Bio-stimulants in

Sub-tropical

crops

Bram Snijder

Afrupro Exporters

Aim of the talk

Supply some back ground on the

Subtropical industry

Current status with regard to fertiliser

recommendation

Work done on Bio-stimulation/control

Future research needed

Introduction

Subtropical industry small in comparison to

the deciduous industry but expanding

Excludes Citrus Industry

Exported as exotic fruit into “niche” markets

Local market still relatively small and often

exclusive

In this talk we concentrate on the 4 industries

which fall under the Sub-trop umbrella

Introduction

Introduction

Crops mostly grown in North-Eastern South Africa

Limpopo – 41% of area, followed by Mpumalanga – 35%

KZN – growing area – especially for the late market opportunity

4 grower association – avocado = strongest in terms of its member cohesion

Always been voluntary organisations

Intro – Avocados

Originated in the central American Forests

from sea level up to 1500m altitude

Under-story tree in rain forest

Its drive is to reach sunlight = strong focus

on growth not fruiting

Very quickly irradiance saturated

Rapid system “shutdown” in warm sunny

conditions

Intro - Avocado

Initial growing system is extensive

Average tree age about 15 years+

Low tree density (100 plants/ha)

Large trees – low productivity/economics

Low yield

Fair percentage of dry-land (20%)

Little cultivar development

Low research budget

Intro - Avocados

Newer plantings more intensive

Newer cultivars

Higher densities (up to 400 plants/ha)

Better yields

Smaller trees (better productivity/economics)

Research started into protective growing in

conjunction with 2 universities

Intro - Litchis

Originated from Tropical South - China

Forest tree with low yield potential

More tropical climates

Climate marginal in South Africa

New cultivars being imported from Israel

and Australia

Extremely small research budget

Intro - Litchis

Trees are grown extensively (100 –

150trees/ha)

Extremely large until recently

Pruning systems introduced

Yield improvements through flush control

in autumn

Yields are very climate sensitive need

either cold or drought stress ± April

Intro - Mango

Originated from India

North-eastern areas in the foothills of the

Himalayas

Wide climatic adaptations

Grown mostly for local market and

processing

Quality issues are largest problem

Intro - Mango

Grown more intensively (800 trees/ha)

Better yields/ha than the other three

crops

Prefers drier climates for yield and

quality(Hoedspruit/Komatipoort)

Related to Marula and Cashew nuts

Small research budget

Statuary levy system on processed fruit

Intro – Macadamia nuts

Originated from Australian rainforests on the east coast of that continent

Many different species found

Some inter specific crosses found

In SA - large industry

2nd largest in the world

Mostly export orientated

Fastest growing industry in the sub-tropical regions of Africa and China.

Intro - Macs

More intense growing systems (up to 600 trees/ha)

Large trees – nuts drop naturally in most cases

Insects most important yield loss factor

Newer trend to keep trees smaller – better spraying penetration

Good research budget but small percentage of paying members

Intro – Botanical aspects Mostly forest originating trees

Leaves have adapted to this

Thick cuticula and small number of stomata

Evergreens

Leaf ages fast – small amount physiological active.

Photosynthesis and transpiration rates are hampered by high light saturation rates

Faster photo saturation point reached (around 08h00)

Intro – Botanical aspects

Root systems have also adapted

Extensive shallow root systems

Sensitive to flooding in most cases

Needs lots of oxygen to grow

Compost loving

Stress conditions “kills” feeder roots off

Winter Photo inhibition reduces root capability (i.e. no water and mineral uptake)

Current fertiliser practices

Mostly very rough guidelines i.e. 2 -3 times/year large quantities

Not properly based on the tree phenology

Little work done i.t.o. nutrients vs yield and quality

Focus on standard N, P, K;little on other elements

Boron received some status

Current practices

Mostly low feeders of N, P, K – correct?

Fertigation practises very limited

Application often done during rainy

season i.e. not necessary the most

optimal time for yield and quality

Root growth cycles also mostly linked with

rainy season and soil temperatures

Current recommendations

Avocado Litchi Mango Macadamia

Nitrogen 9.2 kg/ton 1000 g/tree 420 g/tree 600 g/tree

Phosphate 1.4 100 150 105

Potassium 12.6 500 625 575

Calcium 4.6 ? ? ?

Magnesium 2.2 ? ? ?

Micro nutrients

Currently very little is known

Boron has been studied in conjunction with Fruit set

Limited work done on Zinc with regard to leaf size and fruit retention

Other micro nutrients are thought to be of little influence in sub-ropical crops

Thought to be part of normal fertiliser as part of filler material

Foliar application

Leaf anatomy = little uptake

For salt-formulations might be true

Newer formulations with amino acid /

organic chelation??

Little influence on leaf mineral content

Other factors??

Foliar applications

Timing is critical – mostly when new flushes develop before leaf hardening as this is thought to be the most absorbent time of the year

Ca and B have been stated to be beneficial especially for quality

Sometimes under stress conditions (drought, heat or disease)– Zn, K and N

Other chemicals?

Avocado – main issues

Heat stress during flowering

Low yield and fruit size important

Fruit drop extensive in some years

Fruit quality most important issues

Greypulp,

Pulp spot

Lenticell damage

Avocados -

recommendations

Heat stress – limited research results available

Low yield

Boron applications during flowering

Impact low?? Difficult to measure

Add N and P

Organic chelated products

Fruit set and size (PGR)

Paclobutrazole/Uniconazole together with

phosphates

Avocados - recommendations

Fruit drop

Applications of Zn and N

Fruit quality

Very much calcium related

Soil application during flowering

Foliar applications – include B

Organic chelated products

Humic and Fulvic acids

Becoming standard practice in

deciduous fruit industries

Sub-tropical industry very behind

Blends contain some fulvic acids for foliar

sprays

Soil applied humic acids especially

together with microbial solutions

Mixed results – little controls

Future research

Much needed field of research to intensify

production

Extensive growing systems results are

debatable

Very mixed results under different growing

conditions

However intensive systems becoming

more uniform and better managed

Future research

Bio-stimulation research should focus on:

1. Stress relieve during flowering and fruit set

2. Increased production

3. Decreased fruit drop

4. Fruit size improvement

5. Fruit quality improvement

Thank you for attention and the

opportunity to be here