dear Jefline Kodzwa

It is mg/g or %

Thanks Tony Sajyan, but I think % is not an SI unit .

I think it is mg/kg in other words ppm

It is mg/g or g/kg of the dry weight of plant part (e.g root, shoot biomass or leaf)

mg/kg which is ppm

Plant Nitrogen concentration is usually reported in % which is equivalent to g/kg when multiply by a factor of 10. i. e. g/kg N = % N * 10

Augustus Ilori thank you but I think 1% N = 10g/kg N which is vice versa of what you said.

Yes, that's exactly what I meant.

Thank you all for taking your time to reply this question. I really appreciate your input