About foliar feeding.../O folijarnom prihranjivanju....

About foliar feeding
Most bonsai enthusiasts use foliar feeding as one way of applying fertilisers to plants and as the most efficient way of providing minerals to plants. How is foliar fertiliser absorbed? These are some scientific facts:
Except leaf pores (stomata), wich are openings on the surface of the leaves for exchanging gasses, leaves have one more type of canals, tiny ones called ectodesma. They are responsible for excepting supstances that cannot pass through unpermeable cuticle. Stomata contains air, and considering that, liquids cannot be transported through.
Cuticle is unpermeable waxy layer produced by epidermal cells of leaves.
Example… in a leaf cell, through ectodesmiae can be transported 3-4 (scale for measure ) of some ions, but a 150 of urea!!! That means that urea can be very efficient carrier of anions and cations into the plant cells. Iron (Fe) can be absorbed 3-40 times more in presence of urea than without. Of course, this is active transport, means it requires energy using ATP. This process depends of temperature and light. Some ions will be better absorbed in light, some in dark conditions, and for some ions it doesn't matter. Apsorption is at it's biggest rate in first hour after aplying foliar fertiliser.
Foliar absorption is only possible while leaves are wet. When fertiliser has dried on the leaves, nutrients cannot be absorbed any more. The leaves has to be wet again.


Summary:

S. H. Wittwer1, M. J. Bukovac1, W. H. Jyung1, Y. Yamada1, R. De1, H. P. Rasmussen1, S. N. Haile Mariam1 and S. Kannan1
(1)
Department of Horticulture, Michigan State University, East Lansing, Michigan
Summary Foliar absorption consists of penetration of a cuticular membrane and uptake by living cells within the leaf. A detailed analysis of nutrient absorption by these two systems has revealed that ionic penetration of the cuticular membrane is by diffusion, and that the coupling between active transport and metabolism is at the cellular level. Urea penetrates the cuticular membrane and is absorbed by leaf cells much more rapidly than are nutrient ions. Furthermore, urea facilitates penetration and absorption of other materials simultaneously applied. Penetration of nutrient ions through cuticular membranes has been localized by microautoradiography as occurring around stomatal pores and along periclinal cell walls. Chelation of metals such as iron, manganese and zinc reduces the rate of foliar absorption, but increases the translocation of the absorbed nutrient. At the cellular level the nutrient ion is absorbed and the ligand is excluded.

Ukratko
većina bonsaista koristi folijarna gnojiva kao jedan od načina prihranjivanja. Na koji način hranjivo ulazi u biljku?! Proučavanjem fiziologije bilja dolazi se do slijedećih spoznaja:
Osim puči (stomata), koje su otvori na listovima preko kojih se uglavnom vrši razmjena plinova, listovi imaju i još jednu vrstu otvora; male kanaliće koji se nazivaju ektodezmije. Oni su upravo odgovorni za primanje hranjivih tvari kroz inače nepropusnu kutikulu. Kroz puči nema apsorpcije hranjivih tvari. Razlog je jednostavan, puči sadrže ZRAK.
Kutikula je nepropusni voštani pokrov kojeg stvaraju epidermalne stanice lista, izbojaka i ostalih nadzemnih dijelova biljnog organizma koji nemaju kore niti periderma (zaštitne ovojnice, npr. površinska ovojnica na paradajzu). Kroz kutikulu mineralno hranjivo ne prolazi.

Urea!
Kroz ektodezmije u stanicu lista može ući 3-4 jedinice iona, a 150 jedinica uree. Tako se došlo do zaključka da bi urea mogla biti dobar prenositelj kationa i aniona (pozitivnih i negativnih iona) u stanice. Npr. željeza se preko lista može prenijeti 3-40 puta puta više u prisutnosti uree nego bez nje. Naravno, cijeli taj postupak odvija se aktivnim transportom (za njega je potrebna energija ATP) te je učinkovitost prijenosa ovisna o temperaturi i svjetlosti. Nije svejedno prihranjujemo li folijarno po mraku ili po danu. Prijenos nekih iona bit će učinkovitiji uz prisutnost svjetla, za neke druge će biti bolji mrak, a za neke je svejedno. Najveća apsorpcija folijarno primijenjene prihrane odvija se u prvih sat vremena. Apsorpcija je moguća samo dok je hranjivo na listu u tekućoj fazi, dakle dok otopina folijarnog gnojiva nije osušena. Apsorpcija suhog ostatka hranjiva na listu nije moguća dok ga se ponovo ne smoči i na taj način otopi u otapalu (vodi). Zbog toga su korisna vlažna jutra kada se na lišću stvori rosa. Rosa otapa osušeno mineralno hranjivo na listu zaostalo od zadnje folijarne prihrane pa biljka može ponovo apsorbirati otopljene minerale.