ABSTRACT. It was found that the best source of iron for lettuce grown in peat is Fe-DTPA chelate in the doses of 50 and 75 mg Fe·dm^-3. Chelates Fe-EDTA+DTPA can be used in the dose of 50 mg Fe·dm^-3. Higher doses of iron in the form of these chelate and all doses of Fe-AM-4 chelate used in the experiment caused a decrease of yield and on lettuce leaves there appeared symptoms indicating chelate excess. Chelate AM-4 can not be used for lettuce grown in peat.

The effect of iron chelates on the yielding and iron content
in greenhouse lettuce

Summary

The experiments carried out in spring 2005 and 2006 investigated the effect of Fe-DTPA, Fe-EDTA+DTPA and Fe-AM-4 chelates on the yielding of lettuce and the content of iron in lettuce leaves. Fe levels of the applied chelates were the following: 20 (Control), 50, 75, 100 and 125 mg Fe·dm^-3 peat.

After the application of the above Fe levels, lettuce yields in chelate Fe-DTPA did not differ. Application of the levels 75-125 mg Fe in chelate Fe-EDTA+DTPA significantly decreased the yields and influenced the plants, symptoms indicating chelate excess appeared. After the application of all Fe levels (except for control), in chelate Fe-AM-4, the yields showed further reductions and the symptoms of chelate excess became still more intensive.