A combined chemical-physiological test of the fertility of the soil and the probable reaction of a crop to fertilization is discussed. The full test involves 3 complete analyses: 1) the green leaves of the crop, collected before florification, 2) the surface soil, 3) the subsoil. The leaf analysis will reflect the nutritional condition of the plant, especially as to whether any element is lacking in the soil and whether eventually an injurious lack of balance between the inorganic elements exists. The soil analysis will show the minimum availabilities of alkaline substances and the probable inhibiting effect of lime on the uptake of Mn and K or the antagonistic effect of K on Ca. Because of its rapidity, cheapness, and exactness the quantitative spectral analysis will provide the most suitable method for the determination of cations.