Foliar fertilization is surely more effective in perennial crops compared to annual crops. To what an extent foliar fertilization can meet the total nutrient requirement  either in field crops annual or perennial is a question mark.

Imran my question to you. Why foliar feeding of nutrients is so slow in response. Probably that is the reason we have to spray number of times

Dr. Anoop Kumar your questions is very important because there is a high roar of foliar application of nutrients in the current decade. This is the hot topic of discussion every where and some of the scientists are heard saying that all needs of plants can be met through foliage spray. Your sub-questions are very pertinent to keep the discussion on the right track. Also these questions are of practical nature.

Before I go to answer each sub-question one by one I want to respond answers of Imran and Sikha Deka. Imran you put the same answer here as was in reply to Dr. Rao's question. Your answer is OK except that bulk needs can be met by foliar sprays. Please calculate the total amount even for 10 sprays,it will not be more than 5-6 % of the total requirement of plants. The reason is that you cannot exceed specified concentration of sprays. Sikha Deka! More number of sprays is not due to slow availability of nutrients in the form of foliar sprays but due to concentration of spray material that is fixed.

Now I answer Dr. Anoop Kumar's sub questions.

1. Foliar application can be practiced on almost all the crops (less concentration recommended for sensitive crops) except xerophytic plants which has special anatomy to protect water losses. The cutin and waxes may not  allow absorption of sprayed nutrients. However, spray concentration has to be adjusted considering plant types, nutrient being applied and the climatic factors. Of course, the crop growth stage is very important as well because plants in early stage of growth are very delicate. Short duration crops mostly respond better to foliar sprays, as we discussed in another questions that perennial respond lesser than annuals.

2.  Basic characteristics of crops to respond to foliar sprays are that the leaves should not have protective layers like cutin and waxes, as in case of desert plants. There should be more pores on leaves.

3. It is not necessary to neutralize pH of the solution, rather it will depend upon the nutrient to be applied. Some nutrients are more soluble and available in acidic pH (e.g. Zn, Fe, Cu, Mn) while others require alkaline pH (Mo) still some need pH around neutrality (e.g. P).

4. I am not sure about effect of surfacetant. It may or may not increase efficiency of nutrients applied through foliar spray. Let us hear from our colleagues.

5. Some of the formulations are now in the market that claim containing microbes in sprays. I think their efficiency will depend upon soil and plant conditions. If these favor microbial activity, these perform well. For example, a very high temperature or salt accumulation or rapid changes in pH may worsen microbial activity.

6. Some of the micro nutrients have antagonistic effect, as you pointed out, and cannot be sprayed together. More over concentration of the spraying solution is also very important. It should never be more than 0.2 to 0.5 % depending upon crops.

7. To get higher efficiency, foliar sprays should be of right concentration matching soil, plant and climate in the practicing situation. Remember that all nutrients cannot respond in all crops. The formulation are very important. These are fake claims that a particular formulation can supply so many nutrients. There may be antagonistic effect or supplied quantity may be very low that will not show any significant effect.  

Thanks Dr Nazir .You put the whole discussion on right track.

Dr. Nazir if this is the case. What strategy should we put while supplementing nutrients through foliar spray. To my mind I do not think entire nutrient demand of crop can be met through foliar spray. I feel perennials are better suited for foliar spray than annuals because of longer duration and higher nutrient demands?

Sikha Deka, It is not possible to meet whole demand through foliar spray. You please just calculate how much you are applying in one spray, Then you will know how many sprays will be required to meet full demand, also keep in mind total growth period of annuals or small duration crops.

Yes Dr Nazir I agree with you . It is a total impossibility to feed a plant exclusively through foliar spray how effective it may be. You need to use foluar sprays as a supplemental method of meeting nutrient requirement.

Compatibility amongst different nutrient limits the added advantage of foliar spray. For example Zn versus Fe/Mn as said by Dr. Srivastava. Do you feel such interactions are crop dependent or plant species dependent . How to convert foliar sprays more effective.

Dr Deka we observed such toxicity symptons with commercial salts which could have higher salt index. I am not too sure about water soluble salts. Thats why it is a big challenge to have a comprehensive foliar speay solution having micronutients.

Reyhaneh, I never said that efficacy of foliar supplied nutrients is always better than soil applied. I am just telling my learned colleagues that foliar spray is just a supplemental path of nutrients that may be efficient and highly useful too under certain conditions, especially when plants are showing deficiency symptoms and need immediate corrective measures. This method is also useful when availability of micro nutrients is low in soil due to alkaline pH. Foliar spray will be good to replenish micro nutrients through spray.  The fact should be remembered that all the alternative nutrient supplying methods, as mentioned by Dr. Anoop Kumar in his question, can neither replace soil applied nutrients in total nor can meet full requirements of plants.  

Very well said Dr Nazir. We should always bear in ours mind that foliar spray is best suited for micronutrients , since their requirement for any crop is so low.You simply canit afford to feed total nutrient requirements , especially for macronutrients.Wherevermacronutrients are used they are starter role to play.

Friends what is your opinion if we cleanse the foliage with microbial formulations and then use foliar spray it will lead to better use of applied nutrients. Whats your opinion Dr. Nazir and others.

Dr Deka , you need to look this aspect in the background of using such microbial formulations in disinfecting the phylloplanes and then applying nutrient sprays to add better efficiency of applied nutrienrs , especially for phloem mobile nutrients. Some researchers used humic acids along with nutrients spray. Dr Nazir very rightly highlighted this issue. 

My main crop is Kiwifruit and foliar fertilisation of Mg, Fe, Mn, and Zn is very important because metallic immobilization is a big issue on the soil types that I work with . I choose to use L-Amino acid Chelate fertilisers because there are no nuisance accompanying compounds and the plants have the enzymes for dismantling the molecule to receive the target nutrient. Frequently I see advertised foliar potassium fertilisers for sale and kiwifruit need in excess of 150Kg/Ha Potassium/year, a single application of foliar potassium will contribute about 1Kg/Ha potassium. Do the sums and I think you will agree that the use of foliar major nutrients has only a secondary place in agronomy.  

Foliar fertilizers are dilute fertilizer solutions applied directly to plant leaves. As with soil application of fertilizer, the goal of foliar fertilization is to supply plants with the nutrients needed for good growth.

Important about foliar fertilization:

1. Routine use of foliar fertilizers without a documented need is not recommended.

2. Foliar fertilization is unable to meet the total plant requirements for the major nutrients nitrogen, phosphorus, and potassium.

3. Foliar fertilizers are most effective when soil problems occur that restrict nutrient availability such as iron availability in high pH soils.

4. Foliar fertilization should not be used as a substitute for good soil fertility management. Have your soil tested and fertilize according to soil test recommendations.

http://www.walterreeves.com/tools-and-chemicals/foliar-fertilization-pros-and-cons/

Dr. Philip, I agree with you that applying macro and secondary nutrients through foliar spray is secondary importance and use of this mode is effective only in case of micro nutrients.

Intersting answers Drs Barlow, Kundu and Nazir . What are structural modification in leaf epidermis and parenchymatous tissues , you suggest , are the hallmark of good amount of foliar applied nutrients getting entry into parenchymatous tissues after passing through epidermis as facilitator. My second quarry  is , how can we improve the efficacy of foliarly applied nutrients. What pH of the foliar spray solution is to be preferred , especially when we are using the multi-micronutrient solution ?.

Dr Kundu , nice link , you have provided , thanks.

Hi Dr Anoop. I am recommending that the Spray tank water pH be adjusted to about pH6.6 if it is possible. But this is only based on personal observation, I have not done any trial work.

Let me give the history of foliar nutrition , since I got it , thought , let me share it ;

* Absorption of water  by leaves was diagnosed as early as 1676 by mariotte.

* Absorption of dissolved mineral salts was reported as early as 1877 by Bohm.

* Hiltner further confirmed these results in 1909 -1912.

The efficacy of foliar sprays is largely dependent  on three prime factors  viz.,  soil , plant and environmental factors. Of them , probably plant factors are very important . Age of leaves, cuticular wax, epicuticular wax, stomatal guard cells , trichomes, root hairs, adaxial or abaxial leaf variation , exchange capacity , leaf turgor, surface moisture , mineral composition of leaves , cultivar type , growth stage etc . Since foliar application of micronutrients is most pronounced for micronutrients , there is a strong cuticular affinity  for different micronutrients  in form of Cu followed by Zn and Mn in decreasing order   . Find below a PDF explaining these characteristics . Hope , it will be useful to our colleagues.

Anoop Sir,

When the soil is deficient in any of the nutrients, the foliar supply becomes more effective. Only nearly 10 % of the requirement can be met through foliage. Among the nutrients, nitrogen is absorbed effectively and fast. If N is present others will also be taken in depending upon the need/deficiency.. Since micro-nutrients are required at micro level those can be supplied by foliar means. Other nutrients, P. K, Ca, Mg, S are required in large quantity, those need to be supplied to soil. Only supplemental nutrition of these can be taken up by foliar means. The effectiveness depends on plant also. Some plants absorb quickly and some do not. Since it is limited to only 10 % of the requirement the effectiveness is also limited.

Thanks

Anoop sir,

1. Foliar fertilization is most suitable for vegetable crops.

2. Foliage must be enough for higher efficacy

3. To avoid scorching effect on leaves, it is essential to neutralize

4. Microbial formulations of PSB and others are in market already

5. All together, multi-micro's develop acidity

6. To increase efficacy of foliar applied nutrients, it is necessary to include urea (5-10 g per 16 L tank)

Thanks

Dr Rajakumar if it can supplement only 10 percent of total nutrient requirement , any possible mechanism that you can suggest to elevate the use efficiency of foliarly applied nutrients. My second querry  neither foliar spray is so quick in action in the context of eradication of nutrient constraints in those plants displaying symptoms considering the fact that foliar spay is crop stage sensitive.

Dear Anoop,

* Foliar fertilization is more suitable to which kind  crops?

In all crops foliar nutrition is most effective when there is some difficulty in root absorption due to other active sinks in plant competing for hydrocarbons or recurrent drought problem in root area. 

* What are the basic foliar characteristics of a crop to facilitate better efficacy of foliar applied nutrients? 

Higher trichome density could increase the response dramatically. 

* Do we need to neutralize the pH of the foliar  solution ?

Acidic pH is better as I know possibly due to more proton gradient across membranes which could enhance cation entry to leaf cells.

* Whether use of surfacetant will improve the efficacy of foliar applied nutrients ?

Of course, it increases the contact area and reduces the possibility of toxicity symptoms

* Is there any role of microbial formulations to be a part of foliar sprays ?

This is an area for further research. There are methylotrophic bacteria on leaf that depend on gas emissions from plant leaf but I am not sure if they could have a positive effect or other such bacteria reside on leaf. 

* Why a foliar spray of multi-micronutrients , especially containing Fe, Mn and Zn together  develops toxicity symptoms on the foliage?

When using combination of salts the overall osmotic pressure on leaf increases. There is a criteria for calculation of the total osmotic effect on leaf in literature

* What are ways and means to improve the efficacy of foliar applied nutrients?

Using surfactants as you mentioned and humectants are common. alcohols can increase the absorption but there are many other ways in literature as I have encountered 

*  How can we domesticate the conventional micronutrient fertilizers for effective  foliar sprays?

In each climate and plant the foliage fertilizers should be tailor made to suit  that condition. This could be reached out better by experiment but in more humid climates plant tolerate more concentrations usually.

How effective is foliar fertilization at meeting the nutrient requirement of a crop?

Foliar nutrition is not for addressing the macro-nutrient deficiencies while is enough for micro-nutrients and  biostimulators. If a plant is irrigated from above like sprinkler system, then it could even support the macro-nutrient need of the plant if they are adder to irrigation water as part of them is absorbed from leaves and the rest from the roots.

Anoop sir,

Foliar nutrition is also suitable for indoor plants, green house cul5tivation and folwer crops.

Same crops have specific requierements . An example is fruit crops. We recommend Ca foliar sprays in apple orchards in order to increase a litle bit this nutrient in the fruit, with the purpose of preventing Ca related disorders in the fruits in pre and post-harvest.

Clori , you have a raised a good point . My point is very candid and clear . in perennial fruits , the edible portion of plant parts , what we call it consumable ones , are unfortunately very poor sink for different  nutrients , especially micronutrients having ability to act as non-enzymatic antioxidants . What changes , shall we induce in our conventional foliar sprays so that edible plant parts are better equipped with such nutrient applications.  Afterall  improving fruit yield without having subsequent improvement in fruit quality in terms of nutrient value of fruits  , will probably  not serve any purpose of  fruits claiming as an alternative option of nutritional security  . In such attempts , foliar nutrition will  play very pivotal role.

Whats your opinion friends about the efficacy of application of nano-size fertilizers through foliar fertilization ?

Dear Prof, As we know about nano formulations of fertilizers  usually with larger surface area and its absorption,translocation pathway  is easy in comparison with conventional fertilizers and certainly it will improve the efficacy as well as efficiency of fertilizers. It may be soil application or foliar spray.

While applying fertilizers into soil , the  particle size matters a lot , rightly said about the increase in surface area facilitates the reactive . But the moment , you dissolve the fertilizer and get a clear cut solution , it means the particle size has gone sub-nano size.  In such situation , where is the role of particle size , nano or non-nano particle size?

Dear Prof, We can keep our nano formulations as it is, what ever the size we prepared through use of stabilizing agents or surfactants (Surface active chemicals)  while preparation of novel fertilizers. 

Angamuthu , I am talking of any nono-fertilizer suitable as a nutrient source , if you dissolve it in water , the identity of that nano-size is lost since it is cent percent solubilized in water . On the other hand , you take any  commercial fertilizer ( For example ) , you dissolve it in water , it solubilized cent percent in water . Now compare the efficacy of two fertilizer sources ( Dissolved nano-size fertilizer or dissolved commercial fertilizer)as foliar spray , Do you feel which one will perform better?

Dear Prof, As you rightly pointed out in your answer that cent percent solubility of nano-fertilizers.  Nano formulations will perform better than commercial fertilizers.

Under which condition, it will perform better . only when used for soil application , but  I am doubtful when used through foliar application .  Moment you have solubilized the fertilizer  ,  particle size of fertilizer becomes irrelevant .

Dear Anoop,

I agree with you on the matter. For foliar spray the material should be dissolved so in molecular or ionic size which is the least possible size. So if we dissolve a big crystal or a nano-powder, both give us the same solution.

Yes you got me right Ebrahim.

Thanks Abhishek for excellent feedbacks backed up some outstanding links. Do you have any input about the toxicity symptoms  that are usually observed in most perennial tropical  crops when Fe, Mn , and zn sulphates are disssolved separately but applied by mixing them together in equal quantity ?

Is there any report that foliar fertilization encourages improvements in biological properties of soil ? 

Excellent response Abhishek . This is infact , working premise of foliar fertilization in any crop , annual or perennial in nature..? As long as soils are kept biologically active nad roots and shoots continue to operate in tandem , foliar fertilization will be maximally benefitted , unless soil  has extreme adversities in terms of  calcareousness , salinity , sodicity , or any other contaminants,  disallowing soils to perfom normal for nutrients absorption ...

Interesting work...

Foliar and Seed Application of Amino Acids Affects the Antioxidant Metabolism of the Soybean Crop

Abstract : In recent years, the application of natural substances on crops has been intensified in order to increase the resistance and yield of the soybean crop. Among these products are included plant biostimulants that may contain algae extracts, amino acids, and plant regulators in their composition. However, there is little information on the isolated effect of each of these constituents. The objective of this research was to evaluate the effect of the application of isolated amino acids on the antioxidant metabolism of the soybean crop. Experiments were carried out in a greenhouse and in the field with the application of the amino acids glutamate, phenylalanine, cysteine, glycine in seed treatment, and foliar application at V4 growth stage. Antioxidant metabolism constituents evaluated were superoxide dismutase, catalase, peroxidase, hydrogen peroxide content, proline, and lipid peroxidation. In addition, resistance enzymes as polyphenol oxidase and phenylalanine ammonia-lyase (PAL) were evaluated. In both experiments, the use of cysteine, only in seed treatment and in both seed treatment and foliar application increased the activity of the enzyme PAL and catalase. Also in both experiments, the use of phenylalanine increased the activity of the enzyme PAL when the application was carried out as foliar application or both in seed treatment and foliar application. In the field experiment, the application of glutamate led to an increase in the activity of the catalase and PAL enzymes for seed treatment and foliar application. The use of the set of amino acids was only efficient in foliar application, which led to a greater activity of the enzymes peroxidase, PAL, and polyphenol oxidase. The other enzymes as well as lipid peroxidation and hydrogen peroxide presented different results according to the experiment. Therefore, glutamate, cysteine, phenylalanine, and glycine can act as signaling amino acids in soybean plants, since small doses are enough to increase the activity of the antioxidant enzymes. Source ;   Frontiers in Plant Science https://doi.org/10.3389/fpls.2017.00327

An excellent work indeed...Here is the abstract ....

Pruning System and Foliar Application of MgSO4 Alter Yield and Secondary Metabolite Profile of Rosa damascena under Rainfed Acidic Conditions

Damask rose (Rosa damascena Mill.) is one of the most high-value essential oil-bearing plants in the world. However, the flower yield and quality of essential oil of R. damascena are largely influenced by the pruning practices and balanced supply of plant nutrition. The objective of this study was to test the hypothesis whether the pruning system and foliar fertilization of MgSO4 would influence the flower yield, growth and secondary metabolites profile of R. damascena. A field experiment of 10 treatment combinations comprising two pruning systems (complete and partial) and five levels of MgSO4 (water spray, MgSO4 @ 5.0g L−1 , 10.0g L−1 ,15.0g L−1 , and 20.0g L−1 ) was conducted. The experiment was conducted in randomized block design with factorial arrangement. Overall, the flower yield ranged from 503.66 to 1114.47 g bush−1 , while oil content varied from 0.039 to 0.046% of the fresh flower. Irrespective of foliar spray, partial pruning produced significantly (P ≤ 0.05) higher flower yield (893.02 and 503.66 g bush−1 ) compared with complete pruning system in both the years. Regardless of pruning system, the foliar application of MgSO4 @ 15.0g L−1 registered about 26– 38% higher flower yield compared with water spray control. The major constituents of essential oil were citronellol (19.75–48.88%), E-geraniol (9.63–29.6%), Z-citral (0.07–5.97%), nonadecane (6.76–22.32%), and heneicosane (2.87–10.21%). The principal component analysis revealed that the major hydrocarbons such as nonadecene, nonadecane, and heptadecane are positively and highly correlated with each others. The results suggest that higher yield and quality of R. damascena can be achieved through partial pruning system in combination with foliar application MgSO4 under rainfed acidic conditions.

PDf enclosed for further reading...

Dear Dr kumar;

would you please answer your question about the possible effect of PH on mineral uptake through foliar application? if PH of solution takes part in absorption, how the mechanismwould be?

Nice question posed by Aida, appreciate it..well responded by Abhishek..

Foliar absorption is pH dependent. This is attributed to the effect on the cuticle of

complex electrostatic repulsion and attraction phenomena, which are regulated by pH. It is believed that for each Phosphate, for example, has its greatest absorption and utilization at a pH 3-3.7. There is evidence that Zinc is absorbed best at pH 4.1-4.9. The optimum pH probably varies somewhat with each nutrient and its carrier. Information on optimum pH values for nutrient absorption is extremely limited at this time. However , an ideal pH of the spray should be kept somewhere 5.5 -6.5 for better effectiveness under diverse growing conditions...however , the final pH of the spray solution is governed by the composition of spray , kind of salts that are dissolved ..nature and properties of cuticle of a given crop variety etc...

Dear Dr. Kumar

thank you for your answer. I want to know that if there is any relation between the desired soil pH for nutrient uptake with the pH of solution. what I mean is that, is it possible to conclude that the desired soil pH for nutrient uptake would be the most effective pH for foliar spraying? 

Aida, that way , i dont think, but choice of nutrient application is governed by the soil pH. If soil pH is too acidic or too alkaline , foliar application of nutrients is the choicest method. Regardless of soil pH, the pH of foliar spray should always be maintained somewhere 6.0-6.5 , instead of alkaline pH , more than 7.5

Dear Dr Kumar

thank you so much for the whole information that is gotten about this subject. I really found it worth to pursue. 

Aida

Dear Dr. Kumar Srivastava

nice and challenging question. since i work for a fertilizer company, i thought i can say some words about your question. hope you find it helpful.

first of all, foliar application of nutrient is of course effective. now a days this kind of fertilization is becoming more and more popular across the world and farmers and researchers are finding new horizons and new benefits of foliar application. but there is an important point here that we need to consider: we can't replace root - based fertilization methods with foliar application ! and there is two main reasons for that matter : 

1- because total volume of absorbed nutrient through foliar application is limited, we can't supply the whole plant need for nutrient (specially macro elements) only by foliar application. 

2- when the plant gets used to absorb nutrient only by aerial organs, root development would be limited and the plant's root system will become weak.

so why we even need foliar application ? there is good reasons for that: 

1- absorption of nutrient through root system is a time consuming mechanism. so in situations that plant need the nutrients right away, it just can not wait that long ! (for example when the plant is in a extreme hunger for potassium and micro nutrients due to fast fruit growth stage, or when the plant is deficient in one or two elements and severe damage would happen if plant don't supply it's need)

2- for some reason  root ability to absorb nutrient is limited (nematode attack, unsuitable soil pH, soil salinity, low soil ventilation, unsuitable soil temrature, physical damage to root and ...) 

but this is not all of it ! there is more benefits for foliar application. for example : must of the soil applied fertilizers have high E.C. so when we apply fertilizers to soil we are literally raising soil salinity which is not good at all ! 

also when we apply a huge amount of elements to the soil, in fact we are changing the soil balance which has it's own consequences. we are all aware of antagonism -synergism and competitions that exist between elements in soil that means when we add some elements to soil, absorption of certain elements would be limited. 

we don't face this kind of problems when we use foliar application ! 

now lets review your other questions very briefly : 

* Foliar fertilization is more suitable to which kind  crops?

it can be used for almost all crops but maybe not suitable for cactus and succulent plants because of thick epiderms.

* What are the basic foliar characteristics of a crop to facilitate better efficacy of foliar applied nutrients? 

plants that have broad and relatively thin leaves that has high phloem sap circulation usually absorb nutrients more efficiently

* Do we need to neutralize the pH of the foliar  solution ?

some times, yes. the water used for foliar spray must have low salinity and pH range between 5.5 to 7 depending on conditions. 

* Whether use of surfacetant will improve the efficacy of foliar applied nutrients ?

hell yeah ! there is a large variety of adjuvants in market which is specially designed for increase the efficiency of foliar spray. visit http://www.lamberti.com/ for more info. 

* Is there any role of microbial formulations to be a part of foliar sprays ?

what kind of microbial formulation you mean ? i know that there is some microbial products in market that you spray them on your plant and the bacteria increases the efficiency of nitrogen fixation in plant.

* Why a foliar spray of multi-micronutrients , especially containing Fe, Mn and Zn together  develops toxicity symptoms on the foliage?

are you sure about that ? cause i know many kind of combined micro nutrient fertilizers which is designed for foliar application and they don't show any toxicity sign at all ! in fact they are being sold all over the world for years now with absolutely no problem ! (for example google this: Nutriplus Zelsius)

* What are ways and means to improve the efficacy of foliar applied nutrients?

- use of adjuvants 

- irrigation before spray

- choose the correct time of day and correct date of year for application

- consider weather condition when spray (temperature, rain, wind, etc...)

- use high quality and high tech chelates (EDDHMA, EDDHSA, HBED or glycine chelated micronutrients) 

- consider the right dosage 

- replicate the application depend on plant need as many times as needed. 

-.....

*  How can we domesticate the conventional micronutrient fertilizers for effective  foliar sprays?

- this one is tricky ! you might need to contribute with experienced specialists in leading fertilizer companies around the world. 

Please view an interesting apper entitledTHE INFLUENCE OF FOLIAR FERTILIZER WITH ORGANIC SUBSTANCES ON PHOSPHORUS CONTENT IN MAIZE PLANT

Abstract: Paper presents the experimental results obtained by applying a new foliar fertilizer with organic substances and the influence of the foliar fertilization on the phosphorus content in maize plant. Research was carried out in the green house by INCDPAPM-ICPA Bucharest (2010) and the soil from experiment was Vermic Chernozems. The experiment was organized in Mitscherlich pots with 20 kg of soil. The tested inbred maize line from experience was: PR38A24. The novelty and complexity of new foliar fertilizer consist in the possibility of association of mineral nutrients (macro and micronutrients) from the foliar fertilizer with organic substances as a source of physiologically active. According to the methodology of testing for each variant of treatment a number of three replicates were provided. All the variants received soil fertilization with 50 mg N/kg soil, 50 mg P2O5 /kg soil and 50 mg K2O/kg soil, excepting the control unfertilized in soil. In these conditions, the application of new foliar fertilizer assured positive increases of phosphorus content in dry matter of maize plant as compared to controls.variants of the experiment were: V1-control unfertilized in soil, sprayed with water, V2 – control fertilized in soil, sprayed with water, V3-fertilized with 1% solution, V4-fertilized with 0.5% solution, V5-fertilized with 0.25 % solution (fertilizer with organic substances). The variants V6, V7, V8 were fertilized with foliar fertilizer without organic substances. The experiment was carried out to see the effect of foliar fertilizer with organic substances on dry matter yield, phosphorus content and uptake of maize plant. The foliar application of organic fertilizer on maize crop in green house, led to increased phosphorus content in dry matter yield and exported phosphorus compared with the controls. The phosphorus content was assimilated by the maize plant. This work is part of the doctoral thesis.Foliar fertilization is a ordinary practice for additional stimulation and correction from plant nutrition. The largest increases in phosphorus content were obtained by plant treatment with foliar fertilizer with organic substances. Source ; Research Journal of Agricultural Science, 43 (3), 2011

Please have a look at some interesting work..

Effects of foliar spray of nano-particles of FeSO4 on the growth and ion content of sunflower under saline condition

ABSTRACT

This study investigated the effects of foliar spray of normal and nano-particles of iron sulfate (FeSO4) on the response of sunflower cultivars to salinity. Treatments included five cultivars (Alstar, Olsion, Yourflor, Hysun36 and Hysun33), two salinity levels (0 and 100 mM sodium chloride (NaCl)), and three levels of fertilizer application. Fertilizer treatments were the foliar application of normal and nano-particles of FeSO4. Foliar application of FeSO4 in either form increased leaf area, shoot dry weight, net carbon dioxide (CO2) assimilation rate (A), sub-stomatal CO2 concentration (Ci), chlorophyll content, Fv/Fm and iron (Fe) content and decreased sodium (Na) content in leaves. The extent of increase in chlorophyll a content by foliar spray of FeSO4 nano-particles was significantly greater than normal form. The results showed that the FeSO4 nano-particles increased biomass production of sunflower plants greater in comparison with normal form, although no significant difference was found between two forms. Source ; Journal of Plant nutrition http://dx.doi.org/10.1080/01904167.2016.1240187

Some really interesting work...

Foliar calcium spray confers drought stress tolerance in maize via modulation of plant growth, water relations, proline content and hydrogen peroxide activity

ABSTRACT : Water and nutrient restrictions are the factors that limiting growth of maize in arid/semi-arid climate. Calcium (Ca2+) uptake is affected severely under drought stress (DS). The objectives of this study were to investigate the effects of DS and foliar applied Ca2+ on growth, physiological, biochemical, yield and grain-nutrient content in two maize cultivars i.e. drought- tolerantDekalb-6525 and drought-sensitive Yousafwala-hybrid. The study comprised of two phases; firstly the best rate of Ca2+ (20, 40 and 60 mg L−1) was evaluated. Secondly, optimized rate of Ca2+ (40 mg L−1) was used to assess physiobiochemical  and yield responses of maize under DS. The applied DS caused significant reduction in maize growth, water-status, photosynthesis and grain nutrient contents. Foliar Ca2+ markedly improved plant growth, water-potential (18%), turgor-potential (75%), photosynthesis (45%), stomatal-conductance (46%), transpiration rate (43%) and accumulation of total soluble sugars (20%) along with decline in H2O2 content (23%) in both cultivars under DS. Furthermore, optimized rate of Ca2+ improved maize grain yield and quality under water-deficit conditions. Cultivar Dekalb-6525 presented significant response to Ca2+ over Yousafwala-hybrid. Results of the study surmise that foliar supply of Ca2+ is an effective approach to make plants vigorous to thrive under limited-water supply. Source: ARCHIVES OF AGRONOMY AND SOIL SCIENCE, 2017 ,https://doi.org/10.1080/03650340.2017.1327713..PDF enclosed for further reading..

How can we justify foliar feeding if stomata are closed ?

How much nutrients can be absorbed by transcuticular pores.

Some intriguing facts about foliar nutrition.There are two very important point. Firstly you can cannot fulfil nutrient requirement of the crop , and secondly what is the possibility of producing nutrient dense crops using foliar nutrition.

Thank you guys for all information.