AVOCADO NUTRITION OVERVIEW

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AVOCADO NUTRITION

OVERVIEW

Simon Newett

Department of Primary Industries and Fisheries

Horticulture and Forestry Sciences

Maroochy Research Station


Why bother with nutrition?

Effective nutrition = Yield + Quality = $$$


Why bother with nutrition?

Effective nutrition = Yield + Quality = $$$

Effective nutrition is achieved when …

- each part of the tree

- gets the nutrients it needs

- in sufficient quantity

- when they are needed


THIS PRESENTATION

1. Phytophthora root rot

2. The feeding habits of avocados

3. Soil health

4. The importance of monitoring

5. The complexity of plant nutrition

6. Placement, frequency & application method

7. Fertilising pruned trees

8. The most important elements for avocado


1. PHYTOPHTHORA ROOT ROT

The best avocado fertiliser program

in the world won‟t be much good

if the roots are rotten!






and leaf analysis from

affected trees will be

misleading






and leaf analysis from

affected trees will be

misleading

So … first fix the root rot!


2. FEEDING HABITS

(a) Light feeders

CROP Annual nitrogen (N)

requirement (kg N/ha)

Annual potassium (K)

requirement (kg K/ha)

AVOCADO 100 75

CITRUS 100 110

PINEAPPLE 400 380

BANANA 400 600


(b) Surface feeders

• 80% of the feeder roots are in the top 20cm

• So, its important to have a favourable root

environment - cool & moist in the feeder root zone

• and its suited to small amounts of nutrients often


3. SOIL HEALTH

(a) Why it‟s important for nutrition

• Provide a healthy environment for

feeder roots to grow, thrive and take up

nutrients

• Nutrient retention and availability


(b) Desirable soil health properties

• Physical

– Well aerated/minimum compaction

– Good water holding capacity

– Good drainage/infiltration

– pH 5.5 (root rot vs. nutrient availability)

– Balanced nutrients

– High nutrient holding capacity (CEC)

– High organic matter levels

– Balanced soil fauna & flora

• Chemical

• Biological


Good physical soil properties

adsorbed water

soil particle

air space

capillary water

“…good crumb structure with an open pore structure

and the consistency of crumbly chocolate cake…”


(c) How can you improve soil health?

• Mulch the feeder root area

• Keep feeder root zone moist – not too wet or dry

• Minimise soil compaction

• Avoid heavy single doses of chemical fertilisers

• Add organic matter, e.g. compost & mulch


4. THE IMPORTANCE OF MONITORING

Fertiliser

programs are

largely guess-

work unless

based on

monitoring!

Best to use a

NATA

accredited

laboratory

Soil labs differ but

leaf tissue tests are

consistent across labs


5. COMPLEXITY OF NUTRITION

(a) Soil effects

Nitrogen, potassium

& boron leach easily

High

phosphorus

ties up zinc

Phosphorus and zinc

leach very little, but get

tied up – consider

banding

Calcium and

boron need

each other

Optimum pH 5.5

(6.5 if Mn high)

High pH &/or

calcium ties up

trace elements

Clay soils tie up

phosphorus and

zinc

Pecking order of cations Ca > Mg > K > Na


Effect of soil pH on nutrient availability5.5 6.5


(b) Plant effects

Rootstock effects

• Trees on „Velvick‟ have

higher fruit calcium levels

• „Mexican‟ rootstocks less

efficient at boron uptake

• Trees on „West Indian‟

stocks more tolerant of

high soil pH, salinity &

iron deficiency

Scion effects

• „Fuerte‟ & „Sharwil‟

require less nitrogen

• „Sharwil‟ requires

more boron

Timing

Follow phenological

cycle

Tree size & crop load


6. PLACEMENT, FREQUENCY &

APPLICATION METHOD

• Lime, dolomite & sulphur generally applied

across entire orchard floor

• Apply other nutrients to feeder root area

• Broadcast, fertigate, band

• Little & often (particulary on light soils)

• Foliar applications generally not

recommended…PTO


Foliar applied nutrients?

• Avocado leaf has waxy upper/lower surfaces (next slide)

• No stomata on upper leaf surface

• Foliar applied nutrients lodge in wax and compromise leaf

tissue tests

• Few nutrients are translocated from leaves to other parts of

the plant

• Foliar applied boron targets the flower not the leaf, and these

are minute amounts taken up as a „band aid‟ measure

• Little evidence in the literature (to 2000) to support the use of

foliar applied nutrients in avocado


Scanning Electron Microscope studies

of mature avocado leaves Cross section of upper

surface of avocado leaf

showing continuous wax

layer and absence of

stomata (pores) (X655)

(from Whiley et al, 1988).

Cross section of lower surface

of avocado leaf showing

globular wax layer and

stomata (X775) (from Whiley

et al, 1988).


7. FERTILIZING PRUNED TREES

• Reduce rates in proportion to severity of

pruning e.g. ZERO for staghorned trees

• Base the rates on canopy size

• Take into account N in mulched prunings

under tree – this is substantial

• Monitor colour of canopy and the leaf levels

• If in doubt, err on the low side


8. ESSENTIAL NUTRIENTS

Major (macro) elements

– Nitrogen

– Phosphorus

– Potassium

– Calcium

– Magnesium

– Sulphur

Trace (micro) elements

– Copper

– Zinc

– Iron

– Manganese

– Boron

– Silicon (?)


FOUR NUTRIENTS REQUIRING CAREFUL

MANAGEMENT IN AVOCADO

I. Nitrogen

II. Boron

III. Calcium

IV. Zinc


(i) NITROGEN (N)

– the dynamite of plant nutrients!

You need to control it!


Importance of balance

Too much NToo little N

OPTIMUM

Handle the “dynamite” with care

Greater fruit drop

Small fruit


Effect of N rate on yield & quality

Optimum N

level

Yield

Nitrogen level

Quality


Nitrogen vs. Calcium

• If you apply too much nitrogen, the

calcium levels in the fruit decrease to

the detriment of fruit quality

N Ca


Tailoring nitrogen rates (from AVOMAN)

• Standard annual rate:

– Young tree not yet bearing 70 g N/m2 of canopy area

– Young tree starting to bear 40 g N/m2

– Bearing tree 14 g N/m2

• Crop load: up to 50% more for heavy crop

• Two crops on tree simultaneously: 10% more

• Staghorned & not yet flowering: Zero


Tailoring nitrogen rates (cont.)

• Fuerte & Sharwil: 20% less N than Hass

• Soil Type: 20% more on lighter soils

• Adjustment for leaf N analysis levels:

from 50% more to 50% less or none

• Leaching: up to 20% more


Fruit

Leaf

Flower

Fruit fall

Bud

Bundaberg

Hass

Timing of nitrogen

- Most import need is in Autumn (after fruitlet drop)

- At other times too but in smaller amounts and at frequent intervals

- Reduce through winter

N timing…


(ii) BORON (B)

-tricky to get right!

Potentially dangerous if you don‟t!


Factors that must be considered to

determine an appropriate boron rate

• Soil texture (rates

vary significantly)

• Variety

• Rootstock

• Tree size

• Leaf level

• Soil level

• Degree of leaching

(leaches very easily)

• Soil pH and/or

calcium level

• Root rot status

• (B level in irrig water)


(iii) CALCIUM (Ca)

- necessary for fruit quality, robustness

• The higher the Ca in fruit the better the quality and shelf life

• Calcium is taken up passively in the water stream but only for the first 6 weeks or so of the fruit‟s development until its stomata close up (at this point they turn into lenticels)

• Boron & calcium require each other for effective operation

• Excessive N suppresses Ca in fruit(cont.)


Calcium (Ca) continued…

• Attempts to improve fruit Ca levels by various Ca applications have failed dismally

• Recent trial by Peter Hofman applying regular doses of micro-gypsum through the irrigation actually reduced fruit quality –maybe the excessive Ca applied to the soil displaced K and made it deficient (unbalanced)

• Rootstocks affect fruit Ca e.g. „Hass‟ on „Velvick‟ = higher Ca


(iv) ZINC (Zn)

- plays „hard to get‟

• Tied up in the soil by high phosphorus

• Tied up in the soil by high pH

• Tied up in red (clay) soils

• For these reasons it is often recommended

that you band it

• Lower rate required if you have a good

mulch (zinc can be taken up by feeder

roots in the mulch before it reaches the

soil and gets tied up in soil)


THIS PRESENTATION

1. Phytophthora root rot

2. The feeding habits of avocados

3. Soil health

4. The importance of monitoring

5. The complexity of plant nutrition

6. Placement, frequency & application method

7. Fertilising pruned trees

8. The most important elements for avocado


„TAKE HOME‟ MESSAGES

1. First fix Phytophthora!

2. Effective nutrition is more than just applying fertiliser

3. Take monitoring seriously

4. Avos are surface feeders – „baby‟ the feeder root zone

5. Apply little and often to where the feeder roots are

6. Nutrition is complex – study it &/or get good advice

7. Carefully manage Nitrogen, Boron, Calcium & Zinc


Until next time . . .


What deficiencies or toxicities are

these…..?


Nitrogen deficiency

Yellow leaf

can also

be boron

deficiency


Potassium deficiency

Note black dead spots

Death of inter-veinal area -

Yellowing then death of leaf margins especially leaf tip


Magnesium deficiency

• Note dark green

veins

• Inter-veinal colour

different to iron

deficiency


Boron deficiency

Shot-hole


Boron deficiency

Hooked and

corky fruit


Death of

flowering

shoots

Boron deficiency


Boron deficiency

“Knuckling”

“Arthritis”


Boron deficiency

Trunk

cankers

Watery

soaked

blisters


This leaf symptom plus leaf and fruit drop

Boron toxicity

If you

suspect B

toxicity

contact your

agronomist

immediately

– need to

start

corrective

measures

ASAP


Normal fruitDeficient fruit

Zinc deficiency


Normal fruitDeficient fruit

Zinc deficiency

•<40mg/kg leaf

• Readily tied up so

apply as band along

drip line in sprinkler

area

• Availability is soil-

type dependant, pH

and phosphorous

levels also effect

availability

• Foliar sprays are

ineffective -

contamination risk

with all foliars


Small mottled leaves, short internodes on stems resulting in

leaves bunched together

Zinc deficiency


More common in

areas where soil

pH &/or calcium

is very high

Iron deficiency


Associated with low pH.

Worse in wet conditions.

Manganese toxicity

Manganese oxide

“concretions” in

the soil (hard shiny

black particles)


Chloride toxicity/burn

• Avocados very sensitive to chloride

• Death of leaf tip and margins

• Some soils have high chloride levels and use of KCl can exacerbate this problem

• Use of irrigation water high in chloride – can creep up on you

• Dry years can be dangerous


The end

AVOCADO NUTRITION OVERVIEW

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