Retrieval of Soil Water Transport and Hydraulic Parameters in Apricot Orchards of Southern Ning Mountain Region

Objective To clarify the characteristics of soil water infiltration, capillary water transport, and changes in hydraulic parameters in apricot (Prunus armeniaca L.) orchards in the southern mountainous region of Ningxia.

Method Based on the soils from farmland (CK) and apricot orchard aged 3, 10, 17, 23, and 35-year-old, ring corers were employed to obtain 0-40 cm surface soil samples for bulk density determination. Based on bulk density, CK and soils of different forest ages were reconstructed. One-dimensional vertical soil column experiments were conducted to analyze variations in wetness peak, cumulative infiltration volume, infiltration rate, and capillary water movement characteristics across different forest ages. Four infiltration models were applied to simulate the water infiltration process and evaluate their applicability. In addition, soil hydraulic parameters were inversely estimated using Hydrus-1D, and dynamic simulation of soil profile moisture distribution was conducted.

Result After 280 min of infiltration, compared with CK, the wetting front depth, cumulative infiltration volume, and steady-state infiltration rate all showed a decreasing trend in the 3-, 10-, 17-, 23-, and 35-year-old orchard soils. Horton model performed the best, followed by General empirical model, Kostiakov model, and Philip model. Among the In Hydrus-1D-inverted hydraulic parameters, the inverse of the air suction coefficient α gradually increasesed with orchard age, while the residual water content θ_r, saturated water content θ_s, shape factor n, and saturated hydraulic conductivity K_s gradually decreased. Hydrus-1D simulations of soil profile moisture content showed R² values ranging from 0.91 to 0.96, with RMSE and MAE both ≤2%. Capillary rise height and water uptake gradually decreased.

Conclusion With increasing orchard age, both soil water infiltration capacity and capillary transport efficiency significantly declined, revealing that long-term cultivation of artificial apricot trees exacerbates excessive depletion of deep soil moisture in the southern Ning Mountains. These findings contribute to enhancing productivity in artificial forest lands within the southern Ning Mountains and offer valuable guidance for the establishment and sustainable development of artificial forests in arid and semi-arid regions.