Iron deficiency frequently affects protected crops such as strawberries and causes the characteristic symptoms of interveinal yellowing. In turn this results in yield losses and reduced fruit quality.
The basic cause is high pH of the substrate/nutrient solution and associated increased bicarbonate levels. The problem is exacerbated by poor quality irrigation water, periods of rapid vegetative growth and, it is claimed, by the use of newer alkaline substrates such as coir.
As pH rises above about 6.0 elemental iron is made increasingly unavailable because of precipitation. Because of their chemical stability EDTA and DTPA iron chelates have been used successfully for many years to overcome the problem.
Bicarbonate ions occur naturally under high pH conditions and are produced by plant roots. High concentrations of bicarbonate ions interfere with the natural process of iron uptake by roots. The chemical stability of FeEDTA and FeDTPA chelates is also affected making them less effective.
The problem is easily overcome by substituting with the more robust FeEDDHA. This chelate is unaffected by bicarbonate and has a very wide pH stability range.
Remember though that the solubility (at high concentrations) of FeEDDHA is reduced when the solution pH is less than 4.0 (approx.) so add the chelate to the non-acidified "A" or "Calcium" tank.