Method for determining the optimal quantity of water to be provided to a plot under cultivation, comprising the following steps: b) acquiring information about soil features (TAW, RAW), said information about soil features comprising information about the water quantity available as a whole in the roots area and information about the quantity of water immediately available for the roots; c) acquiring information about the kind of crop, including its developing stage (Kc) and the level of water stress which the same is able to undergo according to the developing stage; d) acquiring information about weather conditions foreseen including the quantity of rain foreseen (P i-1); e) calculating a parameter indicating the level of water stress in the soil at the current time (Ks i-1); f) calculating, according to said parameter (Ks i-1) calculated at point e) and to said information about crop developing stage (Kc) acquired at points c) and d), a parameter indicating the water quantity lost by the soil due to evaporation and transpiration (ETci); characterized in that the method further comprises, before step b) the following step: a) acquiring information about the soil water content at the current time (D i-1); in that said parameter indicating the level of water stress in the soil at the current time (Ks i-1) is calculated according to said information about the soil water content at the current time (D i-1) and according to said information about soil features (TAW, RAW). and in that the method further comprises the following steps: g) calculating, according to said parameter (ETci) calculated at point f), a parameter indicating the water stress in the soil at a time step following the current one (Ks i), in the hypothesis of no irrigation; g1) calculating a water balance of the soil, where soil water depletion at the time step following the current one (D i) is calculated as a function of said soil water content at the current time (D i-1), of said quantity of rain foreseen (P i-1), of the water quantity to be provided at the current time (IRR i-1) and of said water quantity lost by the soil due to evaporation and transpiration (ETci) h) determining, by means of said water balance of the soil calculated at point g1), the water quantity to be provided at the current time (IRR i-1) so that the value of said soil water depletion (D i) has a value such that said parameter (Ks i) calculated at point g) is higher or equal to said level of water stress which the crop is able to undergo according to its developing stage b) acquiring information about soil features (TAW, RAW), said information about soil features comprising information about the water quantity available as a whole in the roots area and information about the quantity of water immediately available for the roots; c) acquiring information about the kind of crop, including its developing stage (Kc) and the level of water stress which the same is able to undergo according to the developing stage; d) acquiring information about weather conditions foreseen including the quantity of rain foreseen (P i-1); e) calculating a parameter indicating the level of water stress in the soil at the current time (Ks i-1); f) calculating, according to said parameter (Ks i-1) calculated at point e) and to said information about crop developing stage (Kc) acquired at points c) and d), a parameter indicating the water quantity lost by the soil due to evaporation and transpiration (ETci); a) acquiring information about the soil water content at the current time (D i-1); g) calculating, according to said parameter (ETci) calculated at point f), a parameter indicating the water stress in the soil at a time step following the current one (Ks i), in the hypothesis of no irrigation; g1) calculating a water balance of the soil, where soil water depletion at the time step following the current one (D i) is calculated as a function of said soil water content at the current time (D i-1), of said quantity of rain foreseen (P i-1), of the water quantity to be provided at the current time (IRR i-1) and of said water quantity lost by the soil due to evaporation and transpiration (ETci) h) determining, by means of said water balance of the soil calculated at point g1), the water quantity to be provided at the current time (IRR i-1) so that the value of said soil water depletion (D i) has a value such that said parameter (Ks i) calculated at point g) is higher or equal to said level of water stress which the crop is able to undergo according to its developing stage