The Dynamics of Soil Macropores and Hydraulic Conductivity as Influenced by the Fibrous and Tap Root Systems

Herbaceous plants influence soil hydraulic conductivity by changing soil macropore structure through their root systems, but the effects of different root types on macropore structure have yet to be clarified. In this study, soil column experiments were conducted to investigate temporal variations in soil macropores and saturated hydraulic conductivity, as influenced by herbaceous plants with fibrous roots ( Cynodon dactylon ) and taproots ( Medicago sativa L.). Computed tomography (CT) scanning was used to quantify soil macropore indices, and the saturated hydraulic conductivity (K s ) was measured from April to November after 3, 5, and 7 months of sowing. The results showed that both soil macropore indices and K s increased with grass growth. The taproots had macroporosity (MP), macropore diameter (MD), and global connectivity (Γ) values that were 1.94, 2.76, and 2.45 times higher than fibrous roots, which are more efficient at increasing the number of soil macropores (PN). This resulted in higher K s values for the fibrous roots during the experimental period than for the taproot herbs. For both plants, the top 5 cm of soil had a higher macropore index and K s values than the bottom layer. The K s for fibrous roots was most closely related to PN. On the other hand, K s for the taproot soil column was most closely related to MP and MD. Based on a combination of soil macropore indices, functions were established to predict K s values for fibrous root and taproot herbaceous plants.