Biological N fixation

Soil surface balance measures the differences between the input or application of nutrients entering the soil (e.g. mineral fertilisers or organic manure) and the output or withdrawal of nutrients from harvested and fodder crops. Farm gate balances measure the nutrient input on the basis of the nutrient contents of purchased material (e.g. concentrates, fertilisers, fodder, livestock, biological N-fixation) and farm sales such as meat, milk, fodder, cereals (OECD 1997). 

Steen Jensen, E. and Hauggaard-Nielsen, H. 2003. How can increased use of biological N, fixation in agriculture benefit the environment Plant and Soil 252 177-186. 

Kauffman et al. (1994) estimated the fuel loads along a vegetation gradient from campo limpo to cerrado sensu stricto near Brasilia. In the cerrado only 27% of the fuel load of 10 Mg ha" was comprised of graminoids the remainder was deadwood and leaf litter. They estimated the nutrient pools in combustible components in the cerrado sensu stricto to be 54.7 kg ha" N, 13.8 kg ha K, 3-5 kg ha P, and 30.5 kg ha" Ca. They concluded that the total biomass of the herbaceous layer of the cerrados was similar to that of other savanna ecosystems. The authors concluded that any loss of N due to fire was negligible compared to the N pool in the soil. Biological N fixation and precipitation inputs would compensate for such losses. Similarly, precipitation inputs would compensate for the loss of P, K and Ca (Schiavini 1983, Coutinho 1979, Pivello-... 

Land use changes, such as conversion of tropical forests to cattle pastures, affect biological N fixation, mineralization, nitrification, and denitrification (Davidson et al. 1993, Keller and Reiners 1994, Matson et al. 1987, Montagnini and Buschbacher 1989, Neill et al. 1995). Matson et al. (1987) estimated that N mobilized annually from deforestation was equivalent to more than half of the industrial N fixed globally and greater than the total amount of N delivered to oceans by rivers. 

Figure 36-6 Net reactive N inputs (Tg N year ) to continental world regions during the mid-1990s, from anthropogenic and natural sources. Anthropogenic sources include N fertilizer use, N fixation in cultivated lands, net N imports in food and feed, and atmospheric N deposition from fossil-fuel combustion. The natural sources include biological N fixation in non-cultivated vegetated lands and N fixation by lightning. Modified from Boyer et al. (2004).

Thus, the following links of nitrogen biogeochemical cycle were accounted for mass balance calculations in Northern-East Asia and the whole East Asian domain input — deposition, fertilizers, biological N fixation, import of food and products, riverine fluxes and output — crop uptake, denitrification, volatilization, runoff, sedimentation and sea water exchange. All calculations were condncted for 1994-1997 and the mean values were used. 

While the first condition applies to all essential elements, the second is specific to N. Biological N, fixation is capable of adding tens to hundreds of kg ha year to ecosystems (Sprent and Sprent, 1990), more than enough to meet plant and microbial demand for N in a short time, and to overwhelm the capacity of... 

Point and nonpoint sources, precipitation, and biological N fixation are the major inputs to wetlands, whereas N losses from wetlands include biotic (denitrification) and abiotic (volatilization) reactions and surface/subsurface flows. Wetlands often function as effective reservoirs of N. 

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