Simultaneous Effects of Deficit Irrigation and Transpiration Reducer on Yield and Yield Components of Corn Single Cross 704 (Zea mays L.)

Corn plant (Zea mays L.) is the main source of energy and has a vital role for birds feeding. Thus, increasing cultivation area and yield improvement are very important. Corn may be highly productive even in winter season in many locations due to its adaptability. Silage of maize is a good source of energy and food for animals and can produce more energy compare to other forages. Drought stress is one of the important factors that limits crop growth in arid and semi-arid environments and imposes a detrimental effect on maize yield. Drought stress imposes many different biochemical and physiological responses in plants. Studies have shown that water stress would directly and indirectly affect the maize yield.

This experiment was conducted as split plot based on complete block design with three replications, in 2017 (1396) in Mehran town in southwest of Ilam, which characters an arid and semi-arid climate. Main factor included of three levels of irrigation (equivalent of 40 mm (Normal), 60 mm and 80 mm of accumulated evapotranspiration of class A pan evaporation). Sub-plots included: 8 different levels of gibberellin application (100 ppm), no application of gibberellin but 4 levels of transpiration reducer including Salicyclic acid (0.5 molar concentration) ascorbic acid (120 mg.l-1), paclobutrazol (50 ppm) and control which was pure water. All treatments imposed at 6-8 leaf stage of plant growth. Each plot consisted of 6 cultivation rows with 4 m length and 0.75 m between rows and 0.20 m within rows distances. Distance between blocks was 3 m and sowing depth was 3-5 cm. Fertilizer requirement was calculated based on soil analysis. Therefore 160 kg.ha-1 of Super phosphate triple, and 100kg.ha-1 urea were applied at sowing and when crops were at 10 leaf stage, before tasseling, 200 kg.ha-1 urea was applied again. 

Irrigation levels showed a significant difference (P≤0.01) effect on grain yield, biological yield, harvest index, 1000-grain weight, grain number per ear, leaf area index, and relative leaf water content. ANOVA results showed that gibberellin had significant (P≤0.05) effect on biological yield. Transpiration reducer also showed significant (P≤0.05) effects on grain yield, biological yield, harvest index, 1000-grain weight, grain number per ear, leaf area index, and leaf water content. Interactive effects of drought stress and transpiration reducer was also significant (P≤0.01) on grain yield, biological yield, and harvest index. Triple interaction significantly (P≤0.01) affect grain yield and harvest index. The highest seed yield under normal irrigation conditions was obtained by simultaneous application of gibberellin and salicylic acid (11.11 t.ha-1). Also, the lowest seed yield was obtained under 80 mm irrigation stress without gibberellin and transpiration reducers (6.42 t.ha-1). Drought stress reduced grain yield compared to normal irrigation treatment. The lowest protein content was under normal irrigation conditions (0.092) and the highest amount was under 80 mm stress conditions (0.1). The highest accumulation of soluble sugars was in 80 mm dry stress (525 mg.g-1) and the lowest accumulation was in normal irrigation conditions (402 mg.g-1). The highest amount of chlorophyll (2.9) was observed in normal irrigation treatment and the lowest level was observed in drought stress treatment of 80 mm (2.46).

This study results showed that a right combination of transpiration reducer and growth stimulants under drought stress can help corn plant to increase its production. This enhancement is because of higher antioxidant activity and also growth conditions. In other words, positive effects of transpiration reducer, result in deduction of stress effects on grain production and biological yield so can increase corn quantity and quality grain yield.