Main subject - nov/dec 2008   continuation: Skips and double seed drops Seed grading It's been a long time since the seed companies working with maize realized the importance of size and shape uniformity to avoid failures and double seed drops. To curb these inconveniences they offer the grower two possible choices concerning seed format, i.e. flat and round. Within each category various sizes are available, according to their length and width. Some maize seed companies have as much as eight different sizes in their portfolios, to cover the widest possible range of consumer needs. This is because among the most important crop species, maize seeds are the ones to show the greatest variation in shape and size within the same seed lot. There are, however, other species such as soybean which also show large differences of size and shape within the same lot. In Brazil, over 90% of the commercial soybean seed is graded into two or three size categories on the basis of their width, so that then each seed lot can be standardized and be delivered as uniform as possible. Employing this strategy the seed companies are seeking to reduce the occurrence of failures and double seed drops and their impact on productivity and costs, respectively. Plantability Seed companies are well aware of the importance of seed grading to maximize production so that they include, among the quality control procedures, the plantability test for all seed lots that have just completed processing. The plantability test essentially determines the number of failures and double seed drops for every 100 m of a row. In this way seed companies marketing maize seed have adopted as a norm that every seed lot showing more than 3% failure or 6% double seed drops should undergo reprocessing and new grading. The estimate is that a range between 5% and 10% of seed lots need reprocessing after having scored low plantability values. The test for plantability performed on maize and soybean by the seed companies is destined to safeguard the efficiency of their end customers, the growers, so that all of the chain links that are involved in the business can benefit with the results. Sowing Test Polymers Seeds need to flow as freely as possible through the different planter parts so that sowing proceeds normally and the target population and distribution can be achieved. Bare seeds or those treated with chemical products tend to have some flowing problems that can end causing failures or double seed drops in large quantities. This inconvenience can reach such levels that growers normally assign an operator to permanently check on how the seeds are flowing through the planter and into the tubes leading to the separator disks. Some products are employed to improve seed flow through the planter, so that with the current technological options applicable to seeds, such as fungicide, insecticide micronutrients and inoculants, it becomes necessary to cover the seeds with polymers or even graphite, so that they be able to flow through the planter without difficulty. Polymers have other important functions on seed coating, but these are not the specific aim of the present article. The maize and soybean seed industries have compromised to quality and are marketing seed lots that deliver low failure and double seed drop rates. To achieve this level they employ the latest technology on seed production and processing, which includes the use of different coating products. The high technology employed aims at producing seed lots of high physiological quality that will minimize stand distribution errors; high technology applied to seed processing refers to grading by width, thickness and length, so that the planting process be simplified. Furthermore, the products added onto the seed (polymers and eventually graphite) are aimed at enhancing their flowing capacity, so that seeds can move freely from the seed box, through the tubes and finally into the row. Finally, the perception by growers of how failures and double seed drops can affect their profit has been the driving force for seed companies to deliver quality seed lots that can make their work much easier.