The expediency of assessment of plant biophile element supply using the feedback principles is shown in this paper. The experimental data on assessment of plant needs for food compounds by chloroplastid activity, the content of positively and negatively charged cation complex compounds, by the photosynthesis parameters of plants developing in soil suspension after bringing the ions under study into the suspension are presented. The methods are based on principle addition into the soil or plants and on the plant feedback analysis and the extremum assessment. The expediency of their use for the assessment of plant needs for food compounds (plant species and cultivars depending on their stage of development) has been shown by their absorption out of the analysed soil suspension, and then out of the culture solution. The assessment of sorption properties of plant root systems is provided.