Weeding out woes

Those who follow organic soil management principles have long known that weeds, especially those that dominate the site, are big clues to the deficiencies and imbalances to be found in the soil.

In this light it can be argued that until you address these underlying soil woes no amount of weed control will be truly effective because conditions are always going to favour the weeds that were thriving there in the first place.

Indeed, farmers who have practised organic soil management and sought to progressively reinstate the natural balance in their soils find that a sweet side benefit to their dogged efforts is the marked decline in the distribution and vigour of once pesky weeds.

Following is a list of typical weeds and what they tell us about the soil.

Weeds found in acid soils:

•Buttercup Ranunculus repens

•Dock Rumex species

•Lotus minor Trifolium sp

•Sorrell Rumex species

•Stinging Nettle Urtica urens

Possible remedies: based on a follow-up soil test, add dolomite at recommended rates. Choose acid-loving replacement species.

Note: you will often see native plants such as rushes, sedges, tea tree and paperbark present and/or reclaiming these areas.

Weeds found in alkaline soils:

•Chickweed Stellaria media

•Cleavers Gallium aparine

•Fumitory Fumaria species

•Onion Weed Asphodelus fistulosus

•Pelargonium Pelargonium peltatum

•Stinkweed

Possible remedies: based on a follow-up soil test, and where possible, add legumes and use appropriate rates of nitrogen, phosphorus and sulphur-based fertilisers as they will start to acidify the soil. In the longer run you will probably be better off choosing appropriate alkaline-tolerant replacement species because changing such a soil can be expensive and of moderate effectiveness.

Weeds found in waterlogged soils:

•Barley Grass Horedum

•Buttercups Ranunculus repens

•Dock Rumex species

•Nut Grass Cyperus rotundus

•Penny Royal Mentha pulegium

•Yellow Buttons

Possible remedies: reduce use of these areas over winter and spring. Use appropriate waterlogging-tolerant species as replacements. In the longer run you can start to reduce waterlogging in these low lying areas with upslope tree planting, pasture establishment and the use of contour and grade banks.

Note: you will often see native plants such as rushes, sedges, tea tree and paperbark present and/or reclaiming these areas.

Weeds found in mild to moderately saline soils:

•Barley Grass Horedum

•Serrated Tussock Nassella trichotoma

Possible remedies: cut back use in these areas, especially over winter and spring, until recovery is well underway. Use appropriate salt-tolerant species as replacements and wherever possible cover the soil with a mulch cover to reduce evaporation. In the longer run reduce waterlogging and salinity in these low-lying areas with upslope planting, pasture establishment and the use of tree-lined contour and grade banks.

Note: you will often see native plants such as samphire, saltbush and or bluebush present and/or reclaiming these areas.

Weeds found in compacted soil:

•Wireweed Polygonum aviculare

•Guildford Grass Romulea rosea

Possible remedies: de-compact the soil with soil aerators and deep ripping. Plant appropriate ‘cover crop’ species that have a deep tap root such as chicory. In the longer run keeping cover on the soil and reducing stock and vehicle traffic, especially in winter and spring, will make a big difference.

Weeds found in fertile soils:

•Chickweed Stellaria media

•Cleavers Gallium aparine

•Fat Hen Chenopodium

•Fumitory Fumaria species

•Marshmallow Malvia species

•Nettles Urtica species

•Sow Thistle Sonchus oleraceus

Possible remedies: focus on replacement with your preferred species.

Where weedy grasses dominate:

Deficient in calcium.

Possible remedies: get a soil test where possible and add dolomite at recommended rates. In the longer run keep up regular soil testing and recommended adjustments to keep the conditions in favour of your preferred plants.

Where broadleaf weeds dominate:

Phosphorus to potassium imbalance, aim to get the ratio to 4:1 for lawns and pasture

Possible remedies: get a soil test where possible to direct the appropriate fertiliser application. In the longer run keep up regular soil testing and recommended adjustments to keep the conditions in favour of your preferred plants.

Where Paterson’s Curse (Echium sp) dominates:

Indicates deficiencies in copper.

Possible remedies: get a soil or leaf tissue test to direct trace element application. In the longer run, keep up regular soil testing and recommended adjustments to keep the conditions in favour of your preferred plants. Don’t overgraze or the blighter will come back.

Where Cape weed (Arctotheca calendula) dominates:

Indicates deficiencies in calcium.

Possible remedies: get a soil test where possible and add dolomite at recommended rates. In the longer run, keep up regular soil testing and recommended adjustments to keep the conditions in favour of your preferred plants. Don’t overgraze.

So who can test my soil?

Choose carefully when you seek out a soil test company because their recommendations for soil improvement will reflect how they think of the soil.

A soil test company aligned with a major chemical fertiliser supplier will generally recommend a big dollop of their own products that will revolve around some combination of superphosphate (phosphorus), urea (nitrogen) and muriate of potash (potassium), and while these ‘big three’ are important they are not the be-all and end-all of plant and soil health.

In this light, I have listed first some of the companies whose attitude towards soil best reflects one of respect and holistic soil and plant health:

•FertiTech Australia —www.fertitech.com

•Stock Tech —www.stocktech.com.au

•Bailey’s Fertilisers —www.baileysfertiliser.com.au

•SWEP Analytical Labs —www.swep.com.au

Any soil test is better than nothing because it will help to guide your applications. The soil can be bursting with clues to help you beat back the wretched weeds. Take the time to get to know these signs and what they mean, add to this some ‘insider information’ from farmers in your district and you won’t look back.