Internal Cycling of Nitrogen and Nitrogen Transformations

Two laboratory incubation experiments were conducted to determine the effect of initial soil water potential on the transformation of urea in large granules to nitrite and nitrate. In the first experiment two soils varying in initial soil water potentials (− 70 and − 140 kPa) were incubated with 2 g urea granules with and without a nitrification inhibitor (dicyandiamide) at 15 °C for 35 d. Only a trace of [Formula: see text] accumulated in a Brookston clay (pH 6.0) during the transformation of urea in 2 g granules. Accumulation of [Formula: see text] was also small (4–6 μg N g−1) in Conestogo silt loam (pH 7.6). Incorporation of dicyandiamide (DCD) into the urea granule at 50 g kg−1 urea significantly reduced the accumulation of [Formula: see text] in this soil. The relative rate of nitrification in the absence of DCD at −140 kPa water potential was 63.5% of that at −70 kPa (average of two soils). DCD reduced the nitrification of urea in 2 g granules by 85% during the 35-d period. In the second experiment a uniform layer of 2 g urea was placed in the center of 20-cm-long cores of Conestogo silt loam with three initial water potentials (−35, −60 and −120 kPa) and the soil was incubated at 15 °C for 45 d. The rate of urea hydrolysis was lowest at −120 kPa and greatest at −35 kPa. Soil pH in the vicinity of the urea layer increased from 7.6 to 9.1 and [Formula: see text] concentration was greater than 3000 μg g−1 soil. There were no significant differences in pH or [Formula: see text] concentration with the three soil water potential treatments at the 10th day of the incubation period. But, in the latter part of the incubation period, pH and [Formula: see text] concentration decreased with increasing soil water potential due to a higher rate of nitrification. Diffusion of various N species including [Formula: see text] was probably greater with the highest water potential treatment. Only small quantities of [Formula: see text] accumulated during nitrification of urea – N. Nitrification of urea increased with increasing water potential. After 35 d of incubation, 19.3, 15.4 and 8.9% of the applied urea had apparently nitrified at −35, −60 and −120 kPa, respectively. Nitrifier activity was completely inhibited in the 0- to 2-cm zone near the urea layer for 35 days. Nitrifier activity increased from an initial level of 8.5 to 73 μg [Formula: see text] in the 3- to 7-cm zone over the 35-d period. Nitrifier activity also increased with increasing soil water potential. Key words: Urea transformation, nitrification, water potential, large granules, nitrifier activity, [Formula: see text] production

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Biochar Volatile Matter and Feedstock Effects on Soil Nitrogen Mineralization and Soil Fungal Colonization

Sustainability ◽

10.3390/su13042018 ◽

2021 ◽

Vol 13 (4) ◽

pp. 2018

Author(s):

Tai McClellan Maaz ◽

William C. Hockaday ◽

Jonathan L. Deenik

Keyword(s):

Hydrolytic Enzyme ◽

Fold Increase ◽

Volatile Matter ◽

Fungal Colonization ◽

Nitrogen Transformations ◽

Production Methods ◽

Carbon And Nitrogen ◽

13C Nuclear Magnetic Resonance ◽

Carbon And Nitrogen Dynamics ◽

Relationship Of

Biochar has important biogeochemical functions in soil—first as a means to sequester carbon, and second as a soil conditioner to potentially enhance soil quality and fertility. Volatile matter (VM) content is a property of biochar that describes its degree of thermal alteration, which can have a direct influence on carbon and nitrogen dynamics in soil. In this study, we characterized the VM in biochars derived from two locally sourced feedstocks (corncob and kiawe wood) and evaluated the relationship of VM content to nitrogen transformations and culturable fungal biomass. Using 13C nuclear magnetic resonance (NMR) spectroscopy, we found that the VM content of biochar primarily consisted of alkyl (5.1–10.1%), oxygen-substituted alkyl (2.2–6.7%), and phenolic carbon (9.4–11.6%). In a series of laboratory incubations, we demonstrated that corncob biochars with high VM (23%) content provide a source of bioavailable carbon that appeared to support enhanced viable, culturable fungi (up to 8 fold increase) and cause nitrogen immobilization in the short-term. Corncob biochar with bioavailable VM was nitrogen-limited, and the addition of nitrogen fertilizer resulted in a four-fold increase in total hydrolytic enzyme activity and the abundance of culturable fungal colonies. In contrast, kiawe biochar with an equivalent VM content differed substantially in its composition and effect on these same biological parameters. Therefore, the rapid measurement of VM content is too coarse to differentiate chemical composition and to predict the behavior of biochars across feedstocks and production methods.

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Soil gross nitrogen transformations in forestland and cropland of Regosols

Scientific Reports ◽

10.1038/s41598-020-80395-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Xiao Ren ◽

Jinbo Zhang ◽

Hamidou Bah ◽

Christoph Müller ◽

Zucong Cai ◽

...

Keyword(s):

Land Use ◽

Southwest China ◽

Nitrification Rate ◽

Land Uses ◽

Nitrogen Transformations ◽

N Losses ◽

Retention Capacity ◽

N Transformations ◽

Autotrophic Nitrification ◽

Land Use Types

AbstractSoil gross nitrogen (N) transformations could be influenced by land use change, however, the differences in inherent N transformations between different land use soils are still not well understood under subtropical conditions. In this study, an 15N tracing experiment was applied to determine the influence of land uses on gross N transformations in Regosols, widely distributed soils in Southwest China. Soil samples were taken from the dominant land use types of forestland and cropland. In the cropland soils, the gross autotrophic nitrification rates (mean 14.54 ± 1.66 mg N kg−1 day−1) were significantly higher, while the gross NH4+ immobilization rates (mean 0.34 ± 0.10 mg N kg−1 day−1) were significantly lower than those in the forestland soils (mean 1.99 ± 0.56 and 6.67 ± 0.74 mg N kg−1 day−1, respectively). The gross NO3− immobilization and dissimilatory NO3− reduction to NH4+ (DNRA) rates were not significantly different between the forestland and cropland soils. In comparison to the forestland soils (mean 0.51 ± 0.24), the cropland soils had significantly lower NO3− retention capacities (mean 0.01 ± 0.01), indicating that the potential N losses in the cropland soils were higher. The correlation analysis demonstrated that soil gross autotrophic nitrification rate was negatively and gross NH4+ immobilization rate was positively related to the SOC content and C/N ratio. Therefore, effective measures should be taken to increase soil SOC content and C/N ratio to enhance soil N immobilization ability and NO3− retention capacity and thus reduce NO3− losses from the Regosols.

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Contributions of external nutrient loading and internal cycling to cyanobacterial bloom dynamics in Lake Taihu, China: Implications for nutrient management

Limnology and Oceanography ◽

10.1002/lno.11700 ◽

2021 ◽

Vol 66 (4) ◽

pp. 1492-1509

Author(s):

Hai Xu ◽

Mark J. McCarthy ◽

Hans W. Paerl ◽

Justin D. Brookes ◽

Guangwei Zhu ◽

...

Keyword(s):

Nutrient Loading ◽

Nutrient Management ◽

Lake Taihu ◽

Cyanobacterial Bloom ◽

External Nutrient ◽

Internal Cycling

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Fate of carbon and nitrogen from plant residue decomposition in a calcareous soil

Plant Soil and Environment ◽

10.17221/3357-pse ◽

2011 ◽

Vol 52 (No. 3) ◽

pp. 137-140 ◽

Cited By ~ 7

Author(s):

F. Nourbakhsh

Keyword(s):

Biochemical Properties ◽

Plant Residue ◽

Plant Residues ◽

Order Kinetic ◽

Nitrogen Transformations ◽

Plant Materials ◽

Carbon And Nitrogen ◽

Residue Decomposition ◽

N Concentration ◽

Order Kinetic Model

Carbon and nitrogen transformations in soil are microbially mediated processes that are functionally related. The fate of C and N was monitored in a clay-textured soil (Typic Haplocambid) which was either unamended (control) or amended with various plant materials at the rate of 10 g residue C/kg soil. To evaluate C mineralization, soils were incubated for 46 days under aerobic conditions. Nitrogen mineralization/immobilization was evaluated at the end of eight-week incubation experiment. All CO2 evolution data conformed well to a first-order kinetic model, Cm = C0 (1 – e–Kt). The product of K and C0 (KC0) was significantly correlated with some chemical and biochemical properties of the plant residues, including N concentration (r = 0.83, P < 0.001), C:N (r = –0.64, P < 0.05) and lignin:N (r = –0.81, P < 0.001). Among the plant residue composition characteristics, N concentration (r = 0.96, P < 0.001), C:N (r = –0.69, P < 0.01) and lignin:N (r = –0.68, P < 0.01) were significantly correlated with the net rates of N mineralization/immobilization (Nm/i).

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Nitrogen Transformations in Lake Ontario

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f87-262 ◽

1987 ◽

Vol 44 (12) ◽

pp. 2133-2143 ◽

Cited By ~ 15

Author(s):

D. R. S. Lean ◽

R. Knowles

Keyword(s):

Surface Waters ◽

Lake Ontario ◽

Ammonium Uptake ◽

Small Cells ◽

Nitrogen Transformations ◽

Size Fractionation ◽

Nitrate Losses ◽

Zooplankton Excretion ◽

Highly Correlated ◽

Chemoautotrophic Bacteria

Concentrations of ammonium plus nitrite in Lake Ontario were highly correlated with ammonium regeneration from zooplankton excretion (r = 0.966), inferring that elevated nitrite concentrations result from nitrification. Nitrapyrin-sensitive dark 14C-labeled bicarbonate assays confirmed high rates of nitrification by chemoautotrophic bacteria. 15N-labeled nitrate experiments showed that nitrate, not ammonium, was the principal form of N used for total microbial protein synthesis. Size fractionation experiments also suggested that small cells were responsible for most of the ammonium uptake, while large cells used mostly nitrate. Nitrate depletion in the surface waters during summer stratification resulted from movement to particulate N, nitrite, and ammonium as well as losses in particulate N due to sedimentation. At least one third, however, was unaccounted for (i.e. 30 mg N∙m−2∙d−1) and may have been converted to protein which would move up the food chain to larger organisms (e.g. fish) not sampled during conventional water chemistry. Nitrous oxide profiles showed that nitrate losses through denitrification are unlikely to occur. Consequently, unless nitrate loading to Lake Ontario is reduced, nitrate concentrations should be expected to continue to increase.

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