Micronutrients in soilless cultures

20 July 2016
Micronutrients in soilless cultures

by Kurt Verhelst, Senior Product Manager
and Dave Pinxteren, Application and Development Manager Horticulture, Prayon

Microelements: iron is the most difficult element to keep available for your plants

MICROELEMENTS: IRON IS THE MOST DIFFICULT ELEMENT TO KEEP AVAILABLE FOR YOUR PLANTSMicronutrients are as important for plants as their sister macronutrients. Only the quantity needed to ensure biochemical processes are not inhibited is mostly a thousand times smaller. Nevertheless, deficiencies of these micronutrients can cause similar symptoms as of nitrogen (N), phosphorus (P) and potassium (K) shortcomings, leading to equal crop damage and possible production loss. Already known for many years, iron is the most difficult element to keep available for your plants. Ferrous (Fe2+) salts are highly water-soluble, however when ferrous iron is exposed to oxygen it converts readily to the ferric state (Fe3+). Ferric iron then reacts with the alkalinity in the water to form iron oxides, iron hydroxides and iron phosphates. The insoluble properties of these end products make it nearly impossible for your crop to take up the iron. As the fertigated iron is lost, an iron deficiency combined with its ,typical interveinal yellowing of young leaves will be the logical next step. This chlorosis will eventually inhibit the plants growth and development. A synthetized organic molecule has been introduced in horticulture to keep iron and other transition metal ions dissolved and available for plants: chelates. However after the metal ion has been taken up by the root system, the fate of these chelating agents is not known. As they are very sensitive to UV light, a significant part will be broken down. Others could be taken up by the plant by passive transport, being accumulated in photosynthetic active areas of the plant. Until now, without chelates it was impossible to grow plants in soilless cultures. A chain of linked orthophosphates:a polyphosphate has been created


The phosphate products industry aimed for horticulture focus mainly on MKP, MAP, DAP and phosphoric acid formulations. They form the standard phosphate sources used in fertigation systems and for water soluble NPK blends. All these fertilizers contain one orthophosphate (H2PO4-) molecule, linked to potassium in the case of MKP and to ammonia in the case of MAP and DAP. Orthophosphates are very sensitive to higher pH levels and will easily precipitate together with other nutrients like calcium and iron. Consequently these elements are locked up in the soil or substrate and become unavailable as a nutrient. Condensation of water between two phosphoric acid molecules combines these two molecules. Repeating this process leads to a chain of linked orthophosphates: a polyphosphate has been created. Used correctly in the right combination and dosage, polyphosphates create possibilities to enhance nutrient uptake, stimulate plant growth and increase yield. Being less sensitive to higher pH levels than orthophosphates, polyphosphates will boost the availability of phosphorus. At root level they are broken down into orthophosphate by hydrolysis and are taken up by the plant. As such they become an easy source of P for the plants. Research has shown higher nutrient levels in the plant when the correct combination of polyphosphates is used. The inorganic nature of polyphosphates prevents them from being broken down by UV light. UV lamps are significantly less polluted by iron deposits, improving their UV light emission and disinfection rate. It is proven that plants grown in UV light sensitive irrigation systems such as mobile gully systems and aeroponics don’t suffer iron deficiencies that easily.
However polyphosphates are currently not widely used as a phosphate source because they are more expensive. In addition, if not handled correctly, they break apart in orthophosphates, ending up as a standard phosphate fertilizer not being able to show their advantages. The combination with micronutrients shows new benefits and is a competitive choice.


Combination of polyphosphates and microelementsDue to the chemical structure of polyphosphates, they are able to smoothly “attract” cations including iron and other microelements. This complexation allows cations to dissolve better in water and stay available for plants, just like chelates do. So a new challenge rises: replacing iron chelates by polyphosphates, combining the positive effects of the absence of chelates and the presence of polyphosphates in the irrigation system. Prayon, leader in phosphate production and innovation, has realized extraordinary results in this field. Since 2012 Prayon started to develop a combination of polyphosphates and microelements. The first product was a combination with iron. At the GroSci 2013, The International Symposium on Growing Media and Soilless Cultivation in Leiden (The Netherlands), researcher Wim Voogt from Wageningen University gave a lecture on his research concerning the new polyphosphate-iron combination. A comparison between iron polyphosphates and chelates in soilless grown crops proves chelates were no longer necessary to grow cucumbers in a soilless medium. During the trial, 15 micromoles of iron were dosed to the plants. The positive control received iron in the form of DTPA chelate, the dosage of iron in the testing object was performed by an equal quantity of iron complexed to polyphosphates. To control the iron input of the used medium and water, a third object was fed with iron sulphate also known as the negative control. As there was no chelating agent nor a complexing molecule present in this object, all iron precipitated immediately causing a severe iron deficiency and finally inhibiting plant growth. Plants grown with polyphosphates, developed equally as the reference plants and never showed any iron deficiency as in the negative control. These trials proved that iron was kept available for the plants, meaning that chelates were no longer indispensable to grow cucumbers in a soilless medium. At Proefcentrum Hoogstraten, a trial center managed by Belgian growers, Prayon designed in 2013 a trial for tomato in soilless culture, comparing standard used chelates with the new iron fertilizer based on polyphosphates. Plants of both objects developed equally and never showed any yellowing of the leaves, indicating iron was sufficiently available. Leaf analysis showed even higher iron levels in the plants
treated with polyphosphates showing a better uptake of the nutrients. As Hoogstraten is very well known for its strawberry production, Prayon tested also the possibilities for the new iron based fertilizer in strawberries at this trial center. The same good results were booked during this trial: equal growth and development, no chlorosis and very good production results. In 2014 Prayon continued its practical research at Wageningen University. Cucumber was grown on different substrates and this time more attention was given to the interaction with the other microelements. Again iron uptake was guaranteed. Likewise the other trace elements were positively evaluated. Keeping in mind that manganese and copper are perfectly soluble in water, their uptake can be enhanced in the absence of chelates as analysis of drain water show very low manganese and copper concentration. Especially zinc levels of the leaves were significant higher compared to the reference where chelates had been added. These results indicated that some chelates could block the availability of zinc. When the iron is taken up by the plant, the chelate molecule searches for a new cation. In many cases zinc is taken out of solution to form zinc-chelates which become unavailable for the plant. Even though zinc is measured in the drain this situation can cause zinc deficiencies in recirculated irrigation systems.

Growing conditions

Tipburn is known as a deficiency of calcium and is widely spread in very divergent crop cultures. Young plant tissue can suffer a lack of calcium whenever calcium uptake and/or transport are hindered. Plant cells formed during this calcium shortage have weak cell membranes making them very vulnerable to burst. Climatic stresses result often in plasmolysis and disintegration of the membranes. These collapsed cells are lost and become necrotic, leading to calcium scorched leaves. Many diseases use these necrotic parts as an entrance to infect the plant. One of them is grey mould, also known as botrytis. This feared fungus has been causing a lot of damage in greenhouse cultures. During the different tests on cucumber researcher Wim Voogt observed a very interesting phenomenon. Plants grown with the new iron based fertilizer showed significant less tipburn. Cucumber growers refer often to this as “umbrella leaves”. On a scale from 0 (absence of tipburn) to 3 (severe tipburn) the reference plants grown with DTPA iron chelates gained an average of 1 or more on this scale. As the tests were achieved during winter time so artificial lighting was necessary, the occurrence of tipburn was as expected. On the other hand, tipburn was almost completely absent on polyphosphate grown plants resulting in an average of 0.2.

Prayon contributes to secure the nutrition of the world’s expanding population

Prayon contributes to secure the nutrition of the world’s expanding population

Headquartered in Belgium, the Prayon Group specializes in phosphate chemicals and operates production sites in Belgium, France and the United States.
Owned equally by OCP SA (Morocco) and the Wallonia Regional Investment Company (SRIW, Belgium), Prayon manufactures and distributes a wide range of purified phosphoric acids, phosphate salts and fluorine products geared towards the food and fertilizer sectors, and for many different industrial applications. Hortipray® products are a complete range of water soluble fertilizers (monoammonium phosphate, monopotassium phosphate, potassium nitrate, calcium chloride, and more) developed to meet the needs of producers and distributors. The new developments as described in this article have been patented and successfully introduced in modern horticulture. In close cooperation with its partners, Prayon is currently entering the market with these new innovations. Together with other trial centers all over the world, Prayon wants to open doors for partnerships for further growth and development. Accepting new challenges in the future, Prayon fulfills its responsible role to secure the nutrition of the world’s expanding population.


Argus FMB East Europe 2016
The Argus FMB East Europe Fertilizer conference takes place this year in the beautiful city of Krakow, Poland, on 15-17 June 2016. 
The countries of eastern Europe boast huge areas of arable land with high agricultural output. However, fertilizer application rates in some parts of East Europe are below the European Union average, suggesting that there is still room for real consumption growth which will achieve optimal productivity. Argus FMB East Europe zooms in on these countries and gives attendees an opportunity both to hear analysis of these local markets and to meet the local manufacturers and distributors who serve them. Over 250 participants attend from all countries in this region, and this year large delegations are expected from Bulgaria, Romania, Hungary, Lithuania and the host country, Poland. A major theme of this year’s conference will be the increasing shift away from ‘straight’ fertilizers towards more speciality products, which provide higher margins for producers as well as higher yields, better return on investment and reduced risk of environmental problems for end users. Experts will examine the most beneficial products for eastern Europe, based on soil type and crop portfolio. Micronutrients, liquid fertilizers and slow and controlled release products will all come under the spotlight. At the same time, this shift towards higher value, blended products has the potential to change the shape of trade in primary nutrients, as more and more producers look to diversify into NPKs and achieve higher added value from the raw materials at their disposal. The agenda will include analysis of the nascent trade in different NPK blends and the impact on the rest of the market. Networking is an important part of all Argus FMB conferences, and delegates will have ample opportunity to meet with potential business partners and catch up with old friends. As well as time during coffee breaks and lunches on the conference days, all delegates are invited to two cocktail parties in the evening which offer the perfect environment to build relationships in an informal and enjoyable environment. Our new networking app for smartphones and tablets makes connecting with other delegates easier than ever. Krakow is a beautiful city with a historic castle as well as a charming old town, centred around the main square and offering many places to eat and drink. A perfect location to welcome the summer and to do business in a region which offers good opportunities for growth for everyone in the supply chain! feature


The Argus FMB East Europe Fertilizer conference takes place this year in the beautiful city of Krakow, Poland, on 15-17 June 2016.
To see more details of the conference as they become available, visit www.argusmedia.com/fertilizer-east-europe

Argus FMB
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