Evaluating the need for an active depth-control system for direct seeding in Portugal

Abstract

The research evaluated the need for an active depth-control system for direct seeding in Portugal. Through the use of an LVDT (linear variable differential transformer) there were observed wide variations on the seed deposition depth (from 17.1 mm to 29.5 mm) during seeding tasks, being recorded by a load cell the force exerted by the seeding arm in order to penetrate the ground. The GPS installed on the tractor showed a variation in the seeding speed from 1 to 5 km/h; thus, a uniform seed deposition was hard to achieve. Problems encountered during the operation of the photocell hindered the obtaining of reliable data, with an achieved seeding dose much lower (2 .7 ± 1.9 seeds/m) than the pre-adjusted dose (5 seed/m). The seeding test confirmed that increasing the pressure of the seeding arm resulted in closer depth to the set-point. Nevertheless, due to soil strength variability (1001 ± 253 kPa by penetrometer resistance) and ground stubble, a high percentage of seeds were deposited on the surface (above 30%, according to chassis seeder displacement measured by the LVDT). In order to improve work quality, the development of an active control system for the seeder under certain soil conditions (heavy field texture with 5.21% of humidity) attains great importance in Alentejo (main grain growing Portuguese region).