Fertilization of Macadamia Nuts

Gerhardus P. Nortjé College of Agriculture and Environmental Sciences, Department of Environmental Sciences, Florida

Campus, Unisa, South Africa

Presenter: Gerhardus Nortjé, College of Agriculture and Environmental Sciences, Department of Environmental Sciences, Florida Campus, Unisa, P.O Box 392, Florida, 1709, +27 (011) 471 2286,

nortjgp@unisa.ac.za

Abstract

Much research has been done over the past 10 years on macadamia production, and pest and

disease management, but very little local research has been done on macadamia fertilisation and its

nutrient requirements. Macadamias do not tolerate poor nutrition. The first signs of deficiencies are

quickly shown in a decrease in production, gradual deterioration in the trees’ condition, with fewer

and sparse leaves. 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

(FSSA, 2003). This presentation draws on the information available from local experience but also

from overseas research, and the general principles of tree nutrition in subtropical fruit tree crops.

Information on leaf and soil sampling is supplied as well as “norms” for leaf and soil analyses results

and some general practical fertiliser guidelines. Practical nutrition problems, experienced first hand

are also highlighted.

Introduction

According to tree sales data received from nurseries, the macadamia industry is still growing rapidly.

The rate of growth is on the increase in all provinces (SAMAC, 2017). In 2016 the South African

macadamia industry planted at least 3 870 hectares (ha). Mpumalanga remains the major

production region in South Africa, still with the highest growth rate. The North Coast of KwaZulu-

Natal has responded to this growth for macadamias and new plantings in this province is increasing

substantially.

According to the latest formal tree census in 2012 there were approximately 19 000 ha established

in South Africa (Nortjé, 2012). Since 2012 the hectares planted increased by 1500 ha per year.

Current estimates of hectares in southern Africa is 28 000 hectares (SA, Swaziland, Malawi,

Mozambique), of which 26 000 is in South Africa (SAMAC, 2017). The updated current (2017/2018)

forecasted crop is 41 430 tons of nut-in shell (1.5% kernel moisture content), which is slightly lower

than the previous forecast of 42 000 tons. South Africa became in 2015 officially the largest producer

of Macadamia nuts in the world.

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The macadamia tree is a member of the Proteacea family and native to the subtropical, coastal

rainforests of eastern Australia, where native trees can still be found in the few small patches of

natural subtropical forest remaining in northern New South Wales and southern Queensland. Most

of the macadamia production is concentrated in Australia, South Africa, Kenya, and the USA. It is

therefore best suited to a coastal subtropical climate (Mac 101).

There are seven species of macadamia endemic to Australia and two are grown for their edible nuts:

Macadamia integrifolia (smooth shelled) and Macadamia tetraphylla (rough shelled) the nut of

which is not as good for roasting as M. integrifolia. Macadamia trees are evergreen and grow slowly

up to 12-15 m after 10 to 15 years (Mac 101). Most cultivars are partly or completely self-

incompatible so insects, especially bees, have an important role in pollination. ‘Beaumont’ remains

the most-widely planted cultivar, comprising 49% of the total sales, followed by A4 (22%) and 816

(16%). Mpumalanga remains the province with the newest plantings, absorbing 49% of the total

trees produced, followed by KwaZulu-Natal (33%), Limpopo Province (10%), Western Cape (3%) and

other destinations (5%) (SAMAC, 2017).

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 (Figure 1).

Figure 1 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).

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Tree phenology

For macadamia orchard management and fertilization, the phenological cycle (Figure 2) is the main

driver of the timing of management inputs, rather than the calendar. The phenological cycle can in

short be described as follows (FSSA, 2003):

May – flower initiation,

August/September – main flowering,

September/October – nut set,

November to January – nut growth and oil accumulation (Nut growth increases linearly up ti

middle December, where after the nuts converts 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.

Figure 2 Macadamia phenology chart

Vegetative growth (commence from about mid-July) - during the growing season between the

months of August and May, there will be four vegetative flushes on average and 4 rest periods.

Given this knowledge, management interventions such as fertiliser and water application can be

timed to fall in line with the needs of the tree at a given point in the phenological cycle. Hence

the chart (Figure 2) indicates that we should apply 25% of the annual nitrogen requirement in

July, 40% in September, 25% in November and 10% in January. The rationale behind this

nitrogen application timing is that we know that nitrogen stimulates vegetative growth, and

although the work of Stephenson et al showed the natural vegetative flush pattern to be a minor

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peak in spring and a major peak in summer, there is good reason to try to reverse this situation

in commercial production. The logic being that if we stimulate vegetative growth as much as

possible in the spring flush, we can minimise the depletion of carbohydrate reserves, shown in

the chart to occur in August / September.

So, nitrogen is used to stimulate the spring and summer vegetative flushes and then reduced to

a small amount in January (up to 10% of the total N can be applied in January) and then stopped,

so as to reduce the late summer / autumn vegetative flush. Here the reasoning is that the tree

needs all of the energy to be channelled to the kernel for the conversion of sugars to oil, with as

little energy as possible being diverted into new vegetative growth. The goal is to produce as

many nuts as possible that have the required oil content of 72% to be classified as premium

grade kernel and to ensure that “immature” kernel, those with less than 72% oil, is minimised.

Here the reasoning is that the tree needs all of the energy to be channelled to the kernel for the

conversion of sugars to oil, with as little energy as possible being diverted into new vegetative

growth. The goal is to produce as many nuts as possible that have the required oil content of

72% to be classified as premium grade kernel and to ensure that “immature” kernel, those with

less than 72% oil, is minimised.

Root growth - As illustrated in figure 2, root growth flushes follow a similar pattern of

distribution over the season as vegetative growth flushes, with the peaks of root growth activity

in spring (August / September) and late summer (mid-January to mid-April). In terms of

managing root growth to ensure healthy and vigorous root systems, it is therefore appropriate

to apply the phosphate fertiliser required to stimulate root growth in July/August and

December/January, so that it is available for these root growth flushes. Growing as it does in its

natural habitat as a small to medium sized tree in the lower layers of coastal sub-tropical forest,

the macadamia tree has a shallow root system designed to forage for nutrients in the top few

centimetres of soil and decomposing leaf litter on the forest floor – an environment high in

carbon and organic matter. In commercial production, we have removed the tree from this safe

haven, exposing it to full sunshine and expecting it to perform, at times in barren soil conditions

low in carbon and organic material.

The need to nourish and care for macadamia tree root systems is often neglected (because we

cannot see them) and cannot be over emphasized. This is best achieved by trying to mimic the

conditions found on the forest floor in the natural habitat:

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Well aerated soil at planting through appropriate soil preparation – deep ripping to a depth

of one metre. Roots need air (as well as water and nutrients),

Use of mulch, either plastic or natural materials, to preserve topsoil moisture and minimise

weed competition,

Improve and maintain adequate levels of carbon and organic matter by applying as much of

the nutrient requirement using organic sources to promote fine root growth and

development of proteoid roots

Nut growth - Flower buds will begin to emerge from mid-July onwards, with the flowering period

extending over approximately three months thereafter (August to October). In commercial

production, the ideal is to have a once off flowering and fruit set over a maximum period of 4 to

6 weeks, so that all of our management inputs can be planned to focus on the growth,

development and maturation of this one nut crop. In practice, however, the timing, extent and

duration of flowering is dependent on location, climate and cultivar.

Fortunately, in South Africa and more specifically in KwaZulu-Natal (one of the main reasons it is

the best place in the world for macadamias), a fairly concentrated flowering takes place in most

seasons. Flower buds are initiated in autumn following accumulation of about 120 hours below

18°C, after which they remain dormant until the onset of warmer weather from mid-July. Most

flowers are produced on wood that is two years old which is growing more horizontally than

vertically, and from fruiting spurs.

Carbohydrate reserves - As depicted in the phenology chart (figure 2), carbohydrate reserves

reach a peak in late July/early August and are then depleted in the spring flush to a low point

around end September/early October. Carbohydrate reserves are then boosted again by the

main summer flush to a second peak in early February before being drawn down again by the oil

formation process to a second low point which coincides with the completion of the nut

maturity process by about April.

Oil accumulation/Nut maturity - The conversion of the sugars in the kernel to oil begins when

the nut has reached full size and the shell has hardened. Although the phenology chart shows

some overlap between these processes of fruit growth, shell hardening and oil accumulation, it

clearly shows that there is no further increase in fruit size after the end of December, when fruit

size remains constant at a diameter of about 30mm. The process of oil accumulation is

completed in about 14 weeks, at the conclusion of which most of the nuts in the tree can be

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considered “mature”, containing around 72% oil or more. There are differences between

cultivars.

Crop nutrient removal, soil and leaf sampling, soil and leaf analyses norms and fertilizer guidelines

Crop nutrient removal

A yield of 3.5 tons NIS/ha (which is the average viable crop/ha), would remove about 63 kg of

nitrogen (N), 3.5 kg of phosphorous (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 keep the tree and the roots system healthy, and to replace at least

the amount of nutrients removed each year by the crop (Mostert, 2015. pers. comm.).

Soil and leaf sampling

Soil and leaf samples should be taken from marked trees every year (leaves), and in the case of soil

sampling every 2 years (Nortjé, personal observation), which is sufficient to monitor soil fertility over

time. Build a history of soil fertility and nutrient status in your orchards 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.

Soil and leaf analyses norms (FSSA, 2003, adapted by Nortjé)

ANALYSIS RESULT NORMSOIL

pH (H2O) 5.5-6.5pH (KCl) 4.5-5.5

P 30-75 (Bray 1) (>100 is toxic)K (exchangeable) 200-300 ppm

Ca (exchangeable) 1200-1800 ppmMg (exchangeable) 180-250 ppmNa (exchangeable) < 5% of exchangeable cations (cmolc/kg)Ca (% of total CEC) 65-70Mg (% of total CEC) 20-25K (% of total CEC) 6-10

Acid saturation (exchangeable) < 10 %Cation ratios (cmolc/kg):

Ca/Mg 2.5-5.0Ca+Mg/K 10-20

LEAFN 1.2-1.6 %P 0.08-0.10 %K 0.6-0.7 %

Ca 0.6-0.9 %Mg 0.08-0.10 %S 0.18-0.25 %B 40-75 ppmZn 15-50 ppm

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Cu 5-10 ppmMn 100-1000 ppm

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,

required on the basis of soil analyses results from samples taken after land clearing, should be

broadcast over the entire surface area prior to ripping and disking. Thorough incorporation of these

soil ameliorants and the aeration of the soil facilitated by deep ripping, will provide an optimal

environment for root development (Mac 101).

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 and soils

subjected to years of cultivation prior to macadamia establishment. Organic material used must be

thoroughly composted before application, otherwise the composting process will continue on the

soil after application, actually withdrawing nitrogen from the soil surface until the composting action

is complete. Beware of using large volumes of chicken 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.

Nutrition of non-bearing trees (planting to year 3)

Immediately after planting, 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.

Nutrition of bearing trees (tree age 4 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 (Mac 101):

a visual appraisal of the trees (including yield data),

historical soil analysis data-historical leaf analysis data and,

any previous fertilizer programmes.

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Table 1 Basic nutrient requirements (g/tree/year) for macadamia (Kuperus & Abercrombie, 2003)

Tree age N P Single Superphosphate (10.5% P) K KCl or (K2SO4)

1 56 21 200 40 80 (95)

2 90 21 200 50 100 (120)

3 112 25 240 75 150 (180)

4 100-160 30 285 125 250 (300)

5 125-200 33 315 150 300 (360)

6 150-250 36 350 200 400 (475)

7 175-280 45 430 250 500 (600)

8 200-300 50 480 300 600 (715)

9-10 225-340 55-65 520-620 350-400 700-800 (830-950)

11-12 250-420 65-79 620-750 425-475 850-950 (1000-1130)

13-14 400-60 84-105 800-1000 500-575 1000-1150 (1200-1370)

15+ 450-800 105-142 1000-1350 600-700 1200-1400 (1430-1700)

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Problems and challenges regarding Macadamia production and fertilization

Since 2011/2012 - macadamia trees, showing very severe nutrient deficiency symptoms,

correctly identified as iron deficiency symptoms. In some cases, tree branches were half dead

(called die-back). The cause of the problem was every time exactly the same when looking at soil

analyses results data: Absolutely grossly high plant-available soil P levels that render Fe

unavailable to plants and/or immobilize Fe in the plants, making it physiologically inactive . In

every case this was further aggravated by far too high soil pH levels, giving a deadly combination

in regard to Fe, Zn and other cationic micro-nutrients. Macadamias are, very sensitive to iron

deficiencies.

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. These are realities. In the

particular cases, the horribly high P levels were not built up by application of chemical fertilizers,

but by injudicious application of cattle manure, specifically manure from dairies, or composts in

which 50 to 70% of dairy manure was included. This has been proven in a statistical research trial

on soil health during 2012. There are numerous research publications from California that warn

against injudicious application of dairy manure because of the danger of running into harmful P

levels as a result of it. According to these publications the diet of dairy cows includes a very high

P level and some farmers include even more. According to the publications more than 70% of

this P is excreted in the manure (Laker, 2017. Personal communication).

Application of chicken manure – In some cases farmers have been applying 30 tonnes of chicken

manure per hectare per year, whereas one would normally not recommend more than two

tonnes per hectare. Chicken manure has a very high P content (1.5%) compared with the 0.5% of

ordinary cattle kraal manure. So, by applying 30 tonnes of chicken manure per hectare per year it

would mean that he was applying 450 kg P per hectare per year.

Crop K-application responses - During more than 20 field experiments with 12 subtropical fruit

crops and nuts at 14 localities over a period of 25 years the findings were as follows

(Langenegger, 1986): On soils where citrus gave positive responses to K there were no yield

responses by papaya, litchi, avocado, coffee, macadamia nut and pecan nut. In the case of

papaya and pecan nut, and to a lesser extent with macadamia nut, the responses rather tended

to be negative.

Sensitivity to Fe-deficiencies - Several crops are highly sensitive to Fe deficiencies. Amongst the

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best known of these are soybeans (or soya beans), citrus, macadamia nuts and peaches.

Macadamias developed on highly weathered soils with abundant plant-available Fe in high

rainfall areas in Australia. So, 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. So, the Fe deficiencies were P induced Fe

deficiencies (Laker, 2017. Personal communication).

Macadamias extremely vulnerability to high soil P levels - Macadamias originate from an area

in Australia with highly weathered acid soils 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.

Unfavourably high pH levels - Publications from Hawaii indicate that Fe deficiencies in

macadamias are found where the soil pH is unfavourably high. In the soil analyses results

mentioned above from South African macadamia orchards with severe Fe deficiencies, the pH

(KCl) was almost invariably 6.5 or higher. This is equivalent to a pH (Water) of 7.5 or higher. This

is far too 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 absolutely disastrous for macadamia trees.

For the vast majority of crops the optimum pH (Water) range is believed to be between 5.5 and

7.0, equivalent to a pH (KCl) of between 4.5 and 6.0. For infertile sandy soil, it should be around

5.5, i.e. pH (KCl) around 4.5. For fertile clay soils, it can be towards the upper side. For

macadamia nuts the optimum pH (Water) is between 5.0 and 6.5, i.e. a pH (KCl) of between 4.0

and 5.5. Thus, it can be seen that a pH (KCl) of 6.5 is far too high for macadamias.

Sub-soil compaction and nutrient deficiencies – several cases of Fe-deficiency symptoms were

investigated by the author in amongst others, the Barberton area. Macadamias were planted on

previous tobacco farms, on soils with high fine sand and silt contents. These soils are highly

susceptible to soil crusting and sub-soil compaction. Smaller trees did not have the symptoms,

but as soon as the trees got bigger (≥4 years), the root systems could not sustain the large trees,

with result of tree dieback (Fe-deficiency). Thorough investigations indicated severe sub-soil

compaction and its symptoms (Tree dieback, shallow roots, sub-soil compacted layers, soil wet

below the compacted layer, and dry above the compacted layer). Nutrients cannot be taken up –

therefore Fe-deficiency!

Conclusions and recommendations

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Although the Australian and Hawaiian guidelines on the fertilization of macadamias, as well as many

years of experience in macadamia production and fertilization in South Africa, have done well for the

commercial production of macadamia, South Africa needs to urgently start its own research on

macadamia nutrition. Local climatic conditions, and soils differ widely from those in Australia and

Hawaii, so that 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.

References

de Villiers, E.H. and Joubert, P.H. (Editors). 2003. The Cultivation of Macadamia. 2003. ARC-

Institute for Tropical and Subtropical Crops.

Kuperus, K. H. and R. A. Abercrombie. 2003. Fertilization. In: The cultivation of Macadamia (ed.

E. A. de Villiers), pp. 89 – 99

Laker, M.C., Nortjé, G.P & Schoeman, S.P. 2012-2017. Personal and email communication with

regards to macadamia recommendations and fertilizer problems in South Africa.

Mostert, 2015. Personal communication. Crop removal by macadamias.

Nortjé, G.P. 2006-2017. Personal Macadamia fertilizer recommendations

Macadamias 101. 2016. An Introductory Guide to Macadamia Production. Compiled by Phillip

Lee, on behalf of the Southern African Macadamia Growers’ Association

FSSA Fertilizer Handbook, 2003. Fifth revised edition, FSSA. Pretoria

SAMAC website www.samac.org.za. Best practice videos: Soil and leaf sampling

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