Effects of pre‐sowing compaction on soil physical properties, soil atmosphere and growth of oats on a clay soil

SUMMARY The effects on a number of soil physical and aeration parameters of compaction during spring pre‐sowing operations were measured on a clay soil (49% clay). A soil‐tyre contact stress of 200 kPa was applied by tractor tyres. Yield of an oat crop was reduced by 30% as a result of compaction. Total porosity of the soil was reduced by 6% v/v owing to loss of pores > 60 μm, and water retention was increased. The resultant decrease in air‐filled porosity greatly reduced gas diffusion and air permeability coefficients of the soil, and, for a time, O 2 content of the soil atmosphere was significantly lowered in the compacted treatment. Penetrometer resistance after sowing was 3.5 MPa in the control and 4.5 MPa in the compacted treatment; in the latter, root growth was inhibited until the soil dried and cracked. By the end of June, canopy temperature measurements indicated water stress in the oat crop on compacted soil but not in that on the control. The results obtained indicated that air permeability, measured in the field, of 1 mm s −1 provides a satisfactory single value below which crop growth is likely to be reduced.