Long-term monitoring of soil strength and crop yield in a no-tillage soybean production system under zero, controlled and random traffic of farm machinery

The long-term effects of zero, seasonally-controlled and ‘random‘ field traffic were monitored by measuring soil strength (used as an indicator of soil physical quality) and yield of soybean over eight cropping seasons. The work showed that significant yield, and therefore, financial penalties may be incurred when soil compaction is not avoided or appropriately managed. Soil cone Index (depth range: 0-450 mm) increased in the order: zero traffic (1.90 ± 0.31 MPa) > seasonally-controlled traffic (2.46 ± 0.19 MPa) > random traffic (3.75 ± 0.21 MPa), respectively. Differences between traffic treatments were consistent across years. Random traffic reported consistently higher cone Index values at the three measured depth intervals (0-150, 150-300, 300-450 mm). Values of cone Index above the suggested threshold limit for root growth of soybean (2 MPa) explained yield penalties when failing to control or avoid field traffic. This was confirmed by relative differences in root biomass between-traffic treatments. Grain yields in zero traffic were fairly consistent between-years, and increased in controlled traffic and decreased in random traffic at average rates of 35 kg ha-1 and 30 kg ha-1 per year, respectively. Therefore, measured yield gaps over eight crop seasons reduced with controlled traffic and increased with random traffic relative to zero traffic. On average, yield penalties equivalent to 5.6 ± 1.1% in seasonally-controlled traffic and 32.8 ± 3.3% in non-controlled traffic may be incurred relative to zero traffic. Random traffic resulted in average gross income penalties of about USD330 per ha and USD390 per ha compared with seasonally-controlled traffic and zero traffic management, respectively. Further economic benefits, and improved in-field system efficiency, could be realized by fully matching farm equipment and by allowing all load-bearing wheels to run on common (permanent) traffic lanes (typically, 3-m spacing between wheel-lanes). Transition from random to controlled traffic farming (CTF) may require historical compaction to be removed through subsoiling prior to establishing the CTF system.