Expression of water repellence in farming systems
There are numerous factors in farming systems which may not directly alter the severity of water repellence itself but can affect the expression of water repellence in the crop or pasture. Expression of water repellence is increased with:
- use of narrow knife points for furrow sowing which allows dry water repellent soil to flow around the knife point into the sown furrow
- level sowing without the use of furrows which negates the water harvesting benefit
- dry or partially dry sowing which increases the likelihood of dry repellent topsoil ending up in the sown furrow
- reduced amount and frequency of autumn rains so there is insufficient moisture present for long enough to overcome the repellence and wet the soil
- annual shallow cultivation which can break up remnant roots and preferred pathways for water entry.
When water repellence can be an advantage
Not all the consequences of water repellence are necessarily unfavourable and some native plants may induce water repellence to give them a competitive advantage in a harsh environment. Water repellence can reduce moisture loss through evaporation by the 'dry mulch' effect of the repellent surface layer. It can also increase the amount of subsoil moisture by diversion flow from the surface through preferential pathways beneath surface hollows and along plant roots. However, there are also possible disadvantages of these processes including increased leaching and overland flow which can result in faster transport of nutrients and agricultural chemicals into water supplies.
Soil water repellence research is supported by the Department of Primary Industries and Regional Development and Grains Research and Development Corporation through DAW00244: 'Delivering enhanced agronomic strategies for improved crop performance on water repellent soils in Western Australia' and other initiatives.