Integrated rotation systems for soil borne disease, weed and fertility management in strawberry/vegetable production

Integrated rotation systems for soil borne disease, weed and fertility management in strawberry/vegetable production

Summary

We continued a rotation trial at the Santa Cruz site. After completing growing strawberries in fall 2012, legume/cereal mixed cover crops (November 2012 – March 2013) and Romaine lettuce (July – September 2013) were grown. No significant difference was found between any treatments in total biomass of cover crop (P>0.66) and marketable yield of Romaine lettuce (P>0.18). Marketable strawberry yield at a demonstration trial at ALBA showed a strong negative correlation with plant mortality caused by Verticillium dahliae (P=0.0001***) and was in order of cauliflower > fallow > broccoli for main plots and ASD > ASD+MS > MC > UTC for sub plots.

Objectives/Performance Targets

Objective 1: To test the effects of 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. (Shennan, Muramoto, Koike, Klonsky, Milazzo, Wong, Tanimura, Noma and Kimes. Years 1-3, Santa Cruz, Salinas).

Objective 2: We propose a series of additional experiments to optimize MC application procedures for improved yields, weed and disease suppression and N provision in strawberries and Romaine lettuce. Specific goals are 1) to establish the optimum time between MC application and lettuce planting; 2) test the effects of MC application rate, depth of incorporation and level of pre-plant 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 CA 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).

Accomplishments/Milestones

Objective 1

1.1       Santa Cruz Site

After the end of the strawberry season, in fall 2012, plants were mowed and the field was disked and spring tooth cultivated. Soil pH was measured at the end of strawberry season (9/28/12) and four tons/acre of dolomite was applied to all plots to correct acidity based on the pH buffer curve developed using the plot soil. A legume/cereal mixed cover crop (45% bell beans, 45% vetch, 10% rye cv. AGS104) was direct seeded at 300 lbs/acre for all plots on 11/6/12 and grown over the winter. On 3/18/13, aboveground cover crop biomass was sampled in a 0.25 m² quadrat in each plot. Fresh biomass for each type of cover crop was recorded and a sub-sample taken for moisture and nutrient analysis. Between 3/20 and 3/27/13, the cover crop was mowed and incorporated by a spader. Soil samples for inorganic N monitoring for top- (0”-6” depth) and sub-soil (6”-12” depth) were taken on 12/13/12, 1/17/13 and 3/11/13.

At the end of July 2013, the field was springtooth cultivated and 36” wide beds were listed. On 7/30/13, Romaine lettuce transplants (cv. Salvius) were planted in a single row per bed with 12” spacing for all plots. Lettuce was harvested on 9/10/15 in block 3-4 and on 9/13/13 in block 1-2. Marketable head yield and total biomass of lettuce was recorded. Two plants per plot were sub-sampled for moisture and nutrients analysis. Top- (0”-6”) and sub- (6”-12”) soils for inorganic N monitoring and chemical analysis were taken before (7/29/13) and after (9/10/13; 9/13/13) lettuce growth.

Work left to do for this trial includes total N analysis of plant samples, estimation of N loss during the winter rainy seasons, soil Verticillium test and economic analysis.

1.2       Salinas Site

This field trial was completed in summer 2012. Work left to do for the trial include total N analysis of plant samples, estimation of N loss during the winter rainy season, a part of soil Verticillium test and economic analysis.

Objective 2

2.1       Mustard Cake Plant Back Time Trial for Transplanting Romaine Lettuce

The trial was conducted in 2012. Work left to do for the trial includes an economic analysis of MC application.

Objective 3

3.1       Demonstration trial at ALBA

A non-replicated demonstration trial (0.1 acre) with the same design as the Santa Cruz trial in Objective 1.1 was established in ALBA, Salinas in 2012. Prior to establishing the trial, tomatoes were planted at the site to increase V. dahliae population. Broccoli and cauliflower were grown on 1/3 of the site in the summer 2012 as main plots. After harvest, crop residues from broccoli and cauliflower were mowed and incorporated. Split plots of ASD, MC, ASD+MC and UTC were created as described in section 1.1 before transplanting strawberries. Strawberries (cv. Albion) were transplanted to all plots on 11/13/12.

A wooden sign in Spanish and English explaining the goals, approaches and funding sources of the trial was established at the demo site in January 2013 (Image 1). Strawberry fruit yield from each plot was monitored throughout the harvest season in 2013.

3.2       Other outreach activities accomplished and to be done

Using the demonstration trial, a field day/workshop on soilborne disease management in organic strawberry production was conducted at ALBA on 7/9/13. Data from rotation trials were presented at multiple ASD workshops/grower meetings in the central coast area. A paper based on this project was submitted to the Eighth International Symposium on Chemical and Non Chemical Soil and Substrate Disinfestation (SD 2014) to be held at Torino, Italy in July 2014 (in review). Outreach meetings/workshops and webinars will be held in 2014. Outreach pamphlet on the integrated approach will also be published. A survey on potential adoption of developed practices was conducted after the ALBA workshop (see Table 1 below) and will be repeated along with outreach meetings/workshops to be held in 2014.

• Image 1. A wooden sign in Spanish and English and the demonstration trial at ALBA, Salinas.

Impacts and Contributions/Outcomes

Objective 1

1.1       Santa Cruz Site

Cover crops grew uniformly across treatments. No significant differences were found between any treatments on total dry aboveground cover crop biomass (Fig. 1). Similarly, uniformity across treatments were observed on each cover crop species biomass (Fig. 2). No difference was found among main treatments, and the only significant difference among split treatments was between ASD and UTC; ASD plots had a higher bell bean biomass compare to UTC (P=0.008**) (Fig. 2a)).

At the end of the strawberry season, soil pH of the ASD+MC, MC and ASD plots was lower than UTC (Fig. 3). All plots showed fairly low pH, ranging from 5.1 for ASD+ MC to 5.4 for UTC plots. The pH reduction by 0.5 to 1 unit after ASD treatment with 9 tons/acre of rice bran has been widely observed in many trials in this area. It is probably due to large NO₃-N release during December – February (see Fig. 5). After liming with four tons/acre of dolomite, pH level for all plots was raised to 5.4 to 5.5 by lettuce transplanting (7/29/13).

Romaine lettuce’s marketable yield showed no significant difference neither in main (P=0.43) or split plots (P=0.18) (Fig. 4). No difference occurred in total yield (heads and residue) where values in main and split plots averaged around one ton/acre (data not shown).

Inorganic N dynamics throughout the experiment are shown in Fig. 5. As crop residues were incorporated in September 2011, and rice bran and MC applied, soil inorganic N in the topsoil rapidly increased and peaked in November to December, reaching to 60-120 mg kg^-1 and 10-30 mg kg^-1 for NO₃-N and NH₄-N, respectively. The NO₃-N peak in December for sub plots was highest in ASD+MC, followed by ASD, MC and UTC (P<0.0001***). Soil inorganic N concentration gradually decreased at all plots regardless of treatment during the strawberry growth period. No significant difference was found in inorganic N at either depth after cover crops were planted in the fall 2012. In the sub-soil, NO₃-N and NH₄-N showed lower overall concentration than top-soil following a similar dynamic pattern with the top soil.

Objective 3

3.1 Demonstration trial at ALBA

Strawberry plants started to show wilt symptom 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 (Image 2). For sub plots, UTC and MC plots had higher mortality compared to ASD and ASD+MC plots. The disease plants were taken to the UCCE diagnostic lab and V. dahliae alone was identified as the pathogen.

Cumulative fruit yield reflected the mortality of the plants; for main plots, the cauliflower plots had the highest yield, followed by the fallow plots, and the lowest in the broccoli plots. For sub plots, the order was ASD > ASD+MS > MC > UTC (Fig. 6). There was a strong negative correlation between mortality and cumulative fruit yield (Fig. 7. P=0.0001***).

Based on earlier studies, the broccoli treatment was included in this rotation trial with the expectation of an additive or synergistic V. dahliae suppression effect with ASD and/or MC. However, it resulted in a higher mortality than the cauliflower and the 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. The workshop mainly targeted Latino growers. We had 14 participants and simultaneous Spanish translation was provided. According to the post-workshop survey, the event was well-received by the most participants (Table 1).

• Fig. 2. Aboveground dry biomass of each cover crop species in main and split plots. Each bar indicates mean ± SEM (n=4). Treatments above the same line are not significantly different (Tukey’s HSD test (P=0.05)).
• Fig. 5a). Inorganic N dynamics at top soil (0”-6” depth) at the Santa Cruz site. Averages of split plots are shown for NO3-N and NH4-N. 1: broccoli and cauliflower transplanting, 2: broccoli and cauliflower harvest, 3: pre ASD, MC treatments, 4: post ASD, MC treatments, 5: strawberry planting, 6: first strawberry harvest, 7: last strawberry harvest, 8: cover crop planting, 9: cover crop incorporation, 10: lettuce transplanting, 11: lettuce harvest. *, **, *** indicates significant at P=0.05, 0.01, 0.001, respectively.
• Fig. 5b). Inorganic N dynamics at sub soil (6”-12” depth) at the Santa Cruz site. Averages of split plots are shown for NO3-N and NH4-N. 1: broccoli and cauliflower transplanting, 2: broccoli and cauliflower harvest, 3: pre ASD, MC treatments, 4: post ASD, MC treatments, 5: strawberry planting, 6: first strawberry harvest, 7: last strawberry harvest, 8: cover crop planting, 9: cover crop incorporation, 10: lettuce transplanting, 11: lettuce harvest. *, **, *** indicates significant at P=0.05, 0.01, 0.001, respectively.
• Fig. 1. Total dry aboveground cover crop biomass in main plot (fallow, cauliflower, broccoli) and split plots (UTC; untreated check, MC; mustard cake, ASD, ASD+MC).
• Fig 3. Soil pH at 0”-6” depth at post-strawberry season (sampled on 9/28/13). Bars indicate mean ± SEM (n=4). Treatments above the same line are not significantly different (Tukey’s HSD test (P=0.05)).
• Fig. 4. Marketable head weight of Romaine lettuce (kg/plant). Each bars indicates mean ± SEM (n=4). Treatments above the same line are not significantly different (Tukey’s HSD test (P=0.05)).
• Image 2. Verticillium wilt of strawberry plants (cv. Albion) at the demonstration trial at ALBA, Salinas. Photo was taken on 5/15/2013.
• Fig. 6. Cumulative marketable fruit yield at the non-replicated demonstration trial at ALBA, Salinas.
• Fig. 7. Correlation between mortality of strawberry plants and cumulative marketable yield of strawberries at the demonstration trial at ALBA, Salinas.
• Table 1. A summary of evaluations for the field day/workshop held at ALBA on 7/9/2013. There was 14 signed participants of whom 10 returned evaluations. Numbers are %.

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