Good nutrient management is essential not only for optimal plant growth, but also for maintaining good plant health and the ability of the plant to withstand biotic and abiotic stressors.  Strawberry, a $3.2 billion commodity in California, requires good nutrient, water, and health management throughout its lengthy fruit production cycle.  In addition to the primary nutrient inputs, certain supplements can be beneficial to the crop.  A study was conducted in fall-planted strawberries from 2017 to 2018 using a plant-based anti-stress agent, humates, and sulfur, and a special formulation of NPK as supplements to the standard fertility program to evaluate their impact on strawberry fruit yields and quality.

Methodology

Strawberry cultivar Albion was planted during the second week of December 2017 in 38” wide beds with two rows of plants per bed.  This study included the following treatments:

1. Grower standard (GS) program included a total of 6.13 gallons of Urea Ammonium Nitrate Solution 32-0-0, 2.59 gallons of Ammonium Polyphosphate Solution, and 6.95 gallons of Potassium Thiosulfate (KTS 0-0-25) to 0.5 acres of the strawberry field.  These fertilizers were applied between 5 January and 18 May 2018 approximately at weekly intervals through the drip irrigation system.  Additionally, 1 quart of Nature's Source Organic Plant Food 3-1-1 was applied on 5 and 22 January 2018 and again on 5 February 2018. 
2. GS + Bluestim at 3.6 lb/ac in 53 gallons applied as a foliar spray with 0.125% Dyne-Amic once every three weeks for a total of six times.  Bluestim is an osmoregulator containing >96% of glycine betaine that is expected to protect plants from abiotic stressors.
3. GS + SKMicrosource Ultrafine powder at 1.4 oz in 4 gallons applied as a foliar spray once a month for a total of three times along with SKMicrosource prill applied at 500 lb/ac at the base of the plant once.  Both products contain elemental sulfur, sulfite, and sulfate along with potassium, micronutrients, and rare earth minerals.  Additionally, the prill form also has humates.  These products are expected to improve plants' natural defenses against biotic stressors like pests and diseases.
4. GS + ISO NPK 3-1-3 at 8 fl oz/ac in 100 gallons once every two weeks for a total of four times.  ISO NPK 3-1-3 contains isoprenoid amino complex extracted from a desert shrub guayule (Pathenium argentatum), which is expected to improve nutrient uptake and protect plants from abiotic stressors.

The first application of supplements for treatments 2-4 started on 1 March 2018.  Each treatment had a 30' long plot marked on a bed replicated four times in a randomized complete block design.  The fruit was harvested one to two times per week between 3 April and 14 June 2018 and the weight of marketable and unmarketable berries was determined for each plot.  Using a penetrometer, fruit firmness was measured from four fruits from each plot on 3, 16, and 23 April and 14 May 2018.  Sugar content was also measured from two fruits from each plot on those four sampling dates.  Postharvest health was measured from the fruit harvested on 16 and 23 April and 21 and 31 May 2018.  Fruit was kept in perforated plastic containers (clamshells) at room temperature and the growth of gray mold (Botrytis cinerea) and Rhizopus fruit rot (Rhizopus spp.) was rated 3 and 5 days after harvest on a scale of 0 to 4 (where 0=no disease, 1=1-25% fruit with fungal infection, 2=26-50% infection, 3=51-75%, and 4=76-100%).  Data were analyzed using the analysis of variance in Statistix software.

Results

There were no statistically significant (P > 0.05) differences among the treatments in any of the measured parameters.  However, the marketable fruit yield was nearly 11% higher in the treatment that received SKMicrosource supplements.  While the average sugar content was 9.5 ^oBx in the grower standard, it varied between 9.7 and 9.8 in other treatments.  Similarly, the average disease rating during the postharvest fruit evaluation was 1.00 for the standard at 3 days after harvest, while it varied between 0.25 and 0.50 for the other treatments.  Average disease rating at 5 days after harvest was between 2.25 and 2.50 for all treatments.

Table 1. Total marketable and unmarketable fruit yield per plot during the study period

Table 2. Fruit firmness and sugar content on four observation dates and their averages

Table 3. Postharvest fruit disease rating 3 and 5 days after four harvest dates

Discussion
The crop was generally healthy during the study period and there were no signs of any abiotic stresses such as salinity, water stress, and extreme temperature fluctuations, or biotic stresses such as pests or diseases except for uniform weed growth in the furrows and some areas of the beds.  Since these supplements are expected to help the plants under stressful conditions, significant differences could not be found, probably due to the lack of unfavorable growth conditions.  It also appears from the manufacturer's studies that ISO NPK 3-1-3 performs better at 4 fl oz/acre - half the rate recommended for this study.  Additional studies can help further evaluate the potential of these supplements both under normal and stressed conditions and at different application rates and frequencies.

Acknowledgments
Thanks to the technical assistance of Dr. Jenita Thinakaran in carrying out the study, the field staff at the Shafter Research Station for the crop maintenance, the financial support of Biobest and Heart of Nature, and to Beem Biologics for providing the test material.

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Transplanting tomatoes

There has been a growing interest in the recent years in exploring the potential of biostimulants in crop production.  Biostimulants are mineral, botanical, or microbial materials that stimulate natural processes in plants, help them tolerate biotic and abiotic stressors, and improve crop growth and health.  Several recent studies demonstrated the potential of the biostimulant or soil amendments in improving crop yields and health.  For example, in a 2017 field study, silicon, microbial, botanical and nutrient materials improved processing tomato yields by 27 to 32% compared to the standard fertility program (Dara and Lewis, 2018).  In a 2017-2018 strawberry field study, some biostimulant and soil amendment products resulted in a 13-16% increase in marketable fruit yield compared to the grower standard (Dara and Peck, 2018).  He et al. (2019) evaluated three species of Bacillus and Pseudomonas putida alone and in different combinations in tomatoes grown in laboratory and greenhouse.  The combination of Bacillus amyloliquefaciens, B. pumilus, and P. putida increased the plant biomass and the root/shoot ratio.  Significant increase in fruit yield, between 18 and 39%, was also achieved from individual or co-inoculations of these bacteria.  A field study was conducted in processing tomato to evaluate the impact of nutrient products containing beneficial microbes and botanical extracts on tomato yields and fruit quality.

Tomato plots - each treatment is marked by a colored flag

Methodology

The study was conducted from late spring to fall of 2018 to evaluate three treatment programs compared to the grower standard.  Tomato cultivar Quali T27 was seeded on 25 April and transplanted on 19 June using a mechanical transplanter.  Due to high temperatures at the time of planting, some transplants died and they were re-planted on 28 June.  Herbicide Matrix was applied on 5 July and Poast was applied on 13 July followed by hand weeding on 27 July.  Crop was irrigated, fertigated, and treatements were applied through a drip system.  Overhead sprinkler irrigation was additionally used immediately after transplanting.  The following treatments were included in the study:

1. Grower standard: 10-34-0 Ammonium Polyphosphate Solution was applied at 10 gal/ac at the time of transplanting followed by the application of UAN-32 Urea Ammonium Nitrate Solution 32-0-0 at the rate of 15 units of N at 3, 6, and 13 weeks after planting and 25 units of N at 7 weeks after planting.

2. Grower standard + BiOWiSH Crop 16-40-0: BiOWiSH Crop 16-40-0 contains 16% nitrogen and 40% phosphate along with B. amyloliquefaciens, B. licheniformis, B. pumilus, and B. subtilis at 1X10⁸ cfu/gram.  Crop 16-40-0 was applied at 1 lb/ac at the time of planting followed by the application 0.5 lb/ac at 3, 6, and 9 weeks after planting.

3. Grower standard 85% + BiOWiSH Crop 16-40-0: Crop 16-40-0 was applied at the same rate and frequency as in treatment 2, but the grower standard was reduced to 85%.

4. RootRx: RootRx contains 5% soluble potash and proprietary botanical extracts and is supposed to stimulate a broad range of antioxidant compounds in the plant.  It was applied at 0.25 gal/ac at the time of planting followed by the application of 0.5 gal/ac at 3, about 7, and 13 weeks after planting.

Each treatment contained 30' long bed with a single row of tomato plants and replicated five times in a randomized complete block design.  Along with the fruit yield, the sugar content of the fruit and leaves [using a refractometer from three fruits (two measurements from each) and four leaves per plot], chlorophyll content (using a digital chlorophyll meter from four leaves per plot), and frost damage levels (using a visual rating on a 0 to 5 scale where 0 = no frost damage and 5 = extreme frost damage with a complete plant death) were also monitored.  Due to an unknown reason, some plants in the fifth replication were stunted halfway through the study.  Data from the fifth replication were excluded from the analysis.  Data were subjected to the analysis of variance using Statistix software and significant means were separated using the Tukey's HSD test. 

Results

Fruit yield: Marketable and unmarketable fruit yield was monitored from 27 August to 13 November.  Seasonal total for marketable fruit was significantly (P = 0.04) different among the treatments where RootRx resulted in a 26.5% increase over the grower standard while Crop 16-4-0 with the full rate of the grower standard had an 8%, and with 85% of the grower standard had a 13.2% increase.  It appeared that a similar improved yield response was also seen when Crop 16-40-0 was used at a reduced rate of the grower standard in other studies conducted by the manufacturer.

Sugar content: Sugar content of the fruit and leaves was measured once after the last harvest and there were no significant (P > 0.05) difference among the treatments.

Chlorophyll content: Chlorophyll content was measured once after the last harvest and there was no significant (P > 0.05) difference among the treatments.

Frost damage: Study was concluded after frosty conditions in November 2018 damaged the crop.  Although there were no statistically significant (P > 0.05) differences, plants treated with RootRx had the lowest rating of 2.

Means and standard errors of the measured parameters

Acknowledgements: Thanks to Jenita Thinakaran and the field staff at the Shafter Research Station for their technical assistance, Plantel Nurseries for providing transplants, and BiOWiSH Technologies and Redox Chemicals for their financial support.

References

Dara, S. K. and D. Peck.  2018.  Microbial and bioactive soil amendments for improving strawberry crop growth, health, and fruit yields: a 2017-2018 study.  UCANR eJournal of Entomology and Biologicals (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=27891)

Dara, S. K. and E. Lewis.  2018.  Impact of nutrient and biostimulant materials on tomato crop health and yield.  UCANR eJournal of Entomology and Biologicals (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=26054)

He. Y., H. A. Pantigoso, Z. Wu, and J. M. Vivanco.  2019.  Co-inoculation of Bacillus sp. and Pseudomonas putida at different development stages acts as a biostimulant to promote growth, yield and nutrient uptake of tomato.  J. Appl. Microbiol.  https://doi.org/10.1111/jam.14273

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California is the leading producer of tomatoes, especially for the processing market (CDFA, 2017).  Tomato is the 9^th most important commodity in California valued at $1.71.  Processed tomatoes are ranked 6^th among the exported commodities with a value of $813 million.  While good nutrient management is necessary for optimal growth, health, and yields of any crop, certain products that contain minerals, beneficial microbes, biostimulants, and other such products are gaining popularity.  These materials are expected to improve crop health and yield, impart soil or drought resistance, induce systemic resistance, or improve plant's immune responses to pests, diseases, and other stress factors (Berg, 2009; Bakhat et al., 2018; Chandra et al., 2018; Shameer and Prasad, 2018).  Maintaining optimal plant health through nutrient management is not only important for yield improvement, but it is also an important part of integrated pest management strategy as healthy plants can withstand pest and disease pressure more than weaker plants and thus reduce the need for pesticide treatments.

Experimental plots, transplanting, and treatment details.

Methodology

A study was initiated in the summer 2017 to evaluate the impact of various treatment programs on tomato plant health and yield.  Processing tomato cultivar Rutgers was seeded on 7 June and transplanted on 18 July, 2017 using a mechanical transplanter.  Monoammonium phosphate (11-52-0) was applied at 250 lb/ac as a side-dress on 7 August as a standard for all treatments.  Since planting was done later in the season, crop duration and harvesting period were delayed due to the onset of fall weather.  Plots were sprinkler irrigated daily or every other day for 3-4 hours for about 2 weeks after transplanting.  Drip irrigation was initiated from the beginning of August for 12-14 hours each week and for a shorter period from mid October onwards.

There were five treatments in the study including the standard.  Each treatment had a 38” wide and 300' long bed with a single row of tomato plants.  Treatments were replicated four times and arranged in a randomized complete block design.  Different materials were applied through drip using a Dosatron injector system, sprayed at the base of the plants with a handheld sprayer, or as a foliar spray using a tractor-mounted sprayer based on the following regimens.

1. Standard
2. AgSil® 21 at 8.75 fl oz/ac in 100 gal of water through drip (for 30 min) every 3 weeks from 31 July to 13 November (6 times).  AgSil 21 contains potassium (12.7% K2O) and silicon (26.5% SiO2) and is expected to help plants with mineral and climate stress, improve strength, and increase growth and yields.
3. Yeti Bloom^TM  at 1 ml/gallon of water.  Applied to the roots of the transplants one day before transplanting followed by weekly field application through the drip system from 7 August to 13 November (15 times).  Yeti is marketed as a biostimulant and has a consortium of beneficial bacteria - Pseudomonas putida, Comamonas testosterone, Citrobacter freundii, and Enterobacter cloacae.  Yeti Bloom is expected to enhance the soil microbial activity and helps with improved nutrient absorption.
4. Tech-Flo®/Tech-Spray® program contained five products that supplied a variety of macroandmicro nutrients.  Products were appliedthroughdrip (for 30 min) at the following rates and frequencies in 300gal of water. 
   1. Tech-Flo All Season Blend #1 1 qrt/ac in transplant water and again at first bloom on 28 August.
   2. Tech-Flo Cal-Bor+Moly at 2 qrt/ac at first bloom on 28 August.
   3. Tech-Flo Omega at 2 qrt/ac in transplant water and again on 11 September (2 weeks after the first bloom).
   4. Tech-Flo Sigma at 2 qrt/ac on 11 September (2 weeks after the first bloom).
   5. Tech-Spray Hi-K at 2 qrt starting at early color break on 25 September with three follow up applications every two weeks.
5. Innovak Global program contained four products.
   1. ATP Transfer UP at 2 ml/liter of water sprayed over the transplants to the point of runoff just before transplanting.  Three more applications were made through drip (for 30 min) on 7 and 21 August and 4 September. This product contains ECCA Carboxy® acids that promote plant metabolism and expected to impart resistance to stress factors.
   2. Nutrisorb-L at 40 fl oz/ac applied through drip (for 30 min) on 31 July, 14 August (vegetative growth stage), 4 and 18 September, and 2 October (bloom through fruiting).  Nutrisorb-L contains polyhydroxycarboxylic acids, which are expected to promote root growth and improve nutrient and water absorption.
   3. Biofit®N at 2 lb/ac through drip (for 30 min) on 31 July, 21 August (3 weeks after the first), and 4 September (at first bloom).  Biofit contains a blend of beneficial microbes – Azotobacter chroococcum, Bacillus subtilis, B. megaterium, B. mycoides, and Trichoderma harzianum.  This product is expected to improve the beneficial microbial activity in the soil and thus contribute to improved soil structure, root development, plant health, and ability to withstand stress factors.
   4. Packhard at 50 fl oz/ac in 50 gal of water as a foliar spray twice during early fruit development (on 11 and 18 September) and every 2 weeks during the harvest period (four times from 2 October to 13 November).  Contains calcium and boron that improve fruit quality and reduce postharvest issues.

A 50' long area was marked in the center of each plot for observations.  Plant health was monitored on 1, 8, and 22 August by examining each plant and rating them on a scale of 5 where 0 represented a dead plant and 5 represented a very healthy plant.  Yield data were collected from 11 October to 5 December on eight harvest dates by harvesting red tomatoes from each plot.  On the last harvest date, mature green tomatoes were also harvested and included in the yield evaluation.  Data were analyzed using analysis of variance and Tukey's HSD test was used for means separation.

Results and discussion

There was no statistically significant difference (P > 0.05) in the health of the plants in August (Fig. 1) or in the overall seasonal yield (Fig. 2) among treatments.  The average health rating from three observations was 3.94 for the standard, 4.03 for AgSil 21, 4.45 for Yeti Bloom, 4.38 for Tech-Flo/Spray program, and 4.35 Innovak Global program.

Fig. 1. Plant health on a 0 (dead) to 5 (very healthy) rating on three observation dates.

When the seasonal total yield per plot was compared, Yeti Bloom had 194.1 lb followed by, Innovak program (191.5 lb), AgSil 21 (187.3 lb), the standard (147.4 lb) and Tech-Flo/Spray program (136.5 lb).  Due to the lack of significant differences, it is difficult to comment on the efficacy of treatments, but the yield from AgSil 21 was 27% more than the standard while yields from Innovak program and Yeti Bloom were about 30% and 32% higher, respectively.

Fig. 2. Seasonal total yield/plot from different treatments.

Fig. 3. Percent difference in tomato yield between the standard and other treatment programs.

Studies indicate that plants can benefit from the application of certain minerals such as silicon compounds and beneficial microorganisms, in addition to optimal nutrient inputs.  Silicon is considered as a beneficial nutrient, which triggers the production of plant defense mechanisms against pests and diseases (Bakhat et al., 2018).  Although pest and disease conditions were not monitored in this study, silverleaf whitefly (Bamisia tabaci) infestations and mild yellowing of foliage in some plants due to unknown biotic or abiotic stress were noticed.  AgSil 21 contains 26.5% of silica as silicon dioxide and could have helped tomato plants to withstand biotic or abiotic stress factors.  Similarly, beneficial microbes also promote plant growth and health through improved nutrient and water absorption and imparting the ability to withstand stresses (Berg, 2009; Shameer and Prasad, 2018).  Beneficial microbes in Yeti Bloom and BiofitN might helped the tomato plants in withstanding stress factors and improved nutrient absorption.  Other materials applied in the Innovak program might have also provided additional nutrition and sustained microbial activity.

The scope of the study, with available resources, was to measure the impact of various treatments on tomato crop health and yield.  Additional studies with soil and plant tissue analyses, monitoring pests and diseases, and their impact on yield would be useful.

Acknowledgements: Thanks to Veronica Sanchez, Neal Hudson, Sean White, and Sumanth Dara for their technical assistance and the collaborating companies for free samples or financial assistance.

References

Bakhat, H. F., B. Najma, Z. Zia, S. Abbas, H. M. Hammad, S. Fahad, M. R. Ashraf, G. M. Shah, F. Rabbani, S. Saeed.  2018.  Silicon mitigates biotic stresses in crop plants: a review.  Crop Protection 104: 21-34.  DOI: 10.1016/j.cropro.2017.10.008.

Berg, G.  2009.  Plant-microbe interactions promoting plant growth and health: perspectives for controlled use of microorganisms in agriculture.  Appl. Microbiol. Biotechnol. 84: 11-18.  DOI: 10.1007/s00253-009-2092-7.

CDFA (California Department of Food and Agriculture).  2017.  California agricultural statistics review 2015-2016. (https://www.cdfa.ca.gov/statistics/PDFs/2016Report.pdf)

Chandra, D., A. Barh, and I. P. Sharma.  2018.  Plant growth promoting bacteria: a gateway to sustainable agriculture.  In: Microbial biotechnology in environmental monitoring and cleanup.  Editors: A. Sharma and P. Bhatt, IGI Global, pp. 318-338.

Shameer, S. and T.N.V.K.V. Prasad.  2018.  Plant growth promoting rhizobacteria for sustainable agricultural practices with special reference to biotic and abiotic stresses.  Plant Growth Regulation, pp.1-13.  DOI: 10.1007/s10725-017-0365-1.

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