Improved grazing systems that enhance water quality
| Project leader: | Dr David Nash RMB 2460 Hazeldean Rd Ellinbank VIC 3821 Phone 0356242253 Mobile 0408338782 Fax 56242200 Email David.Nash@dpi.vic.gov.au |  | |
| This project is led by DPIs Primary Industries Research Victoria (PIRVic) Division under the leadership of Dr David Nash. The project commenced in July 2006 and will finish in June 2009. Overview information is provided below - and additional information will be added as it is developed. Introduction and Background The Gippsland Lakes and the associated wetlands are major regional assets of national and international significance. In 1994, as part of a major productivity trial, the ‘Action on Nutrients for Sustainable Agriculture’ (ANSA) program was established. Through monitoring exports from field (i.e. paddock) sites it has been demonstrated that for well-managed rain-fed and irrigated grazing systems in southern Australia:
|  Direct drilling on Macallister Irrigation Trials at Maffra |
Using the monitoring data and stochastic modelling techniques ANSA scientists have shown that:
- The two most important factors affecting phosphorus loads are soil hydrology (i.e. phosphorus tends to be exported through surface rather than sub-surface pathways) and the annual volume of overland flow,
- The two most important factors affecting phosphorus concentrations in runoff between storms are: (a) the time between fertiliser application and when overland flow occurs; and (b) the time between grazing and when overland flow occurs,
- An additive model, having a base concentration (‘systematic’ component) that varies between years and to which the effects of fertiliser and grazing are added, most appropriately represents the phosphorus concentrations, and to a lesser extent the nitrogen concentrations, for individual storms;,
- The half-life of phosphatic fertilisers in respect to phosphorus exports is in the order of four (4) days, and
- With the effects of fertiliser and grazing removed, the underlying or ‘systematic’ exports of phosphorus, (which are not under management control with current technology) are unacceptably high (1 - 5 mg P/L) and do not comply with the stream target of 0.05 - 0.1 mg P/L (Environment Protection Authority 1995).
In addition the ANSA program has:
- Quantified the water and nutrient flows on an irrigated dairy farm, at bay, section and whole farm scales;
- Quantified the catchment scale impact of phosphorus fertiliser ‘Best Management Practices’ in Gippsland;
- Quantified the attributes of different phosphorus fertiliser compounds and determined how different fertilisers may best be used to minimise direct losses from that source;
- Shown that while management of on-farm drainage systems affects phosphorus transport, for many farms drains are not an effective sink for phosphorus and appear to have little overall impact on phosphorus exports; and
- Shown that a well-managed reuse system can effectively control nutrient exports from irrigated grazing systems.
To address the short to medium term need to reduce nutrient exports, the ‘Improved Grazing Systems that Enhance Water Quality” sub-project was established in 2003. The ‘Improved Grazing Systems that Enhance Water Quality’ was the first DPI project to investigate, meaningfully, farming systems that can decrease ‘systematic’ exports of nutrients in the medium to long term.
| Current Work
In the initial 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 (0-2 cm) following rainfall in August 2001 (as part of a postgraduate study prior to this project commencing) 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 were compared between treatments and sampling dates. Subsequently, the relationships between the soil test data, soil water data and overland flow data have been compared (journal paper prepared and in review). |  Pasture trials at Maffra |
The results of the initial study demonstrate that laser grading, which involves the removal of some surface soil and mixing of the remainder with soil from lower down the profile, altered the forms of phosphorus in the surface soils from which nutrients are mobilised (0-2 cm) and lowered phosphorus and nitrogen concentrations in runoff. For example, three (3) years after treatment, laser grading had decreased phosphorus and nitrogen concentrations in the wetting front, the component of flow entering the drains, by 40% and 29%, respectively. The study also demonstrated that organic phosphorus is extremely important in these soils. Inorganic phosphorus stores were depleted (possibly because phosphorus fertilisers had not been regularly applied) and phosphorus from organic sources made up a significant proportion of the soil water phosphorus (approximately 60%). The most informative soil tests for use in future studies such as this were also identified.
Laser grading every three (3) or four (4) years is without question neither an economical or environmentally practical solution to decreasing the risk of nutrient exports. For that reason the main experiment was established in April/May 2004 to investigate if the effects of laser grading could be replicated using less intrusive treatments. In addition to an untreated control, the treatments were: (i) direct drilling of pasture without spraying (with herbicide); (ii) direct drilling following spraying; (iii) spraying followed by aeration and direct drilling; (iv) spraying followed by cultivation to 100 mm (as is common in cropping); (v) direct drilling and spraying followed by cultivation to 200 mm; (vi) and direct drilling. Again soil, soil water and overland flow samples were compared.
The preliminary results from the main study suggest that cultivation may achieve results comparable to laser grading. Cultivation, particularly the heavy cultivation treatments, had similar effects on soil phosphorus and soil water phosphorus to laser grading (disturbance P<0.001). The trend in runoff phosphorus concentrations was less clear (TDP P=0.07, TP P=0.06) and there was no trend in runoff nitrogen (TDN P=0.83, TN P=0.94). This may well be related to the short-term (i.e. 1-2 year) release of nutrients from organic stores and the continued application of fertiliser. Importantly, the reduction in phosphorus in the soil was directly attributable to changes in inorganic phosphorus, rather than organic phosphorus pools as had been the case in the initial study.
Future Directions
In the second phase of the ‘Improved grazing systems that enhance water quality’ project the changes in soil properties caused by the various forms of cultivation will be investigated along with their longevity. Soil and soil water measurements will again be used to assess changes in various phosphorus and nitrogen stores within the surface soil (0-2 cm) and related to overland flow measurements. As fertilisers are being applied in this study, it will be possible to infer the effects of continuing fertiliser applications on the re-establishment of high nutrient concentrations in surface soil. This is seen as a necessary step in developing farming systems, rather than simply farming practices, which optimise the effects of cultivation in lessening nutrient exports.
References
Environment Protection Authority (1995). Protecting water quality in Central Gippsland. Schedule F5 - Waters of the Latrobe and Thomson River Basins and Merriman Creek Catchment and Draft Policy Impact Assessment. Melbourne, Australia, Environment Protection Authority: 125.
Related Links
Variation of the State Environment Protection Policy (Waters of Victoria) - Insertion of Schedule 5. Waters of the Latrobe and Thomson River Basins and Merriman Creek Catchment (external link). To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).
© The State of Victoria, 1996 - 2008.
This document was last reviewed on 24/09/2008