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.

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. A Global Meta-Analysis of Grazing Impacts on Soil Health Indicators

High nitrogen (N) concentration in bovine urine, which generally exceeds plant N uptake rates, results in the formation of hotspots of N loss when bovine urine is deposited on grazed pasture soils. High spatial variability in the distribution of urine patches in grazed pastures poses a major challenge to mitigate N losses. Some exudates from the roots of several tropical forage grasses were shown to inhibit the activity of soil nitrifiers; a process known as biological nitrification inhibition (BNI). We hypothesized that nitrate (NO3−) production and nitrous oxide (N2O) emissions from urine patches deposited on soils under forage grasses with high BNI capacity are lower than those with forage grasses with low BNI capacity. This hypothesis was tested using field plots of two tropical forage grass cultivars, Brachiaria humidicola cv. Tully (BT) and interspecific Brachiaria hybrid cv. Mulato (BM) which, correspondingly, have high and low BNI capacity. Nitrification rates and amoA gene copy numbers of ammonia oxidizing archaea (AOA) and bacteria (AOB) in soils under the two forage grasses were quantified before and after urine and water (control) application, as well, an additional experiment was conducted to quantify denitrification potential. Moreover, soil N2O emissions from simulated urine (0.123 kg N m−2) and water patches were monitored over a 29-day period. Results showed a greater suppression of nitrification, denitrification and AOA abundance in soils under BT than those under BM. Positive relationships (p < 0.05) existed between AOA and AOB abundance and NO3− contents in soils under BM. Bovine urine resulted in higher cumulative N2O fluxes from soils under BM (80 mg N2O-N m−2) compared to those under BT (32 mg N2O-N m−2). Consequently, N2O emission factors were higher for soils under BM (0.07%) than under BT (0.00002%). We conclude that tropical forage grasses with high BNI capacity play a key role in mitigating N2O emissions from bovine urine patches in archaea-dominated soils. This suggests that wide-spread adoption of tropical forage grasses with high BNI capacity may have a great potential to tighten N cycling in grazed pastures.

Agriculture in California contributes 8% of the state's greenhouse gas (GHG) emissions. To inform the state's policy and program strategy to meet climate targets, we review recent research on practices that can reduce emissions, sequester carbon and provide other co-benefits to producers and the environment across agriculture and rangeland systems. Importantly, the research reviewed here was conducted in California and addresses practices in our specific agricultural, socioeconomic and biophysical environment. Farmland conversion and the dairy and intensive livestock sector are the largest contributors to GHG emissions and offer the greatest opportunities for avoided emissions. We also identify a range of other opportunities including soil and nutrient management, integrated and diversified farming systems, rangeland management, and biomass-based energy generation. Additional research to replicate and quantify the emissions reduction or carbon sequestration potential of these practices will strengthen the evidence base for California climate policy.

Agricultural producers grapple with low farm yields and declining ecosystem services within their landscapes. In several instances, agricultural production systems may be considered largely unsustainable in socioeconomic and ecological (resource conservation and use and impact on nature) terms. Novel technological and management options that can serve as vehicles to promote the provision of multiple benefits, including the improvement of smallholder livelihoods, are needed. We call for a paradigm shift to allow designing and implementing agricultural systems that are not only efficient (serving as a means to promote development based on the concept of creating more goods and services while using fewer resources and creating less waste) but can also be considered synergistic (symbiotic relationship between socio-ecological systems) by simultaneously contributing to major objectives of economic, ecological, and social (equity) improvement of agro-ecosystems. These transformations require strategic approaches that are supported by participatory system-level research, experimentation, and innovation. Using data from several studies, we here provide evidence for technological and management options that could be optimized, promoted, and adopted to enable agricultural systems to be efficient, effective, and, indeed, sustainable. Specifically, we present results from a study conducted in Colombia, which demonstrated that, in rice systems, improved water management practices such as Alternate Wetting and Drying (AWD) reduce methane emissions (~70%). We also show how women can play a key role in AWD adoption. For livestock systems, we present in vitro evidence showing that the use of alternative feed options such as cassava leaves contributes to livestock feed supplementation and could represent a cost-effective approach for reducing enteric methane emissions (22% to 55%). We argue that to design and benefit from sustainable agricultural systems, there is a need for better targeting of interventions that are co-designed, co-evaluated, and co-promoted, with farmers as allies of transformational change (as done in the climate-smart villages), not as recipients of external knowledge. Moreover, for inclusive sustainability that harnesses existing knowledge and influences decision-making processes across scales, there is a need for constant, efficient, effective, and real trans-disciplinary communication and collaboration.