Global inputs of biological nitrogen fixation in agricultural systems

Abstract

Biological dinitrogen (N 2 ) fixation is a natural process of significant importance in world agriculture. The demand for accurate determinations of global inputs of biologically-fixed nitrogen (N) is strong and will continue to be fuelled by the need to understand and effectively manage the global N cycle. In this paper we review and update long-standing and more recent estimates of biological N 2 fixation for the different agricultural systems, including the extensive, uncultivated tropical savannas used for grazing. Our methodology was to combine data on the areas and yields of legumes and cereals from the Food and Agriculture Organization (FAO) database on world agricultural production (FAOSTAT) with published and unpublished data on N 2 fixation. As the FAO lists grain legumes only, and not forage, fodder and green manure legumes, other literature was accessed to obtain approximate estimates in these cases. Below-ground plant N was factored into the estimations. The most important N 2 -fixing agents in agricultural systems are the symbiotic associations between crop and forage/fodder legumes and rhizobia. Annual inputs of fixed N are calculated to be 2.95 Tg for the pulses and 18.5 Tg for the oilseed legumes. Soybean (Glycine max) is the dominant crop legume, representing 50% of the global crop legume area and 68% of global production. We calculate soybean to fix 16.4 Tg N annually, representing 77% of the N fixed by the crop legumes. Annual N 2 fixation by soybean in the U.S., Brazil and Argentina is calculated at 5.7, 4.6 and 3.4 Tg, respectively. Accurately estimating global N 2 fixation for the symbioses of the forage and fodder legumes is challenging because statistics on the areas and productivity of these legumes are almost impossible to obtain. The uncertainty increases as we move to the other agricultural-production systems-rice (Oryza sativa), sugar cane (Saccharum spp.), cereal and oilseed (non-legume) crop lands and extensive, grazed savannas. Nonetheless, the estimates of annual N 2 fixation inputs are 12-25 Tg (pasture and fodder legumes), 5 Tg (rice), 0.5 Tg (sugar cane), <4 Tg (nonlegume crop lands) and <14 Tg (extensive savannas). Aggregating these individual estimates provides an overall estimate of 50-70 Tg N fixed biologically in agricultural systems. The uncertainty of this range Plant Soil (would be reduced with the publication of more accurate statistics on areas and productivity of forage and fodder legumes and the publication of many more estimates of N 2 fixation, particularly in the cereal, oilseed and non-legume crop lands and extensive tropical savannas used for grazing.

Will Elevated Carbon Dioxide Concentration Amplify the Benefits of Nitrogen Fixation in Legumes?

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A Global Geospatial Ecosystem Services Estimate of Urban Agriculture

“…UA offers potential to ameliorate a host of urban environmental problems by increasing vegetation cover and therefore contributing to a decrease in the urban heat island (UHI) intensity (Susca et al, 2011), improving the livability of cities (Frumkin, 2003;Turner et al, 2004) and providing enhanced food security to over half of Earth's population (de Bon et al, 2009;Pearson et al, 2010). UA is connected to multiple metabolic pathways in the urban ecosystem including food provisioning (Zezza & Tasciotti, 2010), regulation of local microclimate and hydrology (Oberndorfer et al, 2007), consumption of nutrient rich "waste" water and biosolids/organic matter (Armstrong, 2009;de Zeeuw et al, 2011;Smit & Nasr, 1992), and fixation of atmospheric nitrogen (Herridge et al, 2008) and carbon (Beniston & Lal, 2012). For pollinators and other wildlife, habitat is created in the city (Goddard et al, 2010).…”

Ribosomal protein biomarkers provide root nodule bacterial identification by MALDI-TOF MS

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