Project Details
Best Management Practices for Nitrogen in Intensive Grazing Systems

Note - the project has now ended, but we maintain the web site to share the information generated
 

1. To formulate practical management guidelines to minimise nitrogen losses while maintaining productivity in dairy pastures in south eastern Australia.
2. To evaluate a range of existing simulation models for their applicability to N cycling in grazed dairy pasture systems in south eastern Australia, and
3. From #1 and #2, above, to identify critical gaps in information essential for refining aims #1 and #2.

Building on the theme that overseas experience, data and technologies (including computer models) can provide a basis from which to acquire specific knowledge for Australian conditions which, in turn, can be used to develop best management practices, the Objectives of this research project are:

1. to develop a decision support system (DSS) for the economic- and environmentally-sustainable use of N fertiliser in intensive, pasture-based dairy production systems in south eastern Australia.
2. to evaluate the applicability and relevance of existing computer simulation models of nitrogen (N) cycling processes in grazed pasture systems, developed in other countries and/or for different livestock systems, to the Australian dairy industry. Particular emphasis will be given to determining how well these models cater for the biophysical characteristics and management practices of dairy farms in the south eastern Australia; and how accurately they predict amounts of N moving through different pathways of the N cycle in controlled field experiments where relevant data are already available or will be collected during the project.
3. from #1 and #2, above, to identify critical gaps in information on N cycling processes and production responses to fertiliser application for Australian conditions that must be addressed to improve model predictions and accuracy of the DSS, and initiate research projects to fill those information gaps. These critical gaps will have to identified, through an annual workshop between collaborators, throughout the life of the project to ensure delivery of a reliable DSS.

1. Practical management guidelines and a prototype decision support system, designed in collaboration with and for use by extension services (i.e. Target 10), industry (i.e. Pivot and Incitec) and producers in south eastern Australia, to optimise economic returns from N fertiliser use;
2. A dynamic simulation model of the N cycle relevant to dairy pastures in south eastern Australia. A simulation model is the only practical option for coping with the diversity encountered between farms in south eastern Australia;
3. Estimates of the rates of N loss from temperate, high-rainfall and flood irrigated dairy systems. These estimates in themselves will be useful in providing industry, advisers and farmers with an indication of the extent of the problem at hand, and
4. Specific objectives for future research on N cycling processes targeted at filling information gaps identified during model evaluation and adaptation and DSS development. These critical information gaps will be identified through an annual workshop with the collaborators.

The use of N fertiliser to boost the supply of forage from pasture in dairy systems in Victoria has increased exponentially over the past 15 years. Some research is currently underway to determine pasture growth responses to different timings, rates and forms of N fertiliser application (Tasmania and Western Victoria; Eckard 1996; McKenzie & Jacobs 1997) to enable producers to optimise production responses through appropriate management practices.

Increased stocking rates and tighter calving patterns have increased demand for feed, particularly during autumn and winter. With the majority of dairy herds in Western Victoria calving between May and July, cows are almost invariably underfed in early lactation due to low winter pasture growth rates. To meet the requirements of a growing dairy industry, management options need to be examined that will allow increased pasture production, particularly during periods of lower pasture availability. One such option is the use of nitrogen fertiliser. However, the strategic use of N to produce additional pasture is poorly understood in Victoria.

There is mounting concern over the magnitude of losses and environmental impacts of N fertiliser use in intensive grazing system in south eastern Australia. Experience in other countries such as Britain, the Netherlands and New Zealand shows that sustained high rates of N fertiliser application can lead to losses of N from farms to waterways and the atmosphere, with potential adverse impacts on the environment and quality of water supplies for human consumption. However, there is insufficient quantitative information readily available on N cycling processes in dairy farm systems in south eastern Australia.

Simulation models are the only practical option for coping with the variability that exists in Australian dairy production systems. Models of the N cycle in grazed pastures have been developed in other countries. However, these models need to be validated for local conditions.

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