Is the result you have shown the concentration of the digested sample as measured by the instrument (in liquid form, hence the units are mg/L), or has this been adjusted for the dilution factor, which should have returned a value in mg/kg?

Perusing (Book Plant Analysis Handbook IV

Do you have any pictures to go with the sample? That may help identify if the plant is experiencing nutrient deficiency or other conditions. Also pertinent to check is:

• what plant part did you measure? Leaf or petiole?
• how old was the material? new, mature, senescent?
• have you checked the calculations used dry mass not fresh weight?

As to whether that is a lot or none at all, it depends on how much plant you have: A large plant (eg 10kg mature plant) with an apparently low concentration (5mg/kg) will have a greater total content (50 mg Fe) than a small plant (0.1 kg seedling with relatively high (say 100 mg/kg) with only 10 mg Fe total content.

@matthew wheal, this is the concentration of the digested sample as measured by the instrument

So now you need some other values:

• Mass of the dried tissue sample used for the digestion, let's use 120 mg (0.12 g) as an example
• Volume of the solution after digestion, let's use 20 ml (0.020 L) for the example

Then, concentration x volume = mass

• 5.43 mg/L in the solution x 0.020 L = 0.1086 mg
• ie 108.6 µg Fe in the dried sample

Then mass(fe) ÷ mass(tissue) = concentration (fe in tissue)

• 108.6 µg ÷ 0.120 g = 905 µg/g or 905 parts per million

Substitute the actual mass and volume and you'll have your results.