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Abstract
Soils are central to sustainable management of any agroecosystem including grazing lands, thus; development of innovative grazing management systems and scientific studies focused on improving soil health is of prime importance. A study was conducted in eight beef-pastures of Southern Piedmont, Georgia, USA, from 2015 to 2018, to assess the effects of existing grazing system (continuous/conventional), a slightly improved continuous system (continuous grazing with hay distribution: CHD), and a collection of better grazing practices (strategic grazing: STR) on soil health, spatial distribution of labile carbon and nitrogen, and runoff water quality. In 2015, a baseline study was conducted to assess soil health indicators (in-situ soil respiration, labile carbon, potentially mineralizable nitrogen, labile nitrogen), spatial distribution of labile carbon and nitrogen, and runoff water quality in historically (>10 years) continuously grazed pastures. In 2016, STR grazing system was implemented in four pasture and CHD grazing system was implemented in four pastures. We found that management factors (such as location of hay, water, and shade), cattle locus index, and landscape factors significantly affect the spatial distribution of soil inorganic nitrogen (was highly uneven) in continuously grazed pastures. Post-treatment, STR pastures experienced increased labile carbon down to 20-cm soil depth, and less yearly variation of soil respiration, as compared to CHD pastures. The exclusion and over-seeding of nutrient-rich vulnerable areas in STR pastures facilitated the mineralization of potentially mineralizable nitrogen (PMN) and soil organic carbon to make the nitrogen readily available for plant uptake. The STR system also significantly reduced runoff nitrate losses as compared CHD system, which was mainly attributed to cattle exclusion and continuous vegetative cover of vulnerable low-lying areas of pasture. The STR system significantly improved the concentration and spatial distribution of labile carbon (POXC) down to 20-cm soil depth. Moreover, the STR system also improved the spatial distribution of inorganic nitrogen. We conclude that the STR grazing system has shown potential to improve the sustainability of grazing systems by enhancing soil health and water quality, and we recommend longer-term studies to fully assess its potential.