Effects of Nano Silica and Salicylic Acid on Yield and Yield Components in Corn (Zea mays L.)-Mungbean (Vigna radiata L.) Monocropping and Intercropping under Drought Stress Conditions

Intercropping is an ecological crop management method in which at least two plant species grow simultaneously on a field. Increased land productivity in intercropping of cereals and legumes is mainly due to the positive interaction between cereals and legumes in the rhizosphere, which increases the efficiency of soil resource utilization, especially nitrogen (N). Mixed cultivation of legumes with cereals provides higher land use efficiency, lower water consumption, and greater environmental benefits than cereal monocultures. Salicylic acid (SA) is a natural plant hormone that affects various physiological and biochemical functions in plants, because it can act as a regulatory and mediating signal in the plant's response to abiotic stresses such as drought. In recent years, nanotechnology has also been introduced into agriculture, and several benefits of nanoparticle applications such as nano-silica (nSiO2) have been reported that can be used to increase the supply of nutrients to agricultural products. The aim of this study was to determine the possible role of growth regulators of salicylic acid and nanosilica particles (nSiO2) on crop yield in maize and mung bean intercropping under drought stress conditions.

The experiment was conducted in 2019-2020 cropping year in the research farm of Agriculture and Natural Resources Campus, the University of Tehran, located in Karaj. The experiment was performed in the form of split- split plots based on a randomized complete block design with three replications. The main plot was drought stress at two levels of full irrigation and cessation of irrigation, the sub plots included different intercropping arrangements of maize and mung bean: (maize monoculture (C100), maize 80: mung bean 40 (C80:M40), maize 80: mung bean 60 (C80:M60), maize 50: mung bean 50 (C50:M50) and mung bean monoculture (M100) and the sub-sub plots were four treatments of silica nanoparticles +salicylic acid, silica nanoparticles, commercial salicylic acid and control. Statistical calculations were performed by SAS 9.2 and Excel software in this study. The mean comparison was performed by LSD test and the probability level was considered 95% in all analyzes.

The results showed that the highest maize grain yield was obtained in the monoculture treatment, Si + Sa combined fertilizer and full irrigation, which was 179% higher than the lowest treatment (C50:M50 intercropping, control and drought stress). The highest biological yield of maize was obtained in the complete irrigation and Si + Sa fertilizer treatment under monoculture conditions. The lowest value of this index was observed in the treatments of drought stress, control without fertilizer and C50:M50 intercropping conditions. The highest yield of mung bean seeds was obtained in monoculture of mung bean, application of Si + Sa fertilizer and complete irrigation. The highest biological yield belonged to mung bean monoculture treatment, nano Si + Sa compound fertilizer and complete irrigation. The lowest was obtained in C50:M50 and C80:M60 intercropping treatments, non- fertilizer application and drought stress. Also, the highest land equivalent ratio was obtained in full irrigation and C80M60 intercropping and nano Si + Sa fertilizer treatment (1.57).

general, the results of this study showed that, drought stress reduced all the studied traits. While intercropping with increasing diversity had a significant effect on important agronomic traits under both optimal irrigation and drought stress conditions. LER values were more than one in intercropping crops that indicated higher ground productivity in these planting patterns than in monoculture of crops. The highest LER value was obtained in C80:M60 intercropping treatment under non- stress and application of nano Si + Sa. Silica nanoparticles and salicylic acid fertilizers had a positive effect on grain and biological yield of both plants as well as land equivalent ratio and reduce the negative effects of drought stress on plants and can be used as suitable approach to achieve sustainable agriculture goals.