Multi-variable diagnostic method of the nutritional status of a crop and for the recommendation of the amounts of nutritional elements to apply to optimize this nutritional state comprising the following steps; • the sampling of the crop's aerial dry matter and the determination of its n marco - elemental histological contents, X, selected from a group consisting of N, P, K, Ca, Mg, and/or S, or even Na, and/or trace elements contents selected from a group comprising Fe, Mn, Zn, Cu, B, Mo, Cl, Si and/or Co; • the establishment of normal histological contents, x n, for each of the n aforesaid nutrients being considered; • with respect to these n x n normal values, the calculation of nutritional indices, Ix n, for each of the n aforementioned nutrients by multiple comparison of nutritional ratios based on the arithmetic means via procedures such as DRIS (diagnosis and recommendation integrated system), the geometric means via procedures such as CND (compositional nutrient diagnosis), or any other multivariate method taking into account the interactions of the above nutrients, age and/or dry matter production of the crop at some given stage of growth; • according to the aforementioned nutritional indices, the establishment of elemental histological levels to be achieve for each of the aforesaid n nutrients; • based on the aforesaid elemental histological levels to be achieved for each of said elements, the recommendation of amounts of such nutritional elements to apply so as to optimize the nutritional status of the crop as warranted by an absence of deficiencies and/or nutritional imbalances; characterized in that; • the n normal values x n are determined by extrapolation of a nitrogen nutritional function, x n = f given that NNI (nitrogen nutrition index) is equal or greater than a certain value between 0.90 and 1.10, that is 1.00 +/- 0.10; • the aforesaid FAN is described mathematically using a function selected from a group comprising of polynomial - preferably of second degree, exponential, power, logarithmic or logistic and/or non-linear functions comprising upper and/or lower asymptotes. • the sampling of the crop's aerial dry matter and the determination of its n marco - elemental histological contents, X, selected from a group consisting of N, P, K, Ca, Mg, and/or S, or even Na, and/or trace elements contents selected from a group comprising Fe, Mn, Zn, Cu, B, Mo, Cl, Si and/or Co; • the establishment of normal histological contents, x n, for each of the n aforesaid nutrients being considered; • with respect to these n x n normal values, the calculation of nutritional indices, Ix n, for each of the n aforementioned nutrients by multiple comparison of nutritional ratios based on the arithmetic means via procedures such as DRIS (diagnosis and recommendation integrated system), the geometric means via procedures such as CND (compositional nutrient diagnosis), or any other multivariate method taking into account the interactions of the above nutrients, age and/or dry matter production of the crop at some given stage of growth; • according to the aforementioned nutritional indices, the establishment of elemental histological levels to be achieve for each of the aforesaid n nutrients; • based on the aforesaid elemental histological levels to be achieved for each of said elements, the recommendation of amounts of such nutritional elements to apply so as to optimize the nutritional status of the crop as warranted by an absence of deficiencies and/or nutritional imbalances; • the n normal values x n are determined by extrapolation of a nitrogen nutritional function, x n = f given that NNI (nitrogen nutrition index) is equal or greater than a certain value between 0.90 and 1.10, that is 1.00 +/- 0.10; • the aforesaid FAN is described mathematically using a function selected from a group comprising of polynomial - preferably of second degree, exponential, power, logarithmic or logistic and/or non-linear functions comprising upper and/or lower asymptotes.