Investigation of Soy Protein–based Biostimulant Seed Coating for Broccoli Seedling and Plant Growth Enhancement

in HortScience

This research presents a novel method of using plant-derived protein hydrolysates as seed coating materials. The objective of this study was to develop seed coating formulations using soy flour, a sustainable, inexpensive, and green source, as a biostimulant using broccoli as the model system. A 10% suspension of soy flour was used as the seed treatment binder in all coatings. The solid particulate filler was composed of mixtures of soy flour, cellulose, and diatomaceous earth, together termed as SCD. All SCD components were homogenized in water, then dried and ground to a fine particle size <106 µm. The SCD coatings were applied with rotary pan seed coating equipment at 25% of the seed weight. Increasing the proportion of soy flour increased the seed coating strength and also the time for the coating to disintegrate after soaking in water. As a result, the seed coatings reduced the percentage germination and the germination rate compared with the nontreated control. However, the 10-day-old seedling root and shoot growth showed significant improvement for all SCD coating treatments compared with controls. Plant growth and development was also measured after 30 days in the greenhouse. Fresh weight (FW) and dry weight (DW), leaf area, plant height, leaf development, Soil-Plant Analyses Development (SPAD) index (chlorophyll measurement), and nitrogen (N) per plant were all greater from coatings with 30%, 40%, and 50% soy flour than the noncoated control. Nitrogen, from the soy flour applied in the seed coatings, ranged from 0.024 to 0.073 mg per seed, while the enhanced N per plant ranged from 1.7 to 8.5 mg. The coating treatment with 0.063 mg N per seed resulted in the greatest plant leaf area and highest N content. Nitrogen applied in the seed coating only accounted for 1% to 2% of the enhanced N in the plants, indicating the soy flour acted as a biostimulant rather than a fertilizer.

Contributor Notes

We are grateful to Catharine M. Catranis and Michael Loos who have been the great resource, assisting with the project, and Hilary S. Mayton and Suemar A. Avelar for reviewing the manuscript. Germination and seedling growth tests were conducted with facilities of the New York State Seed Testing Laboratory. The project was supported by Hatch funds (NYC-329487) from the Cornell University Agricultural Experiment Station to the second and fourth authors.

Corresponding author. E-mail:

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    Broccoli seeds (A) noncoated, encrusted with 25% weight buildup of coating formulation SCD 40:20:40, (B) and SCD 50:00:50, (C), comparison of seedling growth from noncoated and coated broccoli seeds, (D) noncoated, (E) 40:20:40, and (F) 50:00:50. SCD is the proportion by weight of soy flour, cellulose fiber, and Diatomaceous earth in each coating formulation.

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    Dry weight (g, dash line), enhanced nitrogen uptake (mg) per plant (30 d seedlings), and applied nitrogen (mg) per coated seed from coating formulations investigated in Table 2. Standard error bars are shown.

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