The availability of light, water and nutrients determines the capacity of land to produce natural vegetation and agricultural yield. In Australia, long-term availability of resources and the consequent potential for generating yield, can be assessed by examining the mass balances of the key resources: water and nutrients (in this case nitrogen and phosphorus). Mass balance gives a quantitative picture of:
- resource inflows or sources;
- resource outflows (including both production outputs and unproductive losses or leakages);
- the resource stock (the amount available for use); and
- the way that the stock changes with time in response to the various inflows and outflows.The mass balances of water and nutrients are linked by carbon (or biomass) since plant biomass is approximately 50% carbon. Balances and cycles of water, nitrogen, phosphorus and carbon interact and constrain each other.
- The rate of plant biomass production determines how much resource is available for harvest and for maintaining natural and farmed animal populations.
- Production of plant biomass is closely linked to plant water use, and is usually a dominant outflow in the landscape water balance.
- Production of plant biomass is linked with uptake of nutrients from soil into plants, after which the nutrients are locally recycled through litter or removed in plant or animal harvest.
The net rate that plants build up carbon from the atmosphere by photosynthesis is known as 'net primary productivity' and is most important carbon flow.
Two models were developed for determining landscape balances of carbon, nitrogen and phosphorus and estimate of change in net primary productivity:
- an evolving or time-dependent model (BiosEvolve); and
- an equilibrium or statistically steady state model (BiosEquil).
Predictions of these models are designed to determine large-scale patterns rather than the behaviour of individual farms or paddocks, and should never be interpreted at single-cell (5 km) scale. Uncertainties even at a large region scale (100 km by 100 km or greater) for the models are:
- Net primary productivity: 30%
- Organic stores of C, N and P: 50%
- Mineral stores of C, N and P 100%
- Current/pre-agricultural ratios: 50%
- Leaching and drainage fluxes: large uncertainty
|River basin name||Net Primary Productivity (t Carbon/ha/y)||Total Carbon(plant+ soil+ litter ) tC/ha)||Total Phosphorus(kg P/ha)||Total Nitrogen (kg N/ha)|
|Lower Murray River||1||84||542||4,243|
Click on the river basin name or map below to view a report on the nutrient - sediment - landscape budget terms.
- Australian Agriculture Assessment 2001 report
- Landscape balances chapter of the Australian Agriculture Assessment 2001 (theme) report
- Report prepared by CSIRO Land and Water in the development of this work on the coupled balances of water, nutrients and carbon in Australian landscapes (PDF - 3.5 MB)
- Technical report prepared by CSIRO Land and Water in the development of this work on the coupled balances of water, nutrients and carbon in Australian landscapes. (PDF - 1.3 MB)
- Link to the Map Maker to make a map using this information.
- Data Library
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