Aims Managing plant nutrition is a key factor to getting optimum yield quantity and quality. Soybean is an important plant as an oil and protein producer crop as well as a biological nitrogen fixing plant. The aims of current work were studying soybean's responses to some macro and micronutrients deficiency stress as well as the possibility of diagnosing this deficiency using chlorophyll fluorescence technique.Methods The two-year field experiment during 2019 and 2020 growth seasons were conducted based on a randomized complete block design with three replications. Treatments were use and non-use of N, P, Fe, and Mo, accompanied with and without humic acid. N and P were applied in the soil, but Fe, Mo, and humic acid were foliar applied at the final vegetative growth stage. Results Results showed that the effect of fertilizer treatments was significant on all traits. N-P-Fe-Mo improved grain yield and photosynthesis rate, but their application accompanied with humic acid induced a synergistic effect, and the maximum grain yield and photosynthesis were recorded in the N-P-Fe-Mo + HA. Fertilizer application decreased F0 and Fm and increased Fv/Fm. Besides, there was a significant negative correlation between leaf's N, P, Fe, and Mo content with Fm; meanwhile, the negative correlation between leaf's nitrogen and Fm was stronger than the other applied nutrients (r=-0.767). Conclusions Research findings show that, it is possible to use the chlorophyll fluorescence technique as a valid non-destructive physiological indicator and a quick way to monitor the nutritional status of soybean plant about N-P-Fe-Mo to timely fertilizing. Although soybean is a nitrogen fixing plant, but it needs complementary N fertilizer to achieve maximum PSII efficiency, minimum chlorophyll fluorescence, and optimal yield.
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