Baker D. Aljawasim1, Patricia Richardson1, Guillaume Pilot2, and Jayesh B. Samtani1
1Hampton Roads Agricultural Research and Extension Center (AREC), School of Plant and Environmental Sciences, Virginia Tech, Virginia Beach, VA
2School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA

Biostimulants consist of beneficial microorganisms or compounds that can improve crop yields by strengthening plants’ immune systems and enhancing their tolerance to both biotic and abiotic stresses. These substances are generally classified into seven main groups: humic acid (HA) and fulvic acid (FA), protein hydrolysates (PHs), seaweed extracts, chitosan, inorganic compounds, as well as beneficial fungi and bacteria. Biostimulants are formulated to improve several agricultural aspects, such as (i) nutrient use efficiency, (ii) tolerance to environmental stresses, (iii) enhancement of crop quality attributes, and (iv) increased availability of limited nutrients in the soil or rhizosphere. Nonetheless, studies on their use across different plant species indicate that the effectiveness of biostimulants varies significantly depending on the species and growing conditions. A study was conducted in the 2023-2024 growing season to evaluate the effect of biostimulant products on strawberry crop yield and fruit quality. This was the second growing season in which we tried using biostimulants. Findings from the first season were discussed in a previous article that can be accessed in the Fall 2023 newsletter: Biostimulants did not affect crop yield and postharvest strawberry fruit quality | Southern Region Small Fruit Consortium.

Preplant fertilizers 60 lb of N/acre and 75 lb/acre of potassium were applied during bed preparation. Spring fertigation began March end, 2024 alternating on a weekly basis with Plantex 20-20-20, calcium nitrate and potassium nitrate at rate of 7 lb /acre of nitrogen. Each replicate was a bed that was 25 linear ft and had a single drip line in the bed center with separate on/off valves for irrigation, treatment injection and fertigation option via Dosatron injector. ‘Ruby June’ plugs were transplanted on 24 October with 14 plants per replicate spaced 14 inches in two alternating rows of seven. Five treatments with four replicates each were arranged in a randomized complete block design. Biostimulant treatments included Actinovate (rate:177 ml/acre) and TerraGrow Liquid (591 ml/acre) that were applied twice in fall 2023 and three times in spring 2024 at monthly intervals. EZ-Gro N18 (3.5 lb/acre) and iQForte (810 ml/acre) were applied twice in fall 2023 and five times in spring 2024 at biweekly intervals.

Vigor ratings ranging from 1 (low vigor plants in a replicate) to 10 (extremely vigorous plants in a replicate) were documented on a monthly basis, commencing from November 17 until May 22. Fruits were harvested twice a week from April 12 until June 21, 2024 (Photo 1). At each harvest, fruit was categorized as either marketable or non-marketable (weighing less than 10g, deformed, damaged, or diseased), and subsequently weighed accordingly by replicate. The weight of 10 marketable fruits per replicate was measured weekly to estimate fruit size in grams per fruit. Additionally, five marketable fruits were assessed weekly for outer skin firmness using a fruit texture analyzer, then stored at -20 °C for subsequent analysis of pH and total soluble solids (°Brix) using a digital refractometer.

 Photo 1. Harvesting in the study was done twice per week from April 12 until June 21, 2024

EZ-Gro N18, iQForte and Terra-Grow Liquid resulted in only a numerical increase in total strawberry yield (marketable and non-marketable fruit for the season) yielding in the range of 21,000 to 23,000 lb/acre. In comparison, the untreated control yielded around 19,000 lb/acre. Statistically the treatments did not differ. The application of iQForte resulted in improved plant canopy compared to the untreated control. All biostimulant treatments had no impact on the post-harvest fruit quality such as fruit firmness, pH of the fruit juice, or total soluble solids (°Brix). Despite the potential benefits of biostimulants in enhancing yield, their influence on these specific quality parameters was minimal. These findings suggest that the optimal choice of biostimulant and their rate use may require further investigation to have an impact on fruit quality and yield.

Funding sources: Virginia Ag. Council and USDA Hatch Project Number VA-160194

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