Seed Spacing Uniformity of 4-6-8 Rows Precision Drills for Sugar Beet Sowing

Sugar beet sowing is strongly influenced by the utilization of precision drills capable of determining uniform seed spacing between plants within the row. This factor significantly affects quality and yield of several crops and especially for sugar beet. With suitable plant spacing, the roots can grow to the size requested by the sugar industries and fill the row, without reducing the space of the adjacent root. In order to increase the competitiveness of farms and their income levels, the manufacturers of the pneumatic precision drills aim to improve drill design and the accuracy in seed placement, often electronically controlled, in conformity with standard cultivation requirements. Soil refinement, seed selection mechanism and working speed also represent the main factors affecting the drills performances. The purpose of this paper is to evaluate the performance of three precision drills, equipped with double furrow-opener disks and with a different number of sowing units (respectively 4, 6 and 8), through the observation of the quality of the work and tractor-drill system behaviour from the point of view of dynamic and energetic parameters. The field tests have been conducted using graded beet seeds, to evaluate the accuracy of the single seed metering systems, according to ISO 7256/1 standard, in terms of distance between seeds in a furrow and using two speeds (about 5 and 8 km h(-1)). The tested drills showed high values of the index of feed quality (around 90%) testifying the efficiency of the single seed metering systems, even at the higher velocity. The multiple index is generally very low, but the miss index reaches values generally over 10%. The frequency distribution of seed spacing of 6 and 8 row drills shows that the seeds deposited at the theoretical seed spacing increase at higher working speed.