The present invention pertains to plant additives containing a molecule selected in a family of compounds, wherein said molecule can modulate some molecular markers and physiological modifications observed in cases of phosphate deficiency. The apparatus may produce an electrical response to deformation and, thus, function as a strain gauge. The technical result is achieved due to the fact that the test structures are positioned outside the radiographic screen emitting surface and are provided with controlled sources of primary radiation installed so that each test structure is located in the direct ray path from the said sources. The optical thin film is disposed above the dual-wavelength chip. The invention further provides compositions and kits for practicing said methods.