Farmers find these soils often hard to manage. When water is lacking, the clay shrinks and cracks, damaging the plant's existing root system and subjecting it to severe stress that shrinks yield. Agricultural engineers Richard A. Wesley and Lowrey A. Smith, who are in the ARS Application and Production Technology Research Unit at Stoneville, Mississippi, have found the cure for farmers' soybean blues. Current recommendations for soybean production on heavy clay soils call for tillage down only to 4 to 6 inches. When it dries, it forms a blocky structure with large cracks between, representing the weakest part of the soil profile.
Deep tillage breaks up and rearranges the structural blocks that occur below the surface.
With subsoiling, the tool penetrates the soil's blocky structure, creating areas of loose soil and large pores without disturbing crop residue on the soil surface. Subsoiling allows water to infiltrate the lower regions of the profile quickly, where more is stored than would be without subsoiling. Most importantly, since subsoiling doesn't destroy crop residues on the surface and probably is not required every year, the practice is compatible with conservation tillage. Smith conducted similar studies with cotton, though it was previously thought that deep tillage of clay soil planted to cotton was not beneficial.