Straw mulching follows the seeding operation and requires purpose built machinery that blows a stream of chopped straw through a bituminous binder, which tacks the material to a depth of 15mm to 30mm over the seeded area. The bituminous binder is incorporated into the application to give added protection against erosion. Alternatively an organic binder can be applied as a secondary application.
Where possible, prior to topsoiling, the areas should be deep ripped. All areas to be seeded shall be scarified to provide a firm but friable seedbed, free of weed or plant growth, large stones or other debris, and the whole area fallowed and left ready for seeding and straw mulching.
- Oaten or wheaten straw (average of 20kg/bales), at the typical application rate of 250kg/ha. Note: that the straw must be weed free especially when being used in environmentally sensitive areas.
- Approved bituminous binder, at the typical application rate of 2000-3000 litres per /ha or post tacking with an organic binder 80kg/ha
- Seed as per the supplier's recommendation. Typical seeding rates are 100-400kg/ha of exotic species and 5-20kg per ha native grasses.
- The seed mix will vary according to the season, soil condition and location.
- The longer the seeds are mixed in the slurry tank, the greater the potential for breakage and for this reason the seeds are added immediately before application.
- Fertilisers dependent upon soil analysis with typical requirements of 5-10l per ha of a pre starter fertiliser. Adding a fertiliser can reduce the germination of certain native species due to the effects of fertiliser salt on seed imbibition. Therefore a humic acid is used to promote microbial soil activity when using native species @ 5l/ha
Advantages of Straw mulching
- Most cost effective method of stabilising large areas of open ground as a result of earthworks.
- Reduces raindrop impact and slows down water movement over the area much as a layer of grass or vegetation would. Therefore providing an effective barrier prior to the vegetation establishing.
- Allows more water to penetrate the ground and reduces sheet flow and the associated silt migration.
- Greatly improves the results achieved by standard seeding practices because the straw creates a micro climate, retaining both moisture and providing shelter protecting the seed from full sunlight in the summer and maintaining ground surface temperatures in the winter.
- Protects the germinating seed from frosts and bird predation.
- This practice works well to encourage germination of native seeds after a bushfire event
- During the hydoseeding prior to straw mulching a number of soil ameliorants can be added to the slurry mix as well as fertilisers.