Light tractor traffic frequency on soil compaction in the Rolling Pampa region of Argentina

Direct seeding production in Argentina requires frequent traffic with farm machinery, in example 6–12 passes. The initially high level of soil compaction in some no till systems might suggest that the impact of subsequent traffic would be minimal, but data have not be consistent. Our objective was to quantify soil mechanical behavior related to compaction from farm machinery traffic on Typic Argiudoll under wheat (Triticum aestvium L. Merr.), soybean (Glycine max L. Merr.) rotation in the northeastern Rolling Pampa region at Argentina. Treatments included five different traffic frequencies (0, 6, 8, 10 and 12 passes of a two wheel-drive, 52 kW tractor running repeatedly on the same track). Total weight of the tractor was 3.1 Mg, with 1.0 and 2.1 Mg on the front and rear axles using 7.50 × 16 and 18.4 × 34 tyres, respectively. The speed of tractor traffic was 5.5 km h−1. Variables measured were: (1) soil bulk density, (2) cone index in the 0–600 mm depth profile and (3) rut depth. Only 10 and 12 tractor passes produced significant increases in cone index and dry bulk density throughout the soil profile. Dry bulk density and cone index increased with number of passes. All frequencies compacted the top soil generating physical soil conditions that would be unsuitable for seedling emergence. Although soil had high bulk density prior to traffic treatments, a significant increment of compaction still occurred due to the high traffic frequencies applied.