A Primary Tillage is the mechanical manipulation of soil that displaces and shatters soil to reduce soil strength and to bury or mix plant materials and crop chemicals in the tillage layer. Tends to leave a rough soil surface that is smoothed by secondary tillage.

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Other /More definition:
A Primary Tillage is the mechanical manipulation of soil that displaces and shatters soil to reduce soil strength and to bury or mix plant materials and crop chemicals in the tillage layer. Tends to leave a rough soil surface that is smoothed by secondary tillage.