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ANNEX 4: Nitrogen in Agroecosystems
Pages 335-352

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From page 335...
... Fourth, it illustrates how various drivers, especially government policies, can have significant impacts on N-related farming practices and subsequent health, environmental, social, and economic effects. Finally, the example illustrates the value of both empirical measurements and modeling analyses in assessing contrasting systems for using and managing N for food production.
From page 336...
... , where N has multiple unintended consequences, including threats to human health, degradation of air and water quality, and stress on terrestrial and aquatic organisms (Ribaudo et al., 2011; UNEP, 2007; Vitousek et al., 2009)
From page 337...
... Figure 7-A-3 in terms of characterizing the N pathways under different environmental Bitmapped conditions and farming practices. We also describe what we know about the potential health, environmental, social, and economic effects over time and space.
From page 338...
... Decomposition of soil organic matter by microbes transforms organic forms of N (R-NH2) into mineral forms (ammonium [NH4]
From page 339...
... Nitrate contamination of surface water is common in the Corn Belt and is a recurrent challenge to cities such as Des Moines, Iowa, which draws drinking water from the Raccoon and Des Moines Rivers, both of which drain intensively farmed areas. After repeatedly violating the U.S.
From page 340...
... Nitrate also poses a significant threat to groundwater used for drinking water. A recent report focusing on the Tulare Lake Basin and Salinas Valley of California, which together contain 40 percent of the state's irrigated cropland and more than 50 percent of its dairy cattle, found that nitrate poses a significant threat to the health of rural communities dependent on well water, with nearly 1 in 10 people in the two regions now at risk (Harter et al., 2012)
From page 341...
... . The investigators noted that these human health and economic costs indicated "extensive negative externalities," and that taking into account other environmental impacts of agriculture, such as eutrophication, loss of biodiversity, and greenhouse gas emissions, would further diminish the value of agricultural production and exports.
From page 342...
... Market-based instruments for pollution control identified by the report included tradable water quality credits, auctionbased contracting, individual transferable quotas, risk indemnification to protect farmers adopting new practices from uncertainty, and conservation easements. Biophysical and technical approaches identified by the report included decreasing the amount of N fertilizer needed through changes in human diet (principally a reduction in animal protein consumption)
From page 343...
... At the two N fertilizer rates above those recommended for maximum economic return (135 kg N ha–1) , average nitrogen oxide fluxes were 43 and 115 percent higher than were fluxes at the recommended rate.
From page 344...
... . Diversified crop rotation systems that use small grain, forage, and cover crops in addition to corn and soybeans can reduce N emissions to water by increasing inputs of N through biological fixation, increasing the size of soil organic N stocks, reducing requirements for mineral fertilizer, and maximizing crop uptake of soil mineral N (Blesh and Drinkwater, 2013; Drinkwater et al., 1998; Gardner and Drinkwater, 2009; Oquist et al., 2007)
From page 345...
... Farmers, however, might incur greater costs through the use of manure and other soil amendments rather than mineral fertilizer and through the production of non-cash crops. With adequate confidence in the accuracy and precision of plot- and field-level measurements, system-level comparisons of N dynamics can be extended to landscape and watershed scales using biogeochemical process models that are spatially referenced for site-specific soil, climate, and management conditions.
From page 346...
... Figure 7-A-4 Bitmapped FIGURE 7-A-5  Hypothetical N stocks and flows for a cropping with low reliance on mineral N fertilizer, but with emphasis on biological N fixation, manure and organic matter amendments, cover crops, and perennial crops. Boxes representing N stocks and arrows representing N flows are not drawn to scale.
From page 347...
... a continuation of current patterns of land use, mostly corn, soybean, and sugar beet production; (2) the use of "Best Management Practices," including conservation tillage practices, 30-meter wide buffer strips along stream banks, and application of fertilizer rates to match but not exceed crop demands; (3)
From page 348...
... . Although it can be relatively easy to monitor N inputs in the form of mineral fertilizers and manure, and N outputs in the form of harvested crop materials and marketed animal products, accurate measurements of biological N fixation, gaseous losses through denitrification, aqueous losses due to leaching, and N transformations between organic and mineral forms can be technically challenging, subject to considerable temporal and spatial variation, and expensive (Galloway et al., 2004)
From page 349...
... 2012. Do federal farm policies influence surface water quality?
From page 350...
... 2012. Addressing nitrate in California's drinking water with a focus on Tulare Lake Basin and Salinas Valley groundwater.
From page 351...
... 1997. Nitrate losses through subsurface tile drainage in conservation reserve program, alfalfa, and row crop systems.
From page 352...
... 1996. Winter cover crops in a vegetable cropping system: Impacts on nitrate leaching, soil water, crop yield, pests and management costs.


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