Soil water balance simulation of alfalfa (Medicago sativa L.) in the semiarid Chinese Loess Plateau

When ecological restoration is prioritized with consideration of its economic value in the semiarid Chinese Loess Plateau, its hydrological effects have to be evaluated first to assure that multiple values of the lands are realized. Alfalfa (Medicago sativa L.) has been selected to realize the hydrological effects and to meet the economic expectation. To evaluate the hydrological effects of the alfalfa, measured biophysical and meteorological data (1996) were combined with model-simulated data (ET) to assess the alfalfa-related soil water content based on water balance equation. With measured runoff, assumed canopy interception, and modeled canopy transpiration (for full canopy) and modeled soil evaporation (for bare soil), soil water content was modeled with the water balance equation. The monthly variations in the modeled soil water content were then compared with in situ measured soil water content and the comparison assured us that this approach can be adopted to estimate the soil water content in other watersheds where there are no adequate in situ data. Our results show that the simulated monthly water loss (evaporation + transpiration + surface runoff) ranges from 49.76 to 92.40 mm, while measured monthly input of water ranges from 20.20 to 90.70 mm. To sum up, the net change in soil water (ΔSW) is negative in every month of the growing season and the soil water content is approaching to wilting point at the end of the autumn, and the soil water deficit was replenished during the following season. The objective was to interpret the relationship between water supply and demand of alfalfa at the rain-fed agricultural area, and test the hydrological effects of alfalfa in hope that the results can provide some insights into feasibility of a large-scale planning for ecological restoration and agricultural activities in the entire Chinese Loess Plateau. As a result of estimation of water balance and observation of soil water content following season in alfalfa plot, alfalfa can be recommended as a crop for this area.