LidoQuest EDTA chelated manganese 13%, hydroponic fertilizer.
In micronutrient discussions the topic is usually iron, iron and iron. As a major microelement with dose rates sometimes up to 2.5 ppm it is fair to focus the attention on iron. However, we should not forget the importance of Manganese (Mn) as a second major element. Manganese has a very specific role on it’s own and does directly have an impact on the availability of iron in the substrate.
Manganese has the ability to change its form from Mn4+to Mn2+, this is called the reduction reaction or the redox process. This capability of Mn makes it important in many redox processes in the plant, and has specific roles in photosynthesis. Inhibition of photosynthesis occurs even with mild Mn deficiency. Deficiencies disturb the nitrogen metabolism and destruct the chloroplasts causing interveinal chlorosis in mainly middle to young leaves. These symptoms are sometimes hard to distinguish from iron chlorosis. At a later stage red-brown necrosis spots appear. Lower Mn levels also decrease the disease resistance of the plant. Another role as been demonstrated in a recent study (Aktas et al, 2005), where it is suggested that Mn serves as an antioxidant in pepper fruit and that Mn addition to peppers especially grown under high salinity, alleviates blossom-endrot symptoms (BER) in the fruit. An increase of NAD(P)H oxidase activity stimulates the production of reactive oxygen in the fruit. This reactive oxygen contributes to the appearance of BER symptoms. Manganese and zinc however inhibit the NAD(P)H oxidase activity and therefore help preventing BER . This shows the importance of correct Mn nutrient management. You may have already been aware of it, but when Mn is added to the nutrient solution, it does not always do what you think it should do.
..And Its Behavior
What can happen to Mn once it is part of the nutrient solution? There are two major reactions happening: Sometimes the desired levels of ~ 9-12 μmol/l (0.55 – 0.7 ppm) in the substrate are hard to reach and keep steady. Especially growers that grow on organic substrates like cocopeat and peatmoss might have the feeling that for some reason they lose manganese somewhere in the system. The reason behind this can be explained by the interaction of the organic substrate and the manganese. Manganese applied in the form of regular MnSO4 adsorbs to organic matter.
The complexes of organic matter are mainly negatively charged. This provides an excellent bond for the positively charged manganese ion. Laboratory experiments have shown the high adsorption capacity of cocopeat for micronutrients like manganese (graph 1).
The graph shows that cocopeat has a low affinity for Mn-EDTA. In other words manganese protected by a chelating agent like EDTA is more available for your crop and will stabilize your Mn figures in the slab as adsorption is not a disturbing factor anymore. A second important reaction is the interaction with chelated iron. Free manganese competes with the chelated iron for a position in the chelate. This chelate can be EDTA as well as DTPA. Because the Fe bond with DTPA is stronger, the competition with manganese will be less and the Fe-DTPA chelate is better preserved. The result however of this competition is a loss of iron in the substrate. Especially with a relatively weak chelate like Fe-EDTA the loss of iron can be substantial at pH levels around 6-6.5.
As graph 2 shows, manganese is accountable for a significant part of this loss when pH’s move stealthily up. One way to compensate for this iron loss is simply to apply more iron. An option that many growers follow. The other way is to use Mn-EDTA. Growers that have shifted to Mn-EDTA confirmed a decrease in iron chelate use by 10-20% while keeping satisfactory levels of iron in the substrate.
Manganese-EDTA has a different behavior in nutrient solutions and in the substrate than regular MnSO4 has.
- Mn-EDTA hardly adsorbs to organic complexes and will stabilize the available Mn levels in the substrate. The desired level of 3-7 μmol/l (~0.2- 0.4 ppm) is easy to reach.
- Mn-EDTA improves the performance of the Iron-chelate. This can lead to an estimated reduction in Fe use of 10-20%
- Stabilized manganese figures in the substrate
- Improved Iron chelate performance