Abstract:
Poor early growth of wheat was studied in a tillage experiment at Cowra, N.S.W., in the 1986 season to determine the involvement of soil physical and biological factors in this problem. A compaction treatment to achieve bulk density and shear strength comparable with those detected in the direct-drilled soils was imposed on the conventionally cultivated soil. Soil fumigation was used to investigate the significance of biological factors in causing poor early growth. In the absence of fumigation, the dry weight per plant 98 days after sowing for the direct-drill treatments was approximately a third of the conventional treatment. The fumigation treatment was effective in completely eliminating the poor early growth observed in the direct-drilled soils. No significant reduction in shoot growth was detected as a consequence of the compaction treatment, despite a reduction in root growth to the level detected in the nil fallow. The results suggest that poor early growth was caused by micro-organisms present in the direct-drilled soils.