STRAW INCORPORATION AND TILLAGE FOR WINTER BARLEY - SOIL STRUCTURAL EFFECTS

A large-scale field experiment was conducted over four seasons on a gleysol (24% clay in topsoil) in Scotland. Conventional ploughing, shallow ploughing and shallow rotary or tine cultivation were investigated for the incorporation of straw in winter barley. Straw after harvest was either chopped or removed. Thus the residue treatments were either straw plus stubble or stubble only. Incorporation depths ranged from 0-100 to 0-300 mm. The presence of straw changed soil physical conditions after several seasons in which straw was incorporated. In the ploughed treatments, the presence of straw plus stubble decreased the average soil water content and matric potential in the topsoil in comparison to stubble only, indicating more rapid drainage. This was associated with the presence of buried straw in zones of loose soil just above plough depth and with a long-term increase in soil pore continuity related to the presence of straw residues. The presence of straw plus stubble under conventional ploughing decreased thermal diffusivities in the top 150 mm of soil in comparison with stubble only. Shallow incorporation of straw plus stubble gave higher overall strengths, bulk densities, lower water infiltration rates and poorer drainage in the topsoil than deeper incorporation. However, shallow incorporation caused an accumulation of organic matter over the first three seasons. This accumulation probably contributed to the increased aggregate stability and resistance to compaction of the top 50-mm soil layer, indicating improved resistance to erosion and to further compaction. © 1990.