Multiscale variability in soil aggregate stability: Implications for understanding semiarid grassland degradation

TitleMultiscale variability in soil aggregate stability: Implications for understanding semiarid grassland degradation
Publication TypeJournal Article
Year of Publication2007
AuthorsBird S.B., Herrick JE, Wander M.M., Murray L.W.
Date Published04/2007
ARIS Log Number170958
Keywordsdesertification, grassland degradation, soil aggregate, soil structure, stability, variability
AbstractGrassland degradation typifies desertification in many regions of the world. Changes in plant communities and increased soil resource loss and redistribution have been widely documented in degrading grasslands. Increased soil loss and redistribution are commonly associated with changes in soil structure, yet variability in soil structure in arid ecosystems has been little studied. We compared soil aggregate stability in a Chihuahuan Desert grassland at the plant and landscape scales by assessing aggregate stability at four sites in two cover classes (under grass canopy vs. in bare interspace) located within each of three grass cover and land disturbance classes. Soil aggregate stability is a key indicator of soil structure and is correlated with erodibility and water infiltration capacity. To increase measurement sensitivity to changes in soil structure and identify potential early warning indicators for monitoring, we used two different methods for quantifying wet aggregate stability: stability of aggregates > 0.25 mm was assessed in the laboratory and that of 1.5 mm aggregates was assessed in the field. As expected, soil aggregate stability was significantly higher under grass plants than in plant interspaces (44.2 vs. 38.4% for the lab test and 4.4 vs. 3.3 stability class for the field test; p < 0.01). This plant-interspace pattern was consistent at all four study sites, but the absolute values for under plants and in interspaces varied across the landscape. The field test showed higher stability throughout the top 10 cm in plots with higher grass cover throughout the top 10 cm, while disturbance level only affected stability at the soil surface. The laboratory test was insensitive to differences in grass cover and disturbance. High variability at the plant-interspace scale supports earlier work on biogeochemistry, reflecting linkages between the spatial distribution of soil structure, soil organic matter, and nutrient cycling. The established relationship between soil aggregate stability and other soil properties and processes, the relative sensitivity of the field test, and lack of sensitivity of the lab test to differences in grass cover and disturbance support the use of the field test as an indicator for managing both grass cover and soil surface disturbance in arid grasslands.