Jennifer Blesh

The impact of nitrogen source and crop rotation on nitrogen mass balances in the Mississippi River Basin

Nitrogen (N) leaching to surface waters from grain farms in the Mississippi River Basin (MRB), USA, is the primary cause of hypoxia in the Gulf of Mexico. Regional-scale N mass balances indicate that a small, intensively cropped area of the upper MRB contributes disproportionately to nitrate loading. These aggregate balances miss small-scale variability, especially that caused by differences in farm management. We constructed N mass balances for a gradient of farm types, from corn-soybean monocultures to diversified grain farms that rely on biological N fixation (BNF) as a primary N source, to compare the relative efficiency of diverse farming systems in the MRB. Five-year N balances were calculated for a most and least productive field on each farm using data collected from interviews with 95 grain farmers in Iowa, Ohio, Minnesota, and Wisconsin; from legume biomass and corn grain samples collected from a subset of farms; and published values from the literature. Nitrogen balances ranged from high average annual surpluses (149 kg N x ha(-1) x yr(-1)) to large deficits (80 kg N x ha(-1) x yr(-1)), and differed based on N source and crop rotation. Fields with > 50% of total N additions from legume N sources and fields with complex crop rotations that included both annual and perennial species were approximately in balance (3.7 kg N x ha(-1) x yr(-1) and 5.7 kg N x ha(-1) x yr(-1), respectively) compared to fertilizer-based practices in corn-soybean rotations with average annual surpluses near 35 kg N x ha(-1) x yr(-1). Surplus N was also inversely related to the proportion of total N inputs from BNF for medium (80-160 kg N x ha(-1) x yr(-1)) to high (> 160 kg N x ha(-1) x yr(-1)) N rates. Diversified farmers were more likely to adjust their management practices in response to environmental variability compared to fertilizer-based farmers. Taken together, results from this study suggest that significantly reducing surplus N in agroecosystems will require reducing N inputs and increasing C availability to support the internal biological mechanisms for storing N in farm fields.

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.

A social–ecological perspective on harmonizing food security and biodiversity conservation

AbstractThe 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.

Farmers' Attitudes Regarding Agrolandscape Ecology: A Regional Comparison

ABSTRACT A farmer survey was conducted in three different agroecosystem types in the midwestern and southeastern United States. We selected Saline County, Kansas; Knox County, Indiana; and Coffee County, Georgia, representative of former prairie grassland, Midwestern deciduous forest, and Southeastern deciduous forest biome types. A twenty-question, multiple-choice survey was mailed to 300 farmers in each county during summer months of 2002 and 2003. Data were collected in four categories: demographic information, problems related to conventional agriculture, sustainable agriculture approaches, and attitudes toward sustainable agriculture. Survey responses were examined and discussed within the context of the social and ecological consequences of industrial agriculture, the alternatives presented by agroecologists, and the communication network between agroecologists and farmers. One suggestion for achieving sustainability is building stronger connections between university agroecologists and farmers. For example, 58 percent of respondents from Kansas, 57 percent from Indiana, and 70 percent from Georgia view an ecologist as a friend/advisor to the farmer. These data should be useful to agroecologists interested in strengthening their relationship with stakeholders and in disseminating research findings concerning alternative agricultural practices.

Functional traits in cover crop mixtures: Biological nitrogen fixation and multifunctionality

Cover crop mixtures with complementary plant functional traits including biological nitrogen fixation (BNF) may supply nitrogen (N) to farm fields while simultaneously providing other ecosystem functions such as N retention and weed suppression (i.e., multifunctionality). Understanding variation in these relationships across farms can help advance trait-based research in agroecology and ecological approaches to nutrient management. This on-farm experiment explored the contributions of two- and three-species cover crop mixtures, which combined legumes, brassicas and cool season grasses, to ecosystem functions across a gradient of soil fertility levels driven by farm management history. I evaluated the predictions that functional trait diversity of the cover crops would explain variation in multifunctionality, and that legume biomass and BNF within mixtures would be inversely correlated with indicators of soil N availability from organic matter across the farm gradient. Ecosystem functions varied widely across farms. As expected, functional diversity was a significant predictor of multifunctionality, although the relationship was weak. Cover crop mixtures had significantly greater multifunctionality than a cereal rye monoculture, though not at the highest observed levels of each function, indicating trade-offs among functions. Linear regression models showed that legume biomass and BNF were negatively correlated with soil properties indicative of N availability from soil organic matter, whereas non-legume and weed biomass were positively correlated with other measures of soil fertility. Synthesis and applications. Cover crop mixtures can increase functional diversity within crop rotations. Designing mixtures with complementary plant traits may be particularly effective for increasing multifunctionality and agroecosystem sustainability. On-farm research to understand variation in biological nitrogen fixation, which is both a plant trait and a key ecosystem function, across heterogeneous soil conditions, can inform management of soil fertility based on ecological principles.

Feeding Prometheus: An Interdisciplinary Approach for Solving the Global Food Crisis

The current global food system is inadequate to meet the needs of the current world population without compromising future well-being. For example, current intensified production systems lead to undernutrition in some regions coupled with epidemics of obesity in others while compromising their underlying ecological foundations, such as creating areas of ocean hypoxia. Such common observations challenge the research community to ask new types of basic questions and apply novel analytical frameworks for analyzing them. Elaboration of an integrated applied research agenda is imperative to addressing these global food system challenges. We propose that core competencies of a new analytical framework lie at the intersection of four domains: 1) the ecology of agroecosystems; 2) equity in global and local food systems; 3) cultural dimensions of food and agriculture; and 4) human health. This intersection constitutes a new analytical framework for transitions toward global food system sustainability.