Nitrogen fixing trees influence concentrations of ammonium and amino sugar-nitrogen in soils

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Nitrogen fixing trees influence concentrations of
ammonium and amino sugar-nitrogen in soils

• Jing-Shu Wang, Saeed A. Khan, and Jeffrey O.
  Dawson
• Department of Natural Resources and Environmental
  Sciences, University of Illinois, Urbana, IL
  61801, USA

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Introduction

• The recently-developed Illinois Soil Nitrogen
  Test (ISNT) measures the combined concentration
  of ammonium- and amino sugar-N in soils,
  providing a novel, alternative approach to N
  fertility assessment. The nonresponse level to N
  fertilization for corn is 235 (mg kg-1 or 635
  lbs per acre) amino sugar plus ammonium N.

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Introduction

• A positive correlation between soil amino sugar-N
  plus NH4-N values and check-plot yield was
  described by Mulvaney et al. at the U. of
  Illinois. This method to determine soil N
  availability is sensitive and provides a simple
  estimation of soil capacity to supply
  plant-available N.

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Introduction

• Amino sugar-N in soils originates from microbial
  activity rather than from higher plants.
  Therefore, the concentration of amino sugar-N in
  soils reflects the level of mineralizable N and
  soil capacity to supply N to promote plant growth.

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Rationale

• Amino sugar-N is a key soil organic fraction
  associated with soil N fertility. It is different
  from leachable NO3- in that it is more stable. It
  should provide a straightforward and more
  accurate estimate of soil N fertility than other
  methods currently available (total N, lab
  incubations for mineralization, buried bag, resin
  exchange).

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Hypothesis

• Amino sugar-N will increase in concentration in
  soils under nitrogen-fixing trees.

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Objectives

• 1) to determine how different densities, sizes
  and species of nitrogen-fixing trees in different
  soil types affect soil concentrations of amino
  sugar-N (plus ammonium).
• 2) to describe amino sugar-N distribution with
  respect to soil depths in plots with and without
  N2-fixing trees.

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Study Sites in East-Central Illinois

• The University of Illinois Arboretum (N. Lat.
  40o).
• The Douglas-Hart Nature Center (DHNC), a
  50-year-old interplanting of either 2 native
  trees per 1 N2-fixing A. glutinosa or Robinia
  pseudoacacia L. tree or no N2-fixing nurse trees
  at all (spacing 10 10 feet).
• Kickapoo State Park in Vermilion County, IL on
  45-year-old mine spoils.

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Illinois Soil Nitrogen Test

• The samples were analyzed using the ISNT
  technique described by Khan et al. (Soil Sci.
  Soc. Am. J. 651751-1760. 2001).
• H3BO3-indicator solution was suspended from the
  lid of a Mason jar. Sealed jars were heated for 5
  hours in 10 ml of 2 M NaOH at precisely 48 oC.
  After 5 hours of ammonia diffusion, the
  H3BO3-indicator solution was titrated with 0.01 M
  H2SO4 to determine quantity of ammonium from
  amino sugar and ammonium N in the soil samples.

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Individual mean differences in amino sugar
nitrogen concentration (mg kg-1) of soil from
different depths associated with actinorhizal A.
glutinosa trees and a T. americana tree at the
University Arboretum.
1 Means with the same letter for a tree species
are not significantly different (LSD, a 0.05).
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Individual mean differences in amino sugar
nitrogen concentration (mg kg-1) in the top 30
cm of soil associated with actinorhizal A.
glutinosa trees and a T. americana tree at the
University Arboretum.
1 Means with the same letter for a tree species
are not significantly different (LSD, a 0.05).
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Chemical analysis of the surficial 30 cm of soil
at the Arboretum. CEC cation exchange capacity.
Values are means with standard deviation within
parenthesis.
1 Illinois Soil Nitrogen Test
(Khan et al., 2001). 2 Total
nitrogen (Kirsten and Hesselius, 1983).
3 Cation exchange capacity.
4 Base saturation percentage of cation exchange
sites. 5 Means with the same
letter within a column for a given location are
not significantly different (LSD, a
0.05).
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Ammonium and amino sugar-N concentration

• For DHNC, significant differences occurred for
  depths, but not for past alder or black locust
  influence (nitrogen fixing nurse trees mostly
  dead after 50 years).
• There is more biomass in the interplanted stands
  at DHNC, which could constitute a major N pool
  for the site and explain the lack of significant
  differences in soil amino sugar-N.

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Individual mean differences in amino sugar
nitrogen concentration (mg kg-1) of different
soil depths at Kickapoo State Park.
1 Means with the same letter are not
significantly different (LSD, a 0.05).
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Individual mean differences in amino sugar
nitrogen concentration (mg kg-1) in the top 30
cm of soil for different vegetation at Kickapoo
State Park.
1 Means with the same letter are not
significantly different (LSD, a 0.05).
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Chemical analysis of the surficial 30 cm of soil
on mine spoils. CEC cation exchange capacity.
Values are means with standard deviation within
parenthesis.
1 Illinois Soil Nitrogen Test
(Khan et al., 2001). 2 Total
nitrogen (Kirsten and Hesselius, 1983).
3 Cation exchange capacity.
4 Base saturation percentage of cation exchange
sites. 5 Means with the same
letter within a column for a given location are
not significantly different (LSD, a
0.05).
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Soil Depth Strata

• Amino sugar-N concentrations were always highest
  in the top 10 cm of soil consistent with the
  input of organic N from annual litter fall and
  surficial root dieback, but the mount of increase
  over control amount with respect to lower strata
  varied minespoil w N fixersgtmollisols w N-fixersgt

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Arboretum Findings

• The significant 13 increase in soil amino sugar
  N under the A. glutinosa canopy occurred, even
  though soil amino sugar levels indicate high N
  fertility. High N fertility levels can inhibit
  symbiotic nitrogen fixation by plants through
  energy conserving feedback mechanisms.

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Additional Arboretum Findings

• At the University Arboretum under A. glutinosa
  leaf canopies, there were significantly higher
  amino sugar-N concentrations, lower pH values and
  greater proton saturation of CEC exchange sites
  than beyond A. glutinosa canopies in the 0-30 cm
  soil layer. Increased ammonium nitrogen from
  mineralization of litter and sloughed roots of A.
  glutinosa tissue enriched with fixed N is
  oxidized to nitrate via microbial nitrification,
  which can decrease soil pH and thereby increase
  cation leaching. Total N and amino sugar-N in
  soils were not correlated at this site.

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Mine Spoil Findings

• On mine spoils, both E. umbellata and A.
  glutinosa had significantly higher amino sugar-N
  concentrations than the control plot. The E.
  umbellata plot had the highest amino sugar-N,
  followed by the A. glutinosa plot and, lastly,
  the control plot.

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Mine Spoil Findings

• At Kickapoo State Park, the only significant
  correlation was negative (r -0.681) for the
  relationship between amino sugar-N concentration
  and total N. Higher amino sugar-N concentration
  may reflect abundant and easily mineralizable N
  of the actinorhizal plant litter and sloughed
  roots.

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Mine Spoil Findings

• There was higher phosphorus concentration beneath
  A. glutinosa at Kickapoo State Park similar to
  findings of Giardina et al. (1995)

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Conclusions

• ISNT is sensitive to soil nitrogen fertility
  contributions by nitrogen-fixing trees, The test
  itself is simple, precise and employs
  commonly-available materials. The test results,
  when calibrated with corresponding levels of
  productivity, should be able to predict soil N
  fertility and the potential benefits of planting
  N-fixing trees on a particular soil type.

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THANK YOU

• Any questions?