A comparative study of conventional and controlled traffic in irrigated cotton: I. Heavy machinery impact on the soil resource

•Controlled traffic farming increased gross margin for cotton and wheat crops.•Standard, uncontrolled machine traffic of a heavy cotton picker results in a lateral compaction pan.•Rotational wheat provided ineffectual bio-ripping for standard system compaction.

To increase in-field efficiency of mechanical operations, machines have increased in size and capacity, which has resulted in cotton pickers approaching 40 Mg in mass. Such mass presents concern for soil compaction and subsequent crop performance. Controlled traffic farming (CTF) is a useful means to reduce machine impact, but is not highly adopted globally. This investigation was designed to compare a standard cotton picker side-by-side to a CTF converted cotton picker in terms of soil resource impact. A replicated, side-by-side, commercial scale experiment was instigated with a 1.5 m row-spacing CTF system compared against a 1.0 m row-spacing standard cotton system. Soil moisture, bulk density, and strength were measured immediately prior and post harvest, along with crop yield, for two cotton seasons and one wheat season. In depth cotton quality, water use efficiency and economic analysis are undertaken in a companion paper. Both machines were shown to induce comparable soil compaction, effects detectable to 0.8 m soil depth, with the main difference being a 17% reduction in furrow traffic for the CTF system. The inner and outer dual wheel of the standard picking system had similar impact, effectively creating a horizontal compaction pan at ≈0.35-0.40 m depth, perpendicular to the direction of machine travel. Bio-ripping of this compaction pan by wheat was demonstrated as ineffectual. The CTF system grew less cotton plants per hectare, but outperformed the standard system. Bio-ripping more effectively accessed water in the CTF system and out yielded the conventional system by ≈60%.