Effect of no-tillage on pore distribution in soil profile

Soil pore structure plays an important role in soil water movement in both topsoil and subsoil, and it is closely related to soil surface runoff and permeability. CT scanning has accurately revealed the number, size and location of macro-pores (> 1 mm in diameter). Long-term tillage can greatly influence the physical properties of soil profile, while non-tillage can improve soil structure, increase soil fertility and soil porosity, and thereby decrease soil bulk density and promote crop growth. Studies of non-tillage effects on soil pore have mostly been focused on the ploughed layer. Further study is needed to determine the impact of long-term non-tillage on soil pore volume, size and distribution along soil profile by using the CT scanning method and combining with soil structure, soil bulk density and soil moisture parameters investigation by using conventional method, especially for the deep soil (0-100 cm) layer. Thus in order to determine the effect of long-term no-tillage measure on pore characteristics, structure and water parameters of soil, CT scanning was used to quantitatively analyze soil pore volume (80-1 000 μm, > 1 000 μm and > 80 μm), porosity, and pore distribution of the 0-100 cm soil profile under long-term no-tillage and conventional tillage conditions in this study. A conventional method was adopted to determine macro-aggregate amount, bulk density, field water capacity, effective water content and saturated hydraulic conductivity. The results showed that no-tillage treatment increased numbers and porosities of soil pores > 1 000 μm, 80-1 000 μm and > 80 μm. The numbers increased respectively by 55.3%, 58.2% and 57.9%, while porosities increased by 97.4%, 39.4% and 72.6% of > 1 000 μm, 80-1 000 μm and > 80 μm pores under non-tillage treatment compared with the conventional tillage treatment. It was also found that pore shape and pore circularity improved under non-tillage treatment. For different soil layers, no-tillage treatment increased numbers of 80-1 000 μm pores and > 80 μm pores in the 0-25 cm and 80-100 cm soil layers, and number of > 1 000 μm soil pore in the 0-45 cm soil layer. Furthermore, there were significantly increases in porosities > 1 000 μm and > 80 μm soil pores in the 0-20 cm and 25-40 cm soil layers, and porosity of 80-1 000 μm soil pores in the 0-20 cm soil layer under non-tillage treatment compared with those under conventional tillage treatment. In addition, long-term no-tillage increased water content in the 0-25 cm soil layer, saturated hydraulic conductivity and content of water stable aggregates (> 0.25 mm) in the 0-55 cm soil layer. Then long-term no-tillage treatment reduced soil bulk density in the 0-55 cm soil layer compared with conventional tillage treatment. Correlation analysis showed that CT scanning well showed soil pore characteristics, which was related with soil physical parameters measured by conventional method. Also micro-cosmic soil pore characteristics could be used to characterize macroscopic physical properties of the soil. In summary, long-term non-tillage practice was beneficial for improvement of soil structure and pore, and increased soil water availability.