Micronutrient status of a group of soils in Canterbury, New Zealand, as measured by extraction with EDTA, DTPA and HCl, and its relationship with plant response to applied Cu and Zn

Abstract

The Cu, Zn and Mn status of 44 fields from the Canterbury region of New Zealand under winter wheat was investigated in Spring 1993. Micronutrient status was assessed using EDTA, DTPA and HCl as extractants. The Mn status of soils was generally high and unaffected by soil development. However, when samples were separated according to soil series, it was found that extractable Cu and Zn levels in both the 0–15 and 15–30 cm soil layers generally decreased with increasing soil development (increasing soil age and annual rainfall). Twenty-three percent of fields had EDTA-extractable Cu levels <1 μg g−1 whilst 34% had EDTA-extractable Zn levels <1 μg g−1.Twenty-two of the soils were used in a glasshouse experiment in which wheat was grown in the soils with or without the addition of added Cu and/or Zn. Plant dry matter responses to added Cu were recorded in soils with extractable Cu levels <1·1 μg g−1 EDTA, 0·4 μg g−1 DTPA and 0·9 μg g−1 HCl. Responses to added Zn occurred in soils with extractable Zn levels <0·8 μg g−1 EDTA, 0·25 μg g−1 DTPA and 1·4 μg g−1 HCl. Significant linear correlations were found between EDTA-, DTPA- and HCl-extractable Cu and Zn and Cu and Zn uptake respectively by wheat. Correlation coefficients were closer for Cu than for Zn uptake. It was concluded that many sites on the more strongly developed soils of the Canterbury Plains are potentially deficient in Cu and/or Zn and that these can be identified using conventional micronutrient soil tests.