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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