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Dynamics and Model Fitting ofNitrogen Transformations in PigSlurry Amended SoilsCésar Plaza a , Juan C. García‐Gil a & Alfredo Polo a

a Centro de Ciencias Medioambientales, ConsejoSuperior de Investigaciones Científicas, Madrid,Spain

Version of record first published: 18 Aug 2006.

To cite this article: César Plaza, Juan C. García‐Gil & Alfredo Polo (2005):Dynamics and Model Fitting of Nitrogen Transformations in Pig Slurry Amended Soils,Communications in Soil Science and Plant Analysis, 36:15-16, 2137-2152

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Dynamics and Model Fitting of NitrogenTransformations in Pig Slurry

Amended Soils

Cesar Plaza, Juan C. Garcıa-Gil, and Alfredo Polo

Centro de Ciencias Medioambientales, Consejo Superior de

Investigaciones Cientıficas, Madrid, Spain

Abstract: To optimize the efficient use of nutrients in pig slurry by crops and to reduce

the pollution risks to surface and groundwater, a full knowledge of the fate of nitrogen

(N) in amended soils is needed. A 120 day laboratory incubation experiment was

conducted to study the effects of pig slurry application on soil N transformations.

Pig slurry was added at the rates of 50 and 100 g kg21. A nonamended soil was used

as a control treatment. Soil samples were taken after 0, 7, 14, 30, 45, 60, and 120

days of incubation and analyzed for NH4þ-N and NO3

2-N. Initially, the application of

pig slurry produced significant increases in NH4þ-N, especially at the highest appli-

cation rate, whereas NO32-N content was not affected. Nitrification processes were

active during the entire incubation time in the three treatments. In the control soil,

the net N mineralization rate was highest during the 1st week (5.7 mg kg21 d21),

followed by a low-steady phase. Initially, net N mineralization rate was slower in

soil with the lowest slurry rate (2.7 mg kg21 d21), whereas in the treatment with the

highest slurry rate, a net N immobilization was observed during the 1st week

(4.8 mg kg21 d21). Mineral-N concentrations after 120 days were 180, 310, and

475 mg kg21 in soils amended with 0, 50, and 100 g kg21 of pig slurry, respectively.

However, when results were expressed as net mineralized N, the opposite trend was

observed: 74, 65, and 44 mg kg21. Of the six kinetic models tested to describe the min-

eralization process, a two-component, first exponential model (double model) offered

the best results for all treatments.

Keywords: Pig slurry, soil amendment, N mineralization, incubation

Received August 2004, Accepted November 2004

Address correspondence to Cesar Plaza, Centro de Ciencias Medioambientales,

Consejo Superior de Investigaciones Cientıficas, Serrano 115 dpdo., 28006 Madrid,

Spain. E-mail: c.plaza@ccma.csic.es

Communications in Soil Science and Plant Analysis, 36: 2137–2152, 2005

Copyright # Taylor & Francis, Inc.

ISSN 0010-3624 print/1532-2416 online

DOI: 10.1080/00103620500194668

2137

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INTRODUCTION

Pig production has increased dramatically in Spain from 6 to 22 million pigs

between 1970 and 2000, according to statistical data from the Agricultural

Ministry. Furthermore, most farmers have turned to confined animal oper-

ations, where collected wastes are often generated as slurries (i.e., a mixture

of feces, urine, and cleaning water) in large volume. Pig slurry is a low-cost

alternative to mineral fertilizers. It provides a valuable source of N and

other nutrients for crop and forage production (Sharpley and Smith 1995),

and it frequently compares favorably with inorganic fertilizers (Bernal et al.

1992). However, improper manure management practices, such as overappli-

cation, can cause contamination of surface and ground water (Spalding and

Exner 1993; Gangbazo et al. 1995). Many of these problems occur because

of the lack of a clear understanding of the soil-plant system’s ability to

safely assimilate waste materials.

As excreted by the pig, N is in an almost entirely organic state, but urea

and some labile organic compounds are rapidly converted to ammonium

(Flowers and O’Callaghan 1983; Beline 1998). In stored slurry, about half

the total N is usually present in the ammonium form, and other inorganic

forms are generally absent (Evans et al. 1978; Beline et al. 1998; Beline

et al. 2001). Therefore the remaining N is in organic forms of varying resis-

tance to microbial decomposition. From a practical point of view, Sluijmans

and Kolenbrander (1977) recognized three fractions of N in pig slurry:

inorganic N, organic N mineralizable in the year of application, and

resistant organic N, which mineralizes only in subsequent years. McCalla

et al. (1977) suggested that the organic N fraction of animal waste consists

mainly of two forms: 1) proteins that have resisted animal digestion, which

are generally combined with lignin or lignin-like substances and 2) dead

and living microbial cells from the intestinal tract.

After the application of pig slurry to soil, the ammonium contained in it

may be lost by volatilization, fixed by clay minerals, immobilized through

microbial growth, or oxidized to nitrate (nitrification), which can also be lost

by denitrification or leaching. Organic N of pig slurry may be mineralized in

the first phase of ammonium formation (ammonification) and followed by

the same pattern as previously described. As with other chemical and biochemi-

cal reactions in soils, mineralization of organic N is a waste dependent on

the physical and chemical characteristics of the waste itself, as well as those

of the soil receiving the waste material (Chae and Tabatabai 1986), the rate

used, the application methods and timing, and the environmental factors (De

Neve et al. 1996; Benıtez et al. 1998; Honeycutt 1999). It is evident that the

particular characteristics of pig slurry (high pH, high ammonium content,

and often high copper concentration) may affect the transformations of N in

the soil differently than other organic wastes (Flowers and Arnold 1983).

Therefore, the considerable body of information on the fate of other organic

materials in the soil may not be applicable to the N in animal slurries.

C. Plaza, J. C. Garcıa-Gil, and A. Polo2138

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To optimize the efficiency of pig slurry use by crops and to reduce the

pollution risks to surface and groundwater, a full knowledge of the fate of

N in amended soils is needed to provide reliable information regarding the

amount of plant-available N supplied by this waste. Plant-available N is

defined as the sum of initial NO32-N and NH4

þ-N not lost through volatilization

or denitrification plus the organic N that is mineralized for a given time period

(Gilmour and Skinner 1999). For its determination, laboratory methods

involving incubation of soil-waste mixtures under controlled conditions that

promote mineralization of soil N are useful tools (King 1984; Serna and

Pomares 1992; Rogers et al. 2001). Furthermore, laboratory incubations are

also the most widely applied procedures used to develop mathematical

models describing the mineral-N release in soils, which may be applicable

to field conditions (Serna and Pomares 1992; Sanchez et al. 1997). The expo-

nential model proposed by Stanford and Smith (1972) is the most widely used,

although other types have also been tried [e.g., the double exponential model

(Molina et al. 1980), the special model (Bonde and Roswall 1987), the

parabolic model (Broadbent 1986; Marion and Black 1987), the hyperbolic

model (Juma et al. 1984), or the zero-order kinetic equation (Addiscott

1983)].

The objectives of the present work were to study the dynamics of N in pig

slurry amended soils during a 120-day incubation, with special attention on

the mineralization and nitrification processes, to evaluate the influence of

pig slurry rate on N transformations, and to compare the goodness of fit of

six regression models using data of mineral-N released during the incubation.

MATERIALS AND METHODS

Pig Slurry and Soil

A sample of pig slurry was collected from an intensive swine farm, which uses

a closed-cycle production system and is placed in the Toledo province of

Spain. The pig slurry sample was characterized by a small dry matter

content (22.4 g L21), a slightly alkaline pH (7.3), large electrical conductivity

value (19.5 dS m21), a relatively small amounts of total organic C

(11.0 g L21), NO32-N (42 mg L21), and relatively large total N and NH4

þ-N

contents (4.9 g L21 and 3.2 g L21, respectively), with respect to the values

commonly reported for this material (Vanderholm 1984; Ndayegamiye and

Cote 1989).

The soil sample used in this experiment was taken from the arable layer

(Ap horizon, 0–20 cm depth) of a Typic Haploxeralf (Soil Survey Staff 1998)

cropped to barley (Hordeum vulgare L.), which is placed in the experimental

station “La Higueruela” (Toledo, Spain), close to the pig farm. This soil is

representative of the Spanish Mediterranean region and is characterized by

a sandy loam texture (sand 59%, silt 22%, and clay 19%), slightly acidic

N Transformations in Pig Slurry Amended Soils 2139

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pH (5.8), a low electrical conductivity (0.06 dS m21), and low contents of total

organic C (12.9 g kg21), total N (1.2 g kg21), NH4þ-N (86 mg kg21), and NO3

2-N

(20 mg kg21).

Incubation Procedure and Chemical Analysis

The effects of pig slurry application to soil at the rates of 150 (PS150) and

300 m3 ha21 (PS300) in a laboratory aerobic incubation were compared

with a control (soil without fertilization, C). The experiment was carried out

in 500-mL open plastic containers, into which 500 g of air-dried and 2-mm

sieved soil were placed and homogeneously mixed with either 0, 25, or 50 g

of pig slurry, which corresponded to the studied rates assuming a soil bulk

density of 1.5 Mg m23 in the top 20 cm. Three replicates were performed

for each treatment, and, to prevent unnecessary disturbance of the mixtures

by frequent sampling, the three treatments were replicated the number of

times a sample was to be taken (i.e., seven). Water was added to an equivalent

of 60% of the soil water-holding capacity and the containers were incubated in

the dark at 288C to create favorable conditions for biological processes.

Moisture losses were monitored by periodic weighting the containers during

the incubation period and corrected by the addition of deionized water.

Soil samples were taken at 0, 7, 14, 30, 45, 60, and 120 days and analyzed

for NH4þ-N and NO3

2-N contents. NH4þ-N and NO3

2-N were extracted by

shaking the soil with 2 M KCl at a 1 : 10 soil to extractant ratio for 1 h and

subsequently determined by standard colorimetric procedures (Keeney and

Nelson 1982) by using a Technicon Autoanalyzer AAII (Buffalo Grove,

IL). Nitrogen losses by ammonia volatilization were also measured by using

the method described by Polo et al. (1983). In agreement with previous

studies (Flowers and Arnold 1983; Bernal and Roig 1993; Dendooven et al.

1998), negligible amounts of NH3-N were measured during the entire

incubation period (results not shown).

The Models

The six models used in this study to describe N mineralization in soils are

defined by the following equations. The first model, referred to herein as

linear, describes a zero-order kinetics (Addiscott 1983):

Nt ¼ kt ð1Þ

where Nt is the mineral-N (mg kg21) at time t (d) and k is the mineralization

constant (mg kg21 d21). The second model (parabolic) is a parabolic equation

(Broadbent 1986; Marion and Black 1987):

Nt ¼ Atkp ð2Þ

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where A and kp are the regression coefficients. The third model (single

exponential) is a first-order exponential equation (Stanford and Smith 1972):

Nt ¼ N0ð1� e�k0tÞ ð3Þ

where N0 is the potentially mineralizable N (mg kg21) and k0 is the miner-

alization rate constant (d21). The fourth model (double exponential) is also

a first-order exponential equation but with two components (Molina et al.

1980):

Nt ¼ N1ð1� e�k1tÞ þ N2ð1� e�k2tÞ ð4Þ

where N1 and N2 represent the active and resistant pools decomposing at

specific rates of k1 and k2. The sum of N1 and N2 has the same physical

meaning as N0 in Eq. (3) (Deans et al. 1986). The fifth model (special)

proposes an approximation of the double exponential model in the case of

short incubation compared with the half-life of a large resistant pool (Bonde

and Roswall 1987):

Nt ¼ Nað1� e�katÞ þ Ct ð5Þ

where Na and ka have the same meaning of N1 and k1 in Eq. (5) and C (d21)

is a constant identified by the authors as the product of the large resistant N

pool mineralizing at a low and constant rate. The last model (hyperbolic) is

a hyperbolic equation (Juma et al. 1984):

Nt ¼Nht

bNh þ tð6Þ

where Nh is the potentially mineralizable N and b is a constant (d kg mg21).

Despite the differences in the mathematical expressions, the single expo-

nential, double exponential and hyperbolic models have the same feature of

including one or more components that supposedly represent a definable

soil organic N pool with a corresponding mineralization rate constant.

Estimated N0 have been widely used as indices of soil organic N availability

for determining the effects of various agricultural practices on soil fertility

(Dou et al. 1996).

Statistical Analysis

The results were statistically analyzed by two-factor ANOVA (rate applied

and incubation time were the factors), and mean separation was performed

with the least significant difference (LSD) test when F-test was significant

at a 0.05 probability level.

The models were fitted to the observed Nt vs. t data set by using the

nonlinear regression procedure with the Quasi-Newton iterative method in

Statistica 4.0 program for Windows, using a criterion for convergence of

N Transformations in Pig Slurry Amended Soils 2141

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1027. The goodness of fit provided for each model was analyzed by means of

the coefficient of determination (R2) between the cumulative mineral-N

predicted by the equations and that experimentally measured at the

sampling times considered during the incubation (n ¼ 7).

RESULTS AND DISCUSSION

Ammonium and Nitrate Dynamics

Concentrations of NH4þ-N and NO3

2-N in control soil and soils amended with

pig slurry during the incubation are shown in Tables 1 and 2, respectively. The

application of pig slurry initialy increased soil NH4þ-N content, especially at

the higher rate, but the NO32-N concentration was not affected because of

the low amount contained within the slurry. The mineral-N content (NH4þ-N

and NO32-N) of extracts was initially dominated by NH4

þ in all treatments,

ranging from 81.3% in the control soil to 95.4% in the soil amended with

the highest rate. During the first 7 days, the NH4þ-N concentration diminished

in all soils. In the control, NH4þ-N was not detected after then, whereas in soils

amended with pig slurry, elevated levels of NH4þ-N were observed until the

2nd and 4th weeks.

The NH4þ-N persistence during the early stages of the incubation in soils

amended with pig slurry may be attributed to the large quantities added,

because the net decrease was more pronounced in these treatments than in

the control and was even greater as the application rate increased, which

rules out an inhibition in the growth of the nitrifier microorganisms or the

communities able to immobilize it.

Table 1. NH4þ-N concentration in soils amended with pig slurry at rates of 0 (C), 150

(PS150), and 300 m3 ha21 (PS300) during the incubation time

Treatment

Incubation time (d) [mg kg21]

0 7 14 30 45 60 120

C 86 c 0 f 0 f 0 f 0 f 0 f 0 f

PS150 225 b 64 d 0 f 0 f 0 f 0 f 0 f

PS300 411 a 221 b 28 e 0 f 0 f 0 f 0 f

Analysis of variance

Factors df F p value

Rate 2 2016.96 0.0000���

Time 6 4183.31 0.0000���

Rate � time 12 769.73 0.0000���

Values followed by the same letter are not significantly different according to LSD

test (p ¼ 0.05).���p , 0.001; ��p , 0.01; �p , 0.05.

C. Plaza, J. C. Garcıa-Gil, and A. Polo2142

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Biological oxidation of NH4þ to NO2

2 is the first phase in nitrification and

this process is widely carried out by quimioautotrophic bacteria (mainly Nitro-

somonas, Nitrosolobus and Nitrosospira), which use the NH4þ oxidation as an

energy source and assimilate C from carbon dioxide by the Calvin cycle. In a

second phase, the NO22 oxidizes to NO3

2 mainly by the action of Nitrobacter

bacteria. Hastings et al. (1997) found members of Nitrosospira genera in pig

slurry-amended and nonamended soils that were independent of the amount

of the slurry applied. However, they only detected members of Nitrosomonas

genera in those soils that had received large amounts of slurry. Flowers and

O’Callaghan (1983), in a similar incubation experiment, did not find signifi-

cant differences in the number of Nitrosomonas between the control and

soils amended with pig slurry. However, the number of Nitrobacter in the

amended soils was much higher than in the control.

The NO32-N accumulation in soils did not show any initial lag period and

increased significantly as NH4þ-N diminished in all treatments, indicating that

the microorganisms responsible for nitrification were active from the

beginning of the incubation. In addition, the nitrification rate during the 1st

week was higher in the treated soils than in the control, due to the addition

of NH4þ and therefore oxidizable substrate to NO3

2. Nevertheless, the nitrifica-

tion rate in the 1st week was slightly smaller for the high-rate treatment

compared with the lower rate, displaying, on the contrary, a greater diminution

of NH4þ-N. This result suggests a greater contribution of the immobilization

processes in these treatments. Small increases in the concentration of NO32-

N were noted in all treatments from the NH4þ-N pool exhaustion until the

end of the experiment, indicating organic N mineralization. After 120 days

of incubation, the NO32-N concentration was significantly greater in the

Table 2. NO32-N concentration in soils amended with pig slurry at rates of 0 (C), 150

(PS150), and 300 m3 ha21 (PS300) during the incubation time

Treatment

Incubation time (d) [mg kg21]

0 7 14 30 45 60 120

C 20 g 146 f 150 f 164 f 167 ef 173 ef 180 ef

PS150 20 g 200 e 280 d 282 d 289 d 304 d 310 d

PS300 20 g 176 ef 384 c 440 b 456 ab 464 ab 475 a

Analysis of variance

Factors df F p value

Rate 2 1188.10 0.0000���

Time 6 607.68 0.0000���

Rate � time 12 72.64 0.0000���

Values followed by the same letter are not significantly different according to LSD

test (p ¼ 0.05).���p , 0.001; �p , 0.05.

N Transformations in Pig Slurry Amended Soils 2143

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amended soils than in the control, especially in the treatment with the higher

rate of slurry.

Mineralization Rate and Total Nitrogen Mineralized

The concentrations of mineral-N in the control and the amended soils are

shown in Table 3. The incorporation of pig slurry to soil initially produced

a significant increase in inorganic N, especially in the higher-rate treatment.

In the control soil and in that amended with the lower rate, the mineral-N con-

centration increased throughout the incubation, especially in the early stages.

However, the soil amended with the higher slurry rate (PS300) showed a dim-

inution during the 1st week due to microbial immobilization, which was

followed by an increase of the inorganic N concentration until the end of

the incubation. Other studies of incubation also indicate that the addition of

pig slurry (Flowers and Arnold 1983; Bernal and Kirchmann 1992; Morvan

et al. 1997) or other manures (Chae and Tabatabai 1986; Sims 1986) to soil

can give rise to an initial phase of immobilization due to the presence of

easily biodegradable carbon sources. The greater NH4þ addition at the

higher rate may have increased the rate of degradation of the waste by

means of stimulation of the soil microorganisms, resulting in an increase in

the immobilization process. King (1984) and Rogers et al. (2001) also

found an increase in immobilization when adding NH4þ-N to wastes used as

organic amendments.

As noted previously, the evolution of nitrate was parallel to the mineral-N

after the exhaustion of ammonium in soils occurred a few weeks into the

Table 3. Mineral-N (NH4þ-NþNO3

2-N) concentration in soils amended with pig

slurry at rates of 0 (C), 150 (PS150), and 300 m3 ha21 (PS300) during the incubation

time

Treatment

Incubation time (d) [mg kg21]

0 7 14 30 45 60 120

C 106 i 146 h 150 h 164 h 167 h 173 h 180 h

PS150 245 g 264 fg 280 ef 282 ef 289 ef 304 e 310 e

PS300 431 bcd 397 d 412 cd 440 bc 456 ab 464 ab 475 a

Analysis of variance

Factors df F p value

Rate 2 2191.17 0.0000���

Time 6 24.24 0.0000���

Rate � time 12 2.59 0.0113�

Values followed by the same letter are not significantly different according to LSD

test (p ¼ 0.05).���p , 0.001; ��p , 0.01; �p , 0.05.

C. Plaza, J. C. Garcıa-Gil, and A. Polo2144

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experiment indicating that nitrification was proceeding as fast as mineraliz-

ation. As a result, the ammonification rate governed the rate of nitrification

and, subsequently, the mineralization process.

The net N mineralization rate, calculated as the measured amount of

mineral-N in each extract sample divided by the amount of soil and the

span of weeks from the last sampling, evolved differently in each of the

three treatments. In the control soil, the mineralization rate reached its

highest value in the 1st week (5.7 mg kg21 d21), diminished in the 2nd

week, and entered into a low steady phase until the end of the incubation

(Figure 1). These two distinct phases could be interpreted as the result of

both substrate availability and microbial characteristics: 1) the rapid

degradation by the zymogenous microbes of readily available organic

material originating in the soil, released during drying-rewetting, and

microbial cells lysed during the soil sample preparation and 2) the subsequent

slow-steady degradation of more resistant organic matter by autochthonous

microbes (Paul and Clark 1988; Dou et al. 1996). In PS150 treatment, net N

mineralization rate was lower than the control (2.7 mg kg21 d21) initially,

although it was greater in the 2nd week. In the PS300 treatment, a net N immo-

bilization was observed during the 1st week (33 mg kg21), followed by a net

mineral-N release that remained higher than the control treatment and the

PS150 treatment for 45 days At 120 days, the net mineralization rate was

insignificant in all three treatments.

The cumulative mineral-N content after 120 days was 180 mg kg21 in the

control, 310 mg kg21 in the PS150 treatment and 475 mg kg21 in the PS300

Figure 1. Net N mineralization rate during a 120-day incubation for control soil (C)

and soil amended with pig slurry at rates of 150 (PS150) and 300 m3 ha21 (PS300).

N Transformations in Pig Slurry Amended Soils 2145

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treatment. When results are expressed as net mineralized N (i.e., the measured

amount of mineral-N in each extract after 120 days minus the amount at the

beginning of the experiment), the opposite trend is observed: 74, 65, and

44 mg kg21 in soils amended with 0, 150, and 300 m3 ha21 of pig slurry,

respectively. Furthermore, it can be noted that, at the high rate of pig slurry,

490 mg kg21 of total N was added, of which 324 mg kg21 is inorganic. The

other rate of pig slurry added the half of these amounts. Subtracting the

control soil values from the overall mineral-N content of pig slurry-amended

soils at 120 days only about 50–60% of the added N was accounted for in

mineral form. This is about the same percentage of mineral N added initially

added with the pig slurry, which might indicate that the net mineralization of

organic N of pig slurry was essentially negligible.

Several studies, including the present, have been unable to show a net

mineralization in pig slurry-amended soils that was greater than the control

soil, which could be attributed to mineralization of the slurry organic N

(Germon et al. 1979; Flowers and Arnold 1983). These results indicate that

significant amounts of N added with pig slurry may have been lost from the

system over the time of incubation, probably by denitrification and/or

fixation in 2 : 1 clays. Furthermore, there are indications in the literature that

increasing concentrations of mineral N may inhibit decomposition of recalci-

trant material (e.g., lignin) (Fog 1988; Carreiro et al. 2000). These may explain

the increase in the resistance in the decomposition of organic N in pig slurry-

amended soils, although we should not discard the possibility that slurry may

produce a residual effect in soils for the following years after its application

because of long-term organic N mineralization (Bernal and Roig 1993).

Model Fitting

The estimated parameters for six regression models used to describe the data

when the mineral-N accumulation was analyzed as a function of time are listed

in Table 4. Except for the linear equation, all other models offered a good

description of N mineralization kinetics in the control soil and the PS150

treatment (p , 0.001), especially the double exponential model. Never-

theless, when describing the release of net mineral-N in the PS300

treatment, the double exponential and, to a lesser extent, the special model

were significantly better than the others.

The fact that the linear model showed the worst fit to the experimental

data indicates that the degradability of the organic N varied with the incu-

bation time. On the other hand, the main problem with the potential, single

exponential, and hyperbolic models in the PS300 treatment is that cumulative

mineral-N is overestimated in the first 14 days of incubation (Figure 2). That

is, these are unable to take into account periods of net immobilization. In

addition, because soil organic matter is composed of heterogeneous sub-

stances with varying degrees of resistance to mineralization and, considering

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the different phases of microbial activity during the degradation of substrates,

any model that considers multiple N pools, such as the double exponential and

the special models, should be more accurate.

The experimentally obtained values of net mineral-N at the end of the

incubation for the control and the PS150 treatments were higher than the

estimated values of potentially mineralizable N (N0) with the single exponen-

tial model. This result shows another weakness of the single model, because

by definition, N0 is supposedly the upper limit of potentially mineralizable

N and, therefore, it should be greater than the observed cumulative mineral-

N at 120 days. In agreement with the conclusions of other authors

(Dendooven et al. 1990; Dou et al. 1996), the results of the present study

indicate that the parameters derived from this model do not represent the

Table 4. Estimated parameters and coefficients of determination (R2) for control soil

(C) and soil amended with 150 (PS150) and 300 m3 ha21 (PS300) of pig slurry using

the linear, potential, single exponential, double exponential, special and hyperbolic

model

Treatment

Model Parameter C PS150 PS300

Linear k 0.863 0.711 0.388

R2 0.5783� 0.7510� 0.7068�

Potential A 26.2 11.4 0.1

kp 0.222 0.371 1.224

R2 0.9933��� 0.9634��� 0.6697�

Single

exponential

N0 66 62 1001

k0 0.096 0.040 0.0004

R2 0.9559��� 0.9389��� 0.7102�

Double

exponential

N1þN2 75 74 46

N1 32 21 256

k1 2.592 0.196 12.493

N2 43 52 102

k2 0.028 0.016 0.034

R2 0.9975��� 0.9710��� 0.9993���

Special Na 53 26 220

ka 0.155 5.123 96.869

C 0.182 0.367 0.645

R2 0.9861��� 0.9155��� 0.7650��

Hyperbolic Nh 75 74 224504

b 0.105 0.292 2.575

R2 0.9856��� 0.9580��� 0.7069�

���p , 0.001; ��p , 0.01; �p , 0.05.

N Transformations in Pig Slurry Amended Soils 2147

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potential of N mineralization in the soil but, instead, are merely mathematical

parameters obtained by the regression analysis. However, this equation can be

useful in providing a mathematical description of N mineralization kinetics

(e.g., in computer models simulating the N cycle in biological systems).

Figure 2. Comparisons of the observed cumulative mineral-N vs that predicted by

the models for control soil (C) and soil amended with 150 (PS150) and 300 m3 ha21

(PS300) of pig slurry. Error bars indicate the standard errors of the mean of the

observed data (n ¼ 3).

C. Plaza, J. C. Garcıa-Gil, and A. Polo2148

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The double exponential model provided values of potentially mineraliz-

able N (calculated as the sum of N1 and N2), of 75, 74, and 46 mg kg21 for

the soils with 0, 150 and 300 m3 ha21 of pig slurry, respectively. As can be

noted, the values for the control and the treatment with the higher rate of

slurry were similar to the net cumulative mineral-N at the end of the incu-

bation, which indicates, in agreement with King (1984), that a period of 16

weeks was sufficient for the potentially available N to be mineralized in this

soil. Nevertheless, the lower rate treatment indicated an exception to this

rule, because it resulted in a slightly lower mineral-N concentration

compared with the value of potentially mineralizable N. This result

suggested that more inorganic N would have been released in this soil with

more incubation time. On the other hand, the mineralization rate, reflected

by the constants k1 and k2, was greater in the control soil that in the soil

with the lower rate of pig slurry. For the treatment with the higher rate, the

constants were much higher, although in this case k1 represented the speed

of the process of net immobilization, because the first term of the equation

was negative.

The hyperbolic model produced values of potentially mineralizable N

similar to the double exponential model for both the control and the PS150

treatment. Nevertheless, the value for the PS300 treatment was nonrealistic,

because it overstated the total N initially present in the soil. Finally, with the

special model it was not possible to estimate values of N mineralization poten-

tial, although the equation has a component that represents an active N pool.

CONCLUSIONS

Nitrification and mineralization rates and the potentially mineralizable N in

the soil varied with the pig slurry rate. The amount of N added as NH4þ was

larger than that added as organic N, and the amount of inorganic N released

by mineralization of organic N in amended soils was small, even smaller

than in the nonamended soil. As a whole, results obtained would suggest

that about 75% of the mineral N contained in pig slurry is plant available

during an initial growing season. Furthermore, it can be inferred that the

amount and transformations of NH4þ added with pig slurry and its effects on

turnover of organic matter play a fundamental role in any reliable recommen-

dation of rates and timing of application to ensure the maximum benefit for the

crops and the minimum environmental impact. An excessive rate of nitrifica-

tion before the plant is in an advanced development state could result in high

losses of N by leaching or denitrification and, therefore, considerably

increasing the risk of contamination. Nevertheless, it is difficult to

determine when NH4þ-N will be nitrified, how much will be lost by volatiliz-

ation, leaching or denitrification, and how much organic N will be converted

into plant-available forms under field conditions. One option is to apply pig

slurry in rates less than the agronomic application rate, based on inorganic

N Transformations in Pig Slurry Amended Soils 2149

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N concentration and predicted potentially mineralizable N, and to supply

additional mineral-N as needed (e.g., based on a fast soil NO32 test)

(Heckman et al. 1995). The use of nitrification inhibitors to prolong the life

of NH4þ-N in soil until the plant requires higher amounts of N could be a

very useful alternative that may increase the efficiency of pig slurry as a N

fertilizer.

ACKNOWLEDGMENTS

We thank Consejerıa de Agricultura y Medio Ambiente de la Junta de

Comunidades de Castilla-La Mancha for their financial support.

REFERENCES

Addiscott, T.M. (1983) Kinetics and Temperature Relationships of Mineralization andNitrification in Rothamsted Soils with Differing Histories. Journal of Soil Science,34: 343–353.

Beline, F., Martınez, J., Marol, C., and Guiraud, G. (1998) Nitrogen TransformationsDuring Anaerobically Stored 15N-labelled Pig Slurry. Bioresource Technology,64: 83–88.

Beline, F., Martınez, J., Marol, C., and Guiraud, G. (2001) Application of the 15NTechnique to Determine the Contributions of Nitrification and Denitrification tothe Flux of Nitrous Oxide from Aerated Pig Slurry. Water Research, 35: 2774–2778.

Benıtez, C., Bellido, E., Gonzalez, J.L., and Medina, M. (1998) Influence ofPedological and Climatic Factors on Nitrogen Mineralization in Soils Treatedwith Pig Slurry Compost. Bioresource Technology, 63: 147–151.

Bernal, M.P. and Roig, A. (1993) Nitrogen Transformations in Calcareous SoilsAmended with Pig Slurry Under Aerobic Incubation. Journal of AgriculturalScience, 120: 89–97.

Bernal, M.P. and Kirchmann, H. (1992) Carbon and Nitrogen Mineralization andAmmonia Volatilisation from Fresh, Aerobically and Anaerobically Treated PigManure During Incubation with Soil. Biology and Fertility of Soils, 13: 135–141.

Bernal, M.P., Roig, A., Lax, A., and Navarro, A.F. (1992) Effects of the Application ofPig Slurry on some Physico-Chemical and Physical Properties of Calcareous Soils.Bioresource Technology, 42: 233–239.

Bonde, T.A. and Roswall, T. (1987) Seasonal Variation of Potentially MineralizableNitrogen in Four Cropping Systems. Soil Science Society America Journal, 51:1508–1514.

Broadbent, F.E. (1986) Empirical Modelling of Soil Nitrogen Mineralization. SoilScience, 141: 208–213.

Carreiro, M.M., Sinsabaugh, R.L., Repert, D.A., and Parkhurst, D.F. (2000) MicrobialEnzymes Shifts Explain Litter Decay Responses to Simulated Nitrogen Deposition.Ecology, 81: 2359–2365.

Chae, Y.M. and Tabatabai, M.A. (1986) Mineralization of Nitrogen in Soils Amendedwith Organic Wastes. Journal of Environmental Quality, 15: 193–198.

De Neve, S., Pannier, J., and Hofman, G. (1996) Temperature Effects on C and NMineralization from Vegetable Crop Residues. Plant and Soil, 181: 25–30.

C. Plaza, J. C. Garcıa-Gil, and A. Polo2150

Dow

nloa

ded

by [

Duk

e U

nive

rsity

Lib

rari

es]

at 0

6:12

18

Oct

ober

201

2

Deans, J.R., Molina, J.A.E., and Clapp, C.E. (1986) Models for Predicting Potentially

Mineralizable Nitrogen and Decomposition Rate Constants. Soil Science Society of

America Journal, 50: 323–326.

Dendooven, L., Bonhomme, E., Merckx, R., and Vlassak, K. (1998) N Dynamics and

Sources of N2O Production Following Pig Slurry Application to a Loamy Soil.

Biology and Fertility of Soils, 26: 224–228.

Dendooven, L., Verstraeten, L., and Vlassak, K. (1990) The N-Mineralization

Potential: An Undefinable Parameter. In Fetilization and the Environment;

Merckx, R., Vereecken, H. and Vlassak, K., eds.; Leuven University Press:

Leuven, Belgium, 170–181.

Dou, Z., Toth, J.D., Jabro, J.D., Fox, R.H., and Fritton, D.D. (1996) Soil Nitrogen

Mineralization during Laboratory Incubation: Dynamics and Model Fitting. Soil

Biology and Biochemistry, 28: 625–632.

Evans, M.R., Hissett, R., Smith, M.P.W., and Ellam, D.F. (1978) Characteristics of

Slurry from Fattening Pigs. Agriculture and Environment, 4: 77–83.

Flowers, T.H. and O’Callaghan, J.R. (1983) Nitrification in Soils Incubated with Pig

Slurry or Ammonium Sulphate. Soil Biology and Biochemistry, 15: 337–342.

Flowers, T.H. and Arnold, P.W. (1983) Immobilization and Mineralization of Nitrogen

in Soils Incubated with Pig Slurry or Ammonium Sulphate. Soil Biology and Bio-

chemistry, 15: 29–335.

Fog, K. (1988) The Effect of Added Nitrogen on the Rate of Decomposition of Organic

Matter. Biological Reviews, 63: 433–462.

Gangbazo, G., Pesant, A.R., Barnett, G.M., Chauruest, J.P., and Cluis, D. (1995) Water

Contamination by Ammonium Nitrogen Following the Spreading of Hog Manure

and Mineral Fertilizers. Journal of Environmental Quality, 24: 420–425.

Germon, J.C., Giraud, J.J., Chaussod, R., and Duthion, C. (1979) Nitrogen Mineralis-

ation and Nitrification of Pig Slurry Added to Soil in Laboratory Conditions. In

Modelling Nitrogen from Farm Wastes; Gasser, J.K.R., ed.; Applied Science Pub-

lishers Ltd.: London, 170–184.

Gilmour, J.T. and Skinner, V. (1999) Predicting Plant Available Nitrogen in Land

Applied Biosolids. Journal of Environmental Quality, 28: 1122–1126.

Hastings, R.C., Ceccherini, M.T., Miclaus, N., Saunders, J.R., Bazzicalupo, M., and

McCarthy, A.J. (1997) Direct Molecular Biological Analysis of Ammonia

Oxidising Bacteria Populations in Cultivated Soil Plots Treated with Swine

Manure. FEMS Microbiology Ecology, 23: 45–54.

Heckman, J.R., Hlubik, W.T., Prostak, D.J., and Paterson, J.W. (1995) Pre-side Soil

Nitrate Test for Sweet corn. HortScience, 30: 1033–1036.

Honeycutt, C.W. (1999) Nitrogen Mineralization from Soil Organic Matter and Crop

Residues: Field Validation of Laboratory Predictions. Soil Science Society of

America Journal, 63: 134–141.

Juma, N.G., Paul, E.A., and Mary, B. (1984) Kinetic Analysis of Net Nitrogen

Mineralization in Soil. Soil Science Society of America Journal, 48: 753–757.

Keeney, D.R. and Nelson, D.W. (1982) Nitrogen-Inorganic Forms. In Methods of Soil

Analysis, Part 2, Chemical and Microbiological Properties, 2nd edition; Page, A.L.,

Miller, R.H. and Keeney, D.R., eds.; ASA: Madison, Wisconsin, 643–698.

King, L.D. (1984) Availability of Nitrogen in Municipal, Industrial and Animal

Wastes. Journal of Environmental Quality, 13: 609–612.

Marion, G.M. and Black, C.H. (1987) The Effect of Time and Temperature on Nitrogen

Mineralization in Arctic Tundra Soils. Soil Science Society of America Journal, 51:

1501–1508.

N Transformations in Pig Slurry Amended Soils 2151

Dow

nloa

ded

by [

Duk

e U

nive

rsity

Lib

rari

es]

at 0

6:12

18

Oct

ober

201

2

McCalla, T.M., Peterson, J.R., and Jue-Hing, C. (1977) Properties of Agricultural andMunicipal Wastes. In Soils for the Management of Organic Wastes and WasteWaters; Elliot, L.F. and Stevenson, F.J., eds.; ASA, CSSSA, and SSSA: Madison,Wisconsin, 11–43.

Molina, J.A.E., Clapp, C.E., and Larson, W.E. (1980) Potentially MineralizableNitrogen in Soil: the Simple Exponential Model Does not Apply for the First 12Weeks of Incubation. Soil Science Society of America Journal, 44: 442–443.

Morvan, T., Leterme, P., Arsene, G.G., and Mary, B. (1997) Nitrogen Transformationsafter the Spreading of Pig Slurry on Bare and Ryegrass Using 15N-LabelledAmmonium. European Journal of Agronomy, 7: 181–188.

Ndayegamiye, A. and Cote, D. (1989) Effect of Long-Term Pig Slurry and Solid CattleManure Application on Soil Chemical and Biological Properties. Canadian Journalof Soil Science, 69: 39–47.

Paul, E.A. and Clark, F.E. (1988) Soil Microbiology and Biochemistry; AcademicPress: San Diego, California.

Polo, A., Almendros, G., and Dorado, E. (1983) Dispositivo De Incubacion Para ElEstudio De La Mineralizacion De La Materia Organica Del Suelo. Anales De Eda-fologıa y Agrobiologıa, 42: 1335–1340.

Rogers, B.F., Krogmann, U., and Boyles, L.S. (2001) Nitrogen Mineralization Rates ofSoils Amended with Non-Traditional Organic Wastes. Soil Science, 166: 353–363.

Sanchez, L., Dıez, J.A., Polo, A., and Roman, R. (1997) Effect of Timing of Appli-cation of Municipal Solid Waste Compost on N Availability for Crops in CentralSpain. Biology and Fertility of Soils, 25: 136–141.

Serna, M.D. and Pomares, F. (1992) Evaluation of Chemical Indices of Soil OrganicNitrogen Availability in Calcareous Soils. Soil Science Society America Journal,56: 1486–1491.

Sharpley, A.N. and Smith, S.J. (1995) Nitrogen and Phosphorus Forms in SoilsReceiving Manure. Soil Science, 159: 253–258.

Sims, J.T. (1986) Nitrogen Transformations in a Poultry Manure Amended Soil:Temperature and Moisture Effects. Journal of Environmental Quality, 15: 59–63.

Sluijmans, C.M.J. and Kolenbrander, G.J. (1977) The Significance of Animal Manureas a Source of Nitrogen in Soils. In Proceedings of Seminar on Soil Environment andFertility Management in Intensive Agriculture; The Society of the Science of Soiland Manure: Tokyo, Japan, 403–411.

Soil Survey Staff (1998) Keys to Soil Taxonomy, 8th edition; NRCS, USDA: Washing-ton, D.C.

Spalding, R.J. and Exner, M.E. (1993) Occurrence of Nitrate in Groundwater. AReview. Journal of Environmental Quality, 22: 392–402.

Stanford, G. and Smith, S.J. (1972) Nitrogen Mineralization Potentials of Soils. SoilScience Society America Proceedings, 36: 465–472.

Vanderholm, D.H. (1984) Agricultural Waste Manual; New Zeeland AgriculturalEngineering Institute Project Report No. 32, NZAEI, Lincoln College: Canterbury,New Zeeland.

C. Plaza, J. C. Garcıa-Gil, and A. Polo2152

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