2022 Speakers

Compost tea to manage broad leaf weedy species in agricultural systems. A case Study in soil microbial activity

Mary Cole

Mary Cole, Speaker at Plant Biology Congress 2022
The University of Melbourne, Australia
Title : Compost tea to manage broad leaf weedy species in agricultural systems. A case Study in soil microbial activity


Weed management is carried out using herbicides that leave the land bare and damage soil biota.

Methods used to determine quantitative data of soil biota populations were carried out using fluorescent microscopy, Most Probably Numbers MPN counts, direct microscopy and direct identification of nematodes species and based on soil dry weight .

One grazing property using compost and compost tea for more than 25 years and a vineyard using the same products for 4 years were tested for indicators of soil microbial and plant health. Both these properties are in West Gippsland, Victoria, Australia.

The grazing property is 60 acres (24ha) on the Koo Wee Rup peatlands. For 47 years it has been a grazing property with Landcare planted wind breaks for stock protection in all paddocks. Rotational grazing on short grazing times is used with long resting periods. Dung beetles have managed the cow pats; rock dust, fish, kelp and molasses in compost tea have supplied nutrients.  The latest biological reports were taken under very dry conditions. Comparing a 2020 report with a 2017 report of the same paddocks and same time of the year, there has been an average 62% increase in bacterial pools and 61% decrease in the saprophytic fungal pools. In 2017 the soil was compacted and that has been addressed despite the dry conditions. Nematode populations increased in diversity and in number per gram of soil (4.55 to 13.41). Mycorrhizal fungal pool increased from 1% to 21% infested roots. The potential plant available nitrogen generated by the soil biota has increased from 56-84kg/ha to greater than 336kg/ha. Soil texture and pasture growth are evidence of this improvement with little to no capeweed in the pasture at any time during the year.

Cannibal Creek Vineyard and Winery producing wine from hand-picked grapes is in West Gippsland and established around 25 years. No synthetic herbicides or pesticides are used now. Sheep graze the vineyard for grass control. Compost tea with fish, kelp and molasses as amendments are used as nutrient drenches on the vines and weed control in the vineyard.

In the vineyard, indicators of soil health were apparent after two applications over 2 seasons. Visually the soil in the vineyard (compost tea applied) was well structured and held moisture and the headlands (no compost tea applied) was dry and light with very little moisture making them visually different.

Active bacterial pools were similar but the total pool in the vineyard soil was approximately 25% greater and the active fungal pool 92% higher. The total fungal pools were similar. Protozoa populations were 85-87% higher in the vineyard soil and the ciliates were 50% lower. Nematodes numbers had increased as had diversity and the mycorrhizal fungal pool was 16% higher. The amount of plant available nitrogen being produced was similar in the two soils.

No capeweed was visible in the vine rows where compost tea had been applied. The head land soil and beyond was covered with flowering cape weed. The biology showed the vineyard soils to be much more fungal dominated, hence discouraging the fast-growing capeweed.

Audience Take Away Notes : 

  • Weed management can be success without the use of toxic synthetic chemicals poisoning the environment.
  • Soil biology drives soil chemistry resulting in a healthy soil and plants.
  • Soils with active soil biota are more resilient to climate change and changes in rainfall patterns in production systems.
  • Better use of available agricultural land will feed the increasing global population if more care is given to soil health by reducing herbicides, fungicides, pesticides and synthetic fertilisers.


Dr Mary Cole gained her PhD from Monash University, Melbourne, Victoria, Australia in 1998. She started her academic career at Charles Sturt University in Wagga Wagga, New South Wales before returning to Monash and University of Melbourne as the foundation Director for the Centre for Wine, Food & Agribusiness. In 1980, she founded Agpath P/L, a private research and consulting laboratory that provides education in soil microscopy and soil health to students and farmers around Australia, New Zealand, Fiji, Egypt, Zambia and the UAE using compost and natural management regimes to improve soil health, plant health and human health.

Signup for updates

By submitting this form, you are consenting to receive emails and notifications from Magnus Group. You can revoke your consent to receive emails at any time by using the Safe Unsubscribe link, found at the bottom of every email