27 march 2018
In addition to the other nutritional elements a plant also needs sulphate (SO42-) in order to grow well. Sulphate is especially found in the proteins of the chlorophyll and in the vacuoles of cells in the plant. This month in ‘Focus on nutritional elements’ anything you should know about sulphate.
Sulphate (SO42-) is the oxidised form of sulphur and is absorbed by the plant roots. A plant can also absorb sulphur dioxide (SO2) from air. In that case too high concentrations can be toxic for plants. Sulphate doesn’t move so easy through plants. It is especially found in the proteins of the chlorophyll and in the vacuoles of cells. The sulphate contents in the dry matter of the plant is low and is about the 0,1 percent.
Sulphate is added to most potting soil by base fertilisers. According to the RHP requirements the sulphate contents in a substrate has to increase with a rising EC. Sulphate is a so-called anion and is not bound to the adsorption complex. So it remains well in the solution. Only in very high contents (above the 14 mmol/l in the soil solution) it precipitates with calcium as gypsum.
A sulphate deficiency hardly ever till never occurs in practice. The images resemble those of nitrogen deficiency. The only difference is in the fact that sulphate deficiency can be found in the youngest plant parts. That is because sulphate does not move easily through the plant. Sulphate excess is also a rare phenomenon. Plants that get to much sulphate, are dark coloured and do not grow well. This is comparable to the effect of a too high EC.
Sulphate deficiency at tomato.
Sulphate is in most potting soil base fertilisers. The sulphate level of RHP certified products is checked among other things before use in a substrate. For substrates with the RHP Horticulture quality mark, the substrate producer and grower decide together what the sulphate level should be, suitable to the culture.