Physically Active Soil Organic Matter: Key Factor in Arid Lands Reclamation?
Investigators (most current known information)
Large areas of sandy soils throughout the world have been transformed from perennial grasslands to shrublands. This transformation is associated with increased rates of soil loss and internal redistribution of resources by both wind and water. The net result is a patchy distribution of resource-rich shrub islands and resource-poor interspaces. Historic efforts to reclaim these areas have been ineffective, uneconomic, or both. Future approaches must rely on promoting internal resources and recovery processes using limited external inputs. Soil organic matter (SOM) is believed to play a key role in stabilizing these largely apedal sandy soils. Studies in other systems have clearly demonstrated that the contribution of SOM to soil structure depends on its composition and distribution. Little information exists on the relative importance of SOM fractions for soil aggregation in sandy arid soils, or on the spatial distribution of these fractions and stable aggregates relative to vegetation.
Our general objective is to develop an understanding of the function of SOM fractions in sandy arid ecosystems in order to improve its sensitivity as an indicator and enhance our ability to remediate degraded areas through manipulation of internal resources and processes. That objective will be met by pursuing three specific objectives: (1) to compare spatial patterns in soil aggregate stability in a grassland and shrubland system and relate these patterns to vegetation, (2) to identify SOM fractions that are associated with soil macroaggregation, and (3) to identify the probable sources of these fractions (plant species, fungi, cyanobacteria). Based on this and related studies, we will develop management recommendations to promote soil aggregation.
Soil samples will be collected from the USDA-ARS Jornada Experimental Range, located in the Chihuahuan Desert. The relationship between plant cover and the spatial variability in aggregate stability (Objective 1) will be explored by collecting fifty spatially referenced samples from three soil depths (0-0.5 cm, 0.5-2.5 cm, 2.5-10 cm) from a relatively undegraded grassland and a highly degraded shrubland site. The general relationships between macroaggregate stability and location, plant species and surface cover will be evaluated using multiple regression, coefficients of variation and geostatistics.
The specific relationships between aggregate stability, SOM fractions and plant species (Objectives 2 and 3) will be quantified at ten sites located in grass-shrubland transition zones on a sandy loam. At each site, soil will be sampled at three depths beneath the canopy and at a paired location in the adjacent bare interspace for each of five perennial species. The following SOM fractions will be quantified for both the whole soil and the stable macroaggregates: loose/light, particulate, humin and acid hydrolyzable carbohydrates. Fungal hyphal and cyanobacterial length density will be assessed. The texture of all samples and iron oxide and carbonate contents of appropriate composites will also be determined. The relationships between specific SOM fractions, chemical measures, plant species, and aggregate stability will be assessed using regression and ANOVA.
Article in Journal
Bird, S.B., J.E. Herrick, M.M. Wander and S.F. Wright. 2002. "Spatial heterogeniety of aggregate stability and soil carbon in semi-arid range lands." Environmental Pollution 111(3):445-455.
Bird, S.B., J.E. Herrick and M.M. Wander. 2001. "Exploring heterogeneity of soil organic matter in rangelands: Benefits for carbon sequestration, Chapter 5,121-138. In Potential of U.S. Grazing Lands Sequester Carbon and Mitigate the Greenhouse Effect, ed. R.F. Follett. Boca Raton FL. Lewis Publishers.