Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: November 3, 1995
Publication Date: N/A
Active soil organic N can be estimated by quantifying the potentially mineralizable soil N pool. Water-soluble organic N compounds from this pool can be lost through leaching to tile drain water, especially when climate conditions favor high decomposition rates and rapid vertical movement of water through the soil profile. Soil N mineralization potential (POTMIN N) and dissolved organic N (DON) in tile drain water were measured during 1993 and 1994 for a field site in northeast Iowa. In the spring of 1993, average tile drain DON and nitrate concentrations were similar at about 10 ppm. Tile DON increased to about 70 ppm in June and July, but tile nitrate did not change. At the end of 1993, tile DON was less than 10 ppm and stayed low for all of 1994. POTMIN N averaged 250 kg N/ha in the spring of 1993. This was reduced to less than 100 kg N/ha by late June 1993. The large reduction in POTMIN N occurred at the same time of the year that large increases in tile drain DON concentrations were observed in 1993. POTMIN N remained low for the rest of 1993 and all of 1994. These data suggest that DON from the active soil organic N pool may be vulnerable to leaching if the conditions are appropriate, as they were in 1993. DON can be mineralized and nitrified to produce nitrate N, and as a result, increase nitrate N loading of surface waters.