Primary and secondary tillage kills weeds by dislodging roots, burying plants or chopping them into small pieces.Primary and secondary tillage are used primarily to prepare the soil for planting, but they are very effective in controlling weeds.Chisel plows leave over 40% of the plant residue on the soil surface then the field receives secondary tillage to achieve an adequate seedbed. Ridge till forms ridges the previous season and at planting, the top of the ridge is scraped off and seed is planted into exposed soil and then throughout the season the ridges are re-established with specially designed cultivators. Strip till uses coulters to till a narrow band for the crop row while leaving the rest of the field undisturbed. High residue systems use a specialized sweep (sometimes called an undercutter) that operate a few inches under the soil surface to cut weeds at the roots but leaves most of the residue anchored at the soil surface. A lot of options exist between these two extremes. There is a continuum of tillage systems used throughout North America that ranges from no mechanical disturbance of the soil (no-tillage) to complete soil inversion with moldboard plows with secondary tillage passes to achieve a smooth soil surface.
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