Print PageIn water-limited ecosystems, soil profile characteristics can control plant community composition and production through their influence on spatial and temporal patterns of plant available water (PAW). Cemented parts of the soil profile typically are overlooked when evaluating available water holding capacity (AWHC) and measuring PAW. In arid and semi-arid ecosystems, accumulation of carbonates can cement soil particles together creating rock-like nodules and horizons (forming calcic and petrocalcic horizons). These horizons are widespread and often occur within the rooting zone of desert plant species. We report results from a series of studies conducted on sandy soils of southern New Mexico, USA that highlight the importance of carbonate cemented horizons for soil water and plant community dynamics. To investigate water retention and dynamics, two replicated experiments were conducted in a mixed shrub-grass community: a laboratory study evaluating the AWHC of a variety of petrocalcic material and a field study measuring temporal water availability and dynamics across soils with differing degrees of petrocalcic development. To investigate the influence of petrocalcic horizons on ecological potential, we documented the relationship between spatial patterns in depth to petrocalcic horizon and long-term shrub and grass dynamics in a 150-ha pasture using historical imagery and a recent digital soils map. Finally, we compared measured and modeled soil-water content over 20 years to address some basic questions regarding the treatment of carbonate cemented soils in hydrologic models.
Results/Conclusions
Laboratory analyses show petrocalcic material can have high AWHC (3 – 23 % versus 6 % in similar non-carbonate soil). In situ measurements of PAW indicate that high-carbonate horizons can retain much more PAW than similar depths in non-carbonate soils of comparable texture. Long-term (70-years) vegetation dynamics revealed that petrocalcic soils were more resistant to shrub proliferation with greater grass resilience than non-petrocalcic soils. Comparisons of measured and modeled soil water content show that PAW is not accurately modeled using hydrologic parameters measured by the NRCS Soil Survey because they do not account for the porosity of petrocalcic material. Taken together, we draw four conclusions from this body of research: 1) cementation by carbonates dramatically alters the water holding characteristics of soils, 2) carbonate cemented horizons can contain significant amounts of PAW, 3) soils with shallow petrocalcic horizons can be more resilient to grass loss and shrub invasion than similar non-petrocalcic soils, and 4) hydrologic parameters typically used in SWC models do not accurately capture soil-water dynamics in these important soils.
