A method for managing agricultural irrigation of a crop in an area of a field or a subplot thereof during a growing period, the method comprising: receiving data indicative of an irrigation recommendation function of the crop during a growing period (IR(t)), data indicative of a current crop water potential at a time t S within the growing period, data indicative of an evapotranspiration at t S, data indicative of a crop coefficient Kc, and optionally data indicative of a last irrigation time; wherein the data indicative of the current crop water potential are obtained using remote sensing data of said crop canopy and/or direct water potential measurements using in-situ plant sensors; computing a current crop water stress coefficient Ks cur (t S); computing an actual evapotranspiration (ETa) at t S (ETa(t S)) of said crop by taking a product of Ks cur (t S) and a corresponding non-stress crop evapotranspiration (ETc) at t S (ETc(t S)), wherein ETc(t S) = ET0(t S) * Kc(t S); and if ETa(t S) ≥ IR(t S), setting an optimal irrigation time (t opt) by: extrapolating a line L passing through or near a first point P 1 and a second point P 2, P 1 defined by first coordinates (t L, ETc(t L)) comprising a last irrigation time t L, which is earlier than t S, and ETc at t L, and P 2 defined by second coordinates (t S, ETa(t S)); obtaining a third point P 3, where at line L intersects, or is tangent to, a curve defined by IR(t), wherein t opt is equal to the day of the time coordinate of P 3; and setting the forecast irrigation amount by: computing a value v indicative of an integral of IR(t), between t L+1 and t opt, wherein t L+1 equals t L plus one day, wherein the FIA is equal to v. receiving data indicative of an irrigation recommendation function of the crop during a growing period (IR(t)), data indicative of a current crop water potential at a time t S within the growing period, data indicative of an evapotranspiration at t S, data indicative of a crop coefficient Kc, and optionally data indicative of a last irrigation time; wherein the data indicative of the current crop water potential are obtained using remote sensing data of said crop canopy and/or direct water potential measurements using in-situ plant sensors; computing a current crop water stress coefficient Ks cur (t S); computing an actual evapotranspiration (ETa) at t S (ETa(t S)) of said crop by taking a product of Ks cur (t S) and a corresponding non-stress crop evapotranspiration (ETc) at t S (ETc(t S)), wherein ETc(t S) = ET0(t S) * Kc(t S); and if ETa(t S) ≥ IR(t S), setting an optimal irrigation time (t opt) by: extrapolating a line L passing through or near a first point P 1 and a second point P 2, P 1 defined by first coordinates (t L, ETc(t L)) comprising a last irrigation time t L, which is earlier than t S, and ETc at t L, and P 2 defined by second coordinates (t S, ETa(t S)); obtaining a third point P 3, where at line L intersects, or is tangent to, a curve defined by IR(t), wherein t opt is equal to the day of the time coordinate of P 3; and line L intersects, or is tangent to, a curve defined by IR(t), wherein t opt is equal to the day of the time coordinate of P 3; and setting the forecast irrigation amount by: computing a value v indicative of an integral of IR(t), between t L+1 and t opt, wherein t L+1 equals t L plus one day, wherein the FIA is equal to v. computing a value v indicative of an integral of IR(t), between t L+1 and t opt, wherein t L+1 equals t L plus one day, wherein the FIA is equal to v.