Low till refers to an agricultural planting practice - generally using a
"planter" or "seed drill" - in which disturbance of the soil is kept to a
minimum. The structure of the top-soil which determines the water-holding
capacity of the soil and the ease of new plants to put down roots is thus
preserved.
Source: GreenFacts
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In contrast, in conventional farming practices a field is ploughed to aerate
the soil and remove traces of the previous crop before planting occurs. This may
be detrimental to the quality of the soil and delay replanting.