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Modelling changes in soil phosphorus when phosphorus fertiliser Is reduced or ceases


Tyson, J and Corkrey, R and Burkitt, L and Dougherty, W, Modelling changes in soil phosphorus when phosphorus fertiliser Is reduced or ceases, Frontiers in Environmental Science, 8 Article 93. ISSN 2296-665X (2020) [Refereed Article]


Copyright Statement

Copyright 2020 Tyson, Corkrey, Burkitt and Dougherty. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0)

DOI: doi:10.3389/fenvs.2020.00093


In order for land managers and policy makers to manage excessive soil phosphorus (P) concentrations and reduce the risk of this particular source of P from impacting water bodies, models of soil P decline under various scenarios are needed. We modelled the decrease in calcium chloride-extractable P (CaCl2-P), and sodium bicarbonate-extractable P (Olsen-P and Colwell-P) using data from six Australian grazed pasture soils with contrasting P sorption properties, over a period of 4.5 years. Each soil had four initial soil P concentrations (Pinit), each of which received four on-going rates of P fertiliser (Pfert). The model predicts the final P concentration (Pfinal) by taking into account the P concentration previously measured (CaCl2-P, Olsen-P or Colwell-P), Pfert applied since measurement, and time since previous measurement: Final P concentration = (previously measured P concentration + ep x P fertiliser applied) exp (-dp x years since previous P concentration measurement). Where ep is the increase in soil P for each unit of applied P and dp is the decay constant representing how quickly the soil P decreased. The greatest decreases in proportion to Pinit occurred for CaCl2-P, followed by Olsen-P, and then Colwell-P. The model tended to fit the dataset well for Olsen-P and Colwell-P, with mean overestimation (modelled Pfinal concentration greater than actual Pfinal) of the Pfinal concentrations of 6.1 (32%) and 4.3 mg/kg (10%), respectively. Although there was less CaCl2-P data, the model successfully described it, with a mean overestimation of Pfinal CaCl2 of 3.1 mg/kg (26%). The overestimation of Pfinal CaCl2 was possibly due to the high CaCl2-P concentrations of the low P buffering index soils. The model predicted an average of 32 years (ranging from 26 to 49 years) for Olsen-P concentrations of between 55 and 96 mg/kg to decrease to an agronomic optimum of 17 mg/kg. Agronomic optimum was not a reliable indicator of environmental risk as some soils did not exceed the CaCl2-P environmental threshold until Olsen-P concentrations were twice the agronomic optimum, whereas low P sorbing soils tended to exceed the threshold before reaching agronomic optimum. Further work with more soils is required to examine the influence of soil properties such as P sorption on decreases in soil P.

Item Details

Item Type:Refereed Article
Keywords:omit, withdraw, withhold, decline, reduce, Bayesian, phosphorus run-off
Research Division:Agricultural, Veterinary and Food Sciences
Research Group:Agriculture, land and farm management
Research Field:Agricultural systems analysis and modelling
Objective Division:Environmental Management
Objective Group:Terrestrial systems and management
Objective Field:Evaluation, allocation, and impacts of land use
UTAS Author:Corkrey, R (Dr Ross Corkrey)
ID Code:139810
Year Published:2020
Deposited By:TIA - Research Institute
Deposited On:2020-07-07
Last Modified:2021-03-03
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