Laser Grading

Introduction

The Improved Grazing Systems that Enhance Water Quality project was the first DPI project to investigate farming systems that can reduce ‘systematic’ exports of nutrients in the medium to long term. In the first experiment four recently laser graded (<2 years) and four established (lasered >10 years) bays on the Macalister Research Farm were used. Soil on the bays was initially sampled following rainfall in August 2001 and re-sampled in February/March 2004. Soil sampling in 2004 was undertaken following irrigations in which soil water and overland flow samples were also recovered. Initially a range of soil tests for phosphorus (P) were compared between treatments and sampling dates. Effects of laser grading Laser grading, which is the removal of some surface soil and mixing of the remainder with soil from lower in the profile and is used to achieve an even, gentle slope that is suitable for flood irrigation, resulted in: Altered forms of P in surface soil (0-2 cm); Lower P and nitrogen (N) concentrations in runoff water; Decreased P and N concentrations in the wetting front after 3 years by 40 and 29%, respectively; and Depletion of inorganic P stores and increased importance of organic P store.

Differences between direct drilling (front) and cultivation (back) on the Macallister Irrigation Trials at Maffra

Alternatives to laser grading Laser grading every 3 to 4 years is not an economically or environmentally practical solution to decreasing nutrient exports. In the second experiment less intrusive treatments were applied including: Direct drilling of pasture without spraying; Direct drilling followed by spraying; Spraying followed by aeration and direct drilling; Spraying followed by cultivation to 100mm; Direct drilling and spraying followed by cultivation to 200 mm; and Direct drilling. Results and recommendations Initial results suggest that cultivation may achieve results comparable to laser grading. Heavy cultivation had similar effects on soil P and soil water P concentrations to laser grading although the results were equivocal, possibly due to the short-term store release of nutrients from organic stores and the continued application of fertiliser. Changes in inorganic P, rather than organic P, are responsible for the decrease of soil P. Optimising cultivation practices by developing farming systems rather than just farming practices will result in decreased nutrients exports.

Drilling on laser-graded bays at the Macallister Irrigation Trials at Maffra

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