PRODUCTS &TRENDS Phosphites and Phosphates: When Distributors and Growe There has been some confusion lately in Europe and or many years foliar phosphate rocks. Phospho- North America, now spreading to other parts of the applications of sulphur rus is a component of world, over terms used for fertilizers and chemicals Fand some trace elements DNA and RNA and an containing phosphorus. Distributors and growers have such as Zinc, Copper and essential element for all been using phosphate fertilizers for many long years. Manganese have been used in living cells. Due to its high combatting plant pathogens. reactivity, phosphorus is They are familiar with formulations like single super More recently it was also never found as a free ele- phosphate (SSP), triple super phosphate (TSP) proved that e.g. MKP (Mono ment in nature. It is very diammonium phosphate (DAP) but also MAP and MKP Potassium Phosphate) has a reactive and rapidly com- (Monopotassium Phosphate). All of them provide fungicidal activity, not only bines with other elements phosphate derived from phosphoric acid (H3PO4). The MonoPotassium Phosphites! such as oxygen and hydro- phosphate that plants use is in the form HPO4 and So where is the problem? Is it gen. When fully oxidized, H2PO4, which is quickly converted in soil from primarily that the plant pro- it is bonded with four oxy- fertilizers. Recently, new terms are being used including tection industry, which is gen atoms to form the well phosphorous acid (not phosphoric acid), phosphite (not being subject to tough and known phosphate mole- phosphate), and phosphonite or phosphonate. Unlike expensive regulation to mar- cule. If not fully oxidized, the phosphoric acid that contains four oxygen atoms, ket its products including then hydrogen occupies phosphite-based fungicides, the place of one oxygen phosphorous acid (H3PO3) and the related compounds is not happy with the plant atom and the resulting contain only three oxygen atoms. Is that difference of nutrition industry declaring molecule is called phos- one oxygen atom very important? In fact a clear and registering phosphite phite. The most important distinction exists between Phosphoric acid and based products as fertilizers- commercial use of phos- phosphorous acid: the former is a plant nutrient and the generally at no cost and with- phorus-based chemicals is latter has primarily fungicide applications. It is thus very out any delay- even if they the production of fertiliz- obvious that claims suggesting that either compound may have more fungicidal ers, based on phosphates. may exactly fulfill the functions of the other are properties than nutritional In agriculture, an other misleading. Therefore, is the bottom line that on the one impact at the prescribed important use of phospho- side phosphates are what is needed for fertilizer but will application rate? The plant rus-based chemicals is the protection industry may get production of fungicides have no effect on plant diseases and on the other side even more nervous when the based on phosphites. that phosphites are useful in managing diseases but will accompanying promotional This is all very simple but not provide plants with the phosphate they need? Maybe literature for such products it becomes confusing and not so simple! New Ag International went to investigate describes them more as “bios- misleading when some among suppliers and scientists to try sorting out what is timulants and fortifying web literature of a compa- really true, untrue and partly true? Our findings: What is ingredients “ or even “plant ny having pioneered the true is that plants can absorb the phosphorous acid protectors” than as simple use of phosphites (deriv- compounds through roots and leaves. What is also true source of nutrients! ing from Phosphorous is that plants are incapable of using DIRECTLY the acid) as fertilizer, in its SOME BASICS ABOUT FAQ page, compares Phos- phosphorus acid as a nutrient source. What is partly PHOSPHORUS true is that the phosphorous acid compounds can break phorous to Phosphorus Phosphorus is the chemi- (what for?) and describes down in the soil to available forms of P, but this process cal element that has the the latter as “A poisonous is very slow and will not provide adequate P nutrition. symbol P and atomic num- nonmetallic element of the What is untrue is that they can complement and even ber 15. A multivalent non- nitrogen group, obtained replace phosphate fertilizers in all instances. And what is metal of the nitrogen as a white, or yellowish, very true above all is that a number of people from group, phosphorus is com- translucent waxy sub- various bodies entertain confusion in the market! monly found in inorganic stance, having a character- 36 NEW AG INTERNATIONAL PRODUCTS &TRENDS rs alike could get confused! istic disagreeable smell”. ous phosphorus (P) con- and phosphonites) play an phosphonate anion and an Which one would you use taining compounds as fer- important role in agricul- aluminum ion as the after reading this and tilizers. It concluded that ture as active ingredients counter ion. The problem knowing nothing about Phosphite was a poor in fungicide materials. This (see table 2) is that where- chemistry? source of nutritional Phos- market was pioneered by as some of the phosphite phorus since plants treated Bayer Cropscience with compounds are labeled as PHOSPHITES PRIMARILY by phosphite grew weakly. world-famous brands pesticides, which required USED AS FUNGICIDES Therefore at this time Aliette and Fosetyl-Al. the manufacturer/distrib- As early as 1930, a study phosphite couldn’t find a When the patent for the utor to spend the time and was carried out to deter- niche in the market as a trademark Fosetyl-Al money to register the com- mine the efficiency of vari- potential source of plant expired, several other fun- pound, others, in North nutrient. Fourty years later, gicide manufacturers cre- America but also in a num- phosphites returned to the ated phosphite-based ber of European countries market when it was found fungicides by simple for- (Spain, Italy, Germany, that they were very effi- mulation of phosphite etc…) are advertised and cient against the Oomycota with potassium, ammoni- registered as fertilizers, (i.e. species of phytophtho- um, sodium, and alu- which of course bypasses ra and pythium). Today it minum. Trademarks now the expensive and time is well documented that also include, among others consuming registration the toxic effect of phos- ProPhyt (sold by Helena process, and are even now phite to Phytophthora Chemicals), Phostrol tested in organic farming comes from the activation (Nufarm America), Phos- production (e.g. on grapes of defense mechanisms in guard, , etc. Phosphite in France, Germany, Italy)! plants or by direct action fungicides are first formu- These phosphorous acid on this fungal-like organ- lated as ethyl phosphonate compounds, most of them ism, and phosphorous acid by reacting phosphite with based on potassium phos- compounds (phosphite ethanol to form the ethyl phites, although active against the Oomycota and some fungal diseases, are claimed to provide phos- phorus nutrition to the plant. True, untrue, partly true? What is true is that plants can absorb these compounds through roots and leaves and once in the plant, the phosphorous acids compounds are very stable. What is also true is that plants are incapable of using DIRECTLY the phos- phorus acid as a nutrient source. What is partly true is that the phosphorous acid compounds can break down in the soil to avail- able forms of P, but this NEW AG INTERNATIONAL 37 PRODUCTS &TRENDS process is quite slow and Table 1: Some products of the Phosphorus family used in agriculture will not provide adequate Name Symbol Comments and speedy P nutrition. The Phosphate Family What is untrue is that they Phosphorus P The chemical element. can complement and even Does not occur as a free element in nature replace phosphate fertiliz- Phosphoric acid H3PO4 Compound found in most phosphate fertilizers. Contains 32% P ers in all instances. Phosphate PO4 Completely dissociated form of H3PO4 A RENEWED INTEREST ON Phosphorus oxide P2O5 Formula used to express the phosphorus content in fertilizers. PHOSPHITES AS PLANT NUTRIENT It does not occur as a free element in nature SINCE THE EARLY NINETIES Finished Phosphate Fertilizers: Single Super Phosphate SSP Dry fertilizer containing about 19% P2O5 What is also true is that the Di Ammonium Phosphate DAP 18-46-0 dry fertilizer effectiveness of phosphites Triple Super Phosphate TSP 0-45-0 dry fertilizer in controlling plant dis- Monopotassium Phosphate MKP 0-52-34 dry fertilizer eases has been hiding their MonoAmmoniumphosphate MAP 12-0-61 dry fertilizer potential as fertilizers. Ammonium Polyphosphate APP 10-34-0 liquid fertilizer However, interest in the subject was renewed when The Phosphite family: Lovatt (1990), now Profes- Phosphorous acid H3PO3 Compound normally marketed as a fungicide. Contains 39% P sor of Plant Physiology at Phosphonate, Phosphite, Phosphonite PO3 Completely dissociated form of H3PO3 the University of Davis in Some phosphite derived products California and the recent Aluminium Phosphite Only marketed as a fungicide co-author of an article on Potassium Phosphite Marketed as a liquid fertilizer, e.g. 0-58-38, 0-30-20 or 0-24-16 the topic (in Better Magnesium & Calcium Phosphite Marketed as fertilizers Crops/Vol 90, 2006, N°4) Ammonium Phosphite Marketed as fertilizer, e.g. 11-35-0 with Mikkelsen (IPNI), Various micronutrients Marketed as fertilizers discovered that P deficien- phosphites (Zn, Mn) cy in citrus species caused Source: Various changes in nitrogen metab- olism. Through the appli- are available in the Ameri- phosphorous acid and all business logically register cation of potassium can and European markets are registered under the their phosphite based phosphite the biochemical and are sold as fertilizers fertilizer laws.