Compactión produced by combine harvest traffic: Effect on soil and soybean (Glycine max l.) yields under direct sowing in Argentinean Pampas

• One pass a harvester with weight above 93.4 kN produced subsoil compaction.
• When the axle load increase on soils with high bearing capacity soy yields decrease.
• Tyre ground pressure above 89.6 kPa produced topsoil and subsoil compaction.
• Topsoil compaction is directly related to ground pressure.

Soil compaction is caused by the high traffic intensity and tyre ground pressures of tractor and combines in harvesting, especially when these operations are carried out on wet soil or with high ground pressure tyres. Our main objective was to compare the effect of three combine harvester traffic intensities on soil compaction and soybean (Glycine max L.) yields cultivated under direct sowing (DS) in a Typic Argiudoll soil in the east of the Rolling Pampa region, Argentina. The treatments were: (1) combine harvester with high axle load and low ground pressure (C1TLGP), (2) combine harvester with medium axle load and medium ground pressure (C2TMGP) and (3) combine harvester with low axle load and high ground pressure (C3THPG). We hypothesised that the application of the different combine harvester traffic intensities produced soybean yield reductions and subsoil compaction on soil under continuous DS. In the topsoil (0–20 cm), the results show that after three years, the C3THGP treatment aplication produced higher cone index values than for the other treatments. In the subsoil (20–60 cm), the results show that during three growing seasons, the C1TLGP (total load = 152 kN) treatment aplication produced higher cone index values than other treatments The highest average root dry matter per plant (RDM) was found in the first growing season under the C1TLGP treatment. The average dry matter per plant (DMP) measurement was 1.77 g plant−1 in the C1TLGP treatment, followed by 1.55 g plant−1 in the C2TMGP treatment and 1.40 g plant−1 in the C3THGP treatment. The C3THGP treatment resulted in a significantly higher soybean yield (15.3, 21.0 and 22.1% in 2010, 2011 and 2012, respectively) than the C2TMGP and C1TLGP treatments. The main conclusions were that when argiudoll soil under DS system was trafficked with a high axle load >79.70 kN for three years, the cone index peaked in the subsoil to depths below 35 cm and soybean yields were significantly reduced. Soybean seedling emergence was not affected by high topsoil compaction produced by the tyre ground pressure of used combine harvesters. The soybean yield decreased with increased weight of the combine harvester.