Predictive value of resin extraction to determine sulfur and phosphorus response of maize in a range of soils from the New England Tablelands of NSW, Australia

An evaluation of the predictive capacity of resin sulfur (S) and phosphorus (P) extraction was undertaken on 18 soils from the New England Tablelands in northern NSW, Australia. Maize ('Zea mays') plants were grown for 40 days in a glasshouse in the presence or absence of sulfur and/or phosphorus fertiliser, and relative yield was determined. Comparison of the relative yield response against resin extractable S, monocalcium phosphate (MCP) S and KCl40 S using a Cate-Nelson plot revealed little difference between the three S extraction methods when soil test values were below the identified critical levels. However, values above the critical value were better able to identify where fertiliser was not required in the resin and MCP tests. The inability of the KCl40 test to correctly identify when fertiliser would not be needed was related to the short time frame of the trial where the longer term reserves that it identifies are not able to be exploited by potted plants. Evaluation of P responses was not possible due to the responsiveness of all soils to applied P, despite critical values being above previously determined threshold values for more than one third of the soils examined. It remains unclear why all soils responded to P, however tissue P concentrations match with increasing response to soil P test values. In conclusion, there is no benefit in terms of predicting S response to move to a resin extraction method, and we were unable to determine if benefits would accrue with respect to P resin tests.