A model of S, P and N uptake by a perennial pasture
2. Calibration and predictions
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Abstract
Calibration of a model of phosphorus (P), sulfur (S) and nitrogen (N) uptake by a perennial pasture is described. The nutrient model, presented in an earlier paper, is built on soil diffusion theory and plant uptake kinetics, and is set within a larger model which includes soil moisture balance, pasture growth, organic matter cycling and grazing by sheep. The model was calibrated by modifying the radius around the root within which complete nutrient depletion is assumed to occur. Three criteria were used for calibration:
- (i)
the plant yield and clover contents matched those of a four-year field trial which was grazed intermittantly and received a range of superphosphate rates;
- (ii)
the relationship between the soil P and S status and relative plant growth was similar to that which would be expected from other field trials in the region; and
- (iii)
predicted P and S concentrations through the year were close to those found in a frequently monitored grazed pasture.
To achieve an acceptable fit, the base depletion radius for P uptake had to be reduced from that presented in the earlier paper, by a factor of 0.42 for the grass (Phalaris aquatica L.) and 0.38 for the legume (Trifolium repens L.). Equivalent figures for S uptake were 0.28 and 0.24 respectively. No modifications were made for N uptake. These calibration factors were increased during spring to account for high nutrient uptake during this season, and reduced for plants already containing high concentrations of the nutrient to avoid excessive luxury consumption.
Key words
Nutrient modelling pasture modelling Trifolium repens L. Phalaris aquatica L.Preview
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References
- 1.Barrow NJ (1967) Studies on extraction and on availability to plants of adsorbed plus soluble sulfur. Soil Sci 104: 242–249Google Scholar
- 2.Blair GJ, Till A and Smith RCG (1976) The phosphorus cycle — what are the sensitive areas? In: Blair GJ (ed.) Reviews in Rural Science. 3. The Efficiency of Phosphorus Utilization, pp. 9–20. Armidale, NSW: University of New EnglandGoogle Scholar
- 3.Clarkson DT, Smith FW and Vanden Berg PJ (1983) Regulation of sulfate transport in a tropical legume,Macroptilium atropurpureum, cv. Siratro. J Exp Bot 34: 1463–1483Google Scholar
- 4.Colwell JD (1963) The estimation of the phosphorus requirements of wheat in southern New South Wales by soil analysis. Aust J Exp Agric Anim Husb 3: 190–197Google Scholar
- 5.Coughenour MB, Parton WJ, Lauenroth WK, Dodd JL and Woodmansee RG (1980) Simulation of a grassland sulfur cycle. Ecol Model 9: 179–213Google Scholar
- 6.da Roza, GD (1981) Pasture response and optimum fertilizer use. M Ru Sci Thesis. Armidale, NSW: University of New EnglandGoogle Scholar
- 7.Dixson WJ (ed.) (1983) BMDP Statistical Software, Berkley: University of California PressGoogle Scholar
- 8.George JM, Vickery PJ and Wilson MA (1977) Meterological data from the CSIRO pastoral research laboratory Armidale, N.S.W., 1949–1976. CSIRO Animal Research Laboratories Technical Paper No. 5 (CSIRO: Australia).Google Scholar
- 9.Helyer KR and Spencer K (1977) Sodium bicarbonate soil test values and the phosphate buffering capacity of soils. Aust J Soil Res 14: 263–273Google Scholar
- 10.Holford ICR and Gleeson AC (1976) White clover responses to phosphorus and sulfur on granitic soils. Aust J Exp Agric Anim Husb 16: 234–239Google Scholar
- 11.Holford ICR and Gleeson AC (1976) Residual effectiveness of phosphorus on white clover on granite soils. Aust J Agric Res 27: 509–518Google Scholar
- 12.Maynard DG, Stewart JWB and Bettany JR (1983) Sulfur and nitrogen mineralization in soils compared using two incubation techniques. Soil Biol Biochem 17: 251–256Google Scholar
- 13.Maynard DG, Stewart JWB and Bettany JR (1985) The effects of plants on soil sulfur transformations. Soil Biol Biochem 17: 127–134Google Scholar
- 14.McCaskill MR and Blair GT (1988) Development of a simulation model of sulfur cycling in grazed pastures. Biogeochemistry 5: 165–181Google Scholar
- 15.McCaskill MR and Blair GT (1990) A model of S, P and N uptake by a perennial pasture. 1. Model construction. Fert Res 22: 161–172Google Scholar
- 16.Probert ME and Jones RK (1977) The use of soil analysis for predicting the response to sulfur of pasture legumes in the Australian tropics. Aust J Soil Res 15: 137–146Google Scholar
- 17.Silberbush M and Barber SA (1984) Phosphorus and potassium uptake of field-grown soybean cultivars predicted by a simulation model. Soil Sci Soc of Am J 48: 592–596Google Scholar
- 18.Spencer K, Bouma D, Moye DV and Dowling EJ (1969) Assessment of the phosphorus and sulfur status of subterranean clover pastures 1. Environmental factors and pasture response. Aust J Exp Agric Anim Husb 9: 310–319Google Scholar
- 19.Spencer K, Bouma D and Moye DV (1969) Assessment of the phosphorus and sulfur status of subterranean clover pastures 2. Soil tests. Aust J Exp Agric Anim Husb 9: 320–328Google Scholar
- 20.Spencer K and Glendinning JS (1980) Critical soil test values for predicting the phosphorus and sulfur status of subhumid temperate pastures. Aust J Soil Res 18: 435–445Google Scholar
- 21.Wolfe EC (1971) Grass/while clover relationships during pasture development and their relevance to cattle bloat. Ph D Thesis, Armidale, NSW: University of New EnglandGoogle Scholar
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