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 Main subject - sept/oct 2007
continuation: Improving Seed Performance
Modern seed treatment
The application and distribution of products over the seed surface has been traditionally performed by treater machines that employ the small vase system. Today, this system is being substituted by those that spray the different products, and this option, coupled with an efficient seed feeding system to the treater machine ('hat", disc distributor, etc), provides an effective distribution and adherence of the products to the seed surface. Furthermore, the spray treater machine can also apply a film coating through syrup containing various inputs (macro and micronutrients, fungicides, insecticides growth regulators, hydrophobic products, inoculants, etc).
Seed covering or film coating was initially developed to facilitate precision planting and supply the seeds with pesticides aimed at protecting them under adverse soil conditions. After this initial step further treatments were devised such as biological inoculants for legumes, liming to modify the soil pH surrounding the seed, activated charcoal, antibiotics to control bacterial diseases, herbicides and herbicide antidotes or softeners, multilayers to retard germination in spring wheat, calcium peroxide to supply oxygen for flooded rice planting, lanoline oil as hydrophobic material and/or Captan to protect soybean seed in dry of flooded soils, micronutrient application (Mo, Co, B) in soybean, etc.
The main advantages of film coating on seeds are the regulation of the rate of water imbibition, so that damage by rapid moisture entry to the seed is avoided, the transport and release of photoactive chemicals, biological products, environmentally friendly fungicides and insecticides and personnel protection against toxic dust.
The polymer industry has had a fast and aggressive development during the past years, basically through the production of polymers compatible with conventional seed treatments. The use of polymers and dyes has been based on the increasing use of high value cultivars (hybrids, GMOs), lower planting rates, enhanced seed performance, marketing demands for the colored coating, need to avoid loss of applied product before planting and worker protection in the field as well as in the seed processing unit.
The polymers improve the appearance of seeds, providing them with shiny colors which in turn facilitate their handling and planting. Since the market demand defines the added value of seed, polymer composition must comply with the technical specifications, so that the farmer is supplied with high quality seed that will perform accordingly.
In the case of insecticides, there is a wide variety of active ingredients available, targeting different pests, which have a wide distribution, i.e. armyworm and larvae. The damage inflicted by these pests will cause stand failures, since the feed on seeds soon after planting, on roots after germination and on foliage at the seeding stage.
The story for fungicides is not different, and aims at minimizing a possible seed infection or infestation, in addition to providing a wider microorganism control during the initial phase of establishment.
Studies on various crops (soybean, corn, cotton and rice), focusing on the percentage cost in seed production of the application of fungicides show they don't exceed 2%, whereas in case of having to reseed the cost would rise to approximately 18%. When it comes to vegetable seed, it seems unthinkable to plant the seed without being previously treated with systemic or contact fungicides.
Several research papers have mentioned the efficiency of giberellic acid on seed performance, reducing emergence time in up to 2½ days; which could be of crucial importance under low soil temperatures that could delay and compromise seedling emergence.
As for inoculants, nitrogen is the most important nutrient for the soybean crop. It has been estimated that to produce 1000 kg of grain, the plant needs around 80 kg N. The biological fixation of N is the main source for legumes such as soybean, and bacteria from the genus Bradyrhizobium infect the plant roots through its hairs to form nodules. The biological fixation of N depends on its efficiency to supply the needed amount of the nutrient, and some inoculants used today are compatible with fungicides, so that their efficiency is not compromised while the seed gains extra protection against fungal diseases.
Seed preconditioning or priming
The osmotic conditioning of seeds, which consists of a controlled hydration sufficient to promote basic metabolic activity without achieving radicle protrusion, has been developed to deliver a rapid and uniform seedling establishment under varying ambient conditions.
In general, the treatment consists in imbibing the seeds in an osmotic solution for a limited period of time, proceeding to an immediate drying of the seeds so that they return to their initial moisture content.
Hydration of seeds in saline solutions proceeds to a level close to germination, after which the seeds are stored under cool temperatures for a few days to be immediately sown or dried, to be treated at a later time.
The osmotic conditioning of seeds has been used in vegetables, flowers and forage crops, aimed at increasing speed and uniformity of germination and seedling emergence, while enhancing their tolerance to environmental stresses.
The most common beneficial effects of osmotic conditioning of seeds that have been reported are enhanced performance under sub or supra temperatures, in species such as lettuce, sugarbeet, canola, carrots, spinach, water melon, peppers and tomatoes, among others.
Seed conditioning has also improved seeding emergence in saline soils and reduced the effects of damping-off by fungi. The polymers associated to film coating contain additives, also thought to influence the priming of seeds from the species to which they're applied.
Since farmers are always concerned with cost reduction and minimum risk, the first step to a successful production is the achievement of a healthy plant stand. This implies that the growers pursue a seed supply system that is of zero failure and can provide services for adding products to the seed that will further enhance their performance. This is the only way to ensure that the investment made on the seed will pay off, in the way of a better crop performance.
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