Occurrence and correction of lime-induced chlorosis in petunia plants

The effect of various concentrations and ratios of iron (Fe) and manganese (Mn) chelates on growth, micronutrient uptake and chlorophyll content was investigated in a glasshouse experiment using potted petunia plants. The plants were cultivated in a peat substrate amended with dolomitic limestone at rate of 3.0 g/L (control substrate) or 12.0 g/L. The higher rate was established both to restrict the uptake of Fe, Mn and other nutrients and also to test the effectiveness of various Fe and Mn treatments. The plants in all the treatments were fertigated at weekly intervals with a nutrient solution containing macronutrients and micronutrients. Various chelate forms of Fe and Mn were used with the exception of two treatments where these two elements were omitted. The effects of different substrate pH levels (derived from different limestone contents) had a large effect on plant growth, chlorophyll content and content of Fe and Mn accumulated in the plant leaves. The plants in the high-limestone substrate devoid of Fe and Mn had reduced growth and lower chlorophyll content. They also had lower leaf Fe and Mn content than the control plants in the R3 substrate. Regular fertigation with a nutrient solution containing Mn and Fe improved plant growth rate and also increased chlorophyll content. However, its efficiency depended on the chelate form and concentration used. The effect of chelate application on the Fe and Mn leaf content was unclear as it only marginally increased leaf Fe absorption in some treatments. No effect of the various Fe/Mn ratios was observed.