Mineralization and denitrification in upland, nearly saturated and flooded subtropical soil
I. Effect of nitrate and ammoniacal nitrogen |
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Authors: | M S Aulakh Tejinder S Khera John W Doran |
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Institution: | (1) Department of Soils, Punjab Agricultural University, Ludhiana 141004, Punjab, India e-mail: M.Aulakh@cgiar.org, IN;(2) USDA-ARS, Keim Hall, East Campus, University of Nebraska, Lincoln, NE68583, USA, US |
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Abstract: | The influence of fertilizer N applied through nitrate and ammoniacal sources on the availability of nitrate, supply of C,
and gaseous N losses via denitrification (using acetylene inhibition technique) in a semiarid subtropical soil (Typic Ustochrepts)
was investigated in a growth chamber simulating upland 60% water-filled pore space (WFPS)], nearly saturated (90% WFPS),
and flooded (120% WFPS) conditions. The rate of denitrification was very low in the upland soil conditions, irrespective of
fertilizer N treatments. Increasing water content to nearly saturated and flooded conditions resulted in four- to sixfold
higher rates of denitrification within 2 days, suggesting that the denitrifying activity commences quickly. Results of this
study reveal that (1) under restricted aeration, these soils could support high rates of denitrification (∼6 mg N kg–1 day–1) for short periods when nitrate is present; (2) application of fertilizer N as nitrate enhances N losses via denitrification
(∼10 mg N kg–1 day–1) – however, the supply of available C determines the intensity and duration of denitrification; (3) when fertilizer N is
applied as an ammoniacal form, nitrification proceeds slowly and nitrate availability limits denitrification in flooded soil;
(4) the nearly saturated soil, being partially aerobic, supported greater nitrification of applied ammoniacal fertilizer N
than flooded soil resulting in higher relative rates of denitrification; and (5) under aerobic soil conditions, 26 mg mineral
N kg–1 accumulated in control soil over a 16-day period, demonstrating a modest capacity of such semiarid subtropical soils, low
in organic matter, to supply N to growing plants.
Received: 7 June 1999 |
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Keywords: | Denitrification N mineralization Semiarid subtropical soils Flooded rice systems Nearly saturated rice systems |
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