Nitrogen transformations in a flooded soil in the presence and absence of rice plants: 2. Denitrification.

Autor: Chen, D.L., Chalk, P.M., Freney, J.R.
Zdroj: Nutrient Cycling in Agroecosystems; Jul1998, Vol. 51 Issue 3, p269-279, 11p
Abstrakt: Denitrification rates (d) in a flooded alkaline clay were measured following addition of either $$^{15} NO_3^ - or^{15} NH_4^ + $$ to the floodwater, by collecting evolved N2 + N2O in an enclosure in the absence or presence of rice plants. Similar estimates of d were obtained in the $$^{15} NO_3^ - $$ treatment when the isotopic composition of the enclosed atmosphere was determined using arc redistribution or direct mass spectrometric analysis. Approximately 90% of the gaseous products of denitrification were physically trapped in the soil five days after $$^{15} NO_3^ - $$ addition. Mechanical shaking of the soil-water system was an effective method for releasing entrapped gas. Denitrification showed a marked diurnal variation in both $$^{15} NO_3^ - $$ and $$^{15} NH_4^ + $$ treatments planted to rice, with higher rates during the day than at night. Measured rates of denitrification were higher in planted than in unplanted pots for both $$^{15} NO_3^ - $$ and $$^{15} NH_4^ + $$ treatments for normal gas sampling. However, evidence was obtained that this was not a real effect, but was due to release of entrapped gas. Denitrification losses corrected for gas entrapment were estimated at <5% of applied $$^{15} NH_4^ + $$ . The 15N mass balance indicated that a much larger amount of applied ammonium (15–25%) was lost by NH3 volatilisation. The rate of denitrification corrected for gas entrapment was similar to the rate of nitrification estimated by inhibition of ammonium oxidation. Although the inhibitors 2-ethynylpyridine and acetylene prevented denitrification by effectively inhibiting nitrification of $$^{15} NH_4^ + $$ , the total recovery of 15N in the soil-plant system did not increase. The total recovery of $$^{15} NH_4^ + $$ was 7–9% higher in the presence than in the absence of rice. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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