This study aimed to evaluate the efficiency of a mechanical (chisel plough) and biological (forage radish) soil decompaction method or the combination of both to improve the physical properties of a very clayey texture Oxisol and to increase soyabean grain yield under no-tillage. The treatments were: black oat on no-till (NT-O), consortium of forage radish and black oat on no-till (NT-R+O), black oat on chiselled soil (CH-O) and consortium of forage radish and black oat on chiselled soil (CH-R+O). The following properties were evaluated: soil bulk density, macroporosity, microporosity and total porosity in the layers 0-0.05, 0.05-0.10, 0.10-0.15 and 0.15-0.20 m, soil penetration resistance, soil moisture and soil water infiltration at soyabean flowering. The winter cover biomass production and soyabean yield were also measured. The treatments did not affect the soil bulk density significantly at any of the soil depths. However, the treatments NT-R+O and CH-R+O doubled the mean soil macroporosity values in the 0-0.20 m layer, with more pronounced effects in the upper soil layers. The treatments NT-R+O and CH-R+O reduced soil penetration resistance compared to NT+O, while treatment CH-O had intermediate results. The treatments NTR+O and CH-R+O increased the accumulated infiltrated water by 44.6 as compared to treatments NT-O and CH-O. The highest soyabean yields were observed in the treatment CH-R+O (3.73 tonnes/ha), which did not differ significantly from treatment NT-R+O (3.49 tonnes/ha). The effect of winter mechanical chiseling was temporary and nine months later no soil physical improvements were observed, apart from the increase of total porosity and macroporosity in the 0-0.05 m layer. Biological chiselling increased soil macroporosity, reduced soil penetration resistance and improved soil water infiltration. Mechanical chiselling was only efficient to improve the soil physical conditions when associated with biological chiselling, which prevented soil reconsolidation.
