No abstract

Grazing lands support the livelihoods of millions of people across nearly one-half of the globe. Soils are the backbone of stability and resilience in these systems. To determine livestock grazing impacts on soil health, we conducted a global meta-analysis of soil organic carbon (SOC), total N, C/N ratio, and bulk density responses to grazing strategies (continuous, rotational, and no grazing) and intensities (heavy, moderate, and light grazing) from 64 studies around the world. Across all studies and grazing intensities, continuous grazing significantly reduced SOC, C/N, and total N compared with no grazing. Soil compaction (i.e., increased bulk density) was greater under both continuous and rotational grazing compared with no grazing; however, rotational grazing had lower bulk density than continuous grazing. Rotational grazing had greater SOC than continuous grazing and was not different from no grazing. The positive responses of SOC to rotational grazing could create climate change mitigation opportunities. Grazing strategy comparisons were minimally conditioned by aridity class (i.e., arid, subhumid, and humid); however, complete observations were notably limited or missing for many rotational grazing comparisons. For continuous and no grazing strategy comparisons, we found that grazing management can significantly influence soil function and health outcomes; however, site-specific environmental factors play important moderating roles. Greater coordination across regional, national, and global efforts, as well as consistent guidelines for soil health evaluation, would help overcome these knowledge gaps and vastly improve our collective understanding of grazing impacts on soil health, providing greater management and policy impacts.

No abstract

Vegetated buffer strips were evaluated for their ability to remove waterborne Cryptosporidium parvum from surface and shallow subsurface flow during simulated rainfall rates of 15 or 40 mm/h for 4 h. Log 10 reductions for spiked C. parvum oocysts ranged from 1.0 to 3.1 per m of vegetated buffer, with buffers set at 5 to 20% slope, 85 to 99% fescue cover, soil textures of either silty clay (19:47:34 sand-silt-clay), loam (45:37:18), or sandy loam (70:25:5), and bulk densities of between 0.6 to 1.7 g/cm 3 . Vegetated buffers constructed with sandy loam or higher soil bulk densities were less effective at removing waterborne C. parvum (1-to 2-log 10 reduction/m) compared to buffers constructed with silty clay or loam or at lower bulk densities (2-to 3-log 10 reduction/m). The effect of slope on filtration efficiency was conditional on soil texture and soil bulk density. Based on these results, a vegetated buffer strip comprised of similar soils at a slope of <20% and a length of >3 m should function to remove >99.9% of C. parvum oocysts from agricultural runoff generated during events involving mild to moderate precipitation.Cryptosporidium parvum has emerged as a widespread and persistent waterborne microbial pathogen, with specific genotypes able to be transmitted ambidirectionally between livestock and humans (e.g., amphixenotic) (6,42,46,54). Although we still do not know the percentage of annual cases of human cryptosporidiosis that are attributable to livestock-derived waterborne C. parvum (39), reducing the likelihood that animal agricultural operations will contaminate surface water with infective C. parvum oocysts will help safeguard both water quality and public health (51). Several strategies exist for minimizing the likelihood that an animal agricultural operation contaminates surface water with infective C. parvum oocysts. For example, one such strategy is to reduce the incidence of C. parvum infection or the intensity of fecal shedding of C. parvum oocysts by livestock populations, thereby reducing the rate of environmental loading of C. parvum per livestock unit (26,36). These herd-health efforts remain hampered by our poor understanding of the medical ecology of C. parvum within livestock populations (3,4,16,40), how to interrupt transmission between the biological reservoir and susceptible animals (3, 40), and the lack of an affordable vaccine that has been proven to be efficacious in commercial agricultural settings (23,47).A second strategy is to manage the manure produced by livestock so that the survivability and off-site transport of infective C. parvum are substantially reduced (3,20,30,53,55). One strategy being advocated for minimizing the transport potential of C. parvum oocysts from animal manure to surface water is to place vegetated buffer strips between animal agricultural operations and vulnerable surface water supplies (10,12,15,32,38,51,59,60). Optimal design criteria for on-farm vegetated buffer strips currently do not exist for waterborne microbial contaminants. Moreover, studies ...