The potential of using 15N natural abundance in changing ammonium-N and nitrate-N pools for studying in situ soil N transformations

Wood Mountain loam was wetted with water or (NH4)2SO4 solution to provide a factorial combination among three moisture and three NH4-N levels. Samples in polyethylene bags were incubated at 2.5-cm depths in fallow, and in an incubator that simulated the diurnal patterns of temperature fluctuation recorded in the field. During the growing season, treatments were sampled regularly for moisture, NO3− and exchangeable NH4-N. Similar determinations were made on in situ samples taken in fallow Wood Mountain loam. The incubator simulated the effects of growing season temperatures on soil N transformations satisfactorily. Pronounced increases or decreases in temperature led to flushes in N mineralization. However, in the 1972 growing season, temperature was suboptimal and temperature changes were generally small. Consequently, when a stepwise multiple regression technique was used to analyze the data, neither ammonification nor nitrification showed a quantitative relationship to temperature. Comparison of the nitrification occurring in laboratory-incubated soils with that occurring in situ led to the conclusion that 70 to 90% of the NO3-N produced in surface soil resulted from wetting and drying. Estimates of potentially ammonifiable soil N(No) and its rate of mineralization (k) were derived from cumulative ammonification by assuming that the laws of first-order kinetics were applicable. In the 10, 15, and 20% moisture treatments the average No was 27, 41, and 82 ppm, respectively. Under the conditions of this study, the time required to mineralize half of No was about 7 wk.

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Nitrite isotope characteristics and associated soil N transformations

Scientific Reports ◽

10.1038/s41598-021-83786-w ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Dominika Lewicka-Szczebak ◽

Anne Jansen-Willems ◽

Christoph Müller ◽

Jens Dyckmans ◽

Reinhard Well

Keyword(s):

Reference Method ◽

Isotopic Signature ◽

Natural Abundance ◽

Soil N ◽

N Transformations ◽

Promising Tool ◽

Isotopic Analyses ◽

Isotope Studies ◽

Soil N Cycle ◽

Transformation Processes

AbstractNitrite (NO2−) is a crucial compound in the N soil cycle. As an intermediate of nearly all N transformations, its isotopic signature may provide precious information on the active pathways and processes. NO2− analyses have already been applied in 15N tracing studies, increasing their interpretation perspectives. Natural abundance NO2− isotope studies in soils were so far not applied and this study aims at testing if such analyses are useful in tracing the soil N cycle. We conducted laboratory soil incubations with parallel natural abundance and 15N treatments, accompanied by isotopic analyses of soil N compounds (NO3−, NO2−, NH4+). The double 15N tracing method was used as a reference method for estimations of N transformation processes based on natural abundance nitrite dynamics. We obtained a very good agreement between the results from nitrite isotope model proposed here and the 15N tracing approach. Natural abundance nitrite isotope studies are a promising tool to our understanding of soil N cycling.

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Plant nitrate use in deciduous woodland: the relationship between leaf N, 15N natural abundance of forbs and soil N mineralisation

Soil Biology and Biochemistry ◽

10.1016/j.soilbio.2004.05.009 ◽

2004 ◽

Vol 36 (11) ◽

pp. 1885-1891 ◽

Cited By ~ 28

Author(s):

U. Falkengren-Grerup ◽

A. Michelsen ◽

M.O. Olsson ◽

C. Quarmby ◽

D. Sleep

Keyword(s):

15N Natural Abundance ◽

Natural Abundance ◽

N Mineralisation ◽

Soil N ◽

Deciduous Woodland ◽

The Relationship ◽

Leaf N

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Gorse is a 'facultative' N2 fixer

Journal of New Zealand Grasslands ◽

10.33584/jnzg.2016.78.503 ◽

2016 ◽

Vol 78 ◽

pp. 181-184

Author(s):

W.Y.Y. Liu ◽

M. Premaratne ◽

R. Cresswell ◽

D. Dash ◽

D. Jack ◽

...

Keyword(s):

N2 Fixation ◽

Agricultural Land ◽

Reductase Activity ◽

15N Natural Abundance ◽

Natural Abundance ◽

N Availability ◽

Soil N ◽

Soil N Availability ◽

Ulex Europaeus ◽

N2 Fixer

Many legumes reduce their atmospheric N2 fixation per unit biomass in response to increased soil N availability but there are reports that some maintain a constant rate of N2 fixation per unit biomass regardless of soil N levels. These different responses to soil N availability have been described, respectively, as 'facultative' and 'obligate' N2 fixation strategies. Views in the literature differ if gorse is a facultative or obligate N2 fixer. Here, firstly, the proportion of N derived from the atmosphere (%Ndfa) was assessed for mature gorse plants mainly in hedges bordering intensive agricultural land at different sites in the Selwyn district, Canterbury, New Zealand using the 15N natural abundance technique. Secondly, the effect of nitrate (NO3 -) supply on %Ndfa was determined for gorse seedlings under glasshouse conditions using 15NO3 -. Under field conditions, values ranged from 14.7-88.0 %Ndfa. In the glasshouse, %Ndfa values decreased from 97 when no N was supplied to 24 %Ndfa when N supply was increased to the equivalent of 200 kg N/ha. It is concluded that gorse shows a facultative N2 fixation strategy. Keywords: legume, nitrate, 15N natural abundance, nitrate reductase activity, gorse, Ulex europaeus

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