Foliar Fertilization or Foliar Feeding

Foliar fertilization or foliar feeding is applying diluted fertilizer directly to the leaves with the goal of supplying nutrients needed by the plants especially during critical periods of plant growth.

Dr. B.H. Tukey "The leaf is a beautiful mechanism for absorption".

Foliar feeding of plant nutrients became very popular during the 1950's.

A report by Dr. B.H. Tukey and his team from Michigan State University confirmed that "not only can plants absorb nutrients through the roots, but also through the foliage, the fruit, the twigs, the trunk, and even the flowers".

He also comfirmed that "there are regions on the leaf where materials may enter and are actually almost like a blotter, drawing them right down into the leaf".

Foliar feeding has been successfully demonstrated to be very beneficial in many temperate crops such as tomato, corn or maize, apples, citrus, strawberries, and many horticultural plants. In the hot and humid tropics, foliar fertilizers are frequently used for rubber, oil palm, bananas, pineapple, mango, rambutans, longan, citrus, vegetables, ornamentals and many commercial crops.

How does foliar fertilization or foliar feeding in durian production fit in?

Durian production in most Asean countries generally uses the traditional dry fertilizers and numerous fertilizers schedules for durian trees, from planting to fruiting age, are presented by many creditable sources. The use of water soluble fertilizers and foliar fertilization is less widespread except in Thailand where many growers use this method and many modern technology, since the late 1980's or early 1990's, to manage their large commercial durian orchards.

Sprinkler irrigation in a Thai durian orchard

In Thailand, fertilizers are added by irrigation drip lines with N:P:K ratio of 1:1:1 as flowers develop, 2:1:2 at harvest times and 1:1:1 at 4 months after harvest (Watson 1984). This method of mixing soluble fertilizers into the irrigation system is known as fertigation. It is the application of soluble nutrients in liquid form where the majority of the nutrients taken up by plants are absorbed by the roots from the soil.

A Thai farmer hand weeding beside his durian tree and sprinkle pipe-system

Studies on foliar feeding on durian were reported by Punnachit and others (1992) that demonstrated foliar sprays of potassium nitrate and other substances during fruit development increased the overall size of fruits, the edible portion (aril) of the fruit, and seed abortion. These effects were presumably achieved by the reduction of competition for nutrients by inhibition of leaf flushing.

Spray nozzles are placed high up the trunk and directed at fruiting branches (Thai farm)

In the Philippines, Loquias and others (1996) showed that foliar fertiliser containing 20 per cent N; 5 per cent P2O5; 30 per cent K2O in combination with 5 kilograms granular 14-14-14 (N:P2O5:K2O) with micro-elements like, calcium, magnesium, boron, zinc and copper improved the yield and quality of durian with 158 fruits per tree as compared to 41 fruits per tree applied with granular fertiliser (14-14-14) alone while fruit quality, as measured by TSS and percentage edible portion, was improved with the use of foliar fertiliser with 4 per cent N and 48 per cent K2O.

The most comprehensive report of foliar sprays in durian production comes from  Dr. Surmsuk Salakpetch. Her seminar paper entitled "Durian (Durio zibethinus L.) Flowering, Fruit Set and Pruning"  was presented during The 15th Annual International Tropical Fruits Conference held in Hawaii (2005). Dr. Salakpetch  recommends  a package of technologies which includes the use of foliar sprays to promote growth and development of flower buds, fruit set, fruit growth and development, and the control of young shoot development during fruit growth.

The following are excerpts focusing on foliar fertilization from Dr. Salakpetch's paper:

 1. Foliar fertilizers to promote growth and development of flower buds

When the number of flowering branches are less than 60% of total number of branches that are able to flower and the density of flowers is less than 3 inflorescences per 1 meter of branch length, fertilizer management is required to increase the number of flowering branches and flower density.

Potassium nitrate (13N-0-46K2O) at 100 to 200 g and sea weed extract at 60 ml in 20 liter water are foliarly sprayed at an early stage of flower emergence when a very small and creamy white spot, is detected. The application is able to promote an increase in flower number.

2. Foliar fertilizers to promote fruit set
                    
Calcium (Ca), boron (B), magnesium (Mg), and potassium (K) have been proposed as the main nutrients for pollen germination  and pollen tube growth. It was demonstrated that durian pollen requires Ca at 50-90 ppm, B at 30-60 ppm , Mg at 15-30 ppm and 15-30 ppm K for germination.  Lower and higher concentrations will cause poor germination and tube growth.
    
It was found that durian leaves contain Ca, K, and Mg at higher levels than the optimum for germination, whereas B is at a lower level.  This will lead to 337:1 unbalanced ratio between Ca and B, compared to a balanced ratio of 200:1 Ca:B.

Therefore, durian growers spray calcium and boron when flowers have developed to the sixth week after emergence to promote germination of pollen.

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Notes:

The following chart shows when and what foliar fertilizers to use during the various growth and development stages of the durian as discussed by Dr. Salakpetch . You can adjust the time-line (months) to reflect the actual durian situation in your orchard. Please remember that this chart shows only approximate stages of growth for graphic presentations. Each period of growth stage can varies as well as overlap each other,. The number of leaf flushes can also varies from 3 to 5 times and occur at different times of the year.

Durian growth stages and fertilizers application (1 to 4b)

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3. Foliar fertilizers to promote fruit growth and development
      
The source-sink concept is the main principle behind improving production of durian fruits with acceptable quality.

It was reported that developing durian fruits act as stronger sinks when compared to mangosteen and rambutan fruits. This is supported by the growth pattern of durian fruit which shows dramatic increases of up to 16 g/fruit/day, at 8-12 weeks after anthesis.

Therefore, enormous amounts of assimilates will be required to support fruit growth. To obtain better production of durian with marketable quality and  with market acceptance, the source-sink concept and appropriate cultural techniques (irrigation, fertilization, and pest control) should be managed in the following manner during fruit growth.

3.a. The recommended fertilizer to encourage fruit rowth is 12N-12P2O5 - 17K2O+2MgO or 8N-24P2O5-24K2O or 13N-13P2O5-21K2O. This should be applied when fruits are at 5 to 7 weeks after anthesis.

3.b. Another fertilizer, 0-0-50K2O, should be applied when fruits are at 9 to 10 weeks after anthesis to improve pulp quality.

4. Foliar fertilizer to control young shoot development during fruit growth

 New young vegetative shoots during fruit growth will compete with the developing fruit for assimilates.  This is one  of the major factors leading to immature fruit drop, misshapen fruits at 5 to 8 weeks after anthesis and hard or mummy-fleshed  fruits at 8 to 12 weeks after anthesis. The recommended irrigation regime from 3 to 4 weeks after anthesis can reduce new  shoot development to a certain degree. 

 4.a. Growers should carefully examine the trees and if vegetative shoots are found one or two sprays of potassium nitrate at 150 to 200 g per 20- liter water is recommended to inhibit growth of new shoots.

 4.b.If later stages of vegetative development are detected, growers spray of a mixture of 30 ml instant carbohydrate solution, 30 ml humic acid and 60 g 15N-30P2O5-15K2O or 10N-20P2O5-30K2O foliar fertilizer together with 50 ml mepiquat chloride (25% active ingredient) in 20 liters of water.  The mixture of fertilizer will serve as food for young shoot and mepiquat chloride, which is synthetic growth retardant, will retard growth of new shoot by reducing the level of endogenous gibberellins in the tree.

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These recommendations are also found in a technology package entitled "Durian Grower's IPM Notebook" (1999) that is used by extension personnel to train local durian growers on how to improve durian production and quality.

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The Basics of Foliar Fertilization In Durian Production

Here are 10 guidelines to ensure foliar fertilization is effective and efficient:

1. Foliar fertilization is a science as well as an art.

It is a science because growers must understand crop growth and plant nutrition so that they know the why, when and how to use various production materials to manipulate the flowering, fruit-setting and fruit development processes to improve crop production and quality. This is an art that requires a lot of skill, hard-work, dedication and patience.

2. Foliar fertilization is a supplement to the overall fertilizer management practices.

Many proponents claim that foliar fertilization is more efficient than soil application. Certain nutrients are quickly taken up by the leaf and used by the plant. But for the major nutrients (nitrogen, phosphorus, potassium), the quantity absorbed at any one time is small relative to plant needs. Thus, foliar application of these three nutrients can only supply a very small fraction of the total needed by the plant. Therefore, foliar application should be considered only a supplement to supply nutrients during peak periods of demand when an immediate response is needed.

3. Foliar application products in the market.

Many foliar fertilizers to choose from..

Buy only products that meet the nutritional needs of the durian. Labels should disclose the ingredients. Get the sales people to explain and demonstrate how they should best be used. Always observe and evaluate before you buy. This also includes other products derived from sea-weed extracts, plant hormones and organic plant materials.

4. Foliar fertilizers need to be diluted to the correct concentration before use.

Too high a concentration causes leaf burn and may kill the tree. On the other hand,  a low concentration is ineffective and waste money, time and effort.

5. Water used for dilution must be clean and clear.

Water used for dilution must be clean and free from small undissolved particles that can clog spray nozzles. Piped water containing chlorine should be allowed to stand in an open container overnight before use.

6. Spray equipment must be clean and in good working condition.

All spray equipment should be dedicated for specific purposes only and regularly serviced to meet the high requirement of finely atomized sprays. This is usually achieved by using high-pressure sprayers or mist blowers.

7. Foliar applications must be timely and accurate.

Apply foliar sprays when weather conditions are cool, moist, and wind is minimal. The best time is in the early morning and late evening when temperatures are right and wind minimal. Morning dew on the leaves facilitates nutrients adsorption. Foliar application during the heat of the day can cause leaf burn. Applying finely atomized sprays during windy conditions is difficult and wasteful as there will be a lot of spray drift and sprays may not reach the targeted areas.

8. Weather forecasts - check before you spray.

Do not spray if rain is imminent because rain water can wash away plant nutrients from the leaf surfaces. Under normal conditions, it usually takes a day or two for nutrients to be fully absorbed and used by the leaf. To redo the foliar application is costly in terms of money, time and effort.

9. Surfactant to improve efficiency of spray solution.

It is highly recommended that a surfactant be added to the spray solution. The primary purpose of a surfactant or “surface active agent” is to reduce the surface tension of the spray solution to allow more intimate contact between the spray droplet and the leaf surface thus increasing nutrients absorption by the leaf.

10. Fungicide or insecticide added to the spray solution.

To save operation costs, foliar fertilizers can be combined with a fungicide or insecticide. Always read all product labels and consult the sales people if you are uncertain. Be aware of timing conflicts
and material incompatibilities.

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Related Articles and Reports

For further reading to get more information on foliar fertilization or foliar feedings:

1. "Durian (Durio zibethinus L.) Flowering, Fruit Set and Pruning" , by Surmsuk  Salakpetch. Proceedings from The 15th Annual International Tropical Fruits Conference held in Hawaii (2005).

 2. Foliar Feeding of Plant Nutrients - Dr. Tukey  - Extracts from THE CONTRIBUTION OF ATOMIC ENERGY TO AGRICULTURE, Congress of the United States, Research and Development Subcommittee of the Joint Committee on Atomic Energy, Washington, D.C.

3. What is Foliar Fertilizer- General information about foliar fertilization.

4. Foliar Fertilization - Pro's and Con's
When and How to Use Foliar Fertilizers by Carl Rosen and Peter Bierman, Department of Soil, Water, and Climate, University of Minnesota.

5. Foliar Fertilization -  ATTRA - National Sustainable Agriculture Information Service - Download free PDF publication. A very informative booklet.
 
6. Some Myths About Foliar Fertilizer? - A closer look at some myths on foliar fertilization.

7. The Myth of Foliar Feeding - by Linda Chalker Scott. Another good report to understand the correct use of foliar fertilizers. Download PDF.

8. Durian and Mangosteen Orchards - North Queensland Nutrition Survey (2005) -  A report for the Rural Industries Research and Development Corporation, Australia  by Yan Diczbalis and Darren Westerhuis.

9. Horticultural Fertigation - Learn what is fertigation from NSW Department of Primary Industries.

Fertilizers Suppliers S.E. Asia - (for information purposes only)

 1..Agro Activa - Fertilizers supplier (for information purposes only).

2. Agricultural Chemicals Malaysia - Agricultural chemicals including fertilizers (for information purposes only).

3. Behn Meyer -  Foliar fertilizers supplier (for information purposes only).

4. Chemical Company Malaysia -  Foliar fertilizers supplier (for information purposes only).