Joint environmental and social benefits from diversified agriculture.

Agricultural simplification continues to expand at the expense of more diverse forms of agriculture. This simplification, for example, in the form of intensively managed monocultures, poses a risk to keeping the world within safe and just Earth system boundaries. Here, we estimated how agricultural diversification simultaneously affects social and environmental outcomes. Drawing from 24 studies in 11 countries across 2655 farms, we show how five diversification strategies focusing on livestock, crops, soils, noncrop plantings, and water conservation benefit social (e.g., human well-being, yields, and food security) and environmental (e.g., biodiversity, ecosystem services, and reduced environmental externalities) outcomes. We found that applying multiple diversification strategies creates more positive outcomes than individual management strategies alone. To realize these benefits, well-designed policies are needed to incentivize the adoption of multiple diversification strategies in unison.

Mapping cover crop species in southeastern Michigan using Sentinel-2 satellite data and Google Earth Engine.

Cover crops are a critical agricultural practice that can improve soil quality, enhance crop yields, and reduce nitrogen and phosphorus losses from farms. Yet there is limited understanding of the extent to which cover crops have been adopted across large spatial and temporal scales. Remote sensing offers a low-cost way to monitor cover crop adoption at the field scale and at large spatio-temporal scales. To date, most studies using satellite data have mapped the presence of cover crops, but have not identified specific cover crop species, which is important because cover crops of different plant functional types (e.g., legumes, grasses) perform different ecosystem functions. Here we use Sentinel-2 satellite data and a random forest classifier to map the cover crop species cereal rye and red clover, which represent grass and legume functional types, in the River Raisin watershed in southeastern Michigan. Our maps of agricultural landcover across this region, including the two cover crop species, had moderate to high accuracies, with an overall accuracy of 83%. Red clover and cereal rye achieved F1 scores that ranged from 0.7 to 0.77, and user's and producer's accuracies that ranged from 63.3% to 86.2%. The most common misclassification of cover crops was fallow fields with remaining crop stubble, which often looked similar because these cover crop species are typically planted within existing crop stubble, or interseeded into a grain crop. We found that red-edge bands and images from the end of April and early July were the most important for classification accuracy. Our results demonstrate the potential to map individual cover crop species using Sentinel-2 imagery, which is critical for understanding the environmental outcomes of increasing crop diversity on farms.

Feedbacks between nitrogen fixation and soil organic matter increase ecosystem functions in diversified agroecosystems.

Nitrogen (N) losses from intensified agriculture are a major cause of global change, due to nitrate (NO3- ) export and the eutrophication of aquatic systems as well as emissions of nitrous oxide (N2 O) into the atmosphere. Diversified agroecosystems with legume cover crops couple N and carbon (C) inputs to soil and reduce N pollution, but there is a need to identify controls on legume N2 fixation across ecosystems with variable soil conditions. Here, I tested the hypothesis that N mineralization from turnover of soil organic matter (SOM) regulates legume N2 fixation across 10 farms that spanned a gradient of SOM levels. I separated soil samples into two SOM fractions, based on size and density, which are indicators of soil nutrient cycling and N availability (free particulate organic matter and intra-aggregate particulate organic matter [POM]). This study indicates downregulation of legume N2 fixation in diversified agroecosystems with increasing N availability in intra-aggregate POM and increasing N mineralization. Intercropping the legume with a grass weakened the relationship between N in POM and N2 fixation due to N assimilation by the grass. Further, mean rates of N and C mineralization across sites increased with two seasons of a legume-grass cover crop mixture, which could enhance this stabilizing feedback between soil N availability and N2 fixation over time. These results suggest a potential mechanism for the diversity-ecosystem-function relationships measured in long-term studies of agroecosystems, in which regular use of legume cover crops increases total soil organic C and N and reduces negative environmental impacts of crop production.

Exploring the role of ectomycorrhizal fungi in soil carbon dynamics.

The extent to which ectomycorrhizal (ECM) fungi enable plants to access organic nitrogen (N) bound in soil organic matter (SOM) and transfer this growth-limiting nutrient to their plant host, has important implications for our understanding of plant-fungal interactions, and the cycling and storage of carbon (C) and N in terrestrial ecosystems. Empirical evidence currently supports a range of perspectives, suggesting that ECM vary in their ability to provide their host with N bound in SOM, and that this capacity can both positively and negatively influence soil C storage. To help resolve the multiplicity of observations, we gathered a group of researchers to explore the role of ECM fungi in soil C dynamics, and propose new directions that hold promise to resolve competing hypotheses and contrasting observations. In this Viewpoint, we summarize these deliberations and identify areas of inquiry that hold promise for increasing our understanding of these fundamental and widespread plant symbionts and their role in ecosystem-level biogeochemistry.

Peri-Urban, but Not Urban, Residence in Bolivia Is Associated with Higher Odds of Co-Occurrence of Overweight and Anemia among Young Children, and of Households with an Overweight Woman and Stunted Child.

Background: Urban populations have grown globally alongside emerging simultaneous burdens of undernutrition and obesity. Yet, how heterogeneous urban environments are associated with this nutritional double burden is poorly understood. Objective: We aimed to determine: 1) the prevalence of the nutritional double burden and its components in urban, peri-urban, and rural areas of Bolivia; and 2) the association of residence in these areas with the nutritional double burden and its components. Design: We surveyed 3946 randomly selected households from 2 metropolitan regions of Bolivia. Census data and remotely sensed imagery were used to define urban, peri-urban, and rural districts along a transect in each region. We defined 5 nutritional double burdens: concurrent overweight and anemia among women of reproductive age (15-49 y), and children (6-59 mo), respectively; concurrent overweight and stunting among children; and households with an overweight woman and, respectively, an anemic or stunted child. Capillary hemoglobin concentrations were measured to assess anemia (women: hemoglobin <120 g/L; children: hemoglobin <110 g/L), and overweight and stunting were calculated from height, weight, and age data. Results: In multiple logistic regression models, peri-urban, but not urban residence, was associated with higher odds of concurrent overweight and anemia among children (OR: 1.8; 95% CI; 1.0, 3.2) and of households with an overweight woman and stunted child (1.8; 1.2, 2.7). Examining the components of the double burden, peri-urban women and children, respectively, had higher odds of overweight than rural residents [women (1.5; 1.2, 1.8); children (1.5; 1.0, 2.4)], and children from peri-urban regions had higher odds of stunting (1.5; 1.1, 2.2). Conclusions: Peri-urban, but not urban, residence in Bolivia is associated with a higher risk of the nutritional double burden than rural areas. Understanding how heterogeneous urban environments influence nutrition outcomes could inform integrated policies that simultaneously address both undernutrition and obesity.

Crop rotations for increased soil carbon: perenniality as a guiding principle.

More diverse crop rotations have been promoted for their potential to remediate the range of ecosystem services compromised by biologically simplified grain-based agroecosystems, including increasing soil organic carbon (SOC). We hypothesized that functional diversity offers a more predictive means of characterizing the impact of crop rotations on SOC concentrations than species diversity per se. Furthermore, we hypothesized that functional diversity can either increase or decrease SOC depending on its associated carbon (C) input to soil. We compiled a database of 27 cropping system sites and 169 cropping systems, recorded the species and functional diversity of crop rotations, SOC concentrations (g C kg/soil), nitrogen (N) fertilizer applications (kg N·ha-1 ·yr-1 ), and estimated C input to soil (Mg C·ha-1 ·yr-1 ). We categorized crop rotations into three broad categories: grain-only rotations, grain rotations with cover crops, and grain rotations with perennial crops. We divided the grain-only rotations into two sub-categories: cereal-only rotations and those that included both cereals and a legume grain. We compared changes in SOC and C input using mean effect sizes and 95% bootstrapped confidence intervals. Cover cropped and perennial cropped rotations, relative to grain-only rotations, increased C input by 42% and 23% and SOC concentrations by 6.3% and 12.5%, respectively. Within grain-only rotations, cereal + legume grain rotations decreased total C input (-16%), root C input (-12%), and SOC (-5.3%) relative to cereal-only rotations. We found no effect of species diversity on SOC within grain-only rotations. N fertilizer rates mediated the effect of functional diversity on SOC within grain-only crop rotations: at low N fertilizer rates (≤75 kg N·ha-1 ·yr-1 ), the decrease in SOC with cereal + legume grain rotations was less than at high N fertilizer rates. Our results show that increasing the functional diversity of crop rotations is more likely to increase SOC concentrations if it is accompanied by an increase in C input. Functionally diverse perennial and cover cropped rotations increased both C input and SOC concentrations, potentially by exploiting niches in time that would otherwise be unproductive, that is, increasing the "perenniality" of crop rotations.

A social-ecological perspective on harmonizing food security and biodiversity conservation.

The major challenges of improving food security and biodiversity conservation are intricately linked. To date, the intersection of food security and biodiversity conservation has been viewed primarily through an agricultural "production lens"-for example, via the land sparing/sharing framework, or the concept of sustainable intensification. However, a productionist perspective has been criticized for being too narrow, and failing to consider other relevant factors, including policy, equity, and diversity. We propose an approach that conceptualizes rural landscapes as social-ecological systems embedded within intersecting multi-scalar processes. Based on such a framing, empirical research can be more clearly set in the context of system properties that may influence food security, biodiversity conservation, or both. We illustrate our approach through a description of contrasting agricultural systems within Brazil's Cerrado region. We emphasize the need for new empirical research involving systematic comparisons of social-ecological system properties in landscapes threatened by food insecurity and ecosystem degradation.

A Systematic Review of the Measurement of Sustainable Diets.

Sustainability has become an integral consideration of the dietary guidelines of many countries in recent decades. However, a lack of clear metrics and a shared approach to measuring the multiple components of sustainable diets has hindered progress toward generating the evidence needed to ensure the credibility of new guidelines. We performed a systematic literature review of empirical research studies on sustainable diets to identify the components of sustainability that were measured and the methods applied to do so. Two independent reviewers systematically searched 30 databases and other sources with the use of a uniform set of search terms and a priori exclusion criteria. In total, 113 empirical studies were included in the final review. Nearly all of the studies were focused on high-income countries. Although there was substantial heterogeneity in the components of sustainability measured, the estimated greenhouse gas emissions (GHGEs) of various dietary patterns were by far most commonly measured (n = 71 studies). Estimating the GHGEs of foods through various stages of production, use, and recycling with the use of the Life Cycle Assessment approach was the most common method applied to measure the environmental impacts of diets (n = 49 studies). Many components of sustainable diets identified in existing conceptual frameworks are disproportionately underrepresented in the empirical literature, as are studies that examine consumer demand for sustainable dietary alternatives. The emphasis in the literature on high-income countries also overlooks the production and dietary alternatives most relevant to low- and middle-income countries. We propose 3 methodological and measurement approaches that would both improve the global relevance of our understanding of sustainable diets and attend more completely to the existing multidimensional, multiscale conceptual framing of sustainable diets.