Premium
Ammonia Volatilization from Nitrogen Sources Applied to Rice Fields: II. Floodwater Properties and Submerged Photosynthetic Biomass
Author(s) -
Fillery I. R. P.,
Roger P. A.,
De Datta S. K.
Publication year - 1986
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1986.03615995005000010017x
Subject(s) - urea , ammoniacal nitrogen , volatilisation , chemistry , urease , ammonia , zoology , ammonia volatilization from urea , nitrogen , environmental chemistry , biochemistry , biology , organic chemistry
The effects of (NH 4 ) 2 SO 4 , urea, and urea amended with the urease inhibitor, phenyl phosphorodiamidate (PPD), on floodwater properties were studied concurrently as part of a field NH 3 volatilization study. In the (NH 4 ) 2 SO 4 treatment the maximum concentration of ammoniacal‐N in the floodwater (≃ 50 g N m −3 ) occurred immediately after its application to the floodwater. Thereafter, floodwater ammoniacal‐N concentrations declined rapidly and were negligible 6 d after the application of (NH 4 ) 2 SO 4 . Ammoniacal‐N concentrations in the urea treatment reached maxima of ≃ 12 g N m −3 , 3 to 5 d after urea was applied and then declined steadily to negligible concentrations in 7 d. Application of PPD (1% wt/wt) along with urea delayed the buildup of ammoniacal‐N in floodwater until 5 to 7 d after N was applied although the maximum ammoniacal‐N concentration in the floodwater was comparable to that obtained in the urea treatment. Floodwater pH displayed a marked diurnal pattern throughout the experiment in the urea‐amended and background fields. In contrast, pH in the floodwater in the (NH 4 ) 2 SO 4 ‐amended field was buffered at ≃ 8.00 for the first 2 d, probably because high concentrations of NH 4 HCO 3 formed in floodwater. Diurnal fluctuations in pH prevailed after 3 d when ammoniacal‐N concentrations had declined substantially. The partial pressures of NH 3 (pNH 3 ) in the floodwater in all treatments were synchronized with diurnal temperature and pH changes in the floodwater. The maximum pNH 3 in floodwater was similar in both the (NH 4 ) 2 SO 4 ‐ and urea‐amended fields even though ammoniacal‐N concentrations were initially significantly higher in the former. Total titratable alkalinity in floodwater increased after urea and urea/PPD were applied but declined following the application of (NH 4 ) 2 SO 4 . The initial levels of alkalinity in floodwater were double the content of alkalinity in irrigation water, and it is surmised that evaporation and/or respiration contributed significantly to alkalinity in the floodwater. Enumerations of algae present in the flooded soil showed the biomass to be small and dominated by non‐N 2 ‐fixing blue‐green algae ( Syanophyceae ). This biomass, however, was associated with marked diurnal fluctuations in floodwater pH, which coupled with the accumulated alkalinity, were the major factors contributing to the rapid NH 3 loss following the application of (NH 4 ) 2 SO 4 and urea to the floodwater.