Foliage fertilisation

[Muhammad Arif Khan]

Some friend in past have suggested foliar fertilisation for better results,
I am thinking of using the following but am not sure as to the strength and the frequency, any help would be appreciated.

Soluble NPK 20-20-20 dilution Frequency
Potassium Nitrate
Ferus Sulphate
Urea
Magnesium Sulphate
Arif

[Muhammad Arif Khan]

Why no response? not interested or have no idea.

[M Farooq]

Why no response? not interested or have no idea.

It was a difficult question, one needs to do a decent amount of calculations to use appropriate concentrations. And secondly we might need additives in a foliar spray (chelating agents) to bring iron (as ferrous sulfate) in bio-available form.

Do you have a reliable recipe for foliar sprays?

[Muhammad Arif Khan]

Farooq, AoA, reading here and there I have gathered that all water soluble fertilisers get absorbed from the leaves including the micro nutrients, the concentration for spray is much higher than liquid fertilisers used for soil.
Having failed to find much information on net I have decided to experiment using 20-20-20 water soluble fertiliser.

[M Farooq]

Arif sb, You are right as it might be difficult to find a reliable recipe. But just to be on the safe side, start with the lowest possible concentrations to prevent leaf burn after evaporation from salt deposits...at least try the ball park estimate of what is available on the internet for foliar feeding.

[Muhammad Arif Khan]

The information I was able to get from the internet is as follows;
Foliar feeding is a technique of feeding plants by applying liquid fertilizer directly to their leaves.[1] Plants are able to absorb essential elements through their leaves. The absorption takes place through their stomata and also through their epidermis. Transport is usually faster through the stomata, but total absorption may be as great through the epidermis. Plants are also able to absorb nutrients through their bark.
1) Can plants absorb nutrients through their leaves to bypass nutrient uptake through the root system?
The answer to this important question was provided in the 1950s by H.B. Tukey & S.H. Wittwer from Michigan State University, USA. They sprayed plants with radioactive potassium (K) and phosphorus (P) and then with a Geiger counter measured the absorption, movement and utilisation of these nutrients within the plant. They found that the nutrients moved at a rate of about 0.3 m/h to all parts of the plants.
2) Are foliar-applied nutrients directly absorbed through the leaves or are they washed off and later absorbed from the soil?
Urea has been applied in trials to banana, coffee, cacao and apple plant leaves. Up to 65% of the urea was absorbed within 25 minutes, with the majority of this being absorbed by the younger leaves and/or by the underneath side of the leaves. Total absorption of the urea occurred in bananas within 30 hrs and in coffee and cacao within 24 hrs. The underneath side of young apple leaves absorbed the urea far better than the underneath side of older leaves. These trials clearly demonstrated that nutrients are directly absorbed through the leaves. In fact, it is becoming a popular practice to foliar apply urea as a cost-effective alternative to side dressing,
3) How are foliar-applied nutrients absorbed?
Leaves have transcuticular pores (i.e. pores between cell structures) and stomata through which nutrient sprays can enter the plant. The transcuticular pores are on both the upper and lower surfaces of leaves and are open all the time, so foliar-applied nutrients are believed to primarily enter through these pores. Stomata are present in far greater numbers on the underneath side of leaves, and if they are open and the spray is directed to the underneath side, this can be a good entry point for the nutrients. (The uptake efficiency was 10 to 12 times better through the leaves than through the roots). Pasture grasses and sugarcane have stomata distributed on both sides of the leaf so there is not the same requirement for spraying on the underside of these leaves.
4) Is it only the leaves that absorb nutrients?
No. The original experiments of Tukey and Wittwer showed that buds, twigs, the trunk, flowers and fruit all absorbed nutrients. For example, there is an advantage in spraying boron on deciduous trees, like cherries, during dormancy, to ensure that this important mineral is present at good levels for flowering (when it is most required).
5) Do wetting agents improve the efficacy of foliar feeding?
Yes, it is always a good idea to add a wetter/sticker to the spray to help spread the product so that it is absorbed more efficiently. Our spray oil, Cloak™, has proven a great tool to maximise the benefit of foliar fertilisers.
6) Is foliar fertilising just for “touch ups” or can more profound responses be achieved?
Foliar fertilising is perfect for bypassing soil-based lockups to address trace element deficiencies very effectively. However, it can also be used to deliver major elements with poor mobility, like calcium, directly into the fruit where they are required. Foliar feeding of tomatoes during flower set can dramatically increase fruit production and foliar sprays of boron immediately prior to flowering can have a major impact on the flower to fruit ratio (and subsequent yield).
7) Does foliar application of nutrients have drawbacks?
Foliar application involves time and machinery that is not required for fertigation. However, in many cases, there are excesses present in the soil that are reducing the uptake of other minerals through antagonism (antagonism is the decrease in availability to the plant of a nutrient by the action of another nutrient). In this instance, there is little point in ground fertilising or fertigating as you are simply throwing good money after bad. This is where foliars are the tool to choose. Sometimes the value of enhanced nutrient uptake must be offset against the time/cost factor in each individual situation. There is also a problem with trying to apply large amounts of NPK via the foliar route as there is always a potential to burn the foliage with excess salts and acid. Therefore, fertigation may be preferable if a large, rapid NPK boost is required.
8) Can foliar application of nutrients replace soil application?
The jury is still out on this one as there is some citrus research from California which suggests this is possible. However, from a soil life perspective, mineral balance in the soil is critical, particularly the calcium to magnesium ratio, which determines the entry of all-important oxygen into the soil. There are also timing issues involved as some nutrients can be counterproductive when applied at certain stages of the crop cycle. For example, iron should not be applied during flowering of any crop.
Some nutrients are less mobile than others. An interesting example of this is boron (B). In some plants it is very mobile within the plant, yet in others it is immobile. If the plant sap contains sugars such as sorbitol and mannitol, the boron is complexed with these sugars and moves freely through the plant. In citrus plants, sucrose is a major sap sugar and it does not complex with boron, so boron tends to be largely immobile. In this situation it is a good idea to apply boron regularly with each new flush of leaves. It is also a good idea to use kelp regularly in citrus as it is a rich source of mannitol. Fulvic acid should ideally be included with every foliar spray as it has been shown to sensitise the cell membrane to foster a 30% increase in nutrient uptake.
9) Does foliar application have secondary effects?
Foliar applications can have important secondary benefits. When nutrients are provided to foliage it causes the plants to exude more sugars and other compounds into the root zone. This increases microbial activity around the root zone, which in turn enhances the uptake of nutrients by the plant from the soil. This important activity has been barely recognised in any type of agriculture but our research has demonstrated that this is a major benefit of foliar spraying. When you boost chlorophyll density with foliar nutrition the enhanced photosynthesis feeds more beneficial microbes that in turn can deliver more nutrients to the plant.
10) Do hydroponic systems have special needs for foliar feeding?
In systems without soil, such as hydroponics, nutrient interactions can occur within the root zone that makes it difficult for plants to absorb certain minerals due to binding and antagonism between the nutrients. Iron deficiency occurs in many of these crops when they are stressed by low temperatures. Therefore, hydroponics have a special need for foliar feeding. There is also the issue of nitrate oversupply in hydroponics as this is usually the only form of nitrogen used in the two-part hydroponic solutions. The ammonium form of nitrogen can be foliar applied to provide more of a balance (with an associated increase in crop quality).
Potassium Provides Vigour, Strength, Size and Sweetness


There are a variety of key benefits associated with managing optimum potassium nutrition, which include the following:
1. Potassium governs stomatal opening and this is hugely important. There are major implications for production if the uptake of CO2 for photosynthesis is compromised by substandard stomatal opening due to K shortage.
2. Potassium strongly influences stem strength. K shortage can promote loss to lodging following rough weather, or poor presentation of the solar panel (leaf) due to stem weakness.
3. Potassium is a critical vegetative mineral promoting early growth. When early vigour is lacking, the first suspect is a K deficiency. If you are using soil conductivity as a measure of the level of mineral salts in the soil, low soil conductivity is often linked to insufficient potassium.
4. Potassium is also responsible for sugar movement within the plant, which is essential for sizing up fruit, grain and vegetables. In this context, potassium can be the single most important mineral for profit. You will inevitably have disappointingly small produce with insipid flavour, if your crop lacks K. This is graphically evident in a potassium-deficient citrus orchard, where sweetness and size are so obviously compromised.
5. Potassium balance is a key player in plant resilience, where either too much or too little of this mineral can increase disease and pest pressure. There can be exciting yield improvements and cost savings when we manage this mineral efficiently and the best precision strategy involves regular use of a Plant Sap Potassium Meter (available from NTS).

All water soluble fertilisers can be used as foliar fertilisers.
Results from the experiments quantified plant nutrients moving at the rate of about one foot per hour to all parts of the plants after spray.
Nitrogen is absorbed in ½-2 hours
Phosphorus 5-10 Days
Potassium 10-24 Hrs

The strength of fertilisers used in agriculture spraying.
Pot Nitrate 2%
Urea 2%
Fe. Sulf 2%
Mag Sulf 0.2%

Keeping in view the above I have formulated a solution of equal quantity of water soluble 20-20-20 and Potassium Nitrate, light spray of 1% solution hasn't burnt the leaves so far.

YOUR COMMENTS ARE AWAITED.
Arif

[Izhar]

The PPM of your formulation will be:

Nitrogen 1650 ppm
Phosphorus 1000 ppm
Potassium 3200 ppm

Which plants you are using?? how did you get Potassium nitrate??

[Muhammad Arif Khan]

|zhar,
Correct, I kept the PPM low as I want to spray once and twice a week.
Details later.

[Muhammad Arif Khan]

|zhar,
Correct, I kept the PPM low as I want to spray once and twice a week.
Details later.

Three pots of petunia;
O will get fortnightly 200PPM of 20-20-20 and no foliar fertilisation.
I will in addition get weekly foliar spray of strength mentioned above.
II will be sprayed twice a week in addition to routine fertilisation.
What do you expect?
PS, KNO3 is freely available at chemical shops
Arif

[Izhar]

lets see what happens... I expect the "II" plant to be more lush green with comparatively less blooms..

Sir, please also share at which rate KNO3 is available?? In Karachi all the chemical stores i searched told that it is a banned item..