Improved Nitrogen Utilization of Faba Bean (Vicia faba L.) Roots and Plant Physiological Characteristics under the Combined Application of Organic and Inorganic Fertilizers

As one of the most important edible legumes worldwide, faba bean can be grown for grain, feed, vegetable, fertilizer, medicine and deep processing. In this study, experiments were designed to determine the combined effect of organic and inorganic fertilizers on the growth and development of faba bean. Dabaipi (a cultivar of Vicia faba L.) was used for the experiments. Five treatments with different ratios of organic nitrogen (N) to total N were applied, including 0% organic fertilizer (0% OF), 25% OF, 50% OF, 75% OF, 100% OF and 0% OF. Chemical urea was used as an inorganic fertilizer. The experimental results showed that 50% OF resulted in the highest faba bean yield, up to 10,337.39 and 13,595.7 kg ha−1 in 2018 and 2019, respectively. Compared with 0% OF, 50% OF increased the yield by 84.47% and 183.17%, respectively. The regression analysis showed that the yield could be maximized when ROT accounted for 51.1%. The 50% OF treatment significantly increased N accumulation in seeds, resulting in higher N partial factor productivity and N harvest index (NHI). N accumulation in green seeds and aboveground plant parts had a significantly positive linear correlation with the yield and NHI, respectively. The 50% OF treatment maintained appropriate N accumulation in vegetative organs and higher N accumulation in reproductive organs and whole plants. Compared to 0% OF, the 50% OF treatment increased the total nodule number per plant (52.5%), fresh nodule weight (55.8%), nitrate reductase activity (70.7%), glutamine synthetase (18.2%) and glutamate synthase activity (42.4%). Therefore, the combined application of 50% OF and 50% inorganic fertilizer can be recommended for faba bean cultivation. This study will provide a theoretical basis for high-yield cultivation of faba bean.