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Livestock systems play a key role in global sustainability challenges like food security and climate change, yet many unknowns and large uncertainties prevail. We present a systematic, spatially explicit assessment of uncertainties related to grazing intensity (GI), a key metric for assessing ecological impacts of grazing, by combining existing data sets on (a) grazing feed intake, (b) the spatial distribution of livestock, (c) the extent of grazing land, and (d) its net primary productivity (NPP). An analysis of the resulting 96 maps implies that on average 15% of the grazing land NPP is consumed by livestock. GI is low in most of the world's grazing lands, but hotspots of very high GI prevail in 1% of the total grazing area. The agreement between GI maps is good on one fifth of the world's grazing area, while on the remainder, it is low to very low. Largest uncertainties are found in global drylands and where grazing land bears trees (e.g., the Amazon basin or the Taiga belt). In some regions like India or Western Europe, massive uncertainties even result in GI > 100% estimates. Our sensitivity analysis indicates that the input data for NPP, animal distribution, and grazing area contribute about equally to the total variability in GI maps, while grazing feed intake is a less critical variable. We argue that a general improvement in quality of the available global level data sets is a precondition for improving the understanding of the role of livestock systems in the context of global environmental change or food security. [ABSTRACT FROM AUTHOR]

A fall-planted winter cover crop is an agricultural management practice with multi-ple benefits that may include reducing nitrate (NO3) losses from artificial drained agricultural fields. While the practice is commonly used in the southern and eastern United States, little is known about its efficacy in midwestern states where winters are longer and colder, and artificial subsurface drainage is widely used in corn-soybean systems {Zea mays L -Glycine max L.).We used a field-tested version of the Root Zone Water Quality Model (RZWQM) to simulate the adoption of cereal rye (Secale cereale L.) as a winter cover crop and estimate its impact on NO3 losses from drained fields at 41 sites across the Midwest from 1961 to 2005. The average annual nitrogen (N) loss reduction from adding winter rye ranged from 11.7 to 31.8 kg N ha--1 (10.4 to 28.4 lb N ac-1) among four simulated systems. One of the simulated treatments was winter rye overseeded (aerial seeded) into a no-till corn-soybean rotation at simulated main crop maturity (CC2). On average, this treatment reduced simulated N loss in drainage by 20.1 kg N ha-1 (17.9 lb N ac-1) over the sites compared to systems without winter rye (NCC2), from 47.3 to 27.2 kg N ha-1 (42.2 to 24.3 lb N ac-1). Adding spring tillage to this treatment and killing the rye earlier (CC3) reduced simulated N loss from 57.3 (NCC3) to 34.4 kg N ha-1 (30.7 lb N ac-1). Replacing the corn-soybean rotation with continuous corn and spring tillage reduced simulated N loss from 106 (NCC4) to 74.2 kg N ha-1 (CC4) (94.6 to 66.2 lb N ac-1). Adding a winter rye cover crop reduced N loss more in the continuous corn system despite earlier spring termination of the winter rye and slightly less N uptake by the rye possibly because of more denitrification. Regression analysis of the RZWQM vari-ables from these sites showed that temperature and precipitation during winter rye growth, N fertilizer application rates to corn, and simulated corn yield account for greater than 95% of the simulated site-to-site variability in NO3 loss reductions in tile flow due to winter rye. Our results suggest that on average winter rye can reduce N loss in drainage 42.5% across the Midwest. Greater N loss reductions were estimated from adding winter rye at sites with warmer temperatures and less precipitation because of more cover crop growth and more soil N available for cover crop uptake. [ABSTRACT FROM AUTHOR]

Nitrate (NO,) losses from agricultural lands in the Midwest flow into the Mississippi River Basin (MRB) and contribute significantly to hypoxia in the Gulf of Mexico. Previous work has shown that cover crops can reduce loadings, but adoption rates are low, and the potential impact if cover crops were widely adopted is currently unknown. This paper pro-vides an analysis of potential cover crop adoption and relative benefits to water quality across the five-state region of Ohio, Indiana, Illinois, Iowa, and Minnesota in the upper midwestern MRB. Two agricultural counties were selected in each of the five states, and the potential for fall-planted cover crop adoption was estimated based on cash crop rotation and tillage sys-tems. In these 10 counties, an estimated 34% to 81% of the agricultural land could have cover crops integrated into their corn (Zea mays L.) and soybean (Glycine max L.) cropping systems. These adoption rates would in some cases require shifts of current tillage practices from fall to spring, but could be even higher with increased adoption of no-till and mulch-till. Nitrate reduction simulated with the Root Zone Water Quality Model for the tile drained portion of the corn-soybean and continuous corn cropping systems in the five-state area, under the assumed management systems and uniform soil properties, showed that cover crops have the potential to reduce N03 loadings to the Mississippi River by approximately 20%. These predictions suggest that cover crop adoption would have a beneficial impact on water quality in the MBJB and would contribute greatly towards meeting the national goal of significant reduction in N03-nitrogen (N) load entering the Gulf. [ABSTRACT FROM AUTHOR]

A growing population with increasing consumption of milk and dairy require more agricultural output in the coming years, which potentially competes with forests and other natural habitats. This issue is particularly salient in the tropics, where deforestation has traditionally generated cattle pastures and other commodity crops such as corn and soy. The purpose of this article is to review the concepts and discussion associated with reconciling food production and conservation, and in particular with regards to cattle production, including the concepts of land-sparing and land-sharing. We then present these concepts in the specific context of Colombia, where there are efforts to increase both cattle production and protect tropical forests, in order to discuss the potential for landscape planning for sustainable cattle production. We outline a national planning approach, which includes disaggregating the diverse cattle sector and production types, identifying biophysical, and economic opportunities and barriers for sustainable intensification in cattle ranching, and analyzing areas suitable for habitat restoration and conservation, in order to plan for both land-sparing and land-sharing strategies. This approach can be used in other contexts across the world where there is a need to incorporate cattle production into national goals for carbon sequestration and habitat restoration and conservation.

Many international policies encourage a switch from fossil fuels to bioenergy based on the premise that its use would not result in carbon accumulation in the atmosphere. Frequently cited bioenergy goals would at least double the present global human use of plant material, the production of which already requires the dedication of roughly 75% of vegetated lands and more than 70% of water withdrawals. However, burning biomass for energy provision increases the amount of carbon in the air just like burning coal, oil or gas if harvesting the biomass decreases the amount of carbon stored in plants and soils, or reduces carbon sequestration. Neglecting this fact results in an accounting error that could be corrected by considering that only the use of 'additional biomass' - biomass from additional plant growth or biomass that would decompose rapidly if not used for bioenergy - can reduce carbon emissions. Failure to correct this accounting flaw will likely have substantial adverse consequences. The article presents recommendations for correcting greenhouse gas accounts related to bioenergy.

Most prior studies have found that substituting biofuels for gasoline will reduce greenhouse gases because biofuels sequester carbon through the growth of the feedstock. These analyses have failed to count the carbon emissions that occur as farmers worldwide respond to higher prices and convert forest and grassland to new cropland to replace the grain (or cropland) diverted to biofuels. By using a worldwide agricultural model to estimate emissions from land-use change, we found that corn-based ethanol, instead of producing a 20% savings, nearly doubles greenhouse emissions over 30 years and increases greenhouse gases for 167 years. Biofuels from switchgrass, if grown on U.S. corn lands, increase emissions by 50%. This result raises concerns about large biofuel mandates and highlights the value of using waste products.