Among the prominent issues for water reuse in agriculture, there is a need to estimate the benefits and impacts of irrigation with treated wastewater in order to take advantage of the nutrients contained in wastewater, under constraints of health and environmental hazards. Modeling and control of dynamical systems may be used to find new ways of optimizing the whole water reuse chain, such as the dynamic adaptation of wastewater treatment quality to meet the changing needs of plants throughout a growth cycle. In this context, we focus here on determining the water and nutrient requirements of crops when irrigated with reuse water, taking into account the different objectives of maximizing crop biomass and minimizing environmental and irrigation costs. To deal with the high complexity of modern crop models, we propose a double modeling approach, in which we design a dynamic systems model - the 'control model' - and calibrate it using simulation data obtained from a complex crop model. We then show how this allows to recast the multi-objective optimization problem of reuse irrigation as a constrained optimal control problem that can be solved using a dynamic programming method. Numerical simulations of a case study are provided to illustrate the resolution.