Nelson E.
González-Süllow (MS student)
Committee: H.
Lee Allen, Jennifer Bennett, Tom Fox, and Deanna
L. Osmond (NCSU- Soils)
Introduction
Nitrogen availability limits
production in loblolly pine plantation in the
southeast US. Nitrate is generally considered
quite mobile in soils and therefore subject to
leaching if no rapidly assimilated into biomass.
However, nitrate has several potential fates in
soils: 1) denitrification; 2) assimilatory
reduction; 3) immobilization in microbial
biomass, 4) uptake by plants, 5) leaching, and 6)
retention on exchange sites. The first three
fates are microbially mediated, and would only be
minor once nitrate moved into subsoil. If the
subsoil cannot retain nitrate then it may leach
into groundwater, running risks of nitrate
contamination and reduced fertilizer use
efficiency. The objective of this study is to
look for the seasonal patterns of Nitrogen during
the growing season and if there is a treatment
influence.
Methods
The study site is located in a
Piedmont loblolly pine (Pinus taeda L.)
plantation on International Paper Co. land in
Brunswick County, Virginia (36o 40’
42’’ N, 77o 59’ 19’’W)
(Figure 1). Mean annual temperature is 14oC and
mean annual rainfall is 1092 mm. Soil drainage is
classified as well drained. The soil at study
site belongs to the Cecil Series (Fine,
kaolinitic, thermic Typic Kanhapludults). This
site is one of the numerous field trials
installed throughout the Southeast as part of the
Forest Nutrition Cooperative (FNC) Regionwide 18
(RW 18) Study.
The main purpose of the
Regionwide 18 study was initiated to develop a
better understanding of the optimal rates and
frequencies of nutrient application needed to
achieve and maintain high rates of pine
plantation in rapidly growing young stands. The
Regionwide 18 treatment matrix considered two
independent variables: annual average dose and
interval between treatments. The study designs is
a randomized complete block design with 4 blocks
and have complete weed control in all treatments
plots and a meteorological station on the site.
Nutrients rates were 0, 60 every year and 180 kg
Nitrogen (N) per hectare every other year. Other
nutrient applied in a fixed ratio with N were
phosphorus (P) at 0.10 x N on all sites and
potassium (K), and boron (B) applied, at 0.40 x N
and 0.005 x N, respectively, if and when, foliar
analyses indicated a need.
A 40 m x 40 m treatment plot,
with 20 x 20 m measurements plots centered within
each, was established in each block for a total
of 12 plots. The plots were randomly located
within each block with a minimum buffer of 10 m
between each plot.
This particular study (RW
180601) was planted in 1993. Prior to planting,
the site was burned in 1992; herbicide (0.7 L
Arsenal ha-1) was applied as aerial release to
all plots, followed by planting loblolly pine
seedlings at a density of 1680 trees per hectare
in 1993. Urea and diammonium phosphate was
broadcast applied by hand between 1999 through
2003 and has totaled about 335 kg ha-1 as N in
the low fertilize plot up to 603 kg ha-1 as N in
the higher treatment rate applied over a 5 years
period. Fertilization application in the fifth
growing season was done in the spring (early May
to late April).
Sampling was conducted two
weeks after fertilization (May, 2003) and on
additional 6 sampling dates over the growing
season following fertilization. At each sampling
date, composite soil samples were collected from
15-20 cm depth and 90-100 cm depths of the
mineral soil (A horizon). Also soil solution from
lysimeter was collected from the same depth. Each
composite sample consisted of soil obtained from
3 randomly located points within plot using a
soil probe 2 cm in diameter for the 15-20 cm
depth; for the 100 cm depth only one sample was
obtained with an auger.
A 10 – 15 g sub sample was
taken from each sample and dried at 1050C to a
constant weight to determine field moisture
content. Initial levels of ammonium-N and
nitrate-N were determined by shaking fresh 10 g
of soil with 35 ml of 2M KCL and distilled water
for 30 minutes. Following centrifuging the
supernatant was analyzed for ammonium-N and
nitrate-N using an Automated Ion Analyzer
(Quickchem 8000). Soil solution from lysimeter
was measured with the Automated Ion Analyzer
(Quickchem 8000) to analyze for ammonium-N and
nitrate-N.
ANOVA of treatment effects for
all measured and calculated dependent variables.
Analysis will be performing to determine the
effects of nitrate-N and ammonium in the soil.
Analysis will be conducted for each sample date
and for each depth sampled. All test of
statistical significance will use a 0.10 level of
significance.
Preliminary Results
- Levels of Nitrate in KCl
and water extraction at 20 cm depth in
the 5 different dates were statistically
different between treatments. 180 kg N
were greater than control and 60 kg N.
- Nitrate levels increased
and peaked towards July in the 180 kg
Nitrogen (N) per hectare every other
year, and then it decreased to reached
similar values to the ones before the
application of fertilizer. The control
and 60 kg per hectare every year remained
basically flat. Questions remained on the
fate of this nutrient.
- No statistical differences
for ammonium levels in KCl extraction
were found but a couple of dates for
ammonium in water extraction were found.
- In the depth at 100 cm
there was no statistical difference
between treatments except for 148 days
after fertilization where there is a
movement of nitrate from 20 cm to 100 cm.
