Soil moisture use by velvet mesquite (Prosopis juliflora)

Abstract

The primary objective of this yearlong study was to determine the amount of soil moisture used by mature velvet mesquite (Prosopis juliflora var. velutina) trees on an upland site in southern Arizona. Using the neutron thermalization method, soil moisture measurements were made adjacent to four live and four dead trees. Measurements were taken to a depth of 6 m and a distance of approximately 20 m from the trunks. Soil moisture levels at selected distances from the live and dead trees were compared and the differences graphically evaluated to determine seasonal soil moisture use. Moisture use was plotted against distance from the trees. This distribution of use varied from season to season. The maximum distance from the trees at which use was occurring fluctuated considerably from season to season but averaged approximately 20 m from the trunks. These fluctuations were attributed largely to the graphing technique. The mean daily use of soil moisture for an average study tree was 468 1 in the summer, 160 1 in the fall, and 644 1 in the spring. Assuming that use was insignificant during the winter dormancy period, the mean daily use for the entire study year was 322 1.