Critical phosphorus values from the Better Fertiliser Decisions for Pastures project: early insights from validation trials

Authors

David Rogers, Department of Primary Industries and Regional Development Western AustraliaFollow
David Weaver, Department of Primary Industries and Regional Development Western AustraliaFollow
Robert N. Summers, Department of Primary Industries and Regional Development Western AustraliaFollow
Eric Dobbe, Department of Primary Industries and Regional Development Western AustraliaFollow
Ronald Master, Department of Primary Industries and Regional Development Western AustraliaFollow
Robert McFerran, Department of Primary Industries and Regional Development Western AustraliaFollow
Graham Mussell, Graham Mussell Consulting
Luke Dawson, CSBP Limited
Justin Mercy, CSBP Limited
Peta Richards, Department of Primary Industries and Regional DevelopmentFollow
Deborah Holtham, Department of Water and Environmental Regulation

Document Type

Article

Publication Date

5-27-2021

Journal Title

Crop and Pasture Science

ISSN

Print: 1836-0947 Electronic: 1836-5795

Keywords

Colwell P, critical values, pasture, phosphorus, phosphorus buffering index, soil testing

Disciplines

Agricultural Science | Environmental Monitoring | Soil Science

Abstract

Phosphatic fertilisers have made grazing in the south-west of Western Australia (WA) viable. However, there is evidence that a large proportion of pasture paddocks exceed soil test critical values at which 95% of maximum yield is achieved as identified in the national Better Fertiliser Decisions for Pasture (BFDP) project. Of 22 000 soil samples collected between 2009 and 2020, 56% exceeded the critical value for phosphorus (P), although there were constraints to potassium (K) and sulfur (S) and from soil acidity. Soils with available P exceeding the critical value are expected to lead to excessive losses of P to waterways, resulting in eutrophication. A trial program was established to validate the critical P values from BFDP so that concerns can be addressed about the relevance of these critical P values to WA conditions and to contemporary pasture varieties. Measured relative yields for 19 trials in the first year were mostly within 10% of that predicted from BFDP for soils with a P buffering index (PBI) > 10. Soils with PBI < 10 had measured relative yields up to 25% greater than predicted by BFDP, suggesting response calibrations for low PBI soils may require adjustment in the BFDP dataset. Some pasture yield gaps occurred when soil pH and P were low. Application of nitrogen (N), K and S almost doubled the yield when P was limiting or sufficient. Agronomic advice and practice should seek to optimise these multiple inputs, thereby optimising P use rather than applying P to levels above the critical value.

Recommended Citation

Rogers, D, Weaver, D, Summers, R N, Dobbe, E, Master, R, McFerran, R, Mussell, G, Dawson, L, Mercy, J, Richards, P, and Holtham, D. (2021), Critical phosphorus values from the Better Fertiliser Decisions for Pastures project: early insights from validation trials. Crop and Pasture Science, 72 (9), 731-741.
https://library.dpird.wa.gov.au/nrm_research/5