Measuring and modeling water-related soil-vegetation feedbacks in a fallow plot

Land fallowing is one possible response to short- age of water for irrigation. Leaving the soil unseeded implies a change of the soil functioning that has an impact on the wa- ter cycle. The development of a soil crust in the open spaces between the patterns of grass weed affects the soil properties and the field-scale water balance. The objectives of this study are to test the potential of integrated non-invasive geophys- ical methods and ground-image analysis and to quantify the effect of the soil-vegetation interaction on the water balance of fallow land at the local- and plot scale. We measured repeatedly in space and time local soil sat- uration and vegetation cover over two small plots located in southern Sardinia, Italy, during a controlled irrigation exper- iment. One plot was left unseeded and the other was culti- vated. The comparative analysis of ERT maps of soil mois- ture evidenced a considerably different hydrologic response to irrigation of the two plots. Local measurements of soil sat- uration and vegetation cover were repeated in space to evi- dence a positive feedback between weed growth and infiltra- tion at the fallow plot. A simple bucket model captured the different soil moisture dynamics at the two plots during the infiltration experiment and was used to estimate the impact of the soil vegetation feedback on the yearly water balance at the fallow site.