Which operation in mechanized sugarcane harvesting is most responsible for soil compaction?

In sugarcane cultivation, agricultural mechanization causes soil compaction, with a consequent decrease in the yield and longevity of the sugarcane fields. Mechanized harvesting operations can promote soil compaction during the first plant cycle. The aim of this study was to identify the critical mechanized harvesting operation for soil compaction through the analysis of the field soil mechanical resistance to penetration, modelling the spatial distribution and quantifying the effects on the yield of the subsequent crop cycle. The study was conducted in an area covered by Latossolo Vermelho in the Brazilian Cerrado, and the experiment used a randomized block design with seven plots and three replicates. The plots were constructed based on the operating conditions of the following machinery: a track harvester; a tractor and three-axis trailer set; a combination of the track harvester, tractor and three-axis trailer; and maintenance, fire and convoy trucks. In addition, manual harvesting was evaluated as a reference for the soil structure and production potential. The pressures exerted on the soil by the machinery were estimated using Tyres-Tracks and Soil Compaction (TASC), and the impacts of the traffic were evaluated in two evaluation regions: the traffic lane and the planting row. The soil resistance to penetration (SRP) was measured with an automatic penetrometer. The measurements were recorded perpendicular to the traffic lane every 0.08 m at a horizontal distance of 1.52 m up to a depth of 0.50 m, with the water content in the soil profile close to the field capacity. Maps of the spatial variabilities in the SRP in the traffic lane and in the planting row were estimated via ordinary kriging and indicator kriging, respectively. The dissipation of the stresses exerted at the soil-wheel interface was confirmed by the spatial variability maps; these maps showed the high predictive capacity of the TASC tool. The fire truck generated the largest increase in the soil compaction in the traffic lane. Based on the analysis of the percentage of the affected soil profile area, the tractor and trailer dissipated the load to the restrictive values of the SRP both at depth and near the planting row. Consequently, a reduction in soil volume was observed but was not the physical limiting factor for crop development, and greater yield losses occurred in the subsequent cycle. For this reason, transportation operations (the tractor and trailer set) were considered the critical sugarcane harvesting operations; moreover, due to the combination of the track harvester, tractor and three-axis trailer, 60 % of the impacted area exhibited mechanical resistance to penetration exceeding 2.5 MPa and likely restricting the root development. In addition, support truck traffic could damage the soil structure. Thus, the machine traffic in sugarcane areas could exacerbate productivity losses caused by the soil compaction.