Soil translocation by narrow openers with various rake angles

Australian no-till farming often uses narrow point openers to open the soil and place seed and fertiliser in the furrow, in conjunction with spraying pre-emergence herbicides and using press-wheels to pack soil over seeds. At speeds above 6 km h−1 these openers can create excessive soil throw which creates problems for adjacent furrows, such as greater seeding depth and herbicide contamination, as well as increased weed germination and furrow seedbed moisture loss. This study evaluated the effect of 35°, 53°, 72° and 90° rake angles on the soil movement induced by a flat-faced narrow point opener operating at 120 mm depth and 8.2 km h−1. Small cubic plastic tracers were used in a soil-bin environment to quantify soil movement by individual depth layer over the 0–120 mm range. Results of this study showed the large difference in action between low and high rake angle openers. A low rake angle opener was seen to move tracers placed deep in the soil up to the surface and to throw more soil and deeper soil out onto the furrow ridge. Conversely, a larger rake angle opener disturbed a smaller furrow size and achieved slightly more furrow backfill. The widest band within the furrow cleared of surface soil was achieved using the 53° rake angle. Lower rake angles increased the movement from deeper soil layers into the seed zone. These findings have implications for optimising no-till seeding practices such as deep moisture movement, pre-emergence herbicide incorporation and associated crop safety, as well as weed seed germination.