The objective of modern seed-coating technology is to uniformly apply a wide range of active components (ingredients) onto crop seeds at desired dosages so as to facilitate sowing and enhance crop performance. There are three major types of seed treating/coating equipment: dry powder applicator, rotary pan, and pelleting pan with the provisions to apply dry powders, liquids, or a combination of both. Additional terms for coatings produced from these types of equipment include dry coating, seed dressing, film coating, encrustments, and seed pelleting. The seed weight increases for these different coating methods ranges from <0.05% to >5000% (>100,000-fold range). Modern coating technology provides a delivery system for many other materials including biostimulants, nutrients, and plant protectants. This review summarizes seed coating technologies and their potential benefits to enhance seed performance, improve crop establishment, and provide early season pest management for sustainable agricultural systems.

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.

Biostimulant seed coating formulations were investigated in laboratory experiments for their potential to increase maximum germination, germination rate, germination uniformity, and seedling growth of red clover (Trifolium pratense L.) and perennial ryegrass (Lolium perenne L.) seeds. Red clover and perennial ryegrass seeds were coated with different combinations of soy flour, diatomaceous earth, micronized vermicompost, and concentrated vermicompost extract. Coated and non-coated seeds of red clover and perennial ryegrass were evaluated for germination and growth after 7 and 10 days, respectively. Red clover seed was maintained at a constant 20 °C with a 16/8 h photoperiod, whereas for perennial ryegrass seed, the germinator was maintained at 15/25 °C, with the same photoperiod as red clover. Coated treatments significantly improved germination rate and uniformity with no reduction in total germination, compared to the non-treated controls in red clover. In contrast, for perennial ryegrass, the total germination percentage of all coated seeds was reduced and displayed a delayed germination rate, compared with the non-treated controls. Shoot length, seedling vigor index, and dry weight of seedlings of coated seed treatments of both crops were significantly higher when compared to controls for both species. In addition to growth metrics, specific surface mechanical properties related to seed coating quality of seeds of both species were evaluated. Increasing the proportion of soy flour as a seed treatment binder in the coating blend increased the integrity and compressive strength of coated seeds, and the time for coatings to disintegrate. These data show that seed coating technologies incorporating nutritional materials and biostimulants can enhance seedling growth and have the potential to facilitate the establishment of cover crops in agriculture and land reclamation.

The effect of gelatin, used as a biostimulant, was investigated on plant growth in greenhouse studies. Biostimulants are materials that stimulate plant growth, and gelatin, an animal protein hydrolysate, is classified as one type of biostimulant. Gelatin has a unique amino acid composition with a high percentage of proline and hydroxyproline. In a series of experiments gelatin capsules (#3 hard gelatin) containing 7.1 mg nitrogen each, were placed adjacent to seeds of different crop species, at sowing time in individual growing containers and several growth parameters were measured. Different types of hydrolyzed collagen, including granulated gelatin, gelatin hydrolysate, and amino acid mixtures simulating the composition of gelatin were compared on cucumber plant growth. In addition, amino acid mixtures without proline, hydroxyproline, or applied in combination were investigated on cucumber growth. All capsule treatments significantly enhanced crop growth compared to the non-treated control. The treatment with two gelatin capsules placed adjacent to each seed increased shoot dry weight of cucumber, pepper, broccoli, tomato, arugula, and field corn, by 138, 244, 50, 45, 41, and 18 percent, respectively. In an experiment with cucumber alone, there was a positive linear relationship between the number of gelatin capsules from 0 to 3 capsules on plant growth and plant nitrogen content. Cucumber growth and plant nitrogen content was greater from the hydrolyzed collagen treatment compared with the low molecular weight gelatin hydrolysate, a mixture of amino acids or urea and all treatments provided an equivalent amount of nitrogen. Proline and/or hydroxyproline were not responsible for the biostimulant effect. In summary, gelatin provided nitrogen that enhanced plant growth. Moreover, gelatin was an effective biostimulant as the plant growth and nitrogen content was greater from two gelatin capsules compared to amino acid mixture of the same proportion and amount as the gelatin.