Organic NZ – September 2019

Advocate • Connect September/October 2019 47

Farming and horticulture

be growing in a urine patch – take time to
pick the smaller stalks and leaves of the
majority of clover that represents your real
target for understanding.

Testing for trace elements
Soil testing is useful for many trace
elements, while for other trace elements
there may be little correlation between a
soil test and a plant test. In all cases, it is the
plant test that will give a reliable assessment
of what has been taken up by that particular
crop at that time of the year.
Try to avoid soil contamination on the
plant parts that you are sampling, because
soil can exaggerate the levels of iron, cobalt
and some other trace elements. Avoid also
sampling leaves that are starting to senesce
or die, or that are obviously infected with
disease. Also generally avoid very young
leaves unless that is part of a standard
protocol for that particular crop.

Testing fodder crops and pasture
If your interest is for animal nutrition, then
you will want to take a plant test that is
representative of what is being grazed. This
is then quite different from a white-clover-
only test, which is aimed at assessing plant
nutrition.
The mineral nutrition of plants will
change dramatically with the time of year
and according to the varying proportions

Above: A white-clover-only sample assesses a

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is unlucky ( just before is ideal).

Photo: iStock/ouchi_iro

Above: Foliar tests show what the plant has been able to take up from the soil.
Photo: iStock/stevanovicigor

of different plants in the pasture. So

make sure that the sample includes a fair

proportion of the different plants present

in the pasture, and that you interpret the

results in terms of what time of year it is.

Spring growth will be lusher with some

elements at correspondingly lower levels,

but potassium could be relatively high and

magnesium availability may therefore be

low. In contrast, testing stunted plants in

dry summer conditions may reveal high

levels of elements that could actually be low

in plants that are more actively growing.

Dr Tim Jenkins is a microbiologist

and agricultural scientist travelling the

world with a base in Christchurch.

A plant test will give a reliable assessment

of what has been taken up by that

particular crop at that time of the year.