A comparison of soil test calibrations for the estimation of phosphorus fertilizer requirements of wheat

The value of a range of soil analyses as tests for the phosphorus fertilizer requirements of wheat is assessed, for northern New South Wales. The best individual analyses were the standard soil tests, P extracted by ammonium lactate (Egner), 0.5M sodium bicarbonate (Colwell), 0.01N sulphuric acid (Kerr and Von Stieglitz), and Truog's reagent, and the best calibration equation was obtained using both the ammonium lactate and sodium bicarbonate tests. Sorbed phosphate equilibrating with the phosphorus in these extract solutions, estimated by isotopic dilution, made only small contributions to test calibration equations, in the presence of other simpler P analyses. The likely effects of variation in P sorption capacity were represented by analyses for iron and aluminium soluble in Tamm's acid oxalate reagent, but these analyses added little to the calibration equations, suggesting that P sorption capacity is not an important variable affecting wheat production in northern New South Wales. Analyses of variance on the yield data demonstrate the importance of experimental error in field experiments as a factor limiting the precision of soil test calibrations.

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The estimation of the phosphorus fertilizer requirements of wheat in southern New South Wales by soil analysis

Australian Journal of Experimental Agriculture ◽

10.1071/ea9630190 ◽

1963 ◽

Vol 3 (10) ◽

pp. 190 ◽

Cited By ~ 649

Author(s):

JD Colwell

Keyword(s):

Response Surface ◽

Field Experiments ◽

Soil Analysis ◽

New South ◽

New South Wales ◽

Relative Yield ◽

Available Phosphorus ◽

Phosphorus Fertilizer ◽

Absolute Increase ◽

South Wales

The usefulness of five contrasting methods of soil analysis for estimating the phosphorus fertilizer requirements of wheat in southern New South Wales has been investigated, using yield data provided by 27 field experiments. Because the level of yield of wheat is strongly affected by seasonal environmental conditions poor correlations are obtained between soil analysis and absolute or relative yield of wheat, Much better and often significant correlations are obtained between soil analysis and the absolute increase in yield from fertilizer application. The best correlations were obtained with an 0.5M NaHCO3 extraction of soil phosphorus. A regression response surface calculated from these relationships provides a method for making direct estimates of fertilizer requirements for maximum economic return to farmers under average climatic conditions. The precision of these estimates is limited more by the flatness of the response surface and uncontrolled variation in the field data, than by inadequacies in the representation of available phosphorus by the NaHCO3 analysis.

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The calibration, interpretation, and evaluation of tests for the phosphorus fertilizer requirements of wheat in Northern New South Wales

Soil Research ◽

10.1071/sr9680105 ◽

1968 ◽

Vol 6 (1) ◽

pp. 105 ◽

Cited By ~ 45

Author(s):

JD Colwell ◽

RJ Esdaile

Keyword(s):

Field Experiments ◽

New South ◽

General Procedure ◽

New South Wales ◽

Clay Content ◽

Calibration Procedure ◽

Yield Response ◽

Phosphorus Fertilizer ◽

South Wales ◽

Soluble Phosphorus

A general procedure is described for the estimation of fertilizer requirements from measurements on all factors that affect plant response to fertilizer. Tests for fertilizer requirement are defined as all measurements of factors that affect the fertilizer requirements of a crop, and the calibration procedure is based on the prediction of yield response functions for particular sites from test measurements representing the sites. Several tests can be used simultaneously for the prediction of fertilizer requirements, and this is demonstrated by the calibration of the soil tests, NaHCO3-soluble phosphorus, NaHC03-soluble potassium, and pH, against yield response of wheat to phosphorus fertilizer using data from 49 field experiments in northern New South Wales. The value of rainfall and clay content as tests was also investigated but their contributions to the calibration equations were non-significant. The application of economic principles for the estimation of optimal phosphorus fertilizer requirements is demonstrated. Fertilizer requirements decrease with increase in the value of NaHCO3-soluble phosphorus, with increase in pH, and with decrease in NaHCO3-soluble potassium. A statistical and economic evaluation of the tests is made on the basis of the regression surfaces established under the calibration procedure, and it is concluded that the value of testing for phosphorus fertilizer requirements is considerable.

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