||Total plant-available soil phosphorus (P) consists of the organic P in litter and soil plus the plant-available mineral P. Plant-available P stores are far from the total P store in the landscape, because much of the mineral P in the soil is tightly chemically bound to the soil matrix and is therefore only weakly available for plant growth (secondary P) or unavailable in time scales less than centuries (occluded P). However, mineral P values from soil tests include some of this unavailable P. For the plant-available phosphorus budget, the inflows include physical or biological weathering which releases P from inert soil pools, and fertilisation; outflows include leaching, export in runoff (in both dissolved and sediment-bound forms) and removal by harvest. Derived from the BiosEquil model by Raupach et al. (2001a; 2001b).
Soil nutrient outputs of the BiosEquil model
Nutrient status is one of the key limiting factors determining the productivity of Australian vegetation systems, but is only broadly represented by gross nutrient status an attribute compiled from the Atlas of Australian Soils (McKenzie et al. 2000). We therefore additionally compiled the 0.05Â°gridded pre-European (base) predictions of carbon, nitrogen and phosphorous distributions which are outputs of the BiosEquil model by Raupach et al. (2001a; 2001b). These data are available from the Australian Natural Resources Atlas at www.nlwra.gov.au/atlas. Inputs to the pre-European models included meteorological surfaces of daily gridded data at 0.05Â° spatial resolution (for Australia) (Jeffrey et al. 2001), soil characteristics for current conditions derived from the Atlas of Australian Soils (McKenzie et al. 2000), and vegetation characteristics (Leaf Area Index) (Lu et al. 2001). The 0.05Â° gridded data were resampled to 0.01Â° using the cubic algorithm with RESAMPLE in ARCINFO GRID. Zero values were assumed to represent NODATA values (e.g. lakes) and were iteratively filled using the DATA option of the FOCALMEAN command with a CIRCLE expand radius of 3 cells in ARCINFO GRID, as described above.