|Herrick, Jeffrey - Jeff|
Submitted to: Geoderma
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/19/2007
Publication Date: 4/16/2007
Citation: Bird, S.B., Herrick, J.E., Wander, M.M., Murray, L. 2007. Multi-scale variability in soil aggregate stability: Implications for understanding and predicting semi-arid grassland degradation. Geoderma. 140:106-118. Interpretive Summary: Sustainable land management requires an understanding of the key processes and properties that control land degradation and recovery. Both degradation and recovery in arid and semiarid ecosystems are associated with changes in soil erosion rates. Soil aggregate stability is a key indicator of soil structure and is a key factor that limits soil erosion and increases water infiltration, yet variability in soil structure in arid ecosystems has been little studied. This project was designed to quantify variability in soil aggregate stability at multiple scales and to identify factors associated with higher stability. We found that aggregate stability was higher under plants than in plant interspaces. A field test also showed that aggregate stability was higher in areas with high grass cover. The traditional laboratory test was relatively insensitive to these differences. 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.
Technical Abstract: Grassland 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.