Can the increase of irrigation frequency improve the rate of water and salt migration in biochar-amended saline soil?

Abstract

It is difficult to leach salt into the deep layers of saline or sodic soils due to their poor permeability. The frequency of irrigation is a major factor affecting salt-leaching efficiency. Since biochar amendments are known to improve soil permeability, they may affect salt-leaching efficiency indirectly. Here, we investigated whether the increase of irrigation frequency could improve the rate of water and salt migration in biochar-amended coastal saline soil. The effects of biochar amendment on the dynamics of water and salt migration in a coastal saline soil from the Yellow River Delta were monitored through soil column leaching experiments. Three different biochar levels were applied at 0% (control), 1%, and 5% (w/w), while the same irrigation amount was applied in two modes: continuous and intermittent. The total duration of intermittent irrigation water vertical infiltration exceeded that of continuous irrigation. The 5% biochar treatment significantly increased the average water content in the soil profile compared with the control treatment lacking biochar. By contrast, increasing the irrigation frequency reduced the average water content in the soil profile (25.4–29.5%) when compared with continuous irrigation (27.7–31.8%). Electrical conductivity increased by 31.9–64.1% at the 60-cm soil depth for all biochar treatments under intermittent irrigation when compared with continuous irrigation. Under continuous irrigation, the 5% biochar treatment showed the earliest desalinization effect, maintaining the lowest peak value of soil salt across the different soil depths tested. Under intermittent irrigation, soil salt always peaked following each irrigation event, with its lowest peak value provided by the 5% biochar treatment at depths of 30, 45, and 60 cm (but not at 10 cm). Applying an intermittent irrigation to planted crops coupled to a higher biochar amendment (e.g., 5%) may improve salt-leaching efficiency in coastal saline soils. Future empirical studies are required to verify these conclusions under field conditions.