The effect of interactions between particles on soil infiltrability

Purpose Soil infiltrability is an important topic in environmental and agricultural research and influences plant growth, soil erosion and water runoff. In this study, the influences of interactions between soil particles on soil infiltrability were investigated in different MgCl 2 and NaCl solutions. Materials and methods We selected an entisol soil in Chongqing, China. The soil samples were saturated with Na + and Mg 2+ : each air-dried sample was weighed into a 5-L beaker and washed three times with NaCl and MgCl 2 and then deionised water, respectively. The cationic saturated soil samples were then dried at 333 K, crushed and passed through a 1-mm sieve. For water infiltration, the Na- or Mg-saturated soil samples were added and packed to a bulk density of 1.05 g cm −3 in a rectangular acrylic glass column (20 cm × 3 cm 2 ). The NaCl or MgCl 2 solution was selected to leach the soil column with a constant water head, and the depth of the wetted front was recorded at 150 min. For the computed tomography scan, the circular columns of Na- and Mg-saturated soil were wetted by 0.01 mol L −1 NaCl and MgCl 2 solutions, respectively, and then were determined by computed tomography scanner when the position of wetting front reached 3 cm. Results and discussion Soil with relatively weak electrostatic repulsion had a net attractive force, which leads to the unbroken soil aggregate and high infiltrability. The calculated net forces at the critical concentration in MgCl 2 (0.005 mol L −1 ) and NaCl (0.25 mol L −1 ) were attractive and the measured soil infiltrability reached maximum value. The calculations of particle–particle interaction forces also showed that, when the soil aggregate did not break down, the electrostatic repulsive forces caused the soil aggregate to “swell”, which decreased the soil infiltrability. The “swelling” strength in the Mg 2+ solution was much weaker than that in the Na + solution, and the experimentally observed infiltrability values in Mg 2+ were much higher than that in Na + for soil with the same non-breaking aggregates. Conclusions Soil infiltrability was determined by the electrostatic interactions at the soil/water interfaces, which was generated from the net surface charges of soil particles. The net force between soil particles can be repulsive because of the strong electrostatic repulsion, which results in aggregate breakdown and low infiltrability of soils.