Physical and chemical properties of soils under some pinon-juniper-oak canopies in a semi-arid ecosystem in New Mexico

Pinon (Pinus edulis)-juniper (Juniperus monosperma)-ecosystems increased substantially in the western USA during the 20th century. Sustainability of these ecosystems primarily depends on soil quality and water availability. This study was undertaken with the objective of assessing the effect of tree species on soil physical quality in a semi-arid region in the western part of Sugarite Canyon, northeast of Raton, Colfax County, NM (37 degrees 56'32N and 104 degrees 23'00W) USA. Three cores and three bulk soil samples were obtained from the site under the canopy of three juniper, Gambel oak (Quercus gambelii) and pinon trees for 0-10 and 10-20 cm depths. These samples were analyzed for particle size distribution, soil bulk density (rho(b)), water stable aggregation (WSA), mean weight diameter (MWD) of aggregates, pH, electrical conductivity (EC) and soil organic carbon (SOC) and total nitrogen (TN) concentrations and stocks. Sand content was greater under juniper (48%) than oak (32%), whereas clay content followed the opposite trend. The rho(b), WSA, MWD, pH and EC were similar under juniper, pinon, oak canopies for both depths. Estimated (from Philip and Green and Ampt infiltration models) and measured water infiltration parameters did not vary among these sites and were in accord with the values for rho(b), WSA and MWD. The SOC concentrations and stocks were greater under oak (43.1 Mg ha(-1) for 0-10 and 37.5 Mg ha(-1) for 10-20 cm depths) than pinon (23.3 Mg ha(-1) for 0-10 and 18.5 Mg ha(-1) for 10-20 cm depths). The TN concentrations were greater under oak (3.4 g kg(-1)) than pinon (1.7 g kg(-1)) for the 0-10 cm depth only. Accumulation of detritus material under tree canopies reduced soil compaction and crusting caused by raindrop impact and increased SOC, and TN concentrations, and water infiltration. Coefficients of variation ranged from low to moderate for most soil properties except infiltration rate at 2.5 h, which was highly variable. Overall, soil quality for each site was good and soil aggregation, water infiltration and SOC concentrations were high, and Soil rho(b) was low. (c) 2005 Elsevier Ltd. All rights reserved.