Effects of Wetting-Drying Cycles on the CT-Measured Macropore Characteristics under Farmland in Northern China

Wetting and drying (WD) cycles have a strong influence on the structure of soil, especially on the pore distribution, which can significantly affect soil quality and crop growth. Most studies have conducted the controlled cycles effects on soil pores at the laboratory. However, the effects of natural wetting and drying cycles (NWD) on the pore characteristics of soil are still not well understood. This study was to quantify and compare the modifications in computed tomography (CT)-measured macropore parameters induced by cycles under two experimental conditions of NWD at the field and WD at the laboratory. Intact soil cores, 15 cm in diameter and about 20 cm in height, were taken from Calcic Cambisol at cultivated land and scanned using X-ray computed tomography. Two conditions of NWD and WD cycles had obviously different influence on soil macropores, and NWD cycles may have a stronger influence than WD cycles. Soil depths had an obvious effect on soil macropore features during the cycles. Our results suggest that the decrease in soil macropore number, macroporosity, fractal dimension and connectivity density under NWD cycles is adverse to soil water retention, soil quality and crop production.