The amount of cement (adhesive) used for seed pelleting will determine its firmness. The pellets must be sufficiently firm to maintain their physical integrity during handling, processing, transportation and mechanical sowing. However, it is necessary to use the minimum of adhesive, because it inflicts viscosity to the water solution retained in the pores of the pellets after irrigation, affecting the water drainage and consequently, the gas exchange between seed and the environment outside the pellet. To measure the physical resistance of the pellets, a press with a gauge was adapted, making a test-ring with 10 cm2 of internal surface and 8.7 cm2 of piston. The force necessary to reduce each milimeter of the pellet sample layer closed inside the test-ring was determined. The retilineus segment of the curve made by these determinations corresponded to the range between 5% and 20% of the pellet volu me reduction. In this range, the force necessary to reduce each percentage of volume was practically the same for samples of 20, 30, 40 or 50 ml of pellet. A resistance index was proposed as the force necessary to reduce 10% of the sample volume, employing 20 ml of sample and the test-ring of 10 cm2. On the basis of this criteria, fourteen types of pellets were evaluated. Pellets made with sand and bentonite presented the smallest resistance index. The same pellets when covered with a fine lime finishing cover and glue of polivinil acetate (PVA) presented an intermediate value for resistance index and pellets made with lime and PVA glue were the most resistant.
pellet; seed; coat; pellet-quality; firmness.