Al-Rafidain Engineering Journal (AREJ)

A mathematical optimization model for optimum weekly irrigation water requirements for maize crop at Mosul area is developed. The main objective function is to maximize profit. The growing season is divided into (17)weeks with constraints on actual evapotranspiration, soil moisture at the root zone and deep percolation. The total amount of irrigation water requirements is assumed known and limited at the beginning of the season. The results of this approach was compared with a previous simulation model for irrigation water requirement. It is found that optimization model reduce seasonal irrigation water by 13% compared with simulation models. The proposed model is simple for predicting weekly irrigation requirements and can be used for any crop by changing crop data. where simulation models take longer time and do not give optimal solutions. As this model is applied to many crops grown over large areas, a huge amount of irrigation water may be saved

KEYWORDS:optimization ,irrigation scheduling, optimal yield

Abstract
A simulation model for evaluating the effect of water availability in the soil and salinity on yield under deficit irrigation has been developed. The model is based on water volume balance concept for scheduling irrigation using different levels of allowable percent water depletion. To take the effect of salinity on yield into consideration, the crop evapotranspiration is linked to the salinity level in the soil water using the procedure described in FAO (1998). The model was used to study the effect of both water deficit and salinity build-up during the growing season on yield of cotton for different scenarios, assuming zero leaching, with different irrigation water salinity levels, and allowable percent depletion of water in the root zone.
To verify the validity of the model, preliminary one year data from experiment conducted in northern Syria during the summer season of year 2004 for cotton are used. The data included four deficit irrigation levels using drip irrigation system: full irrigation (no deficit); applying 80%, 60%, and 40% of full irrigation. The experiment was laid out in three replications. The main outcome of the study included useful relationships between relative yield with relative crop evapotranspiration as affected by different levels of deficit irrigation and water salinity. Given the salinity of irrigation water and selecting a cretin level of percent water depletion, the relative evapotranspiration (Etcadj/ETc) can be predicted. Upon knowing the relative evapotranspiration, the relative yield under the given conditions can be also evaluated.

Keywords: deficit irrigation, irrigation scheduling, soil salinity, simulation, evapo-transpiration, leaching requirements.