The effect of foliar application of micro-elements on some biochemical traits and wheat yield under water stress conditions

In order to investigate the effect of foliar application of micro-elements on some biochemical traits and wheat yield under water stress conditions, an experiment was carried out in the form of split plots based on a randomized complete block design in three replications in Varamin during the two crop years 2016–2017 and 2017–2018.  The main factors of irrigation regimes at three levels (I1: normal irrigation, I2: cut-off irrigation at the beginning of stem growth, and I3: cut-off irrigation at the beginning of stem growth and seed filling) and sub-factors including foliar spraying of micro-elements at eight levels (M1: control (without foliar spraying), M2: boron foliar application, M3: zinc, M4: iron, M5: zinc+boron, M6: iron+boron, M7: zinc+iron and M8: zinc+boron+iron) were considered. The irrigation was done twice in the autumn and four times in the spring under normal irrigation conditions. The foliar spraying of each of the micronutrients from the sources of iron sulfate, boron sulfate and zinc sulfate with a concentration of 5/1000 was carried out in two stages: stemming and spike emergence. The results showed the effect of irrigation regimes, foliar application of micro-elements and their interaction on the content of chlorophyll a, b and total chlorophyll, the concentration of chlorophyllase enzyme, malondialdehyde and abscisic acid. Also, the simple effect of irrigation and foliar spraying was significant on total sugar concentration and grain yield. The results showed that the interruption of irrigation led to a decrease in total chlorophyll. Foliar spraying of zinc + boron + iron (M8) in all three levels of irrigation regimes led to a significant increase in total chlorophyll. The highest amount of total chlorophyll was obtained under normal irrigation conditions, along with zinc+boron+iron (I1M8) foliar spraying at a rate of 6.03 mg.g-1 of fresh leaves. Also, foliar spraying of zinc+boron+iron in irrigation treatments (I2) and (I3) (respectively, with averages of 5.2 and 4.55 mg.g-1 of fresh leaves) led to an increase in total chlorophyll compared to control. In general, the use of foliar applications of iron, zinc, and boron can improve the physiological characteristics of wheat under stressful conditions while increasing grain yield.