Effects of organic amendments on soil hydraulic characteristics in the Mollisols of Northeast China

Soil degradation in the Mollisol region of Northeast China is ubiquitous partly due to poor soil hydraulic characteristics. Improving soil hydraulic characteristics thus delivers benefits to soil sustainability. In this study, the effects of organic amendments on soil hydraulic characteristics were explored at the laboratory scale. Soil samples were subjected to three low-cost and eco-friendly organic amendments, including corn straw juice (CSJ), fulvic acid (FA), and humic acid (HA). The soil infiltration capacity, soil water characteristic curve (SWCC) and soil water retention capacity were determined by using a steel-ring method and a centrifuge method. The parameters of the SWCC were fitted by a van Genuchten (VG) model, and the specific water capacity [C(h)] was calculated. In addition, bulk density (BD), macroporosity, and soil organic matter (SOM) were measured, and the relationships between the variables and processes were evaluated. The results indicated that the soil infiltration capacity (i.e., initial infiltration rate, cumulative infiltration, and steady infiltration rate) was significantly increased in the CSJ and FA treatments (p < 0.05) but decreased in the HA treatment compared to the control (CK) treatment. All the selected organic amendments improved the soil water release and supply capacity, and the CSJ2 treatment showed the best effect. The incorporation of CSJ, FA, and HA significantly improved the soil water retention capacity by increasing the saturated soil water content, field capacity, and plant available water capacity (p < 0.05). Such changes were significantly associated with macroporosity and SOM (p < 0.05). In this sense, our results showed that the CSJ treatment with 4 L m(-2) and 50% volumetric concentration could be an effective soil amendment to improve the soil hydraulic characteristics in Mollisols and deserves further research.