1. Fertilization of Macadamia Nuts
Fertasa
Soil Fertility & Plan Nutrition Symposium,
23 August 2017,
CSIR, Pretoria
Gerhardus P. Nortjé

2. Abstract
Much research in macadamia, but not so much on fertilization and nutrient
requirement in S.A.
Macadamias need low levels of P and Ca, but high Fe levels
Fe-deficiencies show in tree dieback
(gradual deterioration in the trees’ condition,
with fewer and sparse leaves, lower production)
Macadamias require well-drained soil with pH (H2O) of not less than 5.5.
N, P and K levels should be replenished as required by the tree,
including removal of nutrients by the crop
South Africa draws much on macadamia nutrition from Australia, California and Hawaii
Common nutritional problems exist in all these countries
Some focus on practical experience in macadamias in South Africa

3. Background to macadamias production in South Africa
The Macadamia Industry in S.A. is growing rapidly.
Currently, still the largest producer in the world (since 2015),
with Australia not far behind.
In 2012, the industry had ha established.
Since then growing by 1500 ha per year.
Now stands at ha (S.A).
Southern Africa (S.A, Swaziland, Malawi, Mozambique) at ha,
but plantings growing rapidly in these other Southern African countries.
Biggest growth in S.A. is in Mpumalanga and KZN provinces.
Mpumalanga still the largest producing province.
The updated current (2017/2018) forecasted crop
is tons of nut-in shell (1.5% kernel moisture content),
which is slightly lower than the previous forecast of tons.

4. The Macadamia tree (1)
The macadamia tree is a member of the Proteacea family and native to the subtropical,
coastal rainforests of eastern Australia.
Native trees can still be found in the few remaining small patches of natural subtropical forest
in northern New South Wales and southern Queensland.
There are seven species of macadamia endemic to Australia
and two are grown for their edible nuts:
a) Macadamia integrifolia (smooth shelled) and
b) Macadamia tetraphylla (rough shelled).
Macadamia trees are evergreen and grow slowly up to m after 10 to 15 years.
First crop after 4 years.
‘Beaumont’ remains the most-widely planted cultivar,
comprising 49% of the total tree sales, followed by A4 (22%) and 816 (16%).
Insects, especially bees, have an important role in pollination.

5. The Macadamia tree (2) Macadamias are not heavy feeders
and their lateral root systems with lots of fine roots and proteoid roots
are extremely efficient at absorbing both phosphates and calcium,
even in soils where concentrations of these nutrients are relatively low.
A cluster of the tightly knit small rootlets known as proteoid roots growing from a fine root of macadamia. Proteoid roots are found in all species of the Proteaceae family and are indicative of a healthy macadamia root system, playing an important part in nutrient absorption and especially the uptake of phosphorous.
Source: Philip Lee (Mac 101)

6. Macadamia tree phenology (1)
For macadamia orchard management and fertilization,
the phenological cycle is the main driver of the timing of management inputs,
rather than the calendar.
The phenological cycle can in short be described as follows:
May - flower initiation
August/September - main flowering and root growth
September/October - nut set
November/January - nut growth and oil accumulation (nut growth increases linearly up to middle December, where after the nuts convert starch into oil. The oil accumulation period is very important because nut quality relates very well with oil content)
March/April/May - mature nut drop. Varies between cultivars and season

8. Crop nutrient removal and soil and leaf sampling
A yield of 3.5 tons NIS/ha (which is the average viable crop/ha),
would remove about 63 kg of N, 3.5 kg of P,
70 kg of potassium (K) and 17.5 kg of sulphur (S),
35 kg of Calcium (Ca) and 5.25 kg of Magnesium (Mg),
respectively, per hectare per annum.
The aim of a fertilization program should be to keep the tree and the root system healthy,
and to replace, at least, the amount of nutrients removed each year by the crop
(Mostert, pers. comm.).
Soil and leaf sampling
Soil sampling should be done every 2 years (Nortjé, personal observation),
while leaf samples should be taken from marked trees every year.
This is sufficient to monitor soil fertility over time.
A history of soil fertility and nutrient status in orchards should be built over time.
Leaf samples must be taken during October/November each year
by sampling the fourth leaf behind the growing point of an actively growing shoot
or a shoot that has recently completed a growth flush,
on which the terminal bud is dormant (Mac 101).
Only leaves from healthy plants must be sampled.

9. Problems and challenges regarding macadamia production and fertilization (1)
Since 2011/2012
Macadamia trees, showing very severe nutrient deficiency symptoms,
correctly identified as iron deficiency symptoms (tree dieback).
Bray-1 soil P levels of over 50 mg.kg-1
have negative impacts on macadamia crop performance
The Bray-1 soil P levels in the problem orchards mentioned above
always exceeded 100 mg.kg-1, in most cases
>200 mg.kg-1 and even up to 300 or 400 mg.kg-1.
Application of chicken manure
In some cases, farmers have been applying 30 tons of chicken manure per hectare per year,
whereas one would normally not recommend more than two tons per hectare.

10. Problems and challenges regarding macadamia production and fertilization (2)
Crop K-application responses
On soils where citrus gave positive responses to K there were no yield responses
by papaya, litchi, avocado, coffee, macadamia nut and pecan nut.
Sensitivity to Fe-deficiencies
Macadamias developed on highly weathered soils
with abundant plant-available Fe in high rainfall areas in Australia.
Therefore, the trees are very sensitive to Fe deficiencies.
Plant and soil analyses results from macadamia orchards with serious Fe-deficiencies
- a common feature was that the orchards had extremely high P levels.
Therefore, the Fe deficiencies were P induced Fe deficiencies.
Macadamias extremely vulnerability to high soil P levels
Highly weathered acid soils (Australia) and thus extremely low plant-available P levels.
Therefore, they have developed root systems that feed exceptionally well on P.
Due to this ability to feed very strongly on P
they absorb very high amounts of P from soils with adequate to high P levels.

11. Problems and challenges regarding macadamia production and fertilization (3)
Unfavourably high pH levels
Publications from Hawaii indicate that Fe deficiencies in macadamias
are found where the soil pH is unfavourably high.
The pH (H2O) should preferably not be higher than between 5.5 and 6.0
or pH (KCl) not higher than between 4.5 and 5.0.
The effect of the combination of such high pH and the ridiculously high P levels
on Fe nutrition is disastrous for macadamia trees.
A pH (KCl) of 6.5 is far too high for macadamias.
Sub-soil compaction and nutrient deficiencies – several cases of Fe-deficiency symptoms –
Nutrients cannot be taken up – therefore Fe-deficiency!

12. Dying tree due to Fe-deficiency Breaking up of compacted layers
Problems and challenges regarding macadamia production and fertilization (photos)
Sub-soil compaction
Dying tree due to Fe-deficiency
sub-soil compaction
Soil crusting
Breaking up of compacted layers

13. Soil and leaf analyses norms
ANALYSIS RESULT
NORM
SOIL
pH (H2O)
pH (KCl) P
30-75 (Bray 1) (>100 is toxic)
K (exchangeable)
ppm
Ca (exchangeable)
ppm
Mg (exchangeable)
ppm Fe
15-25 ppm
Na (exchangeable)
< 5% of exchangeable cations (cmolc/kg)
Ca (% of total CEC)
65-70
Mg (% of total CEC)
20-25
K (% of total CEC)
6-10
Acid saturation (exchangeable)
< 10 %
Cation ratios (cmolc/kg):
Ca/Mg
Ca+Mg/K
10-20
LEAF N % % K % Ca % Mg S % B
40-75 ppm Zn
15-50 ppm Cu
5-10 ppm Mn
ppm
ppm

14. Soil amelioration/preparation
The correction of soil acidity and, in many cases soil phosphate levels,
should be done during land preparation and before planting.
Soil ameliorants such as lime, gypsum, potassium and phosphate.
Thorough incorporation of these soil ameliorants and the aeration of the soil,
facilitated by deep ripping, will provide an optimal environment for root development.
Macadamias need lots of organic matter, so the incorporation of as much compost as possible
(up to 10 tons per hectare) prior to planting,
is an added benefit, especially on sandy soils.
Beware of using large volumes of chicken manure,
as well as dairy manure in the compost, as the high phosphate proportion
of chicken manure can lead to phosphate induced iron deficiency,
where chicken manure rich compost is used continuously over a number of years.

15. Nutrition of non-bearing trees (planting to year 3) / Nutrition of bearing trees (tree age 4 plus)
Immediately after planting (non-bearing trees),
the trees need to be given time to settle into their new environment,
overcome any transplanting shock and for the roots
to begin growing out of the potting medium into the surrounding soil.
So, it is appropriate not to apply any fertiliser
to newly planted trees for the first 6 to 8 weeks.
Bearing trees (4 years plus)
Analysis of the analytical data is more meaningful when recommendations are
based on historical trends rather than on only one year’s results.
Any nutrition management programme must take the following onto account:
a visual appraisal of the trees (including yield data),
historical soil analysis data-historical leaf analysis data and,
any previous fertilizer programmes.

16. Conclusions and recommendations
Although the Australian and Hawaiian guidelines on the fertilization of macadamias,
as well as many years of experience in macadamia production and fertilization,
have done well for the commercial production of macadamia in South Africa,
we need urgently to start our own research on macadamia nutrition.
South African climatic conditions and soils differ widely from those in Australia and Hawaii,
so the guidelines developed for those countries and for their conditions
cannot just be copied and applied elsewhere
without testing and adapting it.
Research on different cultivars, with regards to crop nutrient removal,
nutrient norms, under different climatic conditions and different soil types,
as what is currently being done with regards to irrigation research on macadamia in South Africa, should be conducted urgently.