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Previous studies have defined compaction as an important degradation process of agricultural soils. However, there is very little information (under field conditions) on the effects of tractor and grain chaser traffic during harvest operations on soil cropped for 15 years under no‐till cultivation methods. The aim of this study was to quantify the effects of two different total loads of tractor and grain chaser traffic on soil physical properties and sunflower (Helianthus annuus L.) yields. The treatments included a control plot with no tractor or grain chaser traffic (T1), a plot with tractor and grain chaser traffic with a total load of 275.8 kN (94.35 kN km−1 ha−1; T2), and a plot with tractor and grain chaser traffic with a load of 332.2 kN (123 kN km−1 ha−1; T3). Soil physical properties and sunflower yields were analysed over three growing seasons in the western part of the Pampa region, Argentina. In the topsoil (0 to 200 mm), the results showed that after one pass of T2 and T3, infiltration decreased significantly compared with that in T1; a similar trend was observed for total topsoil porosity. Cone index values in T3 were >2.5 MPa and between 3.33 and 4.90 MPa in the subsoil (200 to 600 mm). Dry bulk density values in T3 were >1.70 Mg m−3 in the topsoil and in the subsoil. This study also demonstrated that as the wheel load and ground contact pressure increase, sunflower yields decrease and subsoil compaction increases, even in soils with a high bearing capacity.

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Deep tillage is often performed to alleviate traffic-induced subsoil compaction, but how long do the benefits of this technique last for in intensively-managed arable soils? Heavy traffic on loose soil significantly increases the risk of soil re-compaction at depth. Chiselling and subsoiling are techniques commonly used in Argentina to remediate soil/subsoil compaction. Controlled traffic farming (CTF) through the exclusion of heavy vehicles from the field and axle load reduction (e.g., ≤ 6 Mg per axle) is a strategy occasionally used to mitigate compaction impacts. The objectives of this work were to: (a) quantify changes in the physical properties of a medium-textured soil as a result of tillage operations (subsoiling, chiselling) conducted over two consecutive crop seasons, (b) determine the effect of deep tillage on sunflower yield, and (c) quantify fuel consumption and draft requirements of deep tillage on soil affected by compaction. The experiment was conducted at a site located in the western region of the Argentinean Rolling Pampas, which has a loamy Entic haplustoll soil. Experimental treatments consisted of two tillage operations and a control plot, which had been under zero-tillage for more than 8 years. Deep soil loosening was conducted with a 117 kW, FWA tractor as follows: (1) a V-frame 7-shank subsoiler with 35-mm wide and 550-mm long tines. Shanks were spaced at 500 mm apart, and operated at 450 mm deep at 5.20 km•h-1 (2) a chisel plow with 11 rigidly-mounted, curved shanks, spaced at 285-mm apart, and operated at 280-mm deep and 6.12 km h-1. The tillage treatments were applied to plots, which were laid-out in a completely randomized block design. This work showed that: (a) the beneficial effects of subsoiling and chiselling on removing soil/subsoil compaction lasted for 2 years, (b) these effects became negligible after that time when traffic intensity was greater than about 95 Mg•km-1 •ha-1 due to re-compaction/re-consolidation of the soil profile, particularly in the 300-600 mm depth interval, and (c) the frequency of subsoiling should be therefore every two years if CTF was not practiced. From agronomic and economic perspectives, the results showed that: (a) sunflower yields were sufficiently high to recover the cost of subsoiling, which cost between 18 and 52 USD•ha-1 , (b) in the second year, the yields increases represented a net profit of 12 USD•ha-1 , (c) the chisel plow had lower fuel consumption and draft per shank than the subsoiler because of the relative depths at which tines were operated in both units, and (d) the total cross-sectional area loosened by the chisel plow was 14 % higher than that of the subsoiler, but its overall efficiency was about 85 % less compared with the subsoiler.

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