Background Large pores in soil are an important index to study the characteristics of soil structure, and they are also one of the basic physical properties of soil. In recent years, scholars have studied Pinus sylvestris var. and understory soil from soil moisture, soil microorganisms, and soil aggregate, but there are few studies on the macropores of Pinus sylvestris var. mongolica soil of different ages.

Methods The experiment was located in Zhanggutai Forest Farm, Zhangwu county, Liaoning province, and the barren grassland, 24 a, 38 a, and 49 a Pinus sylvestris var. mongolica were selected as the research objects. Soil samples collected in the field are brought back to the laboratory, laid flat and minimized turbulence to keep the soil sample intact, and brought back to the laboratory to determine the moisture penetration curve. The soil moisture content was determined by stained method, and the soil bulk density and porosity were determined by ring knife method. The equivalent radius, number and distribution of macropores were calculated by using field stained tracer test and Poiseulle equation. Origin.2018 software and Excel.2010 software were used to make graphs and perform related analysis.

Results In the range of 0-20 cm soil layer, the e-flow rate of stained and unstained soil was larger, and in the range of 20-40 cm soil layer, the e-flow rate of stained and unstained soil changed less, and the water infiltration rate of stained area increased by more than 60% compared with that of unstained area in 40-50 cm soil layer. The number of macropores decreased with the increase of the depth of the soil layer of P. sylvestris var. mongolica in the four sample plots, and the number of macropores in each plot was greater than that in the unstained area, and the number of macropores in the 0-3.01 mm radius was mostly concentrated in the radius of 0.78-3.01 mm, and the number of macropores in the 0-10 cm soil layer of each forest age was more, and the number of macropores in the stained and unstained areas in the 38 a 10-20 cm soil layer was less. The overall effect of different forest ages and soil depth on the number of soil macropores was 24 a > 38 a > 49 a > control plots.

Conclusions 1) The pore size of the soil of different ages in the windy sandy land of northwest Liaoning Province was concentrated in the range of 0.52-3.66 mm, and the average pore radius was 0.69 mm.2) With the increase of forest age, the e-flow rate gradually decreased, and the depth of the soil layer and the speed of the e-flow rate also affected the soil macropores. The average radius of macropores was closely related to the e-flow rate, and there was a significant positive correlation (R²=0.874 7, P < 0.01).3) The number of macropores in P. sylvestris var. mongolica was 24 a > 38 a > 49 a > control plots, and the number of macropores showed the characteristics of more surface layer and less deep layer.