SOIL STRENGTH IN THE SEED ZONE OF SEVERAL PLANTING SYSTEMS

The growth in conservation tillage has placed new demands on the perfo rmance of planting systems. Newer openers designed to provide adequate compaction of soil around seeds in hard, dry soils can produce excess ive compaction in wet soils. Occasionally, concern is raised whether o peners are creating compaction in the seed zone. Soil bin tests were u sed to measure soil strength in the seed zone created by planting syst ems used on hoe drills, seeding tillers, row crop planters, and no-til l drills to assess possible soil compaction problems. Each system was operated throughout the range of its adjustments. A multiple-cone pene trometer measured soil strength before and after operation to create c ontour maps showing the ratio of after/before soil strength. Most test s used soil with an initial cone penetrometer soil strength index of 3 50 kPa. All openers reduced soil strength in an area extending from th e surface to 15 to 30 mm below the seed, with no evidence of compactio n. Closing systems provided selectable levels of soil reconsolidation. The system on the row crop planter could provide soil strength in the seed zone ranging from 30 to nearly 200% of the original soil strengt h by using its adjustments and standard accessories. We conclude that openers do not cause compaction. Closing system options, especially on no-till openers, can create a range of soil strengths in the seed zon e, but must be set to avoid compaction in susceptible soil conditions.