Fertilizer inputs from land

F or NjO, estimates of soil emissions are perhaps slightly more straightforward, simply because so much more information on soil NjO emissions is available. For agricultural soils, estimates as a percentage of fertilizer input have been published " and, for the remaining land use classes listed in Table 5, mean annual emissions from a series of long-term flux measurements are available. The total annual soil NjO emissions for the ElK (27 kt N) are very similar to the annual soil NO emissions. Soils, however, have by far a greater impact on the... 

Terrestrial Detritus. Variability in ecosystem response to fertilization may be attributed in part to the interaction of aquatic and terrestrial ecosystems. In contrast to the many aquatic ecosystems in which higher trophic levels are fueled almost entirely by organic matter originating in the water column, other systems are driven by inputs of particulate and dissolved organic matter from land. The importance of this land-water interaction in regulating system metabolism has been obvious to stream ecologists for some... 

The contamination of soil by airborne heavy metals, as well as inputs from several agricultural practices such as specific mineral fertilizing and farmyard manuring, appears to be an important source of loadings. Hence, it is necessary for sustainable land use to regulate the input of relevant heavy metals by ordinances or guidelines. 

A recent review of research on phosphorus input to surface waters from agriculture highlights the variability of particulate and dissolved phosphorus contributions to catchments. The input varies with rainfall, fertilizer application rates, the history of the application of the fertilizer, land use, soil type, and between surface and sub-surface water. The balance struck between export of nutrients from the catchment and recipient-water productivity is the primary factor which controls its quality. 

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).

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