EFFECT OF DEEP TILLAGE ON SOIL PHYSICAL CHARACTERISTICS AND CORN (ZEA-MAYS L.) ROOT-GROWTH AND PRODUCTION

In years of low rainfall, corn (Zea mays L.) grain production in parts of Southern Illinois, USA is drastically reduced. The naturally occur ring claypans and fragipans in the soils of the region and compaction from farming practices have deleterious effects on crop production. An experiment was conducted from 1989-1993 in Carbondale, IL (USA) on a Stoy silt loam soil (fine-silty, mixed, mesic Aquic Hapludalfs) to inv estigate the effects of deep tillage (0, 40, 60 and 90 cm) and annual tillage management practices (reduced till and no-till) on soil physic al characteristics, corn root development and gain yield. Penetrometer resistance and soil bulk density were reduced to the greatest extent by 90-cm depth of tillage and lesser differences were observed with th e other tillage depths. About 35% of the corn root length in the 21-10 0 cm portion of the soil profile was found below 60 cm depth in the de epest tillage, whereas, less than 5% was below 60 cm in the control. D eep tillage increased root proliferation and the depth to which roots penetrated. Zn growing seasons with evenly distributed rainfall and lo wer temperatures, root development was rather uniform in the subsurfac e soil layers. Deep tillage of the soil resulted in increased corn gra in yields with the greatest yield always being obtained with 90 cm til lage. The advantage was dependent on tillage depth and the amount and distribution of rainfall during the growing season. No-till annual man agement resulted in higher yields than reduced till management (for th e 0 and 40 cm tillage depth) mainly because of the moisture conserving properties of the surface residues present. Annual management (no-til l vs. reduced till) had less impact on yield as the tillage depth incr eased. (C) 1997 Elsevier Science B.V.