“Despite all our achievements, we owe our existence to a six-inch layer of topsoil and the fact it rains.” A quote often attributed to long time US radio presenter, Paul Harvey, this quote succinctly captures the critical importance of our topsoil.

What is topsoil, how is it formed and how do we improve it? These fundamental questions were addressed on Thursday, April 7 during a ‘Reboot Your Soils’ workshop with soil whisperer, David Hardwick, hosted by Western Murray Land Improvement Group.

Attendees brought along a bucket of soil and an inquisitive mind, and David provided a crash course in the basics of the principles involved and how to assess your soils.

What are your soil textures, sand, silt or clay? What are the mineral compositions of your soil passed down by the parent material? What is your soil structure like and what role does organic carbon play in the condition of your soil?

Attendees learnt about the lifecycle of plants and how, through photosynthesis, plants utilise carbon and nutrients to grow, storing carbon that can be either lost or stored. Losses occur through oxidation or respiration. Oxidation occurs where organic matter is broken down when exposed to sunlight. During the breakdown, the carbon is released back into the atmosphere. Respiration also results in the release of carbon to the atmosphere and occurs when the organic matter is consumed by soil microbes as food to power them in processing mineral into plant available nutrients.

Tillage of the soil can dramatically increase respiration. As David explained, the addition of oxygen through tillage is like opening the air vent on your wood heater, the microbes go into overdrive and this limits the opportunity for the soil’s beneficial storage of carbon, through humus. Unlike the chickpea derived hummus condiment, humus is an accumulation of organic carbon. When we think of a forest floor or the soil under a tree, we look at the characteristic black or brown build-up of organic carbon.

In an area of low rainfall, it is vital that we have conditions that are conducive to capturing our limited rainfall. Infiltration rate of soil is the speed at which water enters the soil. With a low filtration rate, water can be lost as runoff or evaporation as it cannot enter the ground, recharging soil moisture. Testing on the black Noorong clay soon demonstrated the variability and lost opportunity in capturing those heavy rain events. A filtration tool, a 150mm steel pipe about 180mm long with a bevelled edge, was driven into the ground of three different ground cover scenarios, open ground, perennial grasses and under a tree with high humus.

Once installed, the pipe was filled to a level noted on a steel ruler and then timed for six minutes. After six minutes, the level of the water was again noted and extrapolated out to millimetres of infiltration per hour. The bare ground yielded an infiltration rate of 50mm per hour, the humus under tree rate of 450mm per hour and the perennial grasses rate of 470mm. Stark differences indeed!

Attendees were guided through a soil health checklist which included soil organisms, soil microbes, salinity, ph, structure (compaction, powdery, aggregates) and aggregate strength.

All who attended were given lots of food for thought on how to benefit their soil and, in turn, the bottom line.

This article appeared in The Koondrook and Barham Bridge Newspaper, 14 April 2022.