IRRIGATION AND NUTRITION MANAGEMENT FOR GOOD POSTHARVEST PERFORMANCE JOHN P BOWER Agassiz, Canada Consultant: Horticultural Product Quality Objectives Fruit arrives in the market No external chilling damage No lenticel damage No internal blackening 1
Objectives Fruit arrives hard Fruit ripens normally with ripening protocols or shelf life 7-10 days To achieve this Must have best possible fruit quality at harvest 2
Why is it important? At harvest Cut off water supply Cut off supply of carbohydrates Therefore no new supply of water, minerals or energy to the cells Expect cells to continue biochemical processes In addition Long distance shipping at low temperature causes stress This can cause: Damaging free radicals Membrane breakdown Ripening and physiological disorders 3
How do we produce fruit That can withstand long distance shipping Need to produce fruit with High membrane and structural stability Calcium probably important Sufficient energy Carbohydrates (C7 sugars) High anti-oxidants C7 sugar mannoheptulose may be important 4
Of the factors we can manage Nutrition and irrigation are Probably the most important Have large impact on Tree growth Fruit size and load Fruit quality Mineral nutrition May be complex Both macro and micro elements involved May be interactions 5
Essential elements Macros C, H, O Nitrogen Phosphorous Potassium Calcium Magnesium Sulphur Micros Zinc Iron Copper Manganese Molybdenum Because they are essential All are important But some stand out in terms of fruit quality management Relate to: Cell structure Energy Enzyme control (co-factors) 6
Carbon, Hydrogen and Oxygen Absolutely essential, but: Taken up from water and atmosphere Therefore management does not specifically consider them for a mineral nutrition program Most commonly considered element for quality Calcium 7
Why Calcium? Has been linked to fruit quality disorders in many fruits including avocado Stabilizes membranes (essential for good storage and ripening) Stress conditions such as low temperature can damage membranes (causes internal disorders, chilling damage) Why Calcium? Structural component of cell walls Affects rate of ripening Ripening enzymes have to solubilize and remove calcium strengthening Therefore more calcium, the slower the process and slower ripening 8
Why Calcium? Higher calcium decreases respiration Energy use is slower Ripening is slower Takes longer for cells to run out of energy Storage and shelf life is longer Calcium considered so important that South African exporters use fruit Calcium as a quality prediction factor Found values of > 1000mg kg -1 at end of main cell division period Generally exporters use this as a decision for market destination and storage potential 9
Calcium nutrition management difficult High soil levels do not necessarily result in high fruit levels High leaf levels are not an indicator of high fruit levels Can we spray trees or dip fruit to improve Calcium levels? No probably not Key to fruit Calcium uptake Make the tree take up and allocate calcium to fruit Need to understand the Calcium uptake and allocation process 10
Two processes involved First calcium must be taken up and move to fruit Second calcium must move to the right place in the fruit Fruit Calcium concentration changes Concentration m eq 100g DM -1 30 End of major 25 cell division 20 15 10 5 0 4 8 12 16 20 24 28 32 Weeks after petal fall 11
Important concepts Most calcium moves to the fruit during most rapid cell division phase This is a short period of time It is long before harvest (therefore fruit quality set long before harvest) Not much can be done if window of opportunity is missed However, additional factor Calcium movement towards an organ is also influenced by Water movement Moves with water stream Moves mainly towards areas of highest transpiration 12
Water and therefore Ca affected by supply Concentration m eq 100g DM -1 30 25 20 Good irrigation Poor irrigation 15 10 5 0 4 8 12 16 20 24 28 32 Weeks after petal fall Reproductive to vegetative growth ratio High leaf area New shoot growth Therefore high water flow Results in high competition between leaves and fruit for Calcium 13
How can we modify this competition? Control vegetative vigour Optimize fruit set Create good shoot : fruit ratio Greatest driver of vegetative growth Nitrogen 14
Therefore not surprising Nitrogen found most important element to control for Postharvest quality (Mesocarp discoloration) Observed effects of nitrogen Low nitrogen High nitrogen 15
Nitrogen also used for quality prediction in South Africa Fruit analysis done South African exporters use: N 2 < 1% one month before minimum harvest maturity as quality index Repeat sampling showing a declining trend For mineral nutrition management Nitrogen is a primary driver for shoot growth Has a strong influence on Calcium movement and allocation Fix Calcium allocation by Managing vegetative vigour Limit N 2 during critical fruit growth stage 16
However Nitrogen is an essential element Critical component of amino acids Therefore critical for proteins, enzymes Needed for growth, development Timing and amount supplied is the key Limit Nitrogen during critical fruit growth stage Adjust for crop load Leaf analysis 2.2 to 2.3% Use phenological cycle to help 17
Principles to consider for Nitrogen applications Spike before flowering (high N for protein) Use foliar sprays But hold back spring flush (limit leaf:fruit competition) Stimulate later flush Needs to look after fruit sugar loading, next years crop Adjust for crop load Use phenological cycle to help Small spike in nitrogen Low nitrogen Increase nitrogen to look after summer growth Low nitrogen 18
Importance of carbohydrates for quality Needed to drive Respiration Affects shelf life Normal ripening Main carbohydrates Mannoheptulose Perseitol Mannoheptulose More than one function Energy Possible role in ripening Powerful anti-oxidant Therefore important for quality 19
Carbohydrates in fruit affected by Total supply losses (respiration) Supply affected by Photosynthesis Allocation Allocation affected by Shoot to fruit ratio Strongly affected by tree vigour Tree vigour strongly driven by Nitrogen 20
What about other elements? Must not ignore overall nutrition Key is a healthy tree with balanced crop to leaf ratio Need sufficient photosynthesis for crop development, renewal growth and the next season crop set and early growth What about other elements? Boron may be particularly important Important for pollen tube growth Involved in sugar transport Should be checked as there is a narrow range between deficiency and toxicity Maintain at 50 to 80 ppm 21
Potassium (K) Translocation of sugars, photosynthesis, stomatal control Improves disease and stress resistance Improves size and quality of fruit Leaf norm: 0.75 1.15% Need enough but not too much Phosphorous Used to form nucleic acids (RNA and DNA) Important in storage and transfer of energy (ATP and ADP) Stimulates root formation 22
Magnesium Essential part of the chlorophyll molecule (photosynthesis, sugars) Activator for many plant enzymes Leaf norms: 0.4 0.8% Zinc Essential micronutrient Required in important biochemical reactions Involved with chlorophyll and carbohydrates Leaf norm: 40 100ppm 23
PRINCIPLES OF IRRIGATION MANAGEMENT Avocado sensitive to stress Over irrigation (too wet) - root damage Under irrigation (too dry) stomatal closure Environmental conditions High temperatures Low humidity Rapid water loss stomatal closure PRINCIPLES OF IRRIGATION MANAGEMENT Need to ensure minimal stress but not too wet Some growth stages more important (especially flowering) Slight drying at harvest to prevent lenticel damage 24
Relationship between soil water potential and stomatal resistance Stomatal resistance s cm -1 20 15 10 5 0 0 20 30 40 50 60 70 75 80 Soil water potential kpa Scheduling techniques Soil moisture status eg tensiometer Maintain soil water potential between 35 kpa and 55 kpa 25
Scheduling techniques Tree condition eg water status or stem shrinkage Primary drivers of fruit quality Nitrogen Water Fruit : shoot ratio Fruit calcium Fruit carbohydrates FRUIT QUALITY 26
Good nutrition and irrigation creates potential for good quality Thank you Gracias 27