Effect of seedbed condition on sowing point performance

Abstract

The performance of different sowing points on a hardsetting red duplex soil at Cowra, New South Wales, Australia was evaluated for a range of initial bulk density and soil strength conditions. The soil was modified by either compressing it with a rubber tyred roller, or cultivating to a depth of 180 mm with a plough fitted with rigid tines spaced 330 mm apart and followed by a light compaction with a Cambridge cultipacker roller. The bulk density of the 0–75 mm soil layer was increased from 1.55 t m −3 to 1.70 t m −3 when rolled, and decreased to 1.38 t m −3 when cultivated and lightly rolled with a cultipacker roller. At the higher bulk density, vane shear strength increased slightly from 52.7 to 58.9 kPa whereas a decrease in bulk density lowered shear strength to 13.4 kPa. Penetration resistance was decreased substantially from 1990 to 393 kPa. The penetration and draft forces of individual points were measured during the sowing operation. The high bulk density level significantly increased the vertical force required for combine sowing points to penetrate the soil surface despite only a slight increase in shear strength and penetration resistance. In contrast, the forces required for both winged and lucerne points to penetrate increased only slightly or not at all. The draft forces of all points increased with increasing bulk density. The combine points had the highest and lucerne points the lowest draft forces. Although the sowing points produced varying degreesof soil disturbance within the seed groove, cultivation of the seedbed prior to sowing was more important for high seedling vigour than the selection of a particular point for the sowing operation. However, the selection of a narrow point (lucerne or winged) under more adverse soil conditions, may improve seeder operation because of the lower penetration forces required for these points, and plant establishment because of the lower soil moisture loss from the seed groove.