Evaluation of Stemflow Effects on the Spatial Distribution of Soil Moisture Using TDR Monitoring and an Infiltration Model

The partitioning of crop canopy water may affect soil water distribution and this may in turn affect sprinkler irrigation application efficiency. The aim of this work was to develop a methodology to evaluate spatial and temporal soil water content distribution in the case of sprinkler irrigation application efficiency considering stemflow. Time domain reflectometry (TDR) soil moisture monitoring was carried out on eight soil water sensor locations for both center pivot and traveling big gun irrigation in different phenological and tillage cases. The two case studies were chosen because they show the two opposite limits of the methodology’s application. Two water distribution estimation methods were employed: raw measured soil moisture and model simulation of the infiltration process. The infiltration process was modeled by means of the two-dimensional (2D) Richard’s equation. The simulations were calibrated on the data measured at eight soil water sensor locations. The stemflow and surface runoff conveyed in the interrow by hilling were obtained as additional model-fitting parameters. During center pivot irrigation, 34% of the water delivered in the interrow was conveyed in the row. During traveling big gun irrigation, 88% of the water delivered in the row was conveyed in the interrow. Soil water distributions calculated from measured data overestimated irrigation application efficiency by approximately 15%. The spatial and temporal soil water content distribution obtained from simulation of the water infiltration process allowed mass balance closure in both case studies. The proposed simulation method evaluated stemflow effects on the water distribution profile, leading to accurate application efficiency calculations.