Agronomic performance of sorghum (Sorghum bicolor (L.) Moench) and fertilizer use efficiency as affected by controlled and non-controlled traffic of farm machinery

Compaction adversely affects the physical properties of soils and the ability of crops to efficiently use water (rainfall, irrigation) and nutrients, and therefore reduces the amount of fertilizer recovered in grain. This study was conducted to investigate the effect of traffic compaction on sorghum response to nitrogen (N) fertilization. Soil conditions (density) representative of controlled (CTF) and non-controlled traffic (non-CTF) farming systems were achieved by removing compaction through subsoiling to a depth of approximately 300 mm and by performing six passes of a medium-sized tractor, respectively. The soil type used in the study was a Red Ferrosol (69% clay, 11% silt, and 20% sand), which is commonly used in Australia for grain production. Sorghum was grown during the 2015-2016 season and fertilizer was applied at rates between 0 (control) and 300 kg ha-1 N at regular increments of 100 kg ha-1 N using urea (46% N), urea-ammonium nitrate (UAN, solution, 32% N) and ENTEC® urea (46% N). Grain yield was approximately 40% higher in the traffic treatment representative of CTF compared with that of the non-CTF, and consistent with differences (P