Crop Factor of Maize (Zea mays L.) and Its Relationship to the Salinity of Irrigation Water

Abstract A lysimeters’ experiment was conducted in the fall season of 2022, at the College of Agriculture in Ramadi city west of Iraq, aiming to determine the actual water consumption and crop coefficient (Kc) of maize ( Zea mays L .) under irrigation with saline water. As well, calculating the reference evapotranspiration from evaporation pan data, climate data using Kharrufa equation, and yield coefficient for maize using three different salinity water types, distilled water (S0), saline water (S1), 2ds m −1 and (S2), 4ds m −1 . The results confirmed the existence of an inverse relationship between actual evapotranspiration (ET a ), reference evapotranspiration (ET o ), and crop coefficient (Kc) as irrigation water salinity increased. ETa values risen to 1342.13 mm with distilled water (S0) and declined to 971.11 and 792.61 mm for treatments S1 and S2, respectively. ETo values, computed from evaporation pan, were 961.40 mm for treatment S0, decreasing to 867.18 and 825.25 mm for treatments S1 and S2, respectively. For July, August, and October, actual ET a values reduced by 64.9%, 7.5%, and 19.9%, respectively, compared to ET o values. ET a values calculated using Kharrufa equation, reached 937.15 mm. The total ET o values derived from the equation for treatment S0 were 30.17% lower than the measured values, while for treatment S2 were 22.14% higher. ET o values closely aligned with treatment S1, differing by only 3.49%, indicating ability to adopt of the Kharrufa equation for salinity levels up to 2 ds/m under field conditions during the growing season. Kc values, determined from ET a and ET o data, decreased across all growth stages with increasing irrigation water salinity. Highest Kc values were 0.59, 0.84, 1.55, 1.82, and 1.48 with distilled water (S0), without any change during the germination stage, and decreased by 3.5% and 7.1% for the vegetative stage, 13.5% and 32.2% for the flowering stage, 37.9% and 61.53% for the grain formation stage, and 49.3%, 68.3% for the maturation stage for treatments (S1 and S2), respectively.