Response of soil moisture content to five years of predicted global climate change treatments in the Mojave Desert

Global climate change models have predicted that global warming will increase summer monsoon rains in the Mojave Desert. Increases in urbanization, cattle grazing, and off-road vehicle use will result in increased nitrogen deposition and disturbance of the biological soil crust. Three treatments based on these predictions have been applied to 96 plots (each 14 by 14 m) at the Mojave Global Change Facility (MGCF). These treatments include a summer irrigation, two levels of nitrogen fertilization (10 and 40 kg/ha), and crust disturbance. Soil moisture has been measured by the neutron probe method. Neutron probe measurements have been taken at 20 cm increments starting at the 20cm depth down to the 180 cm depth for a >5 year period. Overall, soil moisture was not significantly different among any of the nitrogen or soil crust interactions at any time during the five year period. We have found significant interactions between irrigated and non-irrigated plots as well as an interaction with the covariate precipitation. Irrigated plots have shown significantly (P<0.01) higher soil water content (%) at the 20, 40, and 60 cm depths. Irrigated plots also have shown significantly (P<0.01) higher total soil water content (mm) than non-irrigated plots. The duration that the irrigation effect lasts is highly dependant on the amount of precipitation received in a given year. If the irrigation effect consistently persists into the following spring growing period it could potentially affect the full suite of vegetation in the Mojave Desert, including species that are only active during the winter-spring growing season.