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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2008.08.001 Byline: Yakov A. Pachepsky (a), Andrey K. Guber (a), Daniel R. Shelton (a), Gregory W. McCarty (b) Abbreviations: EC, electrical conductivity; CSD, cumulative size distribution Abstract: Manure and animal waste deposited on cropland and grazing lands serve as a source of microorganisms, some of which may be pathogenic. These microorganisms are released along with particles of dissolved manure during rainfall events. Relatively little if anything is known about the amounts and sizes of manure particles released during rainfall, that subsequently may serve as carriers, abode, and nutritional source for microorganisms. The objective of this work was to obtain and present the first experimental data on sizes of bovine manure particles released to runoff during simulated rainfall and leached through soil during subsequent infiltration. Experiments were conducted using 200cm long boxes containing turfgrass soil sod; the boxes were designed so that rates of manure dissolution and subsequent infiltration and runoff could be monitored independently. Dairy manure was applied on the upper portion of boxes. Simulated rainfall (ca. 32.4mmh.sup.-1) was applied for 90min on boxes with stands of either live or dead grass. Electrical conductivity, turbidity, and particle size distributions obtained from laser diffractometry were determined in manure runoff and soil leachate samples. Turbidity of leachates and manure runoff samples decreased exponentially. Turbidity of manure runoff samples was on average 20% less than turbidity of soil leachate samples. Turbidity of leachate samples from boxes with dead grass was on average 30% less than from boxes with live grass. Particle size distributions in manure runoff and leachate suspensions remained remarkably stable after 15min of runoff initiation, although the turbidity continued to decrease. Particles had the median diameter of 3.8[mu]m, and 90% of particles were between 0.6 and 17.8[mu]m. The particle size distributions were not affected by the grass status. Because manure particles are known to affect transport and retention of microbial pathogens in soil, more information needs to be collected about the concurrent release of pathogens and manure particles during rainfall events. Author Affiliation: (a) USDA-ARS, Environmental Microbial Safety Laboratory, 10300 Baltimore Avenue, Building 173, Barc-East, Beltsville, MD 20705, USA (b) USDA-ARS, Hydrology and Remote Sensing Laboratory, Beltsville, MD 20705, USA Article History: Received 9 November 2007; Revised 4 April 2008; Accepted 3 August 2008

The study summarizes the current knowledge on infection and recovery of white-tailed deer and cattle, and integrates this knowledge into the Soil and Water Assessment Tool (SWAT) via a new add-on module SIR (Susceptible - Infected - Recovered) for predicting pathogen transmission between livestock and deer. New processes modeled by the SWAT-SIR model include: (a) seasonal changes in deer population and habitat; (b) resource selection and seasonal changes in foliage consumption by deer; (c) ingestion of pathogens with water, foliage and via grooming soiled hide by deer and grazing cattle; (d) infection and recovery of deer and co-grazing cattle; (e) pathogen shedding by infected animals; (f) survival of pathogens in manure; (g) kinetic release of pathogens from applied manure and fecal material. The model output is linked with ARC-GIS to allow spatial and temporal analysis of pathogen distribution across the watershed for specific land use, weather and management scenarios. [ABSTRACT FROM AUTHOR]

Furrow irrigation used in arid areas for maize production is a major cause of groundwater pollution by nitrates, and development of new technologies aimed at reducing pollution is critical for sustainable crop production and water usage. Field experiments and modeling of nitrogen (N) transport were carried out to estimate N losses from compost amended soils under furrow irrigation used for maize production in Pakistan. Press-mud (PrM) and poultry manure (PM) composts were applied at 5 application rates followed by 8 irrigations at rates of 7.5 cm. Changes in inorganic N storage (NH 4 N and NO 3 N) were measured in the top 15-cm soil layer. The HYDRUS-2D model was calibrated and validated on measured data and implemented to estimate N leaching losses from soil profile. A four-pools approach used in the simulations considered transformation and transport of the following pools of N: ‘Slow soil N’, ‘Fast soil N’, ammonium-N, and nitrate-N pools. Results showed that N leaching losses were higher for: (i) PrM compost due to its higher mineralization rate; (ii) wet year due to washing out of N accumulated in ridges; and (iii) 1:1 ridge to furrow aspect ratio in comparison to the 2:1 ratio, due to an increase in N accumulation in wider ridges. Overall, the HYDRUS-2D software appeared to be a useful tool for predicting inorganic N losses in manure amended soil under furrow irrigation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Release of manure components was studied in runoff-box and runoff-plot experiments. [•] Parameters of release model were estimated for six manure components. [•] Reliable parameter estimation required grouping different manure components. [•] Vegetation affected manure release parameters governing shape of release kinetics. [•] Soil texture influenced release parameters governing recovery of manure components. [Copyright &y& Elsevier]

Switchgrass (Panicum virgatum L.) is a promising feedstock for biofuel production, with diverse cultivars representing several ecotypes adapted to different environmental conditions within the contiguous USA. Multiple field studies have demonstrated that monoculture switchgrass cultivation leads to slow to negligible soil carbon (C) gains, an outcome unexpected for such a deep-rooted perennial. We hypothesize that different switchgrass cultivars have disparate impacts on soil C gains, and one of the reasons is variations in physical characteristics of their roots, where roots directly and indirectly influence formation of soil pores. We tested this hypothesis at Great Lakes Bioenergy Research Center's research site in Michigan using two lowland cultivars (Alamo and Kanlow) and four upland cultivars (Southlow, Cave-in-Rock, Blackwell, and Trailblazer). Three types of soil samples were collected: 20 cm diameter (Ø) intact cores used for root analyses; 5 cm Ø intact cores subjected to X-ray computed tomography scanning used for pore characterization; and disturbed soil samples used for microbial biomass C (MBC) and soil C measurements. Path analysis was used to explore interactive relationships among roots, soil pores, and their impact on MBC, and ultimately, on soil C contents across six cultivars. The abundance of very fine roots (<200 μm Ø) was positively associated with fractions of pores in the same size range, but negatively with distances to pores and particulate organic matter. Higher abundance of such roots also led to greater MBC, while greater volumes of medium pores (50–200 μm Ø) and shorter distances to pores increased MBC. Results suggest that the greater proportion of very fine roots is a trait that can potentially stimulate soil C gains, with pore characteristics serving as links for the relationship between such roots and C gains. However, at present, ten years of cultivation generated no differences in soil C among the studied cultivars. • Switchgrass cultivars differed in volumes of very fine (<200 μm diameter) roots. • Very fine roots made direct and indirect positive contributions to increases in soil C. • Increases in medium pore volumes via very fine roots indirectly increase soil C. • Short distances to pores and POM via very fine roots indirectly increase soil C. • Soil structural characteristics functioned as key links for soil C gains. [ABSTRACT FROM AUTHOR]

Root detritusphere is one of the most important sources of N 2 O, however, understanding of how N 2 O emission from the detritusphere is influenced by soil properties remains elusive. Here, we evaluated the effects of pore architecture and soil moisture on N 2 O emission during the decomposition of in-situ grown roots of switchgrass, an important bioenergy crop. We combined dual isotope labeling (15C and 15N) with zymography to gain insights into the location of the microbial N 2 O production in soils with contrasting pore architectures. In the studied soil, the effect of soil pore architecture on N 2 O emissions was 6 times greater than that of soil moisture. Soil dominated by > 30 μm Ø pores (i.e., large-pore soil) had higher chitinase activity than the soil dominated by < 10 μm Ø pores (i.e., small-pore soil), especially near the decomposing roots. The chitinase activity on the decomposing roots was positively correlated with emission of root-derived N 2 O, indicating that N released from root decomposition was an important source of N 2 O. Greater N 2 O and N 2 emission was induced by switchgrass roots in soils dominated by the large- compared to the small-pore soils. The microenvironment developed near decomposing roots of the large-pore soil also resulted in positive N 2 O priming. Our study challenged the traditional view on soil moisture as the main factor of N 2 O production. Production and emission of N 2 O was most intensive in microbial activity hotspots (i.e., rhizosphere legacy) in the large pores, where decomposed roots release mineral N as the main N 2 O source. [Display omitted] • Rhizosphere soil carries a strong legacy effect as it turns into detritusphere. • Pore architecture is 6 times more important than soil water content in N 2 O emission. • N 2 O emission is most intensive in microbial activity hotspots in large pores. • Root- and soil-derived N 2 O emissions both occur near decomposing roots. [ABSTRACT FROM AUTHOR]