Abstract:Biochemical fulvic acid (BFA) has shown favorable application value in improving soil structure, promoting crop growth and improving fertilizer efficiency. In order to explore the effect of BFA addition on the water-salt migration law of saline-alkali soil, and reveal the salt leaching efficiency mechanism of BFA, this research based on one-dimensional vertical soil column infiltration experiment, to investigate the water-salt migration characteristics, the parameters of the infiltration model, and the composition of soil exchangeable base ions of saline alkali soil under different BFA application amounts (0, 1, 2, 4 and 8 g/kg). The results showed that the application of BFA under infiltration conditions could reduce the soil water infiltration rate, prolong infiltration time and improve soil water retention performance. The Kostiakov model, Philip model and algebraic model could all describe the soil infiltration process well. The empirical coefficient K, the absorption rate S and the comprehensive shape coefficient α in the models all showed a trend of decreasing and then increasing with the increasing of BFA application amount. Compared with the control, the application of BFA could improve the soil water holding efficiency and relative desalinization rate. Under the condition of 2 g/kg BFA addition, the average volume water content, average water holding efficiency and relative desalinization rate in 0-20 cm soil layer increased by 3.38%, 10.65% and 36.32%, respectively. In addition, compared with the control, the total exchangeable base (TEB) of soil increased after adding BFA, and the concentration of Ca2+ in TEB increased, while the concentration of Na+ decreased. Therefore, BFA application could significantly affect soil water infiltration and water and salt transport characteristics, improve the distribution of soil water and salt, and had favorable effect on water retention and desalination of saline soil. Moreover, studies have found that BFA application could significantly increase soil TEB, significantly improve soil exchangeable base ion composition and improve soil quality.