Testing for Healthy Avocado Crops
In avocado orchards, autumn is widely accepted as the best time of year to collect soil and leaf samples for nutrient testing. Collecting both the soil and leaf samples at the same time not only provides ease, but has the added benefit of ensuring soil samples are taken at the same time each year. Over time, this annual practice builds a soil fertility history which shows long-term trends.
In autumn, avocado trees are in a quiet state following the summer flush growth, so this is an ideal time for leaf testing. In 2021, we were interested to understand if there was any significant difference in avocado leaf mineral content results across the year. We interrogated our results database for this exercise. It is important to state that this was not a controlled survey as we cannot verify the sampling methods that were used. Additionally, there were small sample numbers for some months. The below whisker box plots show the median value for leaf nitrogen and boron with the corresponding standard deviations and dots as outliers.
Analysis of leaf samples taken across the year, outside of the traditional autumn time shows that the median levels for most elements is generally consistent across the months. For example, while there was some comparatively high variation in some months for nitrogen, the median across all months was within the accepted interpretive range of 2.4% to 2.9% (Figure 1).
Figure 1: Avocado leaf Nitrogen results from samples analysed at Hill Laboratories in 2021.
For boron, more variation in the median results was evident both within and across months, with a decline in winter months (Figure 2). Based on autumn sampling convention, the accepted interpretive leaf boron level in autumn is 30 to 50 mg/kg.
Figure 2: Avocado leaf Boron results from samples analysed at Hill Laboratories in 2021.
The above results support the recommended practice of avocado leaf sampling in the autumn. It also suggests that the accepted interpretive ranges in general would be applicable for spring also. Spring leaf sampling may be useful to diagnose any suspected nutrition problems at that time.
In recent years, orchardists have requested additional total copper and/or cadmium testing on top of their standard soil tests for the purposes of monitoring any potential heavy metal accumulation or as part of a sustainability programme.
Did you know?
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More information on sampling protocol information and the standard tests to request for avocado testing can be found in the Avocado Crop Guide or by contacting us at ag.csm@hill-labs.co.nz or 0508 HILL LABS.
