Soil conservation

Title: Topsoil loss —  Protecting your farm's most valuable asset

Vision: Glenn Sturmfels , Agriculture Victoria kneeling  in a grassy field
Glenn speaking:

'Across Victoria, we are losing significant quantities of topsoil due to sheet, rill and wind erosion. Topsoil is the dark surface layer of the soil and is usually 10 to 20 centimetres in depth.'

Vision: Glenn is digging a hole in the field

Glenn speaking:

'Topsoil is essential for growing crops and pastures, for feed grazing animals and as a source of food for the world's growing population.'

Vision: Close-up of dug hole

Glenn speaking:

'It is priceless and irreplaceable.'

Vision: Sparse windswept field

Glenn speaking:

'Over much of the state we are losing topsoil at an unsustainable rate,  5  to 10 times higher than it is being replaced by natural processes.'

'In a paddock like this the rate of soil loss could be 50 times higher than it's natural replacement rate.'

Vision: Heavy rain falling on ground

Glenn speaking:

'On a yearly basis this would equate to about 13 hectare of lost topsoil, about 130 kg per hectare of lost organic matter and around 15 kg of lost nitrogen, phosphorus and potassium.'

Vision: Sheep moving across a field and barren ground leading to a large dam

Glenn speaking:

'While difficult to quantify in economic terms, this landholder could easily be losing $100/ha/year in fertiliser alone without putting a value on the soil itself, organic matter and offsite impacts.'

Vision: Barren ground and different fields with barren ground

Glenn speaking:

'In some of our more productive horticultural areas we are losing topsoil at an even higher rate due to slope, high rainfall intensity and excessive cultivation.'

Vision: Grassy field and a field of crops

Glenn speaking:

'Topsoil is by far the most precious fraction of our landscape. We rely on topsoil to recycle organic matter, provide a habitat for biological activity and provide all the essential nutrients required for plant growth.'

Vision: Worms in soil

Glenn speaking:

'Topsoil absorbs and stores large volumes of air and water.'

Vision: Pastures with sheep

Glenn speaking:

'It is the powerhouse of our agricultural industry.'

Vision: Barren ground

Glenn speaking:

'Over time erosion leads to surface sealing and compaction which significantly reduce plant establishment and growth.'

Vision: Glenn kneeling in soil eroded field

Glenn speaking:

'What is causing this massive loss of topsoil?'

Vision: Foggy field, exposed land, overgrazed dry crops, bush fire ravaged landscape

Glenn speaking:

'Topsoil loss is brought about by exposing our soils to wind and rain — the result of overgrazing, tillage or natural causes such as bushfire.'

Vision: Man in yellow raincoat with dog in rainy field

Glenn speaking:

Vision: Water runoff in field from rain

Glenn speaking:

'A lack of cover exposes our soil to the enormous energy of raindrops and wind. This results in massive damage to the soil structure and increasing volumes of surface runoff.'

Vision: Grassy hill and sheets of water running down a field

Glenn speaking:

'The problem is magnified on sloping land as soil is swept downslope in a sheet of muddy water.'

Vision: Glenn on haunches demonstrating small gullies of water

Glenn speaking:

'As this flow gathers speed it changes from sheet to channel flow and forms small gullies or rills across the paddock.'

Vision: Different landscapes showing result of wind erosion

Glenn speaking:

'Wind erosion occurs when the speed of the air moving across the soil surface exceeds the ability of the soil particles to stay in place.'

'The very fine fraction of the soil containing most of the soil nutrients becomes suspended in the air and can travel for hundreds or thousands of kilometres.'

'Erosion mostly occurs during summer and early Autumn when our soils are dry, ground cover is low and summer thunderstorms are a common occurrence.'

'Often this erosion is barely noticeable to the eye, however it still has a significant impact.'

'What can we do to prevent sheet and rill erosion?'

Vision: Grassy fields

Glenn speaking:

'In most cases the problem of sheet and rill erosion can be avoided by simply maintaining good ground cover at all times of the year, particularly during summer and late autumn.'

'100% ground cover will give you total protection although this is not always achievable.'

'However on steeper country or any landscape prone to soil erosion, pasture cover should be maintained as close as possible to 100%.'

Vision: Cropped fields

Glenn speaking:

'Cropping should be restricted to slopes less than 5% and use techniques which minimise excessive cultivation.'

'Crop or crop stubble should be maintained to provide at least 50% ground cover and have at least one third of the stubble anchored firmly to the ground.'

'How can you assess ground cover accurately?'

Vision: Glenn demonstrating

Glenn speaking:

'Make a square frame measuring 30 × 30 centimetres out of steel rod, stiff wire or timber.'

'Walk diagonally across a typical section of your paddock tossing the frame in a random fashion onto the ground.'

'Then use benchmark photographs to assess the percentage ground cover within your square frame.'

'Repeat the process 10 times or more and average the results.'