Maintenance of iron and other micronutrients in hydroponic nutrient solutions

Abstract

The chelating agents DTPA, EDTA, EDDHA, HEDTA and others have been used as sources of iron in hydroponic nutrient solutions. Commercial hydroponics would be impossible without them. Although these have resulted in some success, micronutrient balance remains as an important problem in commercial hydroponic operations. Our results suggest that for a given plant species, it does matter which chelating agents are used. For some plant species, the low stability Fe chelates give advantage. The results also suggest that all of the Fe, Zn and Cu depending on pH may be chelated with good results and good control of micro‐nutrients.

In commercial uses of hydroponic nutrient solutions, particularly in the Nutrient Film Technique (NFT), Fe, Zn and Cu concentrations increase with time of recycling. These micro‐nutrients can enter the system via contamination mostly through the air. Soil dust is a major contributor but Zn in metallic structural components in greenhouses is perhaps the prime contributor of Zn. There is some evidence that leaf contamination of these three elements decreases root uptake of them perhaps by a feedback inhibition mechanism. A result is that less of them is taken up in comparison with other nutrients so that eventually an imbalance results in the nutrient solution even though at the start of the cycle there was good balance. The limiting factor on the usability of a nutrient solution in recycling them becomes the build‐up of these three micronutrient elements. Even though Fe can build up as result of contamination, an induced deficiency can result from the imbalance from Zn and Cu. This is one reason why an excess of chelating agent is useful; it protects against excess availability of the zinc and copper which often induces Fe deficiency.

Key words:

• Chelating agents
• iron
• zinc
• copper
• nutrient balance