Hopefully few of us will ever have to deal with the problem of burned paddocks, but as we know, it does happen and a few of our member farms were badly damaged by fire in early March this year. A recent talk by David Shambrook of the Department of Agriculture, Leongatha addressed this topic at a Women on Farms meeting at Ellinbank. Your newsletter editor was given special privilege by WOF to attend this normally “women only” meeting, and we thank WOF for this.
The main points made were:
- It takes a long time to restore pasture and infrastructure after a fire.
- The degree of pasture damage varies with fire intensity, fuel load, pasture species, fertility, soil type and timing of follow-up rains.
- Of particular note, fertility will not be altered long term by fire, but there will be increased potassium initially from the ash deposits. Clover loves potassium and may get an initial boost as the ash is absorbed into the soil. Planting sub-clovers may be indicated to take advantage of this factor.
- Lighter soils will be more adversely affected than heavy soils.
- Annuals are more susceptible to fire although some perennials will tend to die, while newly sown pastures will probably be badly hit.
- Weeds will be the first to recover and there will usually be a flush of broadleaf weeds like Capeweed. Capeweed is a source of cattle feed, but it must not be fed as the only feed to hungry stock because of the acute risk of nitrate poisoning. Hay or other nutrients must be available if stock are put on a Capeweed dominant paddock.
- Soil temperatures at the surface can reach 600 degrees C and typically around 50 to 150 Degrees C in a cool to moderate burn Soil below 15 mm deep is not changed by more than 10 degrees however, – a key reason to consider planting deep rooted grass species in fire prone areas.
- Perennial grass survival has been measured at around 40% in a hot fire, and 80 to 98% in a cool fire. Annuals are much worse hit. Sub clover can fair a little better but its seedbank still reduces by 60% in a moderate fire. White and Strawberry clovers survive moderate temperatures, while lucerne survives even hot burns.
- Since Dock, Sorrel, Onion grass and Capeweed all survive very well, there may be a need to oversow with grass seeds to provide competition to the weeds. Weed control with herbicide may be needed also, or instead of over-sowing.
- Immediately after a fire and after a drought, it may be useful to conduct a trial in a one metre square section of dry pasture by irrigating it and seeing what regrows. This can assist early decisions concerning the need or otherwise for resowing.
- If weeds have gained purchase, heavy harrowing, or spray grazing may be worthwhile with or without resowing, depending on the survival rate of desirable grass seeds.
- Keep stock off burnt pastures for 6 weeks or more to maximize growth of surviving plants.
- If spray grazing is indicated (eg a heavy crop of Capeweed has taken over) BUT cattle cannot be introduced at the desired time a few weeks after herbicide treatment (eg due to a lack of fences), then slashing or mowing should be considered in place of the desired heavy stocking.
- Don’t fertilise unless soil tests indicate this is necessary and then don’t fertilise until there is enough grass visibly growing to use the applied nutrients.
- While early June is still not too late to plant perennial ryegrass (soil temps of 5 to 10 degrees C are acceptable, enabling 75% germination in 10 to 15 days), sub clover may be a better bet if sowing in June. Perennials are needed to ensure ground cover.
- Whilst pasture assessment immediately after a fire is optimal, by June, it is still worthwhile to look between the weed plants and weed areas of burnt paddocks, to assess whether a Spring sowing of a perennial, or a Spring millet crop followed by resowing perennials next autumn. It may be preferable to wait until the following autumn when better assessments will have been possible and a more complete pasture renovation can be undertaken in those parts of the farm needing it.
- Speeding up a return to pasture cover and density is a high priority after a fire. The pasture plants should be encouraged to set seed in the Spring following the fire. This can be assisted by avoiding heavy grazing pressure in the mid to late spring period, and by not cutting the pasture for hay or silage in this first post-fire spring season.
Expect 50% production in the first Spring after a pasture burn, and a complete recovery could be 12 to 18 months or more to get back to full production.