Tillage and traffic effects (planters and tractors) on soil compaction and soybean (Glycine max L.) yields in Argentinean pampas

Direct drilling systems usually have lower traffic intensities than those using conventional tillage, but despite this, after several years of continuous direct drilling yields tend to decrease. This could be the result of increased weed control problems and root diseases as well as a gradual increase in soil compaction due to agricultural traffic. The draft required, soil cone index, root growth, soybean (Glycine max L.) yield and traffic (planters and tractors) compaction over the subsequent three growing seasons were measured. This initially high level of soil compaction in some direct sowing systems might suggest that the impact of subsequent traffic would be minimal, but data have not been consistent. Soil compaction is caused by the high traffic intensity and weight of tractor and seeding machines and combines in harvest operations, especially when these operations are carried out on wet soil or with high ground pressure. The techniques commonly used for control and management of topsoil and subsoil compaction are: subsoiling and chiseling and axle load reduction. Outlined hypothesis was: Traffic with high axle load equipment increases soil compaction and decreases soybean yield. This article quantifies: (a) the effects of subsoiling and chisel plowing were carried out at 350 and 280 mm depth, respectively, on soil compacted under 12 years of direct drill systems and (b) traffic effect on this soil conditions of two equipment for direct sowing (planters and tractors) on soybean yields (G. max L.) with two different loads: light equip (LE) and heavy equip (HE). The study showed that: In topsoil for three growing season, traffic with HE (185 kN) caused mean values of CI of 2178, 1506 and 1406 kPa for direct sowing, chiseled and subsoiled soil, respectively, while for the LE (127 kN) the values were of 1855, 1210 and 1206 kPa, respectively. Also in the subsoil traffic with HE caused higher CI values than the LE in all treatments. The CI mean values of the HE traffic were: 2465, 1920 and 1854 kPa for direct sowing, chiseled and subsoiled soil, respectively, while the LE traffic produced 2298, 1639 and 1637 kPa, respectively. For three growing seasons the HE traffic in soil under direct sowing reduces soybean grain yields close to 460 kg ha−1, while for the LE was 250 kg ha−1. When the traffic was made with LE on subsoiled soil there is an effective increase in soybean grain yields of about 330 kg ha−1.