Fertilizers exports

The wodd s largest sulfur iaveatories are stiH ia Canada. By the end of 1994, after significant vattiag, stocks iacreased by approximately 2.2 x 10 to 7.8 X 10 t. The United States, which had 4.2 million metric tons of sulfur inventories in 1982, reduced sulfur inventories to the lowest levels in a decade during 1992, a record year for phosphate fertilizer exports. This changed during 1993—1994, when phosphate fertilizer production eased and sulfur stocks increased to 1.1 million metric tons. Sulfur inventories in Poland and West Asia have also declined slightly (33). 

Because sulfuric acid has its greatest use in fertilizers, trends in that industry have a significant effect on the sulfuric acid business. Owing to a weak U.S. doUar in the early 1990s and high demand for fertilizer abroad, a considerable portion of U.S. phosphate fertilizer production was exported. High fertilizer exports are expected to continue until Thkd World countries can meet thek own demands. 

Disodium Tetraborate Pentahydrate, Refined pentahydrate consumed in the Urhted States is used in insulation fiber glass, glass, fertilizers, and herbicides. Smaller amounts are used in antifreeze (see Antifreezes and deicing fluids), ceramic glazes, and cleaning agents. About 40% of the pentahydrate produced in the Urhted States is exported (101). A large-scale apphcation of this chemical is in the preparation of perborate bleaches. 

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. 

Increases in phosphorus export from agricultural landscapes have been measured after the application of phosphorus. Phosphorus losses are influenced by the rate, time, and method of phosphorus application, form of fertilizer or manure applied, amount and time of rainfall after application, and land cover. These losses are often small from the standpoint of farmers (generally less than 200 kg P km-2) and represent a minor proportion of fertilizer or manure phosphorus applied (generally less than 5%). Thus, these losses are not of economic importance to farmers in terms of irreplaceable fertility. However, they can contribute to eutrophication of downstream aquatic ecosystems. 

The removal of fertilizer N in the crop as NH4+ does not lead to acidification. Hydrolysis of urea fertilizer—by far the main form of N fertilizer used in wetland rice, together with ammonium bicarbonate in some countries—consumes 1 mol of H+ per mol of NH4+ formed (Table 7.1, Process 1). So although absorption of N as NH4+ leads to a net export of H+ from the roots to balance the resulting excess intake of cations over anions (Table 7.1, Process 5), this acidity is matched by the H+ consumed in urea hydrolysis. Likewise there is no net generation of acidity as a result of NH3 volatilization, although 1 mol of H+ is left behind per mol of NH4+ converted to NH3 (Table 7.1, Process 3). 

Between 1970 and 1978, U.S. sulfur demand grew from 9.2 to about 12 million long tons per year, equivalent to an average annual rate of increase of about 3.4 percent. Over the forecast period, we anticipate an average annual increase of about this same rate. Our estimate assumes that the U.S. will continue to maintain world leadership as an exporter of upgraded phosphates, and that growth in domestic phosphate fertilizer consumption will average about 3 percent per year. 

The Australian domestic nitric acid market was found to suffer from cyclical variations, with seasonal highs and lows each year. This fluctuation is attributed to the major acid consumers (fertilizer and explosives manufacturers) being susceptible to seasonal variations in demand, and to the level of world commodity prices. However, the overall trend has been for 3% annual growth. Current Australian production is 200 000 tonnes each year (100% acid basis). Exports from and imports into Australia are virtually non-existent. A protective barrier in the form of high shipping costs, has in the past effectively closed the domestic market. 

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