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In maize-soybean intercropping system, shade is the major chronic restrain that effected the normal growth of soybean. Different spatial patterns of this system have affected the microclimate of soybean by shading of maize plants. However, the negative impacts of shading stress can be mitigated by providing the optimal ratios of different fertilizers. Therefore, to test this hypothesis, the soybean plants were grown under different light conditions (normal light and shade) to evaluate the response to varying NH4 + /NO3 - ratios. The seed of soybean (Glycine max L. cultivar of "Nan-99-6") were grown in nutrient solution at a total concentration of 5mM N using different NH4 + /NO3 - ratios (To= 0:0, T1= 0:100, T2= 25:75, T3=50:50, and T4= 75:25) for 40 days in greenhouse at PPFD 320.95 μmolm-2 s-1 (low light intensity) and 967.53 μmolm-2 s-1 (normal light intensity). Under low light the growth and photosynthesis of soybean seedlings had significantly decreased as compared to normal light conditions. Nonetheless, the optimal ratios of NH4 + /NO3 - had improved the growth and photosynthesis activities of soybean seedlings under both light conditions. Our results indicated that soybean seedlings supplied with optimal NH4 + /NO3 - ratios (25:75 and 50:50) have showed the maximum biomass yield, chlorophyll pigments, leaf gas exchange, photochemical activities and root growth as compared to high NH4 + /NO3 - ratios (T1 and T4). Since, the higher ratios of NH4 + /NO3 - resulted in lower plant growth due to accumulation in plant tissues; therefore, we suggested that optimal ratios of NH4 + /NO3 - can enhance the shade resistance of soybean seedlings.

Lodging is one of the most chronic restraints of the maize-soybean intercropping system, which causes a serious threat to agriculture development and sustainability. In the maize-soybean intercropping system, shade is a major causative agent that is triggered by the higher stem length of a maize plant. Many morphological and anatomical characteristics are involved in the lodging phenomenon, along with the chemical configuration of the stem. Due to maize shading, soybean stem evolves the shade avoidance response and resulting in the stem elongation that leads to severe lodging stress. However, the major agro-techniques that are required to explore the lodging stress in the maize-soybean intercropping system for sustainable agriculture have not been precisely elucidated yet. Therefore, the present review is tempted to compare the conceptual insights with preceding published researches and proposed the important techniques which could be applied to overcome the devastating effects of lodging. We further explored that, lodging stress management is dependent on multiple approaches such as agronomical, chemical and genetics which could be helpful to reduce the lodging threats in the maize-soybean intercropping system. Nonetheless, many queries needed to explicate the complex phenomenon of lodging. Henceforth, the agronomists, physiologists, molecular actors and breeders require further exploration to fix this challenging problem. National Key Research and Development Program of China | Ref. 2018YFD1000905 Sichuan Innovation Team Project of National Modern Agricultural Industry Technology System | Ref. SCCXTD−2020−20