Abstract: 【Objective】The effect of subsoiling combined with straw returning on soil pore structure of black soil in Northeast China is lack of definite judgment. Aimed at such problem, our research was conducted in order to provide scientific basis for the influence mechanism of this measure on soil structure of black soil and the establishment of reasonable tillage.【Method】In this study, a 5-year field positioning experiment conducted in Qinggang County, Suihua City, Heilongjiang Province, a typical black soil area in Northeast China was used as a platform. Farmers’ conventional treatment (FP) , 25 cm subsoiling alone treatment (T2), 25 cm subsoiling combined with straw returning treatment (T3) and 35 cm subsoiling combined with straw returning treatment (T4) were set. The visualization and quantification of soil pore structure were studied using CT scanning technology, and combined with field capacity and bulk density to explore the effect of subsoiling combined with straw returning on the pore structure of black soil. 【Result】The results showed that the two-dimensional and three-dimensional images of soil pores clearly showed that the pore distribution at 0-20 cm soil layer was significantly less than that at 20-40 cm soil layer in all treatments, while the pore distribution of suboiling combined with straw returning treatment (T3 and T4) was significantly higher than that of FP treatment, and their macropores with more complex structure were increased. Quantitative analysis showed that compared with FP treatment, the total porosity of 20-30 cm soil layer was significantly increased by 103.0% (P<0.05) under 25 cm subsoiling alone treatment (T2), which was achieved by significantly increasing the micropores porosity(pore diameter d≤0.50 mm) by 91.3% and mesopores porosity (0.50 mmP<0.05). While subsowing combined with straw returning treatments (T3 and T4) significantly increased the total porosity of 0-30 cm soil layer by 109.8%—382.7% (P<0.05), which was achieved by significantly increasing the macropores porosity (d>1.00 mm) by 221.5%-661.7% and the mesopores porosity by 105.4%-544.9% (P<0.05). In addition, compared with FP treatment, subsoiling combined with straw returning (T3 and T4) significantly increased the fractal dimension of soil pores at 0-30cm soil layer by 9.9%-17.7% (P<0.05), decreased the Euler number by 32.4%-66.4% (P<0.05), significantly increased the field water capacity by 24.2%-40.6% (P<0.05). Further analysis showed that the different pore size porosity and total porosity was significantly positively correlated with field capacity and fractal dimension, but significantly negatively correlated with Euler number (P<0.01). 【Conclusion】Subsoiling combined with straw returning measure can improve porosity of macropores and mesopores pore of black soil, improve pore structure and connectivity, and increase field capacity, which can be recommended measure for rational tillage construction in black soil of Northeast China.

Key words: Northeast black soil, subsoiling combined with straw returning, CT scanning technology, pore structure in soil