The effect of a slant-legged subsoiler (Trade name, ‘Paraplow’) on the growth of two crops of winter wheat following an intensively grazed grass-clover ley was investigated in 1981–2 and 1982–3. The treatments for the first crop were direct drilling, loosening the soil by shallow cultivation before drilling, loosening by ‘Paraplow’, and a combination of ‘Paraplow’ and shallow cultivation. For the second crop these treatments were repeated and a fifth added, loosening by ‘Paraplow’ after drilling. Seed was sown with a triple disk direct drill and all treatments received the same quantity of fertilizer.
Soil compaction was measured with a cone penetrometer in the autumn of 1982 and spring 1983; root axes were counted and dry-matter weights of shoot, grain yield and components of yield obtained.
Loosening soil by ‘Paraplow’ did not increase significantly the number of roots nor was the uptake of water by the crop in dry periods affected, even though soil strength, measured as cone resistance, was considerably reduced.
Shallow cultivation increased grain yield in the first wheat by 0·34 t/ha (P< 0·05) but had no effect on the second wheat. The ‘Paraplow’ did not increase yield of the first crop but the mean response of 0·65 t/ha in the second crop was significant (P < 0·05). Using the ‘Paraplow’ before or after drilling gave similar yields. Increases in yield were produced by more grains per unit area, not increased 1000-grain weights.
It is concluded that the apparently compacted soil did not restrict the growth of wheat and that the beneficial effect of the ‘Paraplow’ in the second crop was probably due to better drainage in the wet spring.