2.5. Chemical analysis
Total soil organic carbon (SOC) was determined following dichromate oxidation procedure. Multiplying the SOC by 1.72 resulted in the SOM content (Nelson and Sommers, 1982). SOC storage at the 0–20 cm depth was calculated from horizon thickness and soil bulk density. The amount of sequestered organic carbon in 0–20 cm soil depth was determined after deducting the carbon storage that had occurred just before the start of the experiment. Total nitrogen was determined by the Kjeldahl Method (Bremner and Mulvaney, 1982).
Bulk density was determined on undisturbed soil samples using a steel cylinder of 100 cm3 volume (5 cm in diameter, and 5.1 cm in height) for soil depths of both 0–10 cm and 10–20 cm separately. The bulk density was calculated by dividing the weight of the dried soil by the volume of the soil (Blake and Hartge, 1986).
Ten grams soil from 0–10 cm and 10–20 cm layers were sampled to be oven-dried at 105 °C for 48 h to measure the soil water content on 11 June and 9 October, 2014 when were close to the sowing date for summer maize and winter wheat, respectively, and there was no rainfall during the previous two weeks. As adequate amount of soil water content is important for seed germination, if the soil water content was lower, pipe irrigation was practically applied. The pH was measured in a 1:2.5 (w/v) soil/water suspension using a digital pH meter (PB-10, Sartorius, Germany).