Increasing seed performance

Edição XI | 05 - Set . 2007

Leopoldo Baudet - lmbaudet@ufpel.edu.br | Fabricio Becker Peske - fabricio@seednews.inf.br

    In the July/August 2007 edition of SEED News, Prof. Peske wrote an article “Improving   perception of seed value”, which included a graph describing the different costs responsible   for the final prize of soybean seed in Brazil. The aim was to show the array of different technologies available to the grower at the time of executing a rather simple task: place the   seed in the soil and ensure that is completely covered.
    These different technologies involve the seed in the first place, which should be of high quality, as well as the application of products such as fungicides, inoculants, film coating, micronutrients and insecticides, among others.
                                
    Table shows that to take the maximum advantage from these technologies the grower has to be certain that the seed complies with high standards and that the different products were applied properly, in concentration and distribution along the seed surface, so that they can effectively accomplish their function.
    In any business there's a time for investments, a time to collect the revenues and the seed is the best example to this, since the   beginning of time. However, the arrival of the different technologies that transformed agriculture has reinforced this concept.                    
    The use of high quality seeds which grant a good performance is widely cknowledged by farmers as one of the most effective means to minimize costs and risks. Once every possible   measure has been taken to produce quality seed, the farmer can further increase their performance through the improvement of conditions at planting and in the environment that surrounds the seeds.
    The improvement on seed performance will come through special treatments, processing and procedures to improve conditions at planting.
                       
    High technology strategies to match the farmer's expectation on crop performance
    The seed of many species (soybean, cotton, hybrid corn, rice, vegetables and flowers) is currently subjected to intense competition as a result of the acknowledgement by growers   of the importance of seed quality and that any failure in uniformity of germination and emergence will eventually prejudice the product's image.
    The different alternatives that are being implemented to improve seed performance involve covering them with specific products   to deliver protection through an extended period, pre conditioning (osmotic or hydric) or seed priming, the enhancement of processes such as germination and emergence beyond their genetic potential and the enhancement or alteration on seed physical properties that determine its planting capacity. Finally, the application of biochemical treatments such as growth regulations can deliver uniformity and speed of germination and seedling emergence.                    
    Thanks to the seed covering products, it is now possible to stick to the seed powder products as well as liquids and forget about the traditional seed treatments, but rather think of which and how many of the different products we are going to incorporate on the seed.
    This means not only protecting the seed from any potential pathogens present in the soil or carried by the seed itself, but enhance her with micronutrients, hydrophobic products or even hormones.                     
    All these possibilities gain further relevance when the seed in question is of high value, which is the case for hybrids from rice and corn, vegetables and flowers in general, species in which a low percentage of dead seeds or seedlings imply significant losses when we consider their role on the potential population and productivity.
    Several experimental results show that a small investment on seed treatment relative to the seed cost not only improves the performance on germination, emergence and seedling health, but also has an enormous impact on the level of production per hectare.                    
    For rice, the treatment with insecticides has boosted yields by as much as 713 kg/ha, while in vegetables the application of fungicides to the seeds has reduced the incidence of dampingoff in pre and post emergence by Alternaria, Pythium, Phytophora and Rhizoctonia.  
    In the forage grass Brachiaria, the addition of hydrophobic products to the seed ensures that they will germinate only when sufficient soil moisture is available, avoiding the germination waves caused by occasional precipitations.
    Each crop, cultivar or even region can demand or need a different seed treatment. For soybean and corn, the treatment with insecticides amounts to 12 to 22% of the seed cost, since it may be just the only kind of treatment to effectively reach specific soil pests, thus increasing grain yield in up to 128%.                   
    When considering hybrid corn and hybrid rice, the situation is even clearer, since planting rates for these species are lower than for conventional cultivars and the seed has an inherently higher value. Aside from the traditional treatment with fungicides (either systemic or contact) or insecticides (chemical or biological), treatments with giberellic acid (growth   regulator) in rice seeds and lettuce, and with hydrogen peroxide in seeds of soybean, sugarbeet and common bean, have been reported as enhancing seed performance by improving germination and seeding emergence.
                      
    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.

    
    See components costs of various crops in Brazil

    

    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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