One of the measures being adopted for relieving environmental problems arising
from agricultural production is to recycle poultry manure, sewage sludge and
other organic products as fertilizers and soil amendments. Nitrogen (N) is the
most limiting soil nutrient in rice production. The efficiency of applied N
usage in rice is very low, ranging from 15-35% due to dentrification, volatilization
and leaching. Furthermore, continuous use of chemical fertilizers over time
may accelerate the depletion of soil organic matter. Crop N recovery from organic
inputs such as poultry manure and sewage sludge or manures is often less than
20% (Nishida et al., 2004). However, it has been
widely accepted that organic inputs play a significant role in the long-term
build up of soil organic matter. To maximize the potential N benefit of organic
inputs it is necessary to be able to predict the amount of N supplied to the
rice from organic inputs. The amount of N supplied to the rice from an organic
input is dependent on the mineralization of organic forms to plant available
inorganic nitrogen (Ghoneim et al., 2008). The
use of poultry manure and domestic sewage sludge in agriculture is being considered
as one of the methods for recycling of these wastes in an environmentally beneficial
manner. For soil management, its well known that organic matter application
plays an important role in supplying nutrients (Takahashi
et al., 2003), stabilizing pH, EC and CEC, controlling the soil moisture
and enhancing microbial activity and circulation of nutrients (Ghoneim
et al., 2006). These processes are necessary for sustainable agricultural
systems. As a source of organic matter, poultry manure and sewage sludge are
the most abundant organic materials used in farming systems (Mubarak
et al., 2003). Thus, evolution of poultry manure and sewage sludge
from the viewpoint of N is very important for integrated soil management for
sustainable food production and conservation of agricultural land (Ebid
et al., 2008). The utilization of sewage sludge in agricultural fields
is gaining popularity as a means of waste disposal. This organic material can
enhance soil productivity as a consequence of its high organic matter and plant
nutrient content. There is currently much interest in agricultural use of sewage
sludge to reap its benefits as a fertilizer and as an aid in moisture retention.
Information regarding the effect of poultry manure and domestic sewage sludge
on yield and N uptake by rice is scarce. In practical farming, although the
relative efficiency of organic materials (relative uptake of organic material
N to chemical fertilizer N) has been used as an index of organic material efficiency
(Nishida et al., 2004), this index has not been
estimated using 15N labeled poultry manure and domestic sewage sludge.
In a previous study (Ghoneim, 2007), it was reported
that application of poultry manure and sewage sludge increased grain yields
by 34.8 and 38.3%, respectively over the control. Therefore, the objective of
this study was to investigate the fate of N in poultry manure and sewage sludge
in terms of N distribution and N uptake by rice.
MATERIALS AND METHODS
Study area and experimental design: The greenhouse experiment was carried
at the Experimental Farm, Ehime University, Matsuyama city, Japan, (33°57N,
132°47E) with an elevation of 20 m above sea level. The soil was a
low fertility Fluvisol and key chemical characteristics are presented in Table
1. The experiment was set up as a Completely Randomized Block Design (CRBD)
with five replications and the following treatments: control without fertilization
or amendment, chemical fertilization, sewage sludge and poultry manure. Chemical
fertilizer (15NH4Cl, 10.5 atom %) was applied at rate
of 8.0 g m-2 in three splits (basal, tillering and panicle initiation).
Sewage sludge was obtained from Nishida Industry Inc., Matsuyama, Ehime, Japan
with the flowing chemical properties: pH (H2O): 6.1, total N: 7.3%,
P2O5: 2.5%, K2O: 5%, CaO: 0.9%, Zn: 49 mg kg-1,
Cu: 720 mg kg-1, Hg: 0.43 mg kg-1, As: 5.6 mg kg-1,
Cd: 0.4 mg kg-1, C/N ratio: 5.7 and moisture content: 10%.
|| Chemical properties of the upper 20 cm of soil at the study
site (n = 5)
|pH and EC was measured in the soil suspension (1:2.5 and 1:5,
While the poultry manure was obtained from Asakawa Farm Inc., Matsuyama, Ehime,
Japan with chemical analysis: pH (H2O): 8.1, total N: 2.7%, P2O5:
6.9%, K2O: 3.9%, CaO: 2.0%, C/N ratio: 8.3 and 12% moisture content.
The application rates of sewage sludge and poultry manure were 160 and 200 g
Fresh Weight (FW) m-2, respectively added in one application just
before transplanting. The application rate was based on the fresh weight because
these materials are applied on a fresh weight basis in practical farming. In
sewage sludge and poultry manure pots was labeled with a solution containing
0.30 g N m-2 as 15NH4Cl (1.0 atom %) injected
carefully into the soil as 15N tracer one week after transplanting.
Phosphorus as P2O5 and K as KCl were applied as a basal
dose to all pots at the rate of 8 g m-2 one dose just before transplanting.
Wagner pots (0.025 m2) were filled with 3.50 kg air-dried soil mixed
with an equivalent volume of sewage sludge and poultry manure. Three 25-day-old
seedlings of rice cultivar Sakha 103 were transplanted into the center of each
pot with five replicates on 22 June. The pots, which were maintained under flooding
conditions until harvesting, were drained thereafter.
Plant sampling and measurements: Plant height, number of tillers and
leaf chlorophyll content were measured at different growth stages. Chlorophyll
content was measured with a chlorophyll meter (SPAD-502; Minolta Co. Ltd., Japan).
The rice plants were harvested at maturity and then separated into straw and
grain and oven dried at 70°C to a constant weight. The dried samples were
weighed and ground into a fine powder using a vibrating mill (TI-100, C.M.T.
Co. Ltd., Saitama, Japan). Total N and 15N were determined using
a stable isotope mass spectrometer (ANCA-SL; PDZ Europa Ltd., Cheshire, UK).
The loss of N resulted from sewage sludge and poultry manure was calculated
using the following equation:
where, L denotes loss, P denotes plant uptake and I is the amount of N remaining in the soil (assimilation, immobilization and residual N).
Statistical analysis: The obtained data were analyzed statistically and the differences among the mean was analyzed by the Tukey-Kramer test using the software KyPlot (KyensLab Inc., Tokyo, Japan).
A-value approach as indirect 15N isotope method: The poultry
manure and sewage sludge derived N in rice was estimated by the A-value method
as one of the indirect 15N approach. It is assumed that when as sources
of N are present in the soil, the rice will absorb from each of these sources
in proportion to the respective quantities available (Stevenson
et al., 1998). The A-value is a time-integrated estimate of the plant
available nitrogen. The main advantage of the A-value (Fried
and Dean, 1952) is that it allows comparisons of treatment with different
rates of N applied. The assumption is that percentage of N derived from a source
is proportional to the N available (A). The A-value is a measure of the soil
N in fertilizer equivalent.
In present study, the chemical fertilizer pots, 15N-labelled N fertilizer was applied, while in poultry manure and/or sewage sludge pots, 15N tracer and unlabeled poultry manure and sewage were added.
An A-value of the soil, i.e., As in the chemical fertilizer can be estimated from Eq. 1:
where, Acf is the A-value of the chemical fertilizer which represents the amount of 15N labeled chemical fertilizer applied to chemical fertilizer pots. Ndfcf % is the parentage of plant N uptake from chemical fertilizer applied in chemical fertilizer treatment and can be calculated as follows:
The A-value of the chemical fertilizer and poultry manure and/or sewage sludge in the poultry manure or sewage sludge pots can be calculated as:
where, As+OF is the A-value of the chemical fertilizer plus poultry manure and/or sewage sludge and Ndft % is the percentage of rice N uptake from the amount of 15N tracer applied in poultry manure and/or sewage sludge pots and can be estimated from the following equation:
The A-value of 15N tracer (At) is the amount of 15N tracer applied in poultry manure and/or sewage sludge treatment.
Since the A-value of the soil is constant regardless the amount of poultry
manure and/or sewage sludge added to the soil, therefore, the A-value of the
poultry manure and/or sewage sludge (AOF) can be calculated by subtracting
As from As+OF:
The percentage of rice N uptake from the poultry manure and/or sewage sludge applied (NdfOF %) can be estimated as follows:
RESULTS AND DISCUSSION
Total N uptake, N uptake originating from poultry manure or sewage sludge and
dry weight are presented in Table 2. The total N uptake in
the chemical fertilizer treatment was significantly higher than that in the
poultry manure or sewage sludge treatments. It was also observed that the total
N in poultry manure tended to be higher compared with sewage sludge. Since the
application rate of the poultry manure and sewage sludge was based on fresh
weight, the amount of applied N affected the total N uptake.
||Dry matter and total nitrogen uptake by rice grown in unamended
soil and soil amended with either chemical fertilizer, sewage sludge, or
|aN derived from chemical fertilizer or organic
materials, Values in parentheses are N uptake% derived from chemical fertilizer,
sewage sludge, poultry manure and soil, bN derived from soil,
different letters in each column reflect significant differences within
treatment (Tukey-Kramer test, p<0.05, n = 5)
The high total N uptake in poultry manure was due to the high application rate
of N as well as high uptake rate. Poultry manure resulted in the highest total
dry weight compared with other treatments. The higher dry matter yield of rice
in soils amended with poultry manure may be due to better nutrient balance and
relatively lower levels of toxic factors in the material (Matsuyama
et al., 2003).
The data showed that most of the N uptake by rice was from the soil and ranged
from 54 to 64%. Compared with chemical fertilizer, the percentage of 15N
recovered from sewage sludge and poultry manure was 19 and 36%, respectively.
The lower N uptake from organic materials could be attributed mainly to the
rapid immobilization of N due to microbial activity, leading to a significantly
lower amount of available N compared with chemical fertilizer (Zaman
et al., 2004; Ghoneim et al., 2008).
Nitrogen from many organic fertilizers often shows little effect on crop growth
in the year of application, because of the slow-release characteristics of organically
bound N. Furthermore, N immobilization can occur after application, leading
to an enrichment of the soil N pool. However, this process finally increases
the long-term efficiency of organic nitrogen (Stevenson et
al., 1998). It is difficult to directly measure the N uptake from the
poultry manure and sewage sludge using the indirect 15N isotope technique
because immobilization and mineralization occur simultaneously. Since poultry
manure and sewage sludge are frequently added consecutively in practical rice
farming, it is essential to predict the effect of accumulated residual N in
soil using the 15N labeled poultry manure and sewage sludge. In addition,
the relationship between the poultry manure, sewage sludge application rate
and N efficiency would be required.
Table 3 shows N use efficiency, relative efficiency and A-value
estimated indirectly by the 15N method. The A-values were ranked
as poultry manure>sewage sludge>chemical fertilizer. The A-values obtained
for sewage sludge and poultry manure were higher than the A-value of the soil
by 6.5 and 7.6 fold, respectively. It was hypothesized that in the current experiment
the immobilization capacity of soil with poultry manure and sewage sludge applied
was different to that of the no residue control. In the control treatment there
was less immobilization of inorganic N than in the poultry manure and sewage
sludge treatments, resulting in a large labeled N pool available for mixing
with the unlabelled N from basal mineralization. This in turn lead to a higher
15N enriched pool in this treatment than in residue treatments.
||Fertilizer N use efficiency (FNUE) determined by 15N
dilution (FUE15N) and A-values for the final harvest of
rice as affected by sewage sludge and poultry manure application
|*Fertilizer N use efficiency (relative efficiency)
is defined as the uptake rate of sewage sludge or poultry manure N/uptake
rate of chemical fertilizer N
|| Changes in N distribution of applied chemical fertilizer,
sewage sludge and poultry manure
In the poultry manure and sewage sludge treatments it is hypothesized that
there was a greater degree of N immobilization, leaving less available labeled
N for mixing with a similar quantity of N from mineralization, thus resulting
in a lower 15N abundance in the final inorganic N pool (Hood
et al., 1999).
Interactions between added fertilizer N from poultry manure, sewage sludge
and native soil N that change the N content in a given pool are called added
N interactions (Jenkinson et al., 1985). These
interactions may result in different estimates for Fertilizer Use Efficiency
(FUE) as shown in Table 3. The relative efficiency of the
poultry manure and sewage sludge can be defined as the uptake rate of poultry
manure, sewage sludge/uptake rate of chemical fertilizer. The relative efficiencies
of sewage sludge and poultry manure were 80 and 85%, respectively (Table
3). The FUE15N value estimated in this study is comparable
to those estimated by direct method (Nishida et al.,
Figure 1 shows the changes in the distribution rate of applied
sewage sludge, poultry manure and chemical fertilizer. There were no significant
differences observed in the N loss rate and the N remaining into soil after
harvesting among treatments. However, some trends may be related to the properties
of the poultry manure and sewage sludge such as higher residual rate of sewage
sludge and poultry manure compared with chemical fertilizer. Further studies
should be conducted to confirm these properties. By monitoring the behavior
of chemical fertilizer added to the soil it was concluded that most of chemical
fertilizer loss was due to dentrification (Nishida et
al., 2004). Although the role of soil microorganisms was not studied,
soil microbes are considered to be closely associated with the uptake of organic
matter and one of the important factors that control the efficiency of organic
matter applied. For instance arbuscular mycorrhizal symbiosis can enhance the
decomposition and increase N capture from complex organic materials in soil
(Chantigny et al., 2001). However, to evaluate
the effect of organic matter application in soil, further studies with various
organic materials labeled with stable isotopes should be carried out in a range
of soils, plants and environmental conditions.
This study was made possible by the financial support of the Ministry of Education, Culture, Sports, Science and Technology, Japan.