Promote sugar beet cultivation in saline soil by applying humic substances in-soil and mineral nitrogen fertilization

Sugar beet (Beta vulgaris L.), accounting for 30 percent of the total world sugar production, maybe affected by soil fertility and nutrition supply in terms of both its yield and quality. Humic substances have a direct and indirect effect on plants, is it possible to raise this effect by integrate it with mineral nitrogen fertilization in saline soils? Two field experiments were conducted during two seasons. The treatments in split-plot design included without humic substances, soil-addition of humic acid and soil-addition of fulvic acid as main plots and 71, 142 and 213 kg N ha−1 as subplots. Soil-additions of humic substances increased root length, top and root content of α-N and K, the concentration of sucrose, sugar loss and sugar recovery and yield of sucrose, sugar loss and sugar recovery but reduced root content of Na and sugar quality index percentage. Increasing nitrogen fertilization level from 71 to 213 kg N ha−1 significantly increased all traits, except sucrose, sugar recovery and sugar quality index percentage. The highest root yield values were with soil-addition of humic acid with 213 kg N ha−1. On the other hand, the soil-addition of humic acid and fulvic acid with 213 kg N ha−1 increased the recoverable sugar yield of sugar beet by 16.1 and 15.2%, respectively. Therefore, it is preferable to use soil-addition of humic acid at 30 kg ha−1 with 213 kg N ha−1 to obtain the highest yield from the root yield and the extracted sugar yield, especially in saline soils.