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Fluid Journal : Summer 2015
16 The Fluid Journal Summer 2015 powders can still be applied in this manner, but separation during seed handling may be an issue resulting in an irregular dose rate per seed. As with fluids, the seed coat will also influence adherence of the seed treatment and dictate dosage rates. Wheat and cotton, for example, have a relatively coarse seed surface, which assists in the buildup of a liquid or dry seed treatment. Canola and soybeans, on the other hand, have very smooth "slick" seed coats, which can limit both treatment dose and therefore ingredient inclusion. In the case of most fluid micronutrients, concentration of the metal is a limitation, as too much liquid is required to provide an agronomically significant level of metal, particularly when the desired level of fungicide, insecticide, and possibly a microbial inoculant are already standard in the seed treatment liquid. Experimentation Recent advances in polymer and inert technology and the process of seed treatment have all contributed to a renewed interest in practical application of early- season micronutrients to the seed. Our early experimentation concentrated on chelated metals, such as EDTA manganese, added as a fluid to the seed treatment mix and introduced into the treatment machinery with the seed. Concentration was indeed an issue as was the integrity of different polymers used as a sticker in the process. On a number of occasions, we could produce a solid fifty- pound seed "brick" in the bag or at best a poorly flowable seed mix, which would "bridge" in the planter boxes, resulting in missed seed planting and clogged planters. Needless to say, even if the agronomics made perfect sense, the practicality of the technique did not. Elsewhere, other teams had reported varying degrees of field success with soybean (dry EDDHA iron) and rice (zinc oxysulfate/oxide suspension) seed treatment. We had chosen fluid EDTA chelates as we recognized the need for a soluble plant- available micronutrient from germination onwards in the plant life cycle. Concentrated suspensions can be made with inorganic salts such as metal sulfates and oxides, but water solubility (soil solution, rhizosphere) and plant availability are a concern. Release and uptake of the metal are often reliant on root exudates, including solubilizing organic acids as the plant grows--such a process is heavily species and environmentally dependent, another practical uncertainty. Solid contender We are optimistic that progress in material chemistry advances have put practical, reliable seed treatment with dry chelated micronutrients as a solid contender for future agronomic uses. Moreover, our current experimentation includes the interaction of metal with fungicide, insecticide, and inoculant treatments and increasingly a variety of bio-stimulants. Such treatments are also contrasted with major fluid fertility options including starter fertilizers, strip banding, and side-dressing. The subsequent use and rationale of in-season foliar micronutrients to further supplement plant growth and development is another important dimension. Worldwide references A review of literature on the subject of micronutrient seed treatment reveals many worldwide references covering zinc, boron, manganese, molybdenum, cobalt, copper, and iron. Much of the research has concentrated on easy seed application techniques for developing countries to enhance the nutritional quality of grains and legumes with varying success. Our information suggests that for high yield and intensive crop production, supplemental foliar or side-dress applications will be required to assist grain and seed concentration of micronutrients at harvest. Probing deeper Much of the foregoing has covered seed coating and/or pelleting techniques, the norm in developed agriculture. A continuous layer over the seed coat is designed to influence early micronutrient nutrition at a very intimate soil/seed interface, notably zinc. Such influence can improve yield and stress resistance. Since a great deal of stress mitigation after herbicide application or drought is through metalloproteins acting within cells to detoxify compounds or mop up free radicals (e.g. stress induced peroxides), this makes perfect sense. Interestingly, boron seed coats have increased yields of a number of crop species, including legumes. By contrast, early experiments cautioned over use of boron because of phytotoxicity. In legumes, however, adequate root B levels are positively correlated with nodulation--low levels, foiling colonization by N-fixing bacteria. Our early data show a very positive effect from manganese seed treatment in soybeans in the absence of "deficiency". We postulate a role for metalloprotein synthesis and phosphate availability as a possible mechanism. Nickel and molybdenum have also been included in seed costs but concentration can be problematic--Mo can kill inoculant bacteria in some cases and Ni can be a fairly effective herbicide if over-dosed. Nonetheless, molybdenum/cobalt mixes are fairly popular seed applications in South American soybeans. Seed priming An old gardener's trick is to soak seeds in water prior to planting to speed germination and emergence after sowing. In such a manner seeds are partially hydrated and permit the start of metabolic processes without germination. In an agricultural context, such seed priming has involved dilute solutions of micronutrients to elevate seed and young shoot tissue levels to produce positive agronomic effects, including faster emergence, drastic reductions in soil application rates, early growth and subsequent yield enhancement. Such priming with zinc solutions, for example, has improved early seeding development, hormone synthesis (cell extension), stress mitigation, and resistance to soil pathogens. Similarly, seed priming with boron can improve early physiological functions including protein sythesis, hormone production, cell wall integrity, and N metabolism. Molybdenum is also intimately involved with N assimilation in legumes (N-fixation) and non-legumes (soil N utilization, reduced leaf nitrate accumulation). Some others have postulated that seed priming with Mo solutions can be much more effective than soil applications yet the antagonism toward N--fixing bacteria needs further evaluation. The beneficial effects of seed priming with Cu, Co, and Mn have also been documented. Summing up In conclusion, we believe we are on the threshold of a new era for seed treatment methodology and agronomic application that will routinely include micronutrients to attain maximum major nutrient use, pest and disease control, and phenotypic expression of modern genetic plant traits. Much of the positive effects will not necessarily require traditional deficiency levels but will improve cellular and organelle functions to improve productivity on the modern farm matched with modern genetics for many crop species. Seed treatment with micronutrients can be a valid component of an integrated total crop production program. In time, we visualize genotype matching for such programs from germination to harvest by maximizing season-long gene expression. Dr. Smith is Director of Discovery and Innovation and Mr. Vatren Jurin is Director of Agronomy Services at Brandt Consolidated in Springfield, IL. Dr. Smith is also past president, chair, and current Board member of the Fluid Fertilizer Foundation and Mr. Vatren Jurin has served on the Research and Education Committee for the FFF. Brandt Consolidated, Inc. is also one of the founding members of the FFF.