5 SUBSOILER DESIGNS AND THEIR EFFECTS ON SOIL PROPERTIES AND CROP YIELDS

Deep tillage is often prescribed to alleviate subsoil compaction, but how long do the benefits last? Subsoilers from Deere, DMI, Kewanee, Ty e, and Yetter were operated at a 280-mm depth on a compacted 25-ha fie ld in autumn 1990. The different subsoiler designs were evaluated by d raft, crop residue cover, soil physical properties and yield measureme nts over the subsequent two growing seasons. Air porosity and cone pen etrometer measurements showed continuing benefits, from all subsoil op erations, two years after tillage in areas not trafficked. However, tw o passes of a tractor recompacted the soil. Controlled traffic is, the refore, considered essential to obtain long-term benefits from subsoil ing. Compared to check strips, soybean yield increases for the five su bsoilers ranged from 3.0 to 6.9% in 1998 and corn yield increases rang ed from 1.5 to 3.0% in 1992. Economically, the first year yields paid for the subsoiling, second year increases were profit.