Post on 03-Mar-2021
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