Volatilization losses of ammonia from flooded soils: I. Effects of nitrogen source, method of placement and soil type
1985
Sakorn Phongpan (Department of Agriculture, Bangkok (Thailand). Agricultural Chemistry Div.)
Nitrogen loss was measured directly as evolved NH3 from samples of three representative soil types receiving urea, ammonium sulfate and sulfur coated urea fertilizers under flooded conditions. The losses of ammonia due to N application differed with source of N. Appreciable losses of ammonia were observed in soils receiving urea and proceeded rapidly amounting to 16-22 percent of N applied after 35 days of incubation. Ammonia losses from the modified urea (SCU) material occured to a lesser extent while ammonia losses from ammonium sulfate were negligible due to a lack of alkalinity. Losses of NH3 were influenced by soil type, Saraburi soil contributed the larger volatilization losses from urea than did Chachoengsao and Rangsit soils. Incorporation of the N fertilizers into the soils resulted considerably in reduced NH3 loss as compared to surface application. The nature of fertilizer N applied on the soil surface generally reflected the pH of floodwater as well as losses on NH3. Increased acidity from application of ammonium sulfate reduced the amounts of NH3 losses whereas the application of urea and SCU resulted in the higher pH values and consequently the higher NH3 losses. The accumulation of NH3 loss with time in urea treated soils coincided with decreasing ammoniacal N (NH4+-N) and increasing pH in the floodwater indicating that the magnitude of ammonia volatilization was directly related to the concentration of NH4+-N and pH in floodwater. The extent of NH3 losses from urea appeared to be more dependent on some characteristics in the soil, i.e. C.E.C., organic matter content. Relatively high C.E.C. and organic matter content favoured rapid NH3 adsorption and minimized losses from soil
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