Effect of soil compaction and water content on the resulting forces acting on three seed drill furrow openers

Abstract

In rainfed semiarid central Spain, seed drills for conventional and minimum tillage are equipped with chisel-type furrow openers. Recently, seed drill manufacturers have introduced new furrow openers designs that are claimed to be effective alternatives to the former opener. Experiments were conducted in a laboratory soil bin containing a loam soil to assess the combined effect of soil compaction and soil water content on the resulting forces and furrow cross-sectional areas of three commercially available seed drill furrow openers. The furrow openers compared were a chisel-type (FO1), a non-winged combine type (FO2) and a modified Suffolk type (FO3). These furrow openers were driven in the soil by a hydraulic ram at a forward speed of 40 mm s −1 and the resulting force reactions were measured by an L type load cell. Five gravimetric water contents (60, 90, 120, 150 and 180 g kg −1), four soil bulk densities (1.1, 1.2, 1.3, 1.4 Mg m −3) and two working depths (50 and 100 mm) were considered in the experiments. The experimental design consisted in a (5×4×2) complete randomised factorial with three replicates for each test. The greater were the bulk density and water content of the soil the greater was the draft force measured in the three furrow openers, but this effect was more apparent at a working depth of 100 mm than at 50 mm. On average FO1 exhibited the lowest draft force followed by FO2 and FO3. In the three furrow openers the vertical force increased with increasing working depth, soil bulk density and soil water content, and its value was greater for FO1 than for FO3 and FO2. Irrespective of the working depth, the furrow cross-sectional area of the three openers increased with soil water content. While such an area was independent of the soil bulk density at a working depth of 50 mm, it decreased with increasing density at 100 mm. Whatever the working depth, the average draft and vertical forces measured with FO1 fitted different quadratic functions of the soil bulk density. In FO2 and FO3, however, the relationship between draft force and soil bulk density was linear at working depth of 50 mm, and quadratic at a depth of 100 mm. The vertical force acting on these two openers was linearly related to soil bulk density at both working depths.