ABSTRACT

1
ABSTRACT   Currently most nutrient management
plans incorporate a fixed percentage when
accounting for available organic N in the first
year of manure application. The objectives of
this study were to determine the variability in N
mineralization of dairy manures and to determine
if compositional parameters can be used to
predict the available organic N. Dairy manures
(n107) were collected from farms in MD, VA, PA,
NY, and CT. Manure compositions ranged from 14 to
38.6 g/kg dry matter, 0.9 to 9.5 kg/cubic meter
total N, and 0.3 to 4.7 kg/cubic meter
ammonium-N. Manure-amended soil was aerobically
incubated at 25 C and concentrations of ammonium
N and nitrate N were determined at day 2 and day
56. The manures were highly variable in their N
mineralization characteristics, ranging from a
net mineralization of 55 to a net immobilization
of 29 of the organic N. When the compositional
parameters total N, ammonium N, organic N, total
C, DM, lignin, neutral detergent fiber, acid
detergent fiber, hemicellulose, C/N ratio, and pH
were individually regressed against mineralizable
organic N, the highest coefficient of
determination (r2) was 0.14. A stepwise
regression of all 11 variables yielded a maximal
r2 of 0.25. These results suggest that the
availability of dairy manure organic N is highly
variable and that the availability cannot be
predicted by simple compositional parameters.
Mineralization of Nitrogen in Northeastern Dairy
Manures J. S. Van Kessel and J. B. Reeves
III USDA-ARS, Beltsville Agricultural Research
Center, Beltsville, MD
OBSERVATIONS           Results of sample
analysis indicated that the manures were highly
variable in composition (Table 1) and that a very
diverse set of manure samples had been collected.
This strongly supports the necessity for testing
individual manure storage systems rather than
using standard values for manure
composition.           On average, 12.8 (sd
15.1) of the organic N in this set of dairy
manures was mineralizable. However, there was
net immobilization of N in 19 of the samples as
indicated by a net negative mineralization
value. Within the total set of manures, the net
mineralization ranged from 29.2 to 54.9 (Fig.
1).          There were no strong relationships
between compositional parameters and the
mineralization of organic manure N (Table 2).
The highest correlation coefficient amongst these
relationships was 0.12 for ADF and for CNtotal.
Stepwise regression using all of the
compositional parameters likewise yielded a very
low correlation coefficient (0.11).          
From the data in Fig. 2, it appears that no
relationship could be found between NIR spectral
characteristics and N mineralization. This
implies that no simple relationship exists
between N mineralization and compositional
characteristics such relationships are typically
found with NIR.           While near- and mid-IR
spectroscopy are largely based on the same
principles, the mid-IR is capable of determining
factors not possible by near-IR. The
relationship between mid-IR spectra and N
mineralization was still weak (Fig. 3), but the
results do suggest that there is some
relationship between composition and N
mineralization.
MATERIALS AND METHODS   Manure samples (107)
were collected from dairy farms in five states
(MD, PA, VA, NY, and CT) over a 2-month period in
the fall of 1998. Samples were mixed,
sub-sampled, and stored at 4C. A portion of
each sample was dried (55C) and
ground. Nutrient analysis was conducted at the
Univ. of MD Soil Testing Lab. Dry matter content
was determined at 70C NH4-N was analyzed by
distillation organic N and total C were
determined by combustion (Leco CHN 600 analyzer)
total N was determined by summing NH4-N and
organic N and P and K were analyzed by
perchloric and nitric acid digestion. Dried,
ground samples were analyzed for ADF, NDF, and
lignin (Dairy One DHI Forage Testing Laboratory,
Ithaca, NY) using the ANKOM A200 Filter Bag
Technique. The soil was a Sassafras sandy loam
that was air-dried, sieved through a 2-mm mesh
screen, and mixed. Soil was pre-incubated for
7-10 days (80 g kg-1 moisture 25?C). Prior to
adding manure components, soil moisture was
increased such that the final moisture content of
the incubation mixture would be 150 g kg-1.
Manures were mixed with the soil at a rate such
that the final incubations contained 20 mg of N
per 200 g soil (wet weight basis) or about 117 mg
N kg-1 dry soil. Manure amended soil and
soil-only controls were incubated at 25?C under
aerobic, high humidity conditions. Manures were
mixed with 140 g of soil and covered with 60 g of
soil to trap any volatilized ammonia. Moisture
(150 g kg-1) was maintained by misting the
samples twice weekly. Duplicate pots were
destructively sampled at 2 d and 56 d. An 80 g
sample was extracted with 400 mL of 2 M KCl. The
KCl extracts were analyzed for NH4, NO3-, and
NO2- colorimetrically using a Technicon
autoanalyzer system. Soil moisture, (105C), was
also determined on samples from each container.
All data were adjusted to an oven-dry soil
basis. Manure samples were sealed as is in
polyethylene bags and scanned in the
near-infrared region (400 to 2498 nm, 64 scans,
Model 6500 spectrometer). Dried, ground samples
were scanned in the mid-infrared (4000 to 400
wavenumbers (cm-1), 64 scans, Digilab FTS65
spectrometer).
Table 2 Correlation coefficients of
relationships between compositional parameters
and organic N mineralization ().
Variable R2 Variable R2 Variable R2
Dry matter 0.0011 CTotal N 0.1201 HCellOrgN 0.00
20 Total N 0.0083 COrgN 0.0514 CellOrgN 0.0069 N
H44N 0.0285 NDFNH4-N 0.0743 NDFTotalN 0.0312 O
rg N 0.0000 ADFNH4-N 0.0775 ADFTotalN 0.0294 To
tal C 0.0060 LigninNH4-N 0.0446 LigninTotalN 0.
0081 ADF 0.1211 HCellNH4-N 0.0594 HCellTotatN 0
.0279 NDF 0.0787 CellNH4-N 0.0860 CellTotalN 0.
0446 Lignin 0.0271 NDFOrgN 0.0020 HCell 0.0012
ADFOrgN 0.0019 Cell 0.0917 LigninOrg
N 0.0002
Figure 1 Histogram of organic N
mineralization.
INTRODUCTION   The dairy industry is under
increasing pressure to more efficiently utilize
and recycle nutrients within farms and to
minimize the loss of nutrients into the
environment. One of the critical nutrient
control points is land application of manure.
Over-application of nutrients can lead to
contamination of surface or ground water and
under-application of nutrients can result in
reduced crop yield. Soils in some US regions are
replete in P and manure application is P-based in
these areas, however, application rates have more
typically been based on N. Several pieces of
information are required to estimate the
appropriate rate of manure application including
crop nutrient requirements, soil nutrient supply,
and manure nutrient supply. Determining the
available N in manure is not straightforward.
Although inorganic N is immediately available for
plant uptake, organic N must first be
mineralized. Nitrogen mineralization is a
relatively slow microbial process that is
affected by many factors such as amendment
composition, soil type, temperature, pH,
aeration, and moisture. The rate and extent of N
mineralization over a growing season is very
difficult to predict, and many nutrient
management plans incorporate a single, fixed
value for each manure type. For example,
nutrient management planners in New York State
typically use an organic N decay series to
describe organic N availability over four years.
Organic N is estimated to be 35, 12, 5, and 2
in the first through fourth years of dairy manure
application. A 35 mineralization factor is also
used in Maryland for the first year availability
of the organic N fraction. Estimates of
mineralized organic N from cow manure in the
first year of application are highly variable,
and range from 0 to 50. Clearly some of this
variation can be accounted for by soil type and
conditions, but the variation due to manure
source has not been determined. Previous work
demonstrated that amendment composition could
have a significant impact on the rate and extent
of organic N mineralization. Therefore one might
expect substantial variation in the extent of
mineralization between manures and that this
variation is predictable based on compositional
information.
Figure 2 Final calibration results for
mineralized organic N using NIR spectra.
SUMMARY AND CONCLUSIONS           Although the
in vitro data presented here is not directly
transferable to field values, these data clearly
indicate the inaccuracy of using a fixed
mineralization value to estimate the availability
of manure organic N. If the average
mineralizability was used to determine the
crop-available N from a manure application and
the N from the manure was actually immobilized,
the crop would have insufficient N.
Alternatively, if the mineralizability was at the
other extreme (i.e. 40 50), inorganic N would
be in excess of crop requirements and this may
have detrimental environmental implications.
Both cases are clearly undesirable.          
Determining the mineralization potential of a
manure in the laboratory is a labor-intensive and
time-consuming procedure and a more rapid method
is needed. However, it appears that simple
correlations between compositional factors and
mineralization potential do not yield
satisfactory results. The use of NIR is also
unsatisfactory, however, there is some potential
for the use of mid-IR for determining the
mineralization potential of manures.          
Based on the results of this experiment, there is
a strong need for further research into the
development of rapid methods for predicting the
mineralization potential of dairy manures.
RESULTS
Figure 3 Final calibration results for
mineralized organic N using mid-IR spectra.
OBJECTIVES   1)      To determine the extent of
variation of the organic N availability in dairy
manures. 2)      To determine if organic N
mineralization can be predicted by compositional
factors. 3)      To determine if organic N
mineralization can be determined by near - or mid
- infrared spectroscopy.
2
ABSTRACT   Currently most nutrient management
plans incorporate a fixed percentage when
accounting for available organic N in the first
year of manure application and a variable
percentage for ammonium availability. The latter
number is adjusted depending on spreading or
incorporation strategies but the availability of
organic N and ammonium N are considered
independent of each other. We conducted a study
to determine the variability in N mineralization
of dairy manures and to determine if
compositional parameters can be used to predict
the available organic N. Dairy manures (n107)
were collected from farms in MD, VA, PA, NY, and
CT. Manure compositions ranged from 14 to 38.6
g/kg dry matter, 0.9 to 9.5 kg/cubic meter total
N, and 0.3 to 4.7 kg/cubic meter ammonium-N.
Manure-amended soil was aerobically incubated at
25 C and concentrations of ammonium N and nitrate
N were determined at day 2 and day 56. The
manures were highly variable in their N
mineralization characteristics, ranging from a
net mineralization of 55 to a net immobilization
of 29 of the organic N. When compositional
parameters such as total N, ammonium N, organic
N, total C, DM, lignin, neutral detergent fiber,
acid detergent fiber, hemicellulose, C/N ratio,
and pH were individually regressed against
mineralizable organic N, the highest coefficient
of determination (r2) was 0.14. These results
suggest that the availability of dairy manure
organic N is highly variable and that the
availability cannot be predicted by simple
compositional parameters. It is also clear that
the availability of manure ammonium-N can be
impacted by the mineralization characteristics of
the organic N fraction.
Availability of Nitrogen in Northeastern Dairy
Manures J. S. Van Kessel and J. B. Reeves
III USDA-ARS, Beltsville Agricultural Research
Center, Beltsville, MD
OBSERVATIONS           Results of sample
analysis indicated that the manures were highly
variable in composition (Table 1) and that a very
diverse set of manure samples had been collected.
This strongly supports the necessity for testing
individual manure storage systems rather than
using standard values for manure
composition.           On average, 12.8 (sd
15.1) of the organic N in this set of dairy
manures was mineralizable. However, there was
net immobilization of N in 19 of the samples as
indicated by a net negative mineralization
value. Within the total set of manures, the net
mineralization ranged from 29.2 to 54.9 (Fig.
1).          There were no strong relationships
between compositional parameters and the
mineralization of organic manure N (Table 2).
The highest correlation coefficient amongst these
relationships was 0.12 for ADF and for CNtotal.
Stepwise regression using all of the
compositional parameters likewise yielded a very
low correlation coefficient (0.11).          
From the data in Fig. 2, it appears that no
relationship could be found between NIR spectral
characteristics and N mineralization. This
implies that no simple relationship exists
between N mineralization and compositional
characteristics such relationships are typically
found with NIR.           While near- and mid-IR
spectroscopy are largely based on the same
principles, the mid-IR is capable of determining
factors not possible by near-IR. The
relationship between mid-IR spectra and N
mineralization was still weak (Fig. 3), but the
results do suggest that there is some
relationship between composition and N
mineralization.
MATERIALS AND METHODS   Manure samples (107)
were collected from dairy farms in five states
(MD, PA, VA, NY, and CT) over a 2-month period in
the fall of 1998. Samples were mixed,
sub-sampled, and stored at 4C. A portion of
each sample was dried (55C) and
ground. Nutrient analysis was conducted at the
Univ. of MD Soil Testing Lab. Dry matter content
was determined at 70C NH4-N was analyzed by
distillation organic N and total C were
determined by combustion (Leco CHN 600 analyzer)
total N was determined by summing NH4-N and
organic N and P and K were analyzed by
perchloric and nitric acid digestion. Dried,
ground samples were analyzed for ADF, NDF, and
lignin (Dairy One DHI Forage Testing Laboratory,
Ithaca, NY) using the ANKOM A200 Filter Bag
Technique. The soil was a Sassafras sandy loam
that was air-dried, sieved through a 2-mm mesh
screen, and mixed. Soil was pre-incubated for
7-10 days (80 g kg-1 moisture 25?C). Prior to
adding manure components, soil moisture was
increased such that the final moisture content of
the incubation mixture would be 150 g kg-1.
Manures were mixed with the soil at a rate such
that the final incubations contained 20 mg of N
per 200 g soil (wet weight basis) or about 117 mg
N kg-1 dry soil. Manure amended soil and
soil-only controls were incubated at 25?C under
aerobic, high humidity conditions. Manures were
mixed with 140 g of soil and covered with 60 g of
soil to trap any volatilized ammonia. Moisture
(150 g kg-1) was maintained by misting the
samples twice weekly. Duplicate pots were
destructively sampled at 2 d and 56 d. An 80 g
sample was extracted with 400 mL of 2 M KCl. The
KCl extracts were analyzed for NH4, NO3-, and
NO2- colorimetrically using a Technicon
autoanalyzer system. Soil moisture, (105C), was
also determined on samples from each container.
All data were adjusted to an oven-dry soil
basis. Manure samples were sealed as is in
polyethylene bags and scanned in the
near-infrared region (400 to 2498 nm, 64 scans,
Model 6500 spectrometer). Dried, ground samples
were scanned in the mid-infrared (4000 to 400
wavenumbers (cm-1), 64 scans, Digilab FTS65
spectrometer).
Table 2 Correlation coefficients of
relationships between compositional parameters
and organic N mineralization ().
Variable R2 Variable R2 Variable R2
Dry matter 0.0011 CTotal N 0.1201 HCellOrgN 0.00
20 Total N 0.0083 COrgN 0.0514 CellOrgN 0.0069 N
H44N 0.0285 NDFNH4-N 0.0743 NDFTotalN 0.0312 O
rg N 0.0000 ADFNH4-N 0.0775 ADFTotalN 0.0294 To
tal C 0.0060 LigninNH4-N 0.0446 LigninTotalN 0.
0081 ADF 0.1211 HCellNH4-N 0.0594 HCellTotatN 0
.0279 NDF 0.0787 CellNH4-N 0.0860 CellTotalN 0.
0446 Lignin 0.0271 NDFOrgN 0.0020 HCell 0.0012
ADFOrgN 0.0019 Cell 0.0917 LigninOrg
N 0.0002
Figure 1 Histogram of organic N
mineralization.
INTRODUCTION   The dairy industry is under
increasing pressure to more efficiently utilize
and recycle nutrients within farms and to
minimize the loss of nutrients into the
environment. One of the critical nutrient
control points is land application of manure.
Over-application of nutrients can lead to
contamination of surface or ground water and
under-application of nutrients can result in
reduced crop yield. Soils in some US regions are
replete in P and manure application is P-based in
these areas, however, application rates have more
typically been based on N. Several pieces of
information are required to estimate the
appropriate rate of manure application including
crop nutrient requirements, soil nutrient supply,
and manure nutrient supply. Determining the
available N in manure is not straightforward.
Although inorganic N is immediately available for
plant uptake, organic N must first be
mineralized. Nitrogen mineralization is a
relatively slow microbial process that is
affected by many factors such as amendment
composition, soil type, temperature, pH,
aeration, and moisture. The rate and extent of N
mineralization over a growing season is very
difficult to predict, and many nutrient
management plans incorporate a single, fixed
value for each manure type. For example,
nutrient management planners in New York State
typically use an organic N decay series to
describe organic N availability over four years.
Organic N is estimated to be 35, 12, 5, and 2
in the first through fourth years of dairy manure
application. A 35 mineralization factor is also
used in Maryland for the first year availability
of the organic N fraction. Estimates of
mineralized organic N from cow manure in the
first year of application are highly variable,
and range from 0 to 50. Clearly some of this
variation can be accounted for by soil type and
conditions, but the variation due to manure
source has not been determined. Previous work
demonstrated that amendment composition could
have a significant impact on the rate and extent
of organic N mineralization. Therefore one might
expect substantial variation in the extent of
mineralization between manures and that this
variation is predictable based on compositional
information.
Figure 2 Final calibration results for
mineralized organic N using NIR spectra.
SUMMARY AND CONCLUSIONS           Although the
in vitro data presented here is not directly
transferable to field values, these data clearly
indicate the inaccuracy of using a fixed
mineralization value to estimate the availability
of manure organic N. If the average
mineralizability was used to determine the
crop-available N from a manure application and
the N from the manure was actually immobilized,
the crop would have insufficient N.
Alternatively, if the mineralizability was at the
other extreme (i.e. 40 50), inorganic N would
be in excess of crop requirements and this may
have detrimental environmental implications.
Both cases are clearly undesirable.          
Determining the mineralization potential of a
manure in the laboratory is a labor-intensive and
time-consuming procedure and a more rapid method
is needed. However, it appears that simple
correlations between compositional factors and
mineralization potential do not yield
satisfactory results. The use of NIR is also
unsatisfactory, however, there is some potential
for the use of mid-IR for determining the
mineralization potential of manures.          
Based on the results of this experiment, there is
a strong need for further research into the
development of rapid methods for predicting the
mineralization potential of dairy manures.
RESULTS
Figure 3 Final calibration results for
mineralized organic N using mid-IR spectra.
OBJECTIVES   1)      To determine the extent of
variation of the organic N availability in dairy
manures. 2)      To determine if organic N
mineralization can be predicted by compositional
factors. 3)      To determine if organic N
mineralization can be determined by near - or mid
- infrared spectroscopy.