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Evaluation of Biochar Effects on Nitrogen Retention and Leaching in Multi-Layered Soil Columns


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Biochar can play a key role in nutrient cycling, potentially affecting nitrogen retention when applied to soils. In this project, laboratory experiments were conducted to investigate the adsorption properties of bamboo charcoal (BC) and the influence of BC on nitrogen retention at different soil depths using multi-layered soil columns. Results showed that BC could adsorb ammonium ion predominantly by cation exchange. Ammonium nitrogen (NH4 +-N) concentrations in the leachate of the soil columns showed significant differences at different depths after ammonium chloride application to the columns depending on whether BC had been added. Addition of 0.5% BC to the surface soil layer retarded the downward transport of NH4 +-N in the 70-day experiment, as indicated by measurements made during the first 7days at 10cm, and later, in the experimental period at 20cm. In addition, application of BC reduced overall cumulative losses of NH4 +-N via leaching at 20cm by 15.2%. Data appeared to suggest that BC could be used as a potential nutrient-retaining additive in order to increase the utilization efficiency of chemical fertilizers. Nonetheless, the effect of BC addition on controlling soil nitrogen losses through leaching needs to be further assessed before large-scale applications to agricultural fields are implemented. KeywordsBamboo charcoal-Nitrogen leaching-Nitrogen retention-Ammonium nitrogen-Adsorption
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Evaluation of Biochar Effects on Nitrogen Retention
and Leaching in Multi-Layered Soil Columns
Ying Ding &Yu-Xue Liu &Wei-Xiang Wu &
De-Zhi Shi &Min Yang &Zhe-Ke Zhong
Received: 5 July 2009 /Accepted: 17 February 2010 / Published online: 10 March 2010
#Springer Science+Business Media B.V. 2010
Abstract Biochar can play a key role in nutrient
cycling, potentially affecting nitrogen retention when
applied to soils. In this project, laboratory experiments
were conducted to investigate the adsorption properties
of bamboo charcoal (BC) and the influence of BC on
nitrogen retention at different soil depths using multi-
layered soil columns. Results showed that BC could
adsorb ammonium ion predominantly by cation ex-
change. Ammonium nitrogen (NH
-N) concentrations
in the leachate of the soil columns showed significant
differences at different depths after ammonium chlo-
ride application to the columns depending on whether
BC had been added. Addition of 0.5% BC to the
surface soil layer retarded the downward transport of
-N in the 70-day experiment, as indicated by
measurements made during the first 7 days at 10 cm,
and later, in the experimental period at 20 cm. In
addition, application of BC reduced overall cumulative
losses of NH
-N via leaching at 20 cm by 15.2%.
Data appeared to suggest that BC could be used as a
potential nutrient-retaining additive in order to increase
the utilization efficiency of chemical fertilizers. None-
theless, the effect of BC addition on controlling soil
nitrogen losses through leaching needs to be further
assessed before large-scale applications to agricultural
fields are implemented.
Keywords Bamboo charcoal .Nitrogen leaching .
Nitrogen retention .Ammonium nitrogen .Adsorption
1 Introduction
Excessive application of nitrogen fertilizers to agricul-
tural land is regarded as a major contributor to various
ecological problems, such as nitrogen leaching, which
may pose a threat to the quality of surface and
groundwater (Thomsen et al. 1993; Fraters et al.
1998;Alvaetal.2003; Camargo and Alonso 2006;
Bakhsh et al. 2007;Yuetal.2007). In addition,
nitrogen leaching has become an important limitation
to improving the utilization efficiency of nitrogen in
agricultural production. In order to alleviate this
problem, techniques must be developed to keep
applied nitrogen in the topsoil and therefore increase
its utilization efficiency. Either applying slow-release
fertilizers (Gentile et al. 2009)orincreasingadsorption
Water Air Soil Pollut (2010) 213:4755
DOI 10.1007/s11270-010-0366-4
Ying Ding and Yu-Xue Liu contribute equally to this paper.
Y. Ding :W.-X. Wu
Ministry of Agriculture Key Laboratory of Non-point
Source Pollution Control,
Hangzhou 310029, Peoples Republic of China
Y. Ding :Y.-X. Liu :W.-X. Wu (*):D.-Z. Shi :M. Yang
Institute of Environmental Science and Technology,
College of Environment and Resource Science,
Zhejiang University,
Hangzhou 310029, Peoples Republic of China
Z.-K. Zhong
China National Research Center of Bamboo,
Hangzhou 310012, Peoples Republic of China
sites (Lehmann et al. 2003) can meet this demand to
some extent. How effective slow-release fertilizers are
in reducing leaching of applied nitrogen under high
leaching conditions is not well known. An alternative
option could be the application of biochar to soils
(Lehmann et al. 2003).
The environmental impacts of biochar use in
agriculture, including its effects on global climate
change and the soil ecosystem, have resulted in a
growing interest in the fields of atmospheric
science, geology, and environmental science in
recent years (Cheng et al. 2006; Forbes et al. 2006;
Liang et al. 2006;Chengetal.2008;Mathews
2008). Biochar, namely biomass-derived charcoal,
refers to the highly aromatic substance remaining
after pyrolysis and carbonification of biomass under
complete or partial exclusion of oxygen, which can
be produced from a wide range of biomass sources
including woody materials, agricultural residues
such as corncobs and crop straw, livestock manures,
and other waste products. When applied to soil,
biochar has the characteristics of higher stability
against decomposition and excellent ability to absorb
ions as compared to other forms of soil organic
matter, due to its greater surface area, negative
surface charge, and charge density (Liang et al.
2006;Lehmann2007). Recent research found that
biochar was of great importance in increasing soil
carbon storage, improving soil fertility, as well as
maintaining the balance of soil ecosystems, and it
could act as a kind of soil fertilizer or amendment to
increase crop yield and plant growth by supplying
and retaining nutrients (Glaser et al. 2000; Major et
al. 2005; Steiner et al. 2007; McHenry 2009).
Conversion of bamboo into charcoal is of great
significance when considering potential raw materials
for biochar production. With a 1030% annual
increase in biomass versus 25% for trees, bamboo
can yield 20 times more timber than trees on the same
land area. Bamboo can be selectively harvested and
regenerates without replanting. Therefore, bamboo
can replace other wood products as a higher value
crop for biochar production. Bamboo charcoal (BC)
has a highly microporous structure, with an adsorp-
tion efficiency about ten times higher than that of
traditional wood charcoal (Hua et al. 2009). Prior to
this work, the ability of BC to adsorb heavy metal
ions (such as Pb
, etc.) has been studied
(Wang et al. 2008). Some authors have also reported
the adsorption behavior of other kinds of biochar in
soils, such as woody charcoal (Oya and Iu 2002;
Iyobe et al. 2004) and the biochar derived from the
residues of rice straw or wheat straw (Qiu et al. 2008).
Furthermore, biochar was shown to increase the
cation exchange capacity of sandy soils in laboratory
experiments (Tryon 1948). According to these
reports, BC may be a potential amendment in soils
for nutrient retention due to its adsorption properties
and can theoretically retard nitrogen-leaching losses.
However, little information is available about the
effect of BC on inorganic nitrogen adsorption and
cation exchange capacity in agricultural soil under
leaching conditions. Therefore, the influence of BC
on nitrogen retention and leaching to groundwater
during application of chemical fertilizers in soils
needs to be further studied.
The objectives of this study are (1) to detect the
effect of BC on ammonium ion adsorption, and (2) to
investigate the potential capability of BC to retain
ammonium nitrogen and decrease inorganic nitrogen
loss under simulated leaching conditions during the
application of ammonium fertilizers to the soil. We
believe that the results of this study will provide
practical information to guide the exploitation of a
novel amendment to improve nitrogen utilization
efficiency in agricultural applications.
2 Materials and Methods
2.1 Soil and Bamboo Charcoal
The experimental soil for this study was sampled
from two depths, 020 cm and 2040 cm, of a profile
at six different sites within the Haining Agricultural
Development Zone in Jiaxing City (120.8° E, 30.8°
N), Zhejiang Province. The soil is classified as a
permeable type with a texture of sandy silt. This soil
was relatively uniform and permeable along depth.
The soil was air-dried, passed through a 2-mm nylon
sieve, and mixed to get a homogeneous sample of
each original soil depth to be used in the column
experiments. The bamboo charcoal particles (1020
mesh) used in this study were purchased from Linan
Yaoshi Charcoal Production Limited Company locat-
ed in Hangzhou City. The characteristics of the
experimental soil and the bamboo charcoal are shown
in Table 1.
48 Water Air Soil Pollut (2010) 213:4755
2.2 Ammonium Ion Adsorption by BC
In order to study the ability of BC to adsorb
ammonium ions, ammonium chloride (NH
Cl) was
selected as the adsorbate to obtain the adsorption
isotherm in a closed system. Thirty milliliters of
Cl solutions with concentrations of 5, 10, 15, 20,
30, 40, 50, 70, and 100 mg L
were added to
0.2 g of BC, respectively. The solutions with BC
particles were then kept in a thermostatic shaker at
300 rpm and 25°C for 48 h to achieve equilibrium.
2.3 Multi-Layer Column Device
A schematic diagram of the multi-layer soil column
device is shown in Fig. 1, according to the method of
Luo et al. (2003). Each column had an inner diameter
of 10 cm, a height of 52 cm, and four sampling ports
(including three tube sections and one tap) at different
heights from the top, experimentally representing four
soil depths in a profile of 10, 20, 30, and 40 cm. The
three separated sections could be well joined and
sealed during an experiment. Each section had a small
hole drilled in the middle on the tube sidewall for
extraction of soil leachate at different layers in the
profile. A simple water container was used for
supplying distilled water to the column to simulate
2.4 Leaching Experiment
A 5-cm thick, acid-washed cobblestone layer was
placed at the bottom of each column for filtration
of soil leachate. The <2-mm air-dried soil sub-
samples were carefully placed in different column
sections based on the original depth of each layer
in the field and the soil bulk density. The top 0
20-cm and the bottom 2040-cm sections of the
column were filled with the mixed soil subsamples
from the original layers of 020 cm and 2040 cm
in the field, respectively. However, the soil placed
in the 010 cm of the column was subjected to
one of the following treatments: (1) no application
of fertilizer (control, designated as CK), (2)
ammonium chloride application alone at a rate of
400 kg N ha
(designated as A), and (3) ammoni-
um chloride application at a rate of 400 kg N ha
with 0.5% BC (w/w) (designated as AB), with three
Soil Bamboo charcoal
Depth (cm) 020 2040
Organic C (g kg
) 23.0 11.7 Pyrolysis temperature (°C) 600
Total N (g kg
) 3.10 2.30 pH 8.15
Total P (g kg
) 0.68 0.42 C (%) 68.1
pH (1:1) 8.56 8.44 H (%) 2.78
CEC (cmol kg
) 9.65 8.30 N (%) 0.87
Clay (%) 13.7 10.4 Density (g cm
) 0.75
Silt (%) 56.4 53.1 Specific surface area (m
) 330
Sand (%) 29.9 36.5 Water content (%) 6.90
Table 1 Characteristics of
the tested soil and bamboo
Water container
52 cm
10 cm
0 cm
10 cm
20 cm
30 cm
40 cm
Soil profile
Fig. 1 Schematic diagram of the multi-layer soil column
device used in this experiment
Water Air Soil Pollut (2010) 213:4755 49
replicates for each treatment. The leaching experi-
ment was conducted at 25±2°C with a relative
humidity of 65% in an artificial greenhouse in
Zhejiang University.
Before starting the nitrogen leaching experiment,
about 1,600 mL distilled water was added from the
top over a period of 3 days in order to have a
homogeneously moist column at field capacity. The
soil total porosity and water holding capacity in the
columns were about 60% and 40%, respectively.
During the leaching period, an amount of 70100-
mL distilled water was applied every three days from
the top of each soil column to reflect local daily
rainfall corrected for transpiration. Leachate samples
were extracted at different depths in the soil column
profile through the sampling ports at an interval of
3 days in the initial stage and of 7 days in the
following stage. All the sampling ports were sealed
when not sampled.
2.5 Sample Analysis
The leachate samples were stored in the dark at 4°C in
an icebox prior to analysis. After centrifuging at
3,000 rpm for 3 min, the supernatant liquid was
collected and analyzed for concentrations of NH
-N, and NO
-N by ultraviolet and visible
spectrophotometry (Yu et al. 2007). The electrical
conductivity (EC) was determined by an electrical
conductivity meter (Type: DDS-EC).
2.6 Statistic Analysis
The results were expressed as means and standard
deviations. Statistical analysis was performed using
the software of SPSS for windows. Any differences
between the mean values with P>0.05 were not
considered statistically significant.
3 Results and Discussion
3.1 Adsorption of Ammonium Ion on BC
Since plenty of pores were formed during the
pyrolysis of bamboo at high temperature, BC has
achieved high adsorption capacity, which is one of its
important characteristics, with a large specific surface
area (as shown in Table 1, the specific surface area of
the tested BC reached 330 m
when carbonized at
Langmuir and Freundlich models are usually used
to describe the equilibrium adsorption isotherm data.
As such, our experimental data for the adsorption of
on BC was described well by the former. The
linearized form of the Langmuir formula is as follow:
where q
is the equilibrium amount of adsorbate
adsorbed (milligram) per unit mass of adsorbent
(gram), C
is the equilibrium concentration of
adsorbate in solution (mg L
), and the values of q
(mg g
) and k(L mg
) are the maximum adsorption
capacity of adsorbent and the adsorption energy
coefficient, respectively (Zheng et al. 2008; Rocha et
al. 2009).
A linear relationship of the Langmuir isotherm for
adsorption on BC is shown in Fig. 2, with a
good correlation coefficient (R
=0.9975). The maxi-
mum adsorption capacity (q
) and the adsorption
energy coefficient (k) calculated from the slope and
the intercept of the linear regression were 0.852 mg
and 0.125 L mg
at 25°C, respectively.
3.2 Effect of BC on NH
-N Concentration
in Leachate
The temporal changes of ammonium-N (NH
concentration in the leachate of soil columns at 10-cm
depth are shown in Fig. 3a. The leaching NH
concentrations under treatment CK tended to vary
slightly, with values ranging from 7.7 to 12.6 mg L
y = 1.1731x + 9.4061
= 0.9975
0 20406080
(mg L
(g L
Fig. 2 Linear plot of Langmuir isotherm of NH
adsorption on bamboo charcoal
50 Water Air Soil Pollut (2010) 213:4755
Under treatment A, the observed peak of NH
appeared on day 4 with a maximum level of 260 mg
. Thereafter, the concentration of NH
-N de-
creased gradually to 54.9 mg L
at the end of this
experiment. Under treatment AB, the NH
-N con-
centration increased dramatically in the first 4 days,
then slowly rose to the maximum of 207 mg L
day 28. After that, the NH
-N concentration showed
a moderate declining trend, reaching 57.2 mg L
day 70. In summary, in the absence of BC, a peak in
-N concentration in the leachate appeared in the
first 14 days; however, the peak was substantially
delayed for the BC-treated soil at 10-cm depth. The
reason may lie in the porous structure of BC that
reduces the NH
-N transport due to the adsorption
capability of BC.
The leaching behavior of NH
-N in the soil
columns at 20-cm depth (Fig. 3b) was much different
from that at 10 cm. During the initial 14 days, there
was no marked difference of NH
-N concentrations
in the leachate at 20-cm depth among the treatments
CK, A, and AB. The trends for treatments A and AB
were similar from day 21 to day 70, with the NH
concentrations obviously higher than that under
treatment CK. Furthermore, the NH
-N concentra-
tion under treatment AB was lower than that under
treatment A as leaching continued beyond 42 days,
with values of 38.4 and 48.7 mg L
for treatments
AB and A on day 70, respectively. This difference
may also be related to the adsorption effect of BC on
-N in the top 10-cm soil layer.
The NH
-N concentrations in the leachate of soil
columns at both 30 cm (Fig. 3c) and 40 cm (Fig. 3d)
depths showed no obvious difference among the
treatments CK, A, and AB within the 70-day period,
and they were all at a much lower level than the
shallower leachates, with values between 6.6 and
14.4 mg L
Overall, these results suggest that NH
-N can be
retained in the surface soil layer (020 cm) for a
Time (d)
NH4-N (mg L )
0 7 14 21 28 35 42 49 56 63 70
0 7 14 21 28 35 42 49 56 63 70
20 cm10 cm
30 cm 40 cm
(a) (b)
(c) (d)
Fig. 3 Temporal changes of NH
-N concentration in the leachate of soil columns at different depths (treatment: CK: no-fertilizer; A:
ammonium chloride at 400 kg N ha
;AB: ammonium chloride at 400 kg N ha
+0.5% bamboo charcoal)
Water Air Soil Pollut (2010) 213:4755 51
longer time through BC addition, a delay which is
potentially beneficial to nitrogen utilization of crops.
3.3 Effect of BC on Cumulative Losses of NH
Through Leaching
The cumulative losses of NH
-N through leaching
at the 10-cm depth in the soil columns increased over
time (Fig. 4a). The increase of NH
-N losses took
place at a very slow rate under the CK treatment, and
-N losses of 6.5 mg were found on day 70. It
seems that the cumulative leaching losses of soil
-N could be significantly reduced by BC
addition (40.4 mg column
) compared to that with
ammonium chloride application alone (44.8 mg
), according to the results obtained during
the first 14 days in this experiment. Taken all
together, the data in Fig. 4a indicated that the
presence of BC reduced the leaching rate of NH
N, although the NH
-N losses showed no obvious
difference between treatment A and AB from day 21
to 70.
The cumulative leaching losses of NH
-N at 20-
cm depth showed no obvious difference among CK,
A, and AB treatments during the first 14 days
(Fig. 4b). However, the situation was quite different
during the latter stage of the experiment (from day 63
to 70). NH
-N losses of 14.3 mg were observed
under treatment AB within 70 days, which was about
15.2% lower than that (16.8 mg) under treatment A.
Adding BC to surface soils, therefore, may reduce
agricultural losses of NH
-N through runoff or
leaching, especially in areas with high rainfall.
The cumulative losses of soil NH
-N through
leaching at 30-cm (Fig. 4c) and 40-cm depth (Fig. 4d)
in the soil columns both increased over time, but they
showed no obvious difference among the CK, A, and
AB treatments within 70 days.
In the present experiment, we found that the
concentrations of NO
-N and NO
-N in the leachate
(data not shown) were both at low levels and did not
exceed 10 mg N L
. This indicates that the potential
of nitrate leaching from the soil profile might exist,
but at an unsubstantial level.
Time (d)
NH4-N (mg column )
1 4 7 10142128354249566370
1 4 7 10142128354249566370
10 cm 20 cm
30 cm 40 cm
(a) (b)
(c) (d)
Fig. 4 Cumulative losses of NH
-N in the leachate of soil columns at different depths (treatment: CK: no-fertilizer; A: ammonium
chloride at 400 kg N ha
;AB: ammonium chloride at 400 kg N ha
+0.5% bamboo charcoal)
52 Water Air Soil Pollut (2010) 213:4755
3.4 Effect of BC on EC in the Leachate
Electrical conductivity (EC) estimates the amount of
total dissolved salts or the total amount of dissolved
ions in the water. Therefore, EC in leachate measures
the risk of groundwater pollution by dissolved base
ions, such as NH
In the present experiment, a lower EC was found in
the leachate at 10-cm depth of the soil columns under
treatment AB compared to that under treatment A
(Fig. 5a). The observed peaks of EC in the leachate
appeared on day 7 under both treatment A and AB,
with the maximum value of 5.19 and 4.78 mS cm
respectively. Following that, a gradual decline of EC
was found under both treatments, with values of 0.75
and 0.84 mS cm
on day 70, respectively, approach-
ing that under treatment CK (0.54 mS cm
). These
results indicate that leaching did most likely diminish
as the BC adsorbed various ions not by simple
exchange but also by physical adsorption and other
processes, as evidenced by the temporal changes of
-N concentration in the leachate at 10-cm depth.
Temporal changes of EC in the leachate of the soil
columns at 20-cm depth showed very similar tenden-
cies between treatments A and AB (Fig. 5b). The
peaks of EC appeared on day 42, with the maximum
values of 1.97 and 1.79 mS cm
, respectively.
Furthermore, the EC in the leachate was markedly
reduced under treatment AB compared to that under
treatment A. These results indicated a significant
downward movement of dissolved ions such as NH
in the upper soil, with BC influencing this movement
through the adsorption effect.
Application of ammonium chloride led to a higher
EC in the leachate of the deeper soil (2040 cm) at
different stages of the experiment, for example, from
day 35 at 30-cm depth (Fig. 5c) and from day 63 at
40-cm depth (Fig. 5d). No significant difference was
found in EC at this depth between the treatment with
and without BC.
Time (d)
EC (mS cm )
0 7 14 21 28 35 42 49 56 63 70
0 7 14 21 28 35 42 49 56 63 70
10 cm 20 cm
30 cm 40 cm
(a) (b)
(c) (d)
Fig. 5 Temporal changes of electrical conductivity in the leachate of soil columns at different depths (treatment: CK: no-fertilizer; A:
ammonium chloride at 400 kg N ha
;AB: ammonium chloride at 400 kg N ha
+0.5% bamboo charcoal)
Water Air Soil Pollut (2010) 213:4755 53
4 Conclusions
BC could adsorb ammonium ion primarily by ion
exchange, and the maximum adsorption capacity (q
was 0.852 mg g
at 25°C. Addition of 0.5% BC to
the surface soil layer retarded the vertical movement
of NH
-N into the deeper layers within the 70-day
observation time, especially during the first 7 days at
10-cm depth and the later experimental period at 20-
cm depth. Application of BC reduced cumulative
losses of NH
-N via leaching at 20 cm by 15.2%
over the experimental period. A lower EC was
measured in the leachate above 20-cm depth of the
soil columns in the presence of BC. Therefore, as a
kind of biochar, BC could be used as a potential soil
amendment for nutrient retention, especially in
regions with a large amount of rainfall, to mitigate
the vertical transport of ammonium nitrogen. Howev-
er, the effect of BC addition on controlling inorganic
nitrogen losses in soils through leaching needs to be
further assessed before large-scale applications of BC
to agricultural fields can be recommended.
Acknowledgement This research was supported by the
Natural Science Foundation of China (project No. 40873059),
Science and Technology Department of Zhejiang Province
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... This explains the higher sorption capacity of low-temperature biochars for NH + 4 compared to high-temperature biochars. The negative charge of biochar surfaces leads to electrostatic attraction of the positively charged NH + 4 , resulting in cation exchange; Al 3+ , Ca 2+ , and Mg 2+ may be exchanged by NH + 4 (e.g., Cui et al., 2016;Ding et al., 2010;Gai et al., 2014;Li et al., 2018;Zheng et al., 2013bZheng et al., , 2018. In contrast, sequestration in pores plays no decisive role for NH + 4 adsorption to biochars (e.g., Cui et al., 2016;Zheng et al., 2013b). ...
... Biochar has also been reported to significantly reduce leaching of ammonium (NH + 4 ) (e.g. Ding et al., 2010;Lehmann et al., 2003;Sika and Hardie, 2014;Zheng et al., 2013a), phosphorus (P) (e.g. Major et al., 2012;Raave et al., 2014), and potassium (K) (e.g. ...
... One crucial mechanism for NH + 4 retention by biochars is cation exchange (Ding et al., 2010;Zheng et al., 2013b). Positively charged NH + 4 is electrostatically attracted by negatively charged, oxygen-containing functional groups on biochars, and Ca 2+ and Mg 2+ may be exchanged by NH + 4 (Zheng et al., 2013b). ...
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The Caatinga is one of the largest seasonally dry tropical forests in the world. With an estimated area of 600 000 km2 to 900 000 km2 , it is located in the semi-arid north-east of Brazil. The climate is demanding with constant high temperatures, erratic rainfalls, and regular droughts, resulting in general water scarcity. Moreover, the soils in the Caatinga are usually only of low to medium fertility and often shallow and stony. The water-deficient conditions, paired with poor soils, are severely challenging agricultural practice in the region. As the backbone of agriculture, soils play a crucial role in food production. Therefore, the overall aim of this dissertation was to sustainably increase the fertility of Caatinga soils on a long-term basis to promote food security and livelihood of the local smallholders. Two important parameters that impact soil fertility were considered: nutrient retention and soil organic carbon (SOC). First of all, the effects of biochar and clay addition on the nutrient retention of an Arenosol were evaluated. Second, the influence of various factors on SOC stocks, in particular grazing, were studied. All research was conducted in the Itaparica region in the state of Pernambuco, Brazil. For the first thematic part, two locally available and inexpensive soil amendments were selected: a traditionally produced mid-temperature biochar made of the invasive tree species Prosopis juliflora (Sw.) DC and the clayey sediment of a temporarily dry lake. In a batch equilibrium experiment, the sorption of ammonium-N (NH 4+ -N), nitrate-N (NO3- -N), potassium (K+ ), and phosphate-P (PO43- -P) was quantified for substrate mixtures of an Arenosol with increasing shares of biochar and clay, respectively. In a corresponding field experiment using the same substrates, the leaching of NH4+ -N, NO3- -N, and K+ was quantified for two consecutive periods of eight months each by using self-integrating accumulators. Both experiments showed the same tendencies. Biochar addition induced marginal to medium retention of NO3- -N, medium retention for PO43- -P, and medium to strong retention of NH4+ -N. In the field experiment, the biochar showed medium retention of K+ , while it provoked strong K+ release in the batch equilibrium experiment. In contrast, clay addition resulted in the release of NO3- -N and medium to strong retention of NH4+ -N, K+ , and PO43- -P. Both soil amendments showed the potential to enhance the retention of nutrients and, thus, the fertility of an Arenosol. The nutrient retention capacity of the clay remained relatively stable for the 16 months of the field experiment, whereas the retention capacity of biochar significantly dropped for all nutrients by about half in the second observation period compared to the first. The reason was the comparatively low stability of this particular biochar, causing rapid decomposition under the given climatic conditions. Therefore, for future application, the long-term stability of biochar should be enhanced by higher pyrolysis temperatures. In the second thematic part of this dissertation, SOC stocks of Caatinga soils were quantified on 45 study plots for the upper 5 cm of the soil profile and greater soil depths down to bedrock. Along a gradient of light, medium, and heavy grazing intensity, the impact of grazing on SOC stocks was assessed. Additionally, the influence of clay content, distance to the nearest permanent water body, several vegetation parameters, depth to bedrock, and altitude on SOC stocks were analysed. The mean organic carbon content in the area was relatively low with 16.86 ± 1.28 Mg C ha −1 . Heavy grazing significantly reduced carbon stocks in the upper 5 cm of the soil profile but had no significant effect in greater soil depths. Clay content and altitude proved to be the most relevant factors influencing SOC stocks of the total soil profile and the stocks below the upper 5 cm. In summary, grazing has adverse effects on SOC stocks and, consequently, on the fertility of the soils in the Caatinga. In particular, high grazing intensities should be avoided, and animal stocking rates should be reduced and adapted to sustainable local carrying capacities. Conclusively, based on the outcomes of the conducted research, recommendations for agriculture and future research were made.
... Secondly, the CEC of biochar was the most important factor affecting NH 4 + -N adsorption onto biochar (Ding et al., 2010;Zeng et al., 2013). Thirdly, the surface area of the biochar influenced the ability of the biochar to adsorb NH 4 + -N (Cai et al., 2016). ...
... These characteristics of biochar suggested that chemical interactions were more dominant than physical sorption between biochar and NH 4 + -N. For PO 4 3− -P, the components in biochar, including mineral ions, Al/Fe oxides, or organic matter, have a great ability to adsorb it by both electrostatic and non-electrostatic mechanisms (Alling et al., 2014;Cheng et al., 2008;Ding et al., 2010;Kastner et al., 2008;Sparks, 2003). Figure 3b shows that biochar addition had no significant effect on PO 4 3− -P adsorption. ...
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Biochar, a promising exogenous material, is of great interest due to its ability to retain soil nutrients. Understanding the nutrient retention and release characteristics of biochar in soil is crucial to avoid environmental risks. In the current study, batch adsorption experiments were used to explore the adsorption capacity of ammonium (NH4⁺-N) and phosphate (PO4³⁻-P) on Erythrina arborescens biochars produced at 300–700 °C. The biochar produced at 600 °C (BC600) was used to conduct the column leaching experiments under different addition ratios (0, 1%, 3%, 5%, and 10%) to evaluate the effects of biochar on nutrient leaching and soil quality over the short period of time. The results found that BC600 at different addition ratios owned the best adsorption ability to NH4⁺-N, and the highest removal rate was up to 49%. Column leaching experiments displayed that compared to pure soil, the introduction of 1% biochar could reduce the cumulative NH4⁺-N in the leachate by 30.7%. The adsorption of PO4³⁻-P on different biochars was poor, and with the increase of biochar addition ratio, the phenomenon of negative PO4³⁻-P removal rate appeared. Column leaching experiments found that when the biochar addition rate was 1%, the cumulative PO4³⁻-P in the leachate was reduced by 12.9% compared to that in pure soil. Meanwhile, the application of BC600 in soil also improved soil pH, electrical conductivity, cation exchange capacity, and organic matter. These findings suggested that the application of Erythrina arborescens biochar with the appropriate ratio in soil could benefit to mitigate nutrient loss.
... The biochar also has ability to reduce the emission of greenhouse gases . Biochar also could modify the soil physical properties like bulk density, porosity, tensile strength, aggregate size distribution and aggregate stability, water infiltration (Ding et al., 2010;Jien and Wang, 2013;Hardie et al., 2014;Omondi et al., 2016). The biochar due to its low bulk density could reduce the bulk density of soil due to dilution factor. ...
... Similarly, Yao et al. (2012b) reported 34% and 14% decreased in leaching of NO3 --N and NH4 + -N, respectively as compared to biochar unamended soil. In column leaching study using biochar prepared from bamboo charcoal at 600 °C pyrolyzed condition showed a cumulative 15% reduction for 70 days in NH4 + -N loss (Ding et al., 2010). In another similar study, column experiment showed reduction in NO3 -, NH4 + and P, with application of garden waste and poultry litter biochar prepared at 550 o C and P leaching, but addition beyond 20 pore volume (816 mm) water, the reductions were not maintained which might be due to weak interaction of water trapping (Singh et al., 2010). ...
... Langmuir and Freundlich isotherm models were used to analyze the NO3 − adsorption results. The equation of Langmuir isotherm model is as follows [30]: ...
... Langmuir and Freundlich isotherm models were used to analyze the NO 3 − adsorption results. The equation of Langmuir isotherm model is as follows [30]: ...
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The nitrate pollution of groundwater can cause serious harm to human health. Biochar electrodes, combined with adsorption and electroreduction, have great potential in nitrate removal from groundwater. In this study, bamboo chopsticks were used as feedstocks for biochar preparation. The bamboo chopstick biochar (BCBC), prepared by pyrolysis at 600 °C for 2 h, had a specific surface area of 179.2 m2/g and an electrical conductivity of 8869.2 μS/cm, which was an ideal biochar electrode material. The maximum nitrate adsorption capacity of BCBC-600-2 reached 16.39 mg/g. With an applied voltage of 4 V and hydraulic retention time of 4 h, the nitrate removal efficiency (NRE) reached 75.8%. In comparison, the NRE was only 32.9% without voltage and 25.7% with graphite cathode. Meanwhile, the average nitrate removal rate of biochar electrode was also higher than that of graphite cathode under the same conditions. Therefore, biochar electrode can provide full play to the coupling effect of adsorption and electroreduction processes and obtain more powerful nitrate removal ability. Moreover, the biochar electrode could inhibit the accumulation of nitrite and improve the selectivity of electrochemical reduction. This study not only provides a high-quality biochar electrode material, but also provides a new idea for nitrate removal in groundwater.
... This characteristic of the biochar would account for a significant proportion of the improvements in N fertiliser use efficiency noted in several pot trials. Ding et al. (2010) reported that biochar could be used as a potential nutrient-retaining additive in order to increase the utilization efficiency of chemical fertilizers. ...
Commercial crop production has increased nitrogenous fertilizer consumption by two to three times. However, temporal changes and yield stagnation of major crops over three decades urge us to revisit the fertilizer use efficiency through nano-techniques with specific reference to nitrogen fertilizers. Although nanofertilizer technology is quite innovative, literature available in this field is very limited. In this review, literature pertaining to the losses of nitrogen (N) in agro-ecosystems, slow-release N fertilizers, nanofertilizer N formulations with synthesis, characterization and their application in agriculture and associated effects are elaborated. This review serves as a strong database to understand and gain insights into innovative nanotechnologies infusion with N fertilizers research and their benefits in agriculture. Nano fertilizers are capable of enhancing crop yield as well as nitrogen use efficiency (NUE) of crops and may be considered as one of the potential alternatives for soil fertility and plant nutrition for agricultural sustainability.
... Due to abundant pore structure and high specific surface area, biochar is a good adsorbent and amendment [7,8]. Biochar provides multifunctional applications, including improving the water and nutrient retention capacity of soils [9,10], fixing organic carbon [11] and reducing greenhouse gas emissions, etc. [12,13]. Biochar produced by straw or wood chips can adsorb NH4 + -N and NO3 --N from soils and reduce soil N leaching and the environmental impact of N on water bodies [14,15]. ...
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The application of biochar can affect soil properties and retention of fertilizer nitrogen, but its effects and mechanism on the retention capacity of different forms of nitrogen in soils are still uncertain. In this study, an indoor soil column leaching experiment was conducted using vegetable soil samples with 3% rice husk biochar by mass prepared at 450 °C by pyrolysis and 150 mg N/kg 15 N-labeled urea. Adding biochar increased the soil pH, thus alleviating soil acidification caused by fertilizer nitrogen application. It also increased the content of soil organic carbon, total nitrogen and available phosphorus while decreasing that of NH4 +-N and NOX-N(NO3-Nand NO2-N) in soils. NOX-N was the predominant form in the leachate of all treatments, accounting for 63.15-87.90% of the total N loss. Compared to the urea-alone application (the N treatment), incorporating biochar and urea (the RBN treatment) significantly reduced total N and NOX-N loss by 19.99% and 25.95%, respectively, while showing slight effects on NH4 +-N loss. The 15 N results show that fertilizer N retention in soil increased by 13.67%, while inorganic 15 N leaching decreased by 25.97% after the bio-char addition, compared to that in the N treatment. The RBN treatment increased fertilizer N losses in other ways (e.g., organic N leaching, ammonia and NOx volatilization) by 21.72%. Effects of bio-char application on other N losses need to be further investigated. Biochar application can reduce the leaching of inorganic 15 N and improve fertilizer N retention in the soil. Thus, the potential risk of fertilizer N on the quality of water bodies can be reduced.
... Thus, it is still unclear how biochar would act in the presence of both ammonium-N and nitrate-N from urea hydrolysis. Adsorptive affinity towards ammonium-N [18,19,[23][24][25] has been previously reported using unmodified biochar (regular biochar) application. In this case, nitrate-N adsorption becomes weak, possibly due to the presence of negatively charged functional groups on the biochar surface [14,15,26]. ...
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Recovering nitrogen (N) from agricultural wastewater for reuse in planting fields is a more sustainable and economical strategy to limit N pollution than using conventional treatments. Hereby, regular biochar produced by wheat straw pyrolysis and Mg-modified biochar were used as the N carriers to assess inorganic-N adsorption from simulated agricultural wastewater and the potential for reuse of the carried N in a planting system. The results showed that biochar materials have different affinities towards inorganic-N types. The amount of biochar carried-N increased with the increase in inorganic-N concentration and reached 4.44 mg/g as the maximum. The biochar carried ~4 mg/g of inorganic N substituting nearly 40% of N fertilizer following a 1% w/w addition rate for vegetable planting. After a trial season, 34.7–42.7% of the carried N from biochar was assimilated by the plant, 45.9–53.7% was retained by the soil, and only about 10% was lost. In comparison to the condition with all N inputs from chemical fertilizer, the addition of part of N by the N–biochar matrix significantly reduced the N loss by improving the plant N uptake or increasing the N content in the soil. This study demonstrates that biochar materials could be used as N carriers to recover N from wastewater for reuse in soil, carrier stability, and bioavailability preservation.
... 1.04 × 10 9 (7.96 × 10 7 )a 2.39 × 10 9 (4.88 × 10 8 )a 3.70 × 10 9 (4.33 × 10 8 )a 4.89 × 10 6 (2.14 × 10 6 )a under laboratory-based conditions (Ding et al. 2010;Lv et al. 2021). The changes in soil inorganic N contents when biochar is applied may be affected by a number of abiotic and biotic factors (Clough and Condron 2010). ...
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Purpose Nitrogen (N) is an important element for crop yield and its availability may be affected by biochar. The mechanisms through which biochar influences N availability and thus crop productivity remain largely unclear, although they seem to be principally mediated by microbial processes. The objective of this study was to assess the effects of rice straw biochar on soil N availability and microbial functional genes (MFG) involved in N transformations under field experiment. Materials and methods The field experiment was performed using biochar amendment (0, 20, 40 t ha⁻¹) with or without N fertilizer application in a rice paddy in central China. Results The results suggested that the soil NH4⁺-N content showed a decreasing trend during the early stage of rice growing season while increasing its availability during the later stage in the plots with biochar amendment as compared with control. Nonetheless, soil NO3⁻-N was not affected by biochar addition, N fertilization, and their interaction at most of the sampling times. With the increase of N fertilizer and biochar application, soil MBC and MBN increased in most of the sampling times during the first and second seasons. The N uptake was significantly positively correlated with soil MBC and MBN in the first and second seasons. Biochar addition also affected some MFG involved in N transformations, causing a general decrease in the abundance of bacterial ammonia oxidizers during mature stage and narG (nitrate reduction) at heading stage during the second season independent of biochar application rates, while increase in nifH (nitrogen fixation) at heading stage during the first season in 40 t ha⁻¹ biochar treatments with N application, as compared with the control. However, there is lack of significant relationships between measured soil inorganic N and genetic data for each season. Conclusion As a result, the application of biochar had a slow release effect on soil NH4⁺-N and regulated the N uptake in rice. However, we believe that the dynamic of soil N availability during rice growing seasons may have been dominantly driven by abiotic factors rather than microbially mediated processes in double rice-cropping system.
... Additionally, the retention of ions increased due to dual adsorption capacity, where it binds both charged ions onto its surface exchange sites [12]. Studies have shown that biochar, with a pool of negative charges, adsorbs more cations which increase the potential for biochar to be a nutrient-retaining material [13]. Besides, biochar has also been used to modify the acid soil as an alternative approach to liming. ...
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Urea fertilizer as a nitrogen source is used widely and globally. However, N loss through ammonia volatilization from applied urea has become a major drawback to agriculture. A pot experiment was conducted to determine the effect of rice straw biochar on (1) total N, soil exchangeable NH4 + , and available NO3 − (2) uptake of N, P, and K in rice plants. The treatments evaluated were: (S: Soil only, U: soil + 175 kg ha−1 urea, B1: soil + 175 kg ha−1 urea + 5 t ha−1 rice straw biochar, B2: soil + 175 kg ha−1 urea + 10 t ha−1 rice straw biochar, CB1: 50% soil + 50% commercial biochar potting media and CB2: 100% commercial biochar potting media). The addition of rice straw biochar at 5–10 t ha−1 in the pot experiment significantly increased the soil total N availability by 33.33–46.67%. Treatments B1 and B2 also had significantly increased exchangeable NH4 + , NO3 −, P, and K in the soil over U. The soil availability nutrients increment in soil was attributed to the higher adsorption capacity of the rice straw biochar. Increment in soil nutrient availability such as N, P, and K increased the plant height, tiller number, greenness, and panicle number because of effective rice plant absorption. This resulted in dry matter production increment in line with plant nutrient uptake and use efficiency. Rice straw biochar at 5–10 t ha−1 can improve the productivity of rice plants by increasing N retention in soil.
The use of Layered Double Hydroxides (LDHs) and zeolite to reduce nitrate leaching in greenhouse maize farming was investigated. A research was conducted using a completely randomized factorial design experiment with 5 different treatments of zeolite and LDH application, 3 treatments of LDH (4, 8 and 16 g LDH per kg of soil), 1 zeolite treatment (16 g zeolite per kg of soil), 2 amounts of nitrate fertilizer with urea source (150 and 300 kg urea per hectare), 2 urea fertilizer installments with the control sample. In this research, the irrigation was repeated four times to collect the effluent. The results showed that the highest concentration of nitrate output in effluent was related to treatments without LDH and zeolite, and the lowest level was obtained with 16 g LDH kg⁻¹ soil treatment. Using 16 g LDH kg⁻¹ soil reduced N-nitrate leaching loss by up to 75% compared to the control sample. Comparison of using 16 g LDH kg⁻¹ soil with 16 g zeolite kg⁻¹ soil showed that LDH has a much higher ability to absorb nitrate from soil and prevent its leaching. Such that the lowest amount of LDH, 4 g LDH kg⁻¹ soil, had more impact on mean reduction of effluent’s nitrate concentration compared to 16 g zeolite kg⁻¹ soil. With increasing the use of LDH and two-installment application of fertilizer increased the number of green leaves and biological yield.
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The removal efficiency of NH 3, (CH 3)NH 2, (CH 3) 2NH and (CH 3) 3N into woody charcoal carbonized at 500°C and activated carbon was determined by the attenuation of their concentrations in the 51 bags at cool (5°C) and room temperature (20°C). A discussion follows on the deodorization performance against four gases with attention to the physical and chemical characteristics of adsorbent surfaces. It was found that the high acidity of woody charcoal surface was more suitable for the adsorption of NH 3 and (CH 3)NH 2 gases than the activated carbon under both temperatures, and the activated carbon having larger micro, meso pore volumes following an increase in specific surface area showed higher capacity for (CH 3) 3N gas adsorption than the woody charcoal. Also the activated carbon is more suitable for (CH 3) 2NH gas adsorption than the woody charcoal at 5°C, but its removal efficiency using the activated carbon is lower than the woody charcoal at 20°C. Much acidic functional groups on the adsorbent has high adsorption potential just like chemical adsorption is necessary to enhancement of (CH 3) 2NH gas at 20°C.
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Soil fertility and leaching losses of nutrients were compared between a Fimic Anthrosol and a Xanthic Ferralsol from Central Amaznia. The Anthrosol was a relict soil from pre-Columbian settlements with high organic C containing large proportions of black carbon. It was further tested whether charcoal additions among other organic and inorganic applications could produce similarly fertile soils as these archaeological Anthrosols. In the first experiment, cowpea (Vigna unguiculata (L.) Walp.) was planted in pots, while in the second experiment lysimeters were used to quantify water and nutrient leaching from soil cropped to rice (Oryza sativa L.). The Anthrosol showed significantly higher P, Ca, Mn, and Zn availability than the Ferralsol increasing biomass production of both cowpea and rice by 38–45% without fertilization (P
The aim of this work was to investigate changes in molecular form and surface charge of black carbon (BC) due to longtermnatural oxidation and to examine how climatic and soil factors affect BC oxidation. Black C was collected from 11 historical charcoal blast furnace sites with a geographic distribution from Quebec, Canada, to Georgia, USA, and compared to BC that was newly produced (new BC) using rebuilt historical kilns. The results showed that the historical BC samples were substantially oxidized after 130 years in soils as compared to new BC or BC incubated for one year. The major alterations by natural oxidation of BC included: (1) changes in elemental composition with increases in oxygen (O) from 7.2% in new BC to 24.8% in historical BC and decreases in C from 90.8% to 70.5%; (2) formation of oxygen-containing functional groups, particularly carboxylic and phenolic functional groups, and (3) disappearance of surface positive charge and evolution of surface negative charge after 12 months of incubation. Although time of exposure significantly increased natural oxidation of BC, a significant positive relationship between mean annual temperature (MAT) and BC oxidation (O/C ratio with r = 0.83;P < 0.01) explained that BC oxidation was increased by 87 mmole kg Cˉ1 per unit Celsius increase in MAT. This long-term oxidation was more pronounced on BC surfaces than for entire particles, and responded 7-fold stronger to increases in MAT. Our results also indicated that oxidation of BC was more important than adsorption of non-BC. Thus, natural oxidation of BC may play an important role in the effects of BC on soil biogeochemistry.
Understanding the temporal distribution of NO3-N leaching losses from subsurface drained ‘tile’ fields as a function of climate and management practices can help develop strategies for its mitigation. A field study was conducted from 1999 through 2003 to investigate effects of the most vulnerable application of pig manure (fall application and chisel plow), safe application of pig manure (spring application and no-tillage) and common application of artificial nitrogen (UAN spring application and chisel plow) on NO3-N leaching losses to subsurface drainage water beneath corn (Zea mays L.)–soybean (Glycine max L.) rotation systems as a randomized complete block design. The N application rates averaged over five years ranged from 166 kg-N ha−1 for spring applied manure to 170 kg-N ha−1 for UAN and 172 kg-N ha−1 for fall applied manure. Tillage and nitrogen source effects on tile flow and NO3-N leaching losses were not significant (P −1) compared with the spring manure-NT system. Corn plots with the spring applied manure-NT system gave relatively lower flow weighted NO3-N concentration of 13.2 mg l−1 in comparison to corn plots with fall manure-CP (21.6 mg l−1) and UAN-CP systems (15.9 mg l−1). Averaged across five years, about 60% of tile flow and NO3-N leaching losses exited the fields during March through May. Growing season precipitation and cycles of wet and dry years primarily controlled NO3-N leaching losses from tile drained fields. These results suggest that spring applied manure has potential to reduce NO3-N concentrations in subsurface drainage water and also strategies need to be developed to reduce early spring NO3-N leaching losses.
The integrated soil fertility management paradigm, currently advocated in Sub-Saharan Africa for rehabilitating its soils, recognizes the possible interactive benefits of combining organic residues with mineral fertilizer inputs on agroecosystem functioning. Residue quality may be a controlling factor for any beneficial interactions. The objectives of this study were to determine the effect of different quality organic residues and mineral fertilizer on N cycling under field conditions in Embu, Kenya. We hypothesized that combining low quality residue with mineral N would reduce potential system losses of N by synchronizing N release with plant uptake. Residue treatments consisted of a control (no residue input), high quality tithonia (Tithonia diversifolia) residue (C to N ratio of 13:1) and low quality maize (Zea mays) stover residue (C to N ratio of 42:1) applied at a rate of 1.2MgCha−1. Subplots of each residue treatment received either 0 or 120kgNha−1 in a split-application, and maize was cultivated each season. During the 11th growing season of the trial (March–September 2007), we monitored soil mineral N, potential gross mineralization and nitrification rates, and plant N content. Extractable mineral N in the soil profile varied with residue and fertilizer inputs throughout the growing season. The tithonia treatments showed early season N release of 22kgNha−1 in the upper 30cm of the soil profile. The maize+fertilizer treatment displayed an immobilization of 34kgNha−1 after the application of N fertilizer. However, the lower mineral N of the maize+fertilizer treatment did not reduce crop N uptake, as mineral N in the other fertilizer treatments was leached from the upper soil (0–60cm) at 57d after planting. The interactive effect on crop yield and N uptake of combining residue with fertilizer-N changed from negative to positive as residue quality decreased. The benefit of combining low quality residue with N fertilizer in reducing N losses indicates that this soil fertility management strategy should be adopted in environments subject to high N leaching losses.
A deodorant was prepared by drying charcoal particles after dipping in aqueous H3PO4 solutions. The deodorization performances of the samples against NH3 and (CH3)3N odor gases were examined by a detection test tube method and compared with those of a conventional coconut shell-derived active carbon loaded with H3PO4 in the same manner. The charcoal particles with H3PO4 exhibited higher performances than those of the other against both the odor gases. Ammonia gas was caught on the sample surface through reaction with the loaded H3PO4 to form NH4H2PO4 and further (NH4)2HPO4 but the deodorization mechanism for (CH3)3N could not be decided. The high performances of the charcoal particles loaded with H3PO4 were due to its characteristic porous structure consisting of large pores, i.e., such pores were suited for loading a large amount of H3PO4 and were not apt to be blocked by the loaded H3PO4. Also large pores were not blocked by expansion of H3PO4 on the pore surface through the deodorization reactions. The active carbon being composed of a large number of micropores did not exhibit these advantages.
Leaching of nitrate from a sandy loam cropped with spring barley, winter wheat and grass was compared in a 4-year lysimeter study. Crops were grown continuously or in a sequence including sugarbeet. Lysimeters were unfertilized or supplied with equivalent amounts of inorganic nitrogen in calcium ammonium nitrate (CAN) or animal slurry according to recommended rates (1N) or 50% above recommended rates (1.5N). Compared with unfertilized crops, leaching of nitrate increased only slightly when 1N (CAN) was added. Successive annual additions of 1.5N (CAN) or 1N and 1.5N (animal slurry) caused the cumulative loss of nitrate to increase significantly. More nitrate was leached after application of slurry because organic nitrogen in the slurry-was mineralized. With 1N (CAN) the leaching losses of nitrate were in the following order: continuous spring barley undersown with Italian ryegrass < continuous ley of perennial ryegrass < spring barley in rotation and undersown with grass < perennial ryegrass grown in rotation = winter wheat grown in rotation < sugarbeet in rotation < continuous winter wheat < continuous barley < bare fallow. At recommended levels of CAN (1N), cumulative nitrate losses over the four years were similar for the crops when grown in rotation or continuously. When crops received 1.5N (CAN) or animal slurry, nitrate losses from the crops grown continuously exceeded those from crops in rotation. Including a catch crop in the continuous cropping system eliminated the differences in nitrate leaching between the two cropping systems.
Soils of the lowland tropics in the central Brazilian Amazon are generally highly leached, acidic and nutrient-poor. Charcoal, combined with other soil amendments, might improve fertility but this, in turn, could lead to increased weed problems for agricultural production. This experiment was conducted to assess weed pressure and species composition on plots receiving various inorganic and organic soil amendments, including charcoal. Additions of inorganic fertilizer, compost and chicken manure resulted in increases in weed ground cover of 40, 22 and 53%, respectively, and increases in species richness of 20, 48, and 63%, respectively. When chicken manure was applied, dominance by a few weed species was reduced, such that different species were more evenly represented. Although charcoal additions alone did not significantly affect weed ground cover or species richness, a synergistic effect occurred when both charcoal and inorganic fertilizers were applied. The percentage ground cover of weeds was 45% within plots receiving inorganic fertilizer, 2% within plots receiving charcoal and 66% within plots receiving both amendments. Improvements in the fertility of nutrient-poor soils of the tropics might increase weed pressure and make the development of effective weed management strategies more critical. These effects on weed populations were observed nearly 2.5 years after the addition of charcoal, chicken manure and compost, and > 1 year after the last application of inorganic fertilizer.
Drinking water monitoring data have indicated anincrease in nitrate-nitrogen (NO3-N) concentration ingroundwater in some parts of the citrus production region ofFlorida. A proactive, incentive-based program of developingcrop-specific best management practices (BMP) began with theFlorida N-BMP legislation passed in 1994. A combination ofcareful irrigation and nitrogen (N) management is needed toimprove N uptake efficiency and to minimize potential leaching ofnitrate (NO3-N) to the groundwater. An improved Nmanagement practice is considered as a BMP, only if that practiceis proved to decrease NO3-N leaching into groundwater incommercial groves without adversely impacting the economics ofproduction. Therefore, long-term evaluation of horticulturalresponses as well as monitoring of groundwater NO3-N wereconducted in five commercial groves representing different soiltypes, citrus variety and rootstock, tree age, and culturalpractices to determine the impact of changes in N managementand/or irrigation scheduling. Groundwater NO3-N, leafnutrient concentrations, fruit yield and fruit quality weremonitored for 15 months under the growers' routine managementand, subsequently for 48 months, with improved N and irrigationmanagement practices. The N management practices evaluated inthis study included broadcast application of a combination ofwater soluble and slow release granular products, fertigation,and a combination of foliar application and fertigation. Irrigation management was improved by using tensiometer set pointof 10 and 15 cbar. This article presents the fruit yield, andconcentrations of N, P, K in six-month spring flush during thestudy period. The study showed that 5 to 8 yr old Valenciatrees on Volkamar lemon rootstock produced high quality fruit inthe range of 59 to 81 Mg ha-1 with 168 kg N ha-1 asfertigation combined with improved irrigation scheduling. Fruityield of 36 yr old Valencia orange trees on Rough lemonrootstock was greater with application of 180 kg N ha-1 yr-1 as fertigation compared to that of the trees whichreceived a similar rate of N as three broadcast applications ofgranular product. Fertilizer program comprising three foliarapplications of N using low biuret urea to deliver 66 kg N ha-1 yr-1 and an additional 76 kg N ha-1yr-1as fertigation was the most effective for decreasing the surficialgroundwater NO3-N while maintaining optimal fruit productionand nutritional status of the leaves. This study demonstratedthat economically and technically feasible N-BMPs can bedeveloped for citrus grown on sandy soils with a combination ofimproved N management and irrigation scheduling.