorporation and irrigation (Figure 2). The cost of steam added $10,440 per acre compared to $800 per acre for Pic-Clor 60. Therefore, although the yields and gross revenues were comparable across treatments, the net returns above treatment and harvest costs were highest for the Pic-Clor treatment followed by the ASD with rice bran. The lowest net revenue was for the steam plus mustard meal treatments due to the high cost of the steam treatment. Therefore, the need for more efficient steam injection systems is critical to adoption in a commercial setting. Recent advances with steam application equipment can reduce the cost of steam treatment to less than $5,500 per acre with the potential to further reduce costs.