2.3 Analysis Method
The current through soil was read by the connected ammeter (Pro’sKit, Shanghai, China) each day.
Soil moisture was determined by weighing the wet soil and dry soil. When the test stopped, about 50 g of soil were collected from the soil column at different locations, weight the mass recorded as m1. Afterwards, drying them in the oven (105 ℃, 101-2AB, Tianjin Tester Instrument Co. Ltd, China), continuously weight the dry soil weight and records it as m2 when the weight values stabilized. And the soil moisture calculated by:
θ=(m1-m2)/m2 ×100%
where θ is the soil moisture (%), m1 is the mass of wet soil (g), m2 is the mass of dry soil (g).
Sampled dry soil 5.00 g in 50 ml bottles with 25 ml deionized water before shaken 30 min at 20±1℃ (200 r/min, QE-1, Tianjin Aunuo Instrument & Meter Co. Ltd, China). Supernatant solution was collected after centrifuged for 30 min (3000 r/min, TGL-16M, HuNan XiangYi Centrifuge Instrument Co. Ltd, China). EC were detected using supernatant solution by Conductivity meter (LAQUA EC-33, Horiba Corporation of Japan). Remaining supernatant solution filtered through 0.45 μm membrane before cations (Na+, K+, Ca2+, Mg2+) and anions (Cl-, NO3-, SO42-) detections using ion chromatography (YC3000, Qingdao Ailun General Technology Co., Ltd, China). The volume of injection was 10μl, and the method detection limit were as follows: Na+: 0.011 mg/L, K+: 0.011 mg/L, Ca2+: 0.022 mg/L, Mg2+: 0.011 mg/L; Cl-: 0.007 mg/L, NO3-: 0.0167 mg/L, SO42-:0.0187 mg/L. Similar as the above preparation of supernatant except the ratio of soil and water was 1:2.5. Then the value of pH was detected by pH meter (LAQUA pH-22, Horiba Corporation of Japan).
Results and discussions