Introduction:
Iron is one of the elements whose total amount in Iranian soils is significant. This element is nutritionally essential for the plant, but too much of it can cause toxic conditions. It is noteworthy that wetland conditions affect the solubility of this metal and its high content can also cause clogging of drains. Soil pH is the most important factor affecting the absorption of iron and in anaerobic and acidic conditions, the amount of iron increases to toxicity. Increasing the solubility of iron due to physicochemical interactions of wetlands not only increases the absorption of iron as a micronutrient and essential element for the plant, but also affects its leaching. This study was conducted to investigate the effect of controlled drainage on iron concentration in drainage water and its uptake by maize.

Methods:
This study was conducted in two cropping years 2018 and 2019 (spring and autumn cultivation) in the experimental farm of Shahid Chamran University of Ahvaz at 400 m2 (length and width equal to 20 m) was done. In this study, single-cross 647 hybrid maize was used in spring planting and single-cross 704 in autumn planting. For this purpose, factorial experiment was performed based on a completely randomized design with four treatments and three replications in two planting seasons; i.e. spring and fall on the experimental fields. The first treatment was free drainage (FD), the second treatment was variable water table (CD-Var) (with a fixed distance from the water table to the root development area), the third treatment was water table stabilization at a depth of 50 cm (CD50) and the fourth treatment was water table stabilization at depth 50 cm and release after 24 hours after irrigation (CD-In). Controlled drainage experiments were performed using cylindrical lysimeters made of corrugated polyethylene with a diameter of 80 cm and a height of 120 cm with an underground drainage system.

Results:
According to results in two planting seasons the controlled drainage had a significant effect on the concentration of iron in drainage water, iron uptake by maize and the yield of maize components at the level of one percent. The highest concentration of iron in drainage water in spring and autumn cultivations was related to controlled drainage treatment with variable water table (CD-Var) of 1.92 and 1.56 mg / l respectively, and the lowest concentration of iron in drainage water was related to free drainage treatment (FD) equal to 0.83 and 0.8 mg / l were obtained in spring and autumn cultivations respectively. The results showed that the concentration of iron in the grain was higher than the stem and leaf. The highest concentration of iron in grain for CD-Var treatment in spring and autumn cultivation was 103 and 80 mg / kg, respectively, and the lowest concentration of iron in grain for FD treatment in spring and autumn cultivation was 32 mg / kg and 30 mg / kg, respectively.
On the other hand, controlled drainage increased crop yield in CD-Var treatment compared to other treatments. 1000-seed weight in CD-Var treatment in spring and autumn cultivation were 282 and 313 g, respectively, and these values were 207 and 222 g for FD treatment, respectively.
Also, iron concentration in soil, seeds, stems and leaves in CD-Var treatment was higher than other treatments. The results showed that controlled drainage increases plant yield and water use efficiency. Also, in terms of water use efficiency, controlled drainage between different treatments has created a significant difference at the level of five percent. Controlled drainage has significantly increased water use efficiency in different treatments. The highest effect on water use efficiency was related to CD-Var treatment at 9.44 and 10.69 kg / ha and the lowest effect was related to FD treatment at 7.37 and 8.27 kg / ha for spring and autumn cultivation, respectively. but on the other hand, based on the results of iron concentration in the drainage water and its increasing trend, there is the potential for ochre production in CD-Var and CD50 treatments. In CD-In treatment, in terms of ochre production potential, it was in the low potential range. In free drainage treatment, the concentration of iron in the drain in both seasons and during the growth period was less than one milligram per liter and can be neglected in terms of the potential for ochre production.