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 Main subject - nov/dec 2006
Technologies that add value to soybean seed
Dr. Ademir A. Henning
henning@cnpso.embrapa.br
Dr. Francisco C. Krzyzanowski,
Dr. José B. França Neto and
Dr. Nilton P. Costa
The production of high quality soybean seed depends on the adoption of special technologies. Lack of implementation of such technologies will result in the production of low quality seed, mainly if there are produced in tropical or subtropical regions. Additionally, seed producers must adopt special measures in the seed quality control system that must be applied in all phases of seed production, with the purpose of overcoming some limitations that are imposed by the different factors that affect seed quality.
Soybean seed quality may be affected by several factors that occur in the field before and during harvesting and during all other phases of production, such as drying, processing, storage, transportation and sowing. Such factors include high temperature during maturation, alternating environmental moisture conditions including drought, nutritional deficiencies of the plants, insect damage, additionally to the adoption of inadequate harvesting, drying and storage techniques.
Seed quality control plays an important role in assuring the production of high quality seed in all phases of production, from the field before harvesting to processing and latter stages of storage.
Seed Quality Control
COMDIA - Complete Diagnosis of Soybean Seed, a quality evaluation method that encompasses the tetrazolium and seed pathology tests, evaluates both physiological and sanitary qualities of the seed.
This technology, developed by Henning & França-Neto in 1980, provides a precise soybean seed quality evaluation and also identifies the major causes of seed lot discard due to low germination at the laboratory. The tetrazolium test (TZ test) provides information on viability and vigor of the seed lot without any interference of the infection process caused by seed borne fungi. Additionally, the test diagnoses the major problems that may reduce seed quality, such as mechanical damage, seed weathering and stink bug damage. The seed pathology test, by the blotter method, identifies the major fungi (Phomopsis sp. and Fusarium semitectum) that interfere with the germination test conducted with the rolled paper towel substrate. The information provided by both tests confers the Complete Diagnosis (COMDIA) of the causes of reduced soybean seed quality. Therefore, by using the COMDIA it is possible to avoid rejection of good seed lots that show poor germination in the laboratory due to seed infection by these two fungi. Thus, COMDIA provides the diagnosis of the problems that cause reduction in seed quality, so that correcting measures can be adopted for improving seed quality. Besides, it allows the identification of important seed borne fungi that may be reducing seed quality, providing the selection of the most adequate fungicide for seed treatment.
Hypocloride test for determination of mechanical damage in soybean seeds
The TZ test may be applied in the field as seed mature, providing accurate determination of seed quality even before harvesting, providing important information with regards to seed vigor and viability and also on the level of stink bug and weathering damages.
During harvesting, the TZ test allows the monitoring of the occurrence of mechanical damage to the seed during threshing with the combine harvester. Monitoring of this type of damage is also done by the sodium hypochlorite test and by the split seed test. Maximum tolerated levels of mechanical damage are established for each test, so that soybean seed will present the minimum possible levels of mechanical damage and maximum physiological quality.
When the seed arrives to the Seed Processing Unit, it is important to determine the percentage of seed mechanically damaged, level of impurities, and presence of green and immature seed. Additionally, the physiological quality must be determined by the alternative methodology of the tetrazolium test, electrical conductivity and pH of seed exudates.
During seed processing, it is essential to monitor vigor, viability and mechanical damage levels, to be sure that the grading and cleaning processes are improving seed quality and also to verify that all machines are well adjusted. Special attention must be given to the precision of the adjustments of the seed size graders and specific gravity machine.
Field emergence test
Varietal mixture and mechanical damage are serious potential problems that can reduce seed quality during seed processing. The major sources of mechanical damage during seed processing are: excessive number of falls by the seed; use of inappropriate and unadjusted elevators; and the conveying the seed on high speed belts. The ideal elevators recommended for seed are the ones that present positive discharge or by gravity as used in chain elevators. Maximum elevating speed should not exceed 40 meters per minute.
The best sequence of equipments for processing soybean seeds is: reception; pre-cleaning; temporary storage in aerated silos; drying; temporary storage in aerated silos for flow adjustment; air-screen machine for cleaning; spiral separators; size graders; gravity table; and packaging scale.
Precise seed quality control deserves special attention during storage, since, depending on environmental conditions, with regards to temperature and relative humidity of the air, the level of soybean seed deterioration may sharply progress and, consequently, vigor and viability will be reduced at the time of marketing and planting. Applying the COMDIA, accelerated aging, TZ and pathology tests are essential tools for precisely monitoring seed quality during this phase.
At the time of seed commercialization and delivery it is important to evaluate seed quality by the test field emergence, since this test simulates the real performance of the seed lot when sown in the field, under ideal conditions.
Seed grading
The option of size grading soybean seed has been adopted by several seed producers. This operation is performed by seed graders with flat screens using round perforations. These machines are allocated in the processing flow between the spiral separators and gravity tables.
The major reason for classifying soybean seed by size (screens) is due to today's technological demand for precise sowing, since modern soybean cultivars require lower population than older ones, in the range of 200,000 to 300,000 plants/ha. This population will provide the basis for maximum yields, and no plant lodging will occur. Therefore, sowing with improper seed density is not tolerated, because the risk of obtaining inadequate plant population, that will ruin all inputs applied to the crop, will result in great losses regarding soil preparation, fertilizer application, weed control and seed treatment. Additionally, the risk of replanting will also result in expressive losses in yields, since the best panting date will be skipped.
Another important aspect in soybean seed processing is its classification by density, which is done with success by well adjusted gravity tables. An important parameter that must be used in adjusting this equipment is determining the bulk weight of the seed in several positions of the discharge deck of the equipment. Only seed with high bulk weight should follow to the next phase of the processing process. In general, soybean seed has a bulk weight of 770 kg/m3. High quality soybean seed present values above 800 kg/m3.
Seed cooling during storage
Soybean seed cooling to temperatures of 15°C or lower before packaging has been a promising technology to preserve its high quality during storage. This technology is feasible in Brazil, since national companies perfected the cooling process for seed and grain. Several seed companies in Brazil have already adopted this technology and are pleased with its performance.
Research data collected by the Seed Technology Team of Embrapa Soybean have shown the excellent performance of this technology in preserving physiological and sanitary qualities of soybean seed during storage.
After sale follow up
Monitoring the performance of the sold seed lots after field sowing, determining its plantability and uniform seedling emergence, represents positive marketing and technical attitudes. This fact assures the high performance of the seed in the field and generates customer satisfaction.
Soybean seed quality and treatment
Soybean in the field is attacked by a number of pathogens. Fungi, bacteria, and viruses may cause serious losses to the crop. For most of these pathogens the seed is the means of survival and the vehicle of dissemination to long distances.
High quality seed and with moisture damage
Seed with mechanical injury and attacked by insect
In soybean farming, the achievement of adequate plant population depends on the utilization of several agronomic practices. Good soil preparation, planting at the appropriate time, in soil with adequate moisture contents, use of herbicides, good regulation of the planting machinery (seeding rate and planting depth) are essential practices. However its success depends on the use of high quality seed.
page 2 ->> Technologies that add value to soybean seed
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