Cumulative compaction of a clay loam soil by annually repeated field traffic in autumn

The cumulative effects of annually repeated field traffic on soil properties and barley yield were investigated in a field experiment on clay loam. Experimental traffic was applied with a tractor-trailer combination prior to autumn ploughing for four successive years. The trailer single axle load was 5 Mg. The loading intensity was 0, 100 and 300 Mg km ha(-1), and both standard and low-profile trailer tyres were used. The effect of early summer irrigation on the yield was also studied. The yield and nitrogen uptake of the crop were determined for four successive years. Soil penetrometer resistance was measured annually after the second loading. The traffic compacted the soil to 0.35 m depth. On average, soil compaction reduced barley yield by 5% and nitrogen uptake by 7%. No annual cumulative increase in the compaction depth or yield reductions was found. Probably only the first loading compacted the subsoil, because the soil was drier than field capacity in the 0.2-0.3 m layer in the following autumns. The use of trailer low-profile tyres did not reduce the depth of compaction or yield losses. On average, early summer irrigation increased grain yield by 34% and nitrogen uptake by 25%, but it did not significantly decrease yield or nitrogen uptake reductions due to compaction.