Soil Macropore Structure Characterized by X-Ray Computed Tomography Under Different Land Uses in the Qinghai Lake Watershed, Qinghai-Tibet Plateau

Quantification of soil macropores is important to enhance our understanding of preferential pathways for water, air, and chemical movement in soils. However, the soil architecture of different land uses is not well understood in elusive alpine regions. The objective of this study was to quantify the architecture of soil macropores in a Kobresia meadow, farmland, and sand in the Qinghai Lake watershed of northeastern Qinghai-Tibet Plateau, China using X-ray computed tomography. Nine soil cores at 0-50 cm depth were collected at three sites with three replicates. At each site, the three collected cores were scanned using a GE HiSpeed FX/i medical scanner （General Electric, USA）. To analyze soil architecture, the number of macropores, maeroporosity, and mean macropore equivalent diameter within the 50 cm soil profile were determined from the X-ray computed tomography. Analysis of variance indicated that land use significantly influenced macroporosity, mean macropore equivalent diameter, and number of macropores. The soils of the Kobresia meadow and farmland had greater macroporosity and developed deeper and longer maeropores than that of sand. For the Kobresia meadow, macropores were distributed mainly in the 0-10 cm soil layer, while they were distributed in the 0-20 cm soil layer for the farmland. The large number of macropores observed in the soils of the Kobresia meadow and farmland could be attributed to greater root development. The results of this study provided improved quantitative evaluation of a suite of soil macropore features with significant implications for non-equilibrium flow prediction and chemical transport modeling in soils.

Near-saturated soil hydraulic conductivity and pore characteristics as influenced by conventional and conservation tillage practices in North-West Himalayan region,India

Tillage plays an important role in modifying soil hydraulic properties.The objective of the present study was to evaluate the effect of conservation tillage practices in a maize-wheat cropping system on nearsaturated soil hydraulic properties and pore characteristics in the North-West Himalayan region,India.Three treatments viz.conventional tillage(CT),minimum tillage(MT),and zero tillage(ZT)were evaluated in terms of field saturated hydraulic conductivity(ks),unsaturated hydraulic conductivity k(h),the inverse of capillary length(a),flow-weighted mean pore radius(r0),numbers of pores per square meter(n0)and water-conducting macroporosity(Ɛ).The above hydraulic conductivity and pore characteristics were derived from steady-state water flux(q)measured using hood infiltrometer at 0,1,and3 cm pressure head for each treatment after seven years of establishment of this tillage experiment.Results revealed significantly(p<0.05)higher values of ks,k(h),a,andƐin ZT as compared with CT.MT had intermediate values.Higher a values suggested a greater gravity-dominated flow under ZT and MT as compared with CT.Analysis of r0 values indicated better connectivity of pores in ZT and MT as compared with CT.Macropore flow suggested that on average pore radii,>0.50 mm conducted about 63.60,68.01,and 75.97%of total flow(at 0 cm pressure head)in the corresponding water-conducting macroporosity of 0.00030,0.00044,and 0.00069%of soil volume under CT,MT,and ZT,respectively.Overall,zero-tillage based agriculture system was found to improve near-saturated soil hydraulic properties.