Changes in soil cone resistance due to cotton picker traffic during harvest on Australian cotton soils

Abstract

Australian cotton growers have rapidly adopted new picking technology of round module balers on dual tyres. These machines weigh twice that of previous basket pickers, usually on single tyres, being replaced. This raises some concern about implications for subsoil compaction (>0.4m depth) from harvest traffic. The objective of this study was to quantify changes in soil strength due to picker traffic during harvest. Measurements of soil strength were undertaken before and after traffic by new round module baler (32t) and current basket (16t) pickers during one cotton picking season. Soil cone resistance, water content and plastic limit (PL) were measured in the upper 0.6m depth at eight sites during normal picking operations. Results showed that soil strength increased after traffic of either picker compared with before traffic and increases were detected to a depth of 0.6m. Despite differences in soils and profile water content, the change in strength was similar under the round module baler and the basket pickers. A zone of greater soil strength (3MPa) occurred closer to the soil surface under the round module baler (0.3m) compared with the basket picker (0.4m). Zones of increased soil strength were also detected at 0.6m depth under both pickers indicating possible subsoil compaction. The OZCOT cotton simulation model was used to determine the frequency at which the soil profile was wetter than the PL for both irrigated and dryland systems. Simulations showed that the soil profile could be expected to be wetter than the PL 75% and 14% of the time under irrigated and dryland systems, respectively, at harvest over the period from 1960 to 2012. This indicates that cotton picking in irrigated systems has a high probability of occurring when the soil is susceptible to compaction, with the risk of subsoil compaction greater with the round module baler.