Influence of Prairie Restoration on CT-Measured Soil Pore Characteristics

Clark J. Gantzer, Harold Garrett, Ranjith Udawatta, Research Projects 2008, Stephen Anderson,

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Principle Investigators: Ranjith P. Udawatta, Stephen H. Anderson, Clark J. Gantzer, and Harold E, Garrett

Institution and/or Affiliation: University of Missouri 

Abstract:

Restored prairies are expected to improve soil physical properties, yet little is known about the extent of change to soil properties and how rapidly these changes take place. The objective of this study was to compare eff ects of prairie restoration on computed tomography (CT)-measured pore parameters. Undisturbed soil cores (76 mm diam. by 76 mm long) from
native prairie (NP), restored prairie (RP), conservation reserve program (CRP), and no-till corn (Zea mays L.)-soybean (Glycine max (L.) Merr.; CS) sites were collected with six replicates from the 0- to 40-cm depth in 10-cm increments. Five CT images were acquired from each soil core using a medical CT scanner with 0.2 by 0.2 mm pixel resolution with 0.5 mm slice thickness, and then the images were analyzed. Soil bulk density and hydraulic conductivity (Ksat) were also measured. Soils under NP, RP, CRP, and CS areas had 83, 43, 48, and 26 pores on a 2500 mm2 area, respectively, for the 0- to 40-cm depth. Th e number of pores, number of macropores (>1000 μm diam.), macroporosity, mesoporosity (200-1000 μm diam.), and fractal dimension were significantly higher and pore circularity was lower for NP, RP, and CRP than the CS treatment. Th e CT-measured mesoporosity and macroporosity of the CS treatment were 20 and 18% of the values for the NP site. CT-measured number of pores and macropores explained 43 and 40% of the variation for Ksat. The study showed that prairie restoration improves CT-measured soil pore parameters and decreases bulk density which are related to soil water infi ltration.

The Udawatta et al. (2008; reprint enclosed) study demonstrated that prairie restoration improves computed tomography-measured pore parameters and morphological characteristics, porosity, and hydraulic conductivity; and reduces soil bulk density. These soil properties improve soil water and gas movement. Therefore, these changes directly and indirectly affect soil microbial processes that involve degradation of agri-chemicals, nutrient cycling, carbon sequestration, and other soil processes. However, their study did not compare biological processes associated with prairie restoration, resilience of microbial communities in prairie soils, and spatial distribution of microhabitats. ‘Microbial resilience’ generally refers to the ability or capacity of a soil microbial community to return to original levels of functional activity and structural or genetic diversity optimal within a given ecosystem. Resilience can be measured in terms of soil quality or soil health using various indicators including C and N utilization patterns, enzyme activities, diversity (structural, physiological, genetic), or microbial biomass. Such resilience measurements are useful in determining progress in restoration or reclamation of soils from any number of perturbations (intensive tillage under continuous cropping, deforestation, strip mining, etc.) during conversion to improved or more natural ecosystems (grassland, restored forest, restored riparian areas). Soil scientists are now attempting to look inside the soil system and find better methods to predict water and gas movement and to assess the effects of management on soil pore parameters, microbial habitats, and carbon sequestration, as well as treatment effects on root development. It is known that soil microstructure governs the flow of resources through the pore space of the soil media and creates spatial and temporal differences in the media (Young and Crawford, 2004; Zhang et al., 2005). An understanding of microbial community structure, their spatial distributions, as well as their functions are important to explain soil processes and functions (Nannipieri et al., 2003). Literature lacks information on how physical habitat controls biological processes within soil, and this limits developing sustainable management strategies (Feeney et al., 2006). The proposed study intends to examine microbial resilience and spatial distribution of microhabitats with respect to soil aggregate structure and surfaces. We anticipate that the results of the study will help understand carbon sequestration, soil processes, degradation of various compounds, and aggregate stability as well as movement of liquids, gas, and heat within soils as influenced by management.

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