- Fruits: berries (strawberries)
- Vegetables: broccoli, cauliflower
- Crop Production: crop rotation, cover crops, fallow, fertigation, irrigation, nutrient cycling, organic fertilizers, tissue analysis
- Education and Training: extension, networking, on-farm/ranch research, participatory research, workshop
- Farm Business Management: budgets/cost and returns
- Pest Management: biological control, economic threshold, field monitoring/scouting, mulching - plastic
- Production Systems: organic agriculture
- Soil Management: green manures, soil analysis, nutrient mineralization, organic matter
- Sustainable Communities: ethnic differences/cultural and demographic change
Strawberry/vegetable producers in coastal California face soilborne disease, nutrient, and weed management challenges. Non-fumigant solutions for controlling soilborne diseases and weeds are becoming increasingly crucial for both conventional and organic growers. Objectives of the project were 1): to test the effects of anaerobic soil disinfestations (ASD), broccoli residue incorporation, mustard cake (MC) application, alone and in combination, on crop yields, Verticillium. dahliae suppression, weed suppression, N provision, production costs, and net returns in strawberries and lettuce grown in typical crop rotation systems on organic and conventional farms with high V. dahliae pressure, 2): to optimize MC application procedures for improved yields, weed and disease suppression and N provision in strawberries and Romaine lettuce, and 3) to disseminate results to growers and agricultural professionals in coastal CA and beyond.
For Objective 1, we conducted two replicated trials; one at an organic farm (Org) and the other at a conventional farm (Conv). Main plots were crop rotations (broccoli, cauliflower or fallow – strawberries – winter cover crop*–Romaine lettuce*. * Org only) and sub plots were ASD, MC, ASD+MC, untreated control (UTC), and fumigant (Pic-Clor 60. Conv only) applied prior to strawberry. Yield was measured for each crop. Weed density and disease level were monitored during the strawberry season and soil inorganic N dynamics for the entire period. Partial net returns of each crop rotation were examined. For strawberries, ASD+MC produced greater fruit yield than UTC and MC at both sites and ASD at Org site. At Conv site, ASD+MC and ASD produced similar fruit yields as fumigant. MC and rice bran applied with the ASD treatment released high concentrations of soil inorganic nitrogen for two months after application. This resulted in increased early fruit yield, especially at the Org site where no pre-plant fertilizer was added. On the other hand, a large amount of N was lost during the winter rainy season from ASD and MC plots in both sites, ranging from 116 to 223 kg-N/ha at the Org. site and from 75.2 to 134 kg-N/ha at the Conv. site. Optimization of N management in these treatments warrants further studies. Infection of strawberry plants with V. dahliae at the end of the season in the Org site was reduced by ASD and ASD+MC. Weed suppression by ASD and MC was limited. The effect of broccoli rotation on V. dahliae and weed suppression was also limited and no synergistic effect of broccoli rotation with ASD and MC was observed. Nonetheless, the highest net return was recorded from the broccoli ASD+MC treatment despite higher treatment costs, mainly due to the high yields of strawberry and lettuce crops. Overall, ASD improved net returns for all rotations. Importantly, at the Org site, the number of V.dahliae microsclerotia in the soil after the lettuce crop, two years after ASD treatment, were still lower in the ASD plots than the UTC, indicating a lasting suppressive effect of this treatment.
For Objective 2, we conducted a field trial to optimize MC application procedures for transplant Romaine lettuce. A split-split plot experiment with four replicates was initiated with: mustard cake (MC. Brassica juncea: Sinapis alba,1:1 by weight) 0.5 ton/acre, MC 1ton/acre, and pelleted organic fertilizer (OF. Perfect Blend 4-4-2. Chicken manure-based) 0.5 ton/acre (grower’s standard) as main plots; plant back period ( 1, 2, 3 and 4 weeks) as split plots; and with and without plastic mulch (clear TIF film) as split-split plots. MC 1 t/ac with TIF and three week plant back time produced the highest yield. Without TIF, however, there was no difference in head weight between any plant back time period indicating even one week is sufficient. MC application did not show any effect on weed density of either monocots or dicots regardless of application rate, use of TIF or not, and plant back period.
For Objective 3, a non-replicated demonstration trial with the same design as the Org trial was established in ALBA, Salinas in 2012. Strawberry plants started to show wilt symptom caused by V. dahliae in April 2013, and by May significant plant mortality occurred. For main plots, mortality was highest in the broccoli plots, followed by the fallow plots, and the lowest in the cauliflower plots. For sub plots, UTC and MC plots had higher mortality compared to ASD and ASD+MC plots. Cumulative fruit yield reflected the mortality of the plants. Unexpectedly, broccoli plots resulted in higher mortality than the cauliflower and fallow plots. A multi-cut broccoli variety De Cicco was used in this broccoli treatment suggesting that the effect of broccoli residue incorporation on V. dahliae suppression may be variety dependent. Using this demonstration trial, a field day/workshop on soilborne disease management in organic strawberry production was conducted at ALBA on 7/9/13 and again on 9/25/14. Each workshop was attended by 14 to 15 people and simultaneous Spanish translation was provided. Both events were well received. Outcomes of this project were also presented at multiple extension and academic meetings.
Project objectives:div style="margin-left:1em;">
Objective 1: To test the effects of ASD, broccoli residue and mustard cake (MC) incorporation, alone and in combination, on: crop yields, V. dahliae suppression, weed suppression, N provision, production costs, and net returns in strawberries and lettuce grown in typical crop rotation systems on organic and conventional farms with high V. dahliae pressure. (Shennan, Muramoto, Koike, Klonsky, Milazzo, Tanimura, Noma and Kimes. Years 1-3, Santa Cruz, Salinas).
Objective 2: To: 1) establish the optimum time between MC application and lettuce planting; 2) test the effects of MC application rate, depth of incorporation and level of preplant fertilizer on yields, disease and weed suppression in lettuce production; 3) as for goal 2 but for strawberries, and 4) assess the economic feasibility of MC use in lettuce and strawberries. (Shennan, Muramoto, Koike, Klonsky, Pedersen and Kimes. Years 1-3, Watsonville).
Objective 3: To disseminate results to growers and agricultural professionals in coastal California and beyond through a variety of approaches including workshops, a field demonstration (at an NGO farm that works with low resource Hispanic organic farmers), field trips, YouTube, eOrganic, and written materials (All team members. Years 2 and 3).