Food Sovereignty and Fome Zero: Connecting Public Food Procurement Programmes to Sustainable Rural Development in Brazil

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135228/1/joac12131.pd

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.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141003/1/eap1648_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141003/2/eap1648.pd

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

Against the odds: Network and institutional pathways enabling agricultural diversification

Farming systems that support locally diverse agricultural production and high levels of biodiversity are in rapid decline, despite evidence of their benefits for climate, environmental health, and food security. Yet, agricultural policies, financial incentives, and market concentration increasingly constrain the viability of diversified farming systems. Here, we present a conceptual framework to identify novel processes that promote the emergence and sustainability of diversified farming systems, using three real-world examples where farming communities have found pathways to diversification despite major structural constraints. By applying our framework to analyze these bright spots in the United States, Brazil, and Malawi, we identify two distinct pathways—network and institutional—to diversification. These pathways emerge through alignment of factors related to social and ecological structure (policies, institutions, and environmental conditions) and agency (values, collective action, and management decisions). We find that, when network and institutional pathways operate in tandem, the potential to scale up diversification across farms and landscapes increases substantially

Change in soil

Effect sizes for measured soil properties (i.e., the change in the property following two years of the cover crop mixture compared to the no cover control), calculated by subtracting the final value for each soil parameter measured in the mixture treatment from the final value measured in the no cover crop control at the May 2017 sampling

Soil and N2 Fixation

Merged baseline data from soil samples collected in fall 2014 or spring 2015 with data on biological nitrogen fixation by hairy vetch at biomass sampling in spring of 2016

N2 Fixation 2017

Aboveground biomass and nitrogen content for hairy vetch and cereal rye, and biological nitrogen fixation by hairy vetch, measured in May, 2017

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 (N2O) 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.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152835/1/eap1986.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152835/2/eap1986-sup-0001-AppendixS1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152835/3/eap1986_am.pd