Validation and Modification of the Van Genuchten Model for Eroded Black Soil in Northeastern China

The soil water characteristic curve is highly related to soil physical characteristics, which may be affected by the soil erosion degree. To explore the applicability of the soil moisture characteristic curve model in northeastern China, two erosion degrees, (1) lightly and (2) severely eroded black soil sampled from 15 sites, were collected. The soil water contents at eight soil water suctions were measured and the parameters of the Van Genuchten (VG) model were estimated. Then, two input sets—SSCBD (sand, silt and clay percentages and bulk density) and SSCBDθ33θ1500 (SSCBD, and water contents at 33 and 1500 kPa suction) based on the Rosetta model were compared for the VG model prediction. The results showed that the parameters in the VG model had significant difference under the two eroded soils of the saturated water content (θs), but the opposite was true for the residual water content (θr), the scale parameter (α) and the shape parameter (n). In addition, the θs and θr had no significant differences but the opposite was true for the α and n under the two input sets. The simulated soil water content values of the VG model parameters derived from the Rosetta model underestimated the measured ones, except the water contents at 0 kPa. Therefore the relationships between m and n were modified for accuracy. The validation results showed that the VG model performed well when the sand content was less than 80% for the input set of SSCBD. Using the input set of SSCBDθ33θ1500 can lead to higher simulation accuracy and wider applicability compared with SSCBD under black soil.

Performance Assessment of Five Different Soil Moisture Sensors under Irrigated Field Conditions in Oklahoma

Meeting the ever-increasing global food, feed, and fiber demands while conserving the quantity and quality of limited agricultural water resources and maintaining the sustainability of irrigated agriculture requires optimizing irrigation management using advanced technologies such as soil moisture sensors. In this study, the performance of five different soil moisture sensors was evaluated for their accuracy in two irrigated cropping systems, one each in central and southwest Oklahoma, with variable levels of soil salinity and clay content. With factory calibrations, three of the sensors had sufficient accuracies at the site with lower levels of salinity and clay, while none of them performed satisfactorily at the site with higher levels of salinity and clay. The study also investigated the performance of different approaches (laboratory, sensor-based, and the Rosetta model) to determine soil moisture thresholds required for irrigation scheduling, i.e., field capacity (FC) and wilting point (WP). The estimated FC and WP by the Rosetta model were closest to the laboratory-measured data using undisturbed soil cores, regardless of the type and number of input parameters used in the Rosetta model. The sensor-based method of ranking the readings resulted in overestimation of FC and WP. Finally, soil moisture depletion, a critical parameter in effective irrigation scheduling, was calculated by combining sensor readings and FC estimates. Ranking-based FC resulted in overestimation of soil moisture depletion, even for accurate sensors at the site with lower levels of salinity and clay.