Changes to Avocado Soil Test Mehlich3 Copper Reporting
In mid-2017, NZ Avocado raised concern at the way Hill Laboratories histogram reports portray most Mehlich3 copper (m3Cu) soil test results as being very high or excessive. This was causing alarm with some growers and some resistance to using copper-based sprays for fungus control. We could see a problem existed, and in consultation with industry stakeholders set about finding a solution that would satisfy everyone’s concerns.
We now appreciate the interest in soil copper levels in avocado soils is not only sufficiency of supply to the plant, but also monitoring that the levels are not so high as to preclude alternative land uses in the future or potentially adversely affect soil ecosystems.
We have recently adopted upper interpretive levels for m3Cu in avocado soils based on the potential risk for soil contamination, following identification of the relationship between m3Cu and total Cu on the same samples. This ‘deviation’ in interpretation philosophy will be highlighted in an Analyst’s Comment on each report and is more fully described in our Technical Note: Avocado Soil Testing - Interpretation of Mehlich3 Trace Element Levels.
The upper histogram range levels for Mehlich3 Zn have also been adjusted upwards due to a similar issue arising with typical soil test levels for zinc.
This change refers specifically to Mehlich3 extractable copper and zinc tests, which are indicative-only of potential accumulation of these elements in terms of their eco-toxicological effects. It is recommended that soil 'total' trace element tests be carried out on samples collected by a suitably qualified or experienced consultant where requirements under the National Environmental Standards are to be met.
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