CONVENTIONAL AND PLOUGHLESS TILLAGE SYSTEMS WITH NORMAL AND LOW TYRE INFLATION TRAFFIC

The effects of low-inflation relative to normally inflated tyres on so il physical properties and crop yield were compared in tillage systems with either mouldboard ploughing to 25 cm or tine chiselling to 10-15 cm. Two field experiments were started in 1991 on silty clays near Up psala, Sweden. The normal tyres were dual 16.9-38 R with an inflation pressure of 80 kPa, whilst the low inflation pressure tyres were dual mounted Trelleborg TWIN 600-26.5, inflation pressure 30 kPa. Measureme nts of soil physical properties were carried out in 1994, the same yea r in which the experiments were terminated. In the uppermost layer (0- 15 cm), the soil properties was more or less identical in the differen t tillage treatments. At a greater depth than 15 cm, the unploughed so il had higher bulk density, greater penetration resistance and greater aggregate tensile strength than the mouldboard ploughed soil. Neverth eless, the air permeability was higher in the unploughed soil at the s ame air-filled porosity, suggesting a greater degree of pore continuit y. There were mainly small and insignificant differences between the d ifferent tyre equipment treatments. In a separate study, it was shown that the use of low inflation tyres resulted in the same bulk density and soil stress as did the conventional tyres, probably because of the ir smaller diameter and the design of the tyre carcass. Crop yield was little effected by inflation pressure in conventional tillage, wherea s low inflation pressure seemed to increase yield in ploughless tillag e. Such increases in yield may have been caused by more evenly distrib uted recompaction of soil loosened by chiselling with the use of wider tyres. Key words: Soil compaction, ploughless tillage, tyre inflation pressure, crop yield, air permeability.