Friday, 3 August 2012

Controlling paddock erosion during development

“Erosion results in the loss of the biologically active top soil, depletes nutrients and organic matter, and reduces crop or pasture productivity and farm viability. Prevention of soil degradation is always substantially cheaper than the cost of restoration.” – Striking the Balance (O’Gara 2010)

At a recent field day in the Douglas Daly, farmers, foresters and NT Government soil scientists came together to discuss how new paddocks can be developed without causing unacceptable levels of erosion. Here are some of the outcomes:

·         Choose the right land to develop – Survey and assess the limitations of the land so that management requirements and potential detriment to the business or environment are understood. Take others onto your land to get their advice.

·         Work machinery and vehicles along the contour - Any cultivation or other vehicle / machinery movement on bare soil should be on the contour to minimise the risk of concentrating overland flow down slope.

·         Remove non-engineered windrows - Unless specifically designed for soil conservation purposes, obstructions to overland flow will increase the risk of flow concentration and erosion of exposed soils. The most common obstructions on cleared land are windrows of soil and / or cleared vegetation pushed into piles.

·         Manage velocity and concentration of flow - The length of slope and the associated risk of rill erosion can be reduced by using contour banks that remove overland flow from the paddock at low velocity into sills or designed waterways. Construction of contour banks is most applicable where heavier rainfall occurs and where the risk of concentrated flow increases, and enables quick establishment of the development.

Alternatively, strips of vegetation may be retained within the cleared paddock to mitigate concentration of flow and reduce run-off velocity and volume. Retained strips, banks and waterways must be maintained and disturbance minimised to be effective. (Note: these practices will not control particle detachment and sheet erosion between each bank or strip.)

·         Minimise the extent and duration of soil exposure - The rapid re-establishment of groundcover following clearing reduces erosion potential. Sow or cultivate at least with one fast growing species as early as possible. Using cheap seed such as silk sorghum may make this a more viable option.

·         Treat erosion and maintain conservation structures - Failure to maintain or repair existing soil conservation structures or neglecting to repair small areas can exacerbate erosion.

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