A furrow is a groove in the surface of the soil that allows sowing onto moisture and water harvesting from the ridges into the furrow. Historically furrow sowing has been used as a tool to manage non-wetting soils as it allows placement of the seed deeper in the soil — in the lower topsoil or shallow subsoil — which is often more consistently wet.
During water harvesting, water sheds from the ridges and is channelled into the base of the furrow, so that moisture penetrates around the seed and fertiliser improving germination and establishment.
Furrow sowing is not normally a technique which reduces soil repellence rather it is a manipulation of the surface soil to harvest water and direct it towards the area where the seed and fertiliser have been placed.
The largest risk of this practice is erosion and wind shear at the ground surface and raindrop impact can erode ridge material into the furrow. Large quantities of water movement down slope along a furrow can cause rill erosion and expose or remove seed. Some herbicides can also be harvested into the furrow base if there is heavy rain soon after application.
Recently it has been suggested that furrow sowing using knife points is often unsuccessful because dry water repellent top soil is flowing around the knife point into the seed slot and being concentrated with the seed and fertiliser in the base of the furrow. As a consequence it has often been found that the soil in the furrows is actually more repellent and drier than the soil in the ridges where knife point seeding systems have been used.
To improve the efficacy of furrow sowing on water repellent soils a number of approaches involving modifying aspects of the design and configuration of the knife point seeding system have been identified including:
- addition of wings to the knife point and/or to the seeding boot to help grade the dry repellent topsoil into the ridges away from the furrow
- reducing the distance between the knife point and the closer plate/seeding boot to reduce the opportunity for soil to flow into the slot
- increasing the speed of seeding to increase soil throw away from the furrow
- changing the rake angle of the seeding point to provide more soil lift in front of the point and increase the flow of soil away from the furrow
- using a banded wetting agent applied to the base of the furrow behind the sowing press wheel to improve water entry into the furrow.
Note: These are possible approaches to improve furrow sowing and they are still the subject of ongoing research.
See also: Knife versus winged points