Waste Management 29 (2009) 2151–2159

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Waste Management

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Nutrient release from bisulfate-amended phytase-diet poultry litterunder simulated weathering conditions

Mingxin Guo a,*, Maria Labreveux b, Weiping Song c

a Department of Agriculture and Natural Resources, Delaware State University, Dover, DE 19901, USAb Kentucky Science and Technology Corporation, Lexington, KY 40507, USAc Department of Chemistry, Delaware State University, Dover, DE 19901, USA

a r t i c l e i n f o a b s t r a c t

Article history:Accepted 26 February 2009Available online 28 March 2009

0956-053X/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.wasman.2009.02.012

* Corresponding author. Tel.: +1 302 857 6479; faxE-mail address: mguo@desu.edu (M. Guo).

Poultry litter generated on the Delmarva Peninsula is from phytase-modified bird diet and bisulfateamendment. To establish agronomic application rates in conservation tillage systems, bisulfate-amendedphytase-diet poultry litter was investigated for its nutrient release kinetics and supply capacity undersimulated weathering conditions. Delmarva poultry litter was packed in PVC columns (15 cm i.d. � 25 cmheight) to a depth of 5 cm and leached intermittently with 600 mm of water for 190 days. Concentrationsof various nutrients in leachate were analyzed and nutrient release kinetics were modelled. Poultry litterleachate contained high contents of dissolved organic carbon (DOC, 35–11,800 mg L�1), nitrogen (N6–2690 mg L�1), phosphorus (P 45–225 mg L�1), potassium (K 20–6060 mg L�1), and other nutrients.Release of the nutrients occurred primarily in the starting 5 weeks and mostly followed a first order Expo-nential-Rise-to-Maximum model. Under the specified conditions, the poultry litter demonstrated a nutri-ent supply capacity of 11.7 kg N Mg�1, 5.4 kg P Mg�1, and 36.8 kg K Mg�1. Release of the potentiallyplant-available N and K was nearly finalized within 190 days of leaching/weathering, but it would requiretwo years for full release of the leachable P. The results indicate that with consideration of field condi-tions, surface application of bisulfate-amended phytase-diet Delmarva poultry litter at recommended6.6 Mg ha�1 to conservation tillage systems would largely provide P 25.0 kg ha�1, N 106.6 kg ha�1, andK 245.5 kg ha�1 to seasonal crops.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Land application is the prevailing method to dispose of morethan 600,000 Mg of poultry litter annually generated on theDelmarva (Delaware, Maryland, and Virginia) Peninsula from theconcentrated broiler production (Kleinman et al., 2007). Repeatedand excessive application of poultry litter to limited land areashas resulted in elevated soil phosphorus (P) and residual nitrogen(N) levels (Vadas and Sims, 1998; Codling et al., 2000), causing non-point nutrient losses via runoff and leaching to natural waterbodies. In Delaware, 93% of the rivers and streams and 64% of theponds and lakes are impaired by nonpoint-source P and N mainlyfrom historic over-application of poultry litter (DNREC, 2006).

Conventional poultry litter contains relatively high contents ofP as a result of indigestible phytate in typical broiler diet ingredi-ents such as corn and soybean (Nelson, 1967). To improve bird uti-lization of phytate P and consequently reduce the P in poultrylitter, Delaware has mandated since 2006 that all poultry feed besupplemented with phytase enzymes (DNMC, 2006). Studies

ll rights reserved.

: +1 302 857 6455.

showed that addition of phytase in chicken diet decreased P con-tent in poultry litter by 23–30% (Hansen et al., 2005; Angel et al.,2006). Nevertheless, the dietary modification did not affect watersoluble P in poultry litter (Maguire et al., 2004), but reduced NaOH-and HCl-extractable organic P (McGrath et al., 2005). The effect ofphytase-diet may alter availability and movement of nutrients inpoultry litter-fertilized soils. Smith et al. (2005) reported thatextractable P in soils amended with phytase-diet poultry litterwas slightly to moderately lower than in soils amended withequivalent conventional poultry litter. In short-term (7–14 days)trials with simulated rainfall, Foster et al. (2003) and Maguireet al. (2005) observed lower P runoff losses from microplots orboxes receiving phytase-diet poultry litter than from those receiv-ing conventional poultry litter, especially at the initial stage afterfertilization. However, DeLaune et al. (2004) reported that P con-centrations in runoff increased 100% from pasture soils amendedwith a phytase-diet manure relative to with a standard-diet man-ure. This is probably due to promoted transformation of insoluble Pin manure to water soluble forms in the presence of phytase en-zyme (Turner et al., 2002). So far, the effect of phytase additionon availability and release patterns of nutrients in poultry litter fol-lowing land application remains unclear.

Table 1Selected physical and chemical properties (on the dry mass basis) of bisulfate-amended, phytase-diet Delmarva poultry litter.

Attributes Values

Moisture content, % 75.0 ± 1.2Organic matter content, g kg�1 791 ± 15Ash content, g kg�1 209 ± 12Total organic carbon, g kg�1 377 ± 1Total nitrogen, g kg�1 40.40 ± 1.06Total phosphorus, g kg�1 15.12 ± 0.71Total potassium, g kg�1 38.50 ± 0.89Total calcium, g kg�1 25.51 ± 0.32Total magnesium, g kg�1 7.21 ± 0.22Total iron, g kg�1 0.76 ± 0.08pHa 7.1Electrical conductivitya, dS m�1 25.10 ± 0.59Water extractable componentsb, g kg�1

Dissolved organic carbon 75.68 ± 1.68Water soluble phosphorus 1.77 ± 0.01Water soluble nitrogen 15.52 ± 0.83NO3–N 0.002 ± 0.000NO2–N n.d.c

Cl� 11.43 ± 0.48SO2�

4 11.27 ± 0.24PO4–P 1.33 ± 0.03NH4–N 5.20 ± 0.14K+ 33.04 ± 0.86Na+ 7.30 ± 0.34Ca2+ 2.05 ± 0.14Mg2+ 1.19 ± 0.07Fe3+ 0.046 ± 0.002

a Measured with poultry litter-water mixtures at 1:5 dry mass/water ratio.b Extract the poultry litters at 1:10 dry solid/water ratio for 8 h.c Non-detectable.

2152 M. Guo et al. / Waste Management 29 (2009) 2151–2159

Sodium bisulfate (trademarked PLT) is widely used on the Del-marva Peninsula as a poultry litter amendment to suppress in-house ammonia emissions (Malone, 2002). The chemical is usuallybroadcast to rototilled poultry litter in broiler houses at 25 kg/100 m2 for each bird flock (Blake, 2001). Compared with other lit-ter acidifiers (e.g., alum: aluminum sulfate; poultry guard: mixtureof sulfuric acid and clay) or blank treatments, the PLT treatmentmay impart poultry litter particular mineral composition, nutrientexisting forms, and microbial activity. It has been demonstratedthat PLT amendment reduces litter pH and total bacteria (Popeand Cherry, 2000), but does not influence litter moisture and nitro-gen level (Terzich et al., 1998). So far, nutrient dynamics of Del-marva poultry litter from phytase-diet and PLT amendment arestill inexplicable.

Application of poultry litter to conservation tillage systems iscommon (Sharpe et al., 2004). There are nearly 1000,000 ha oflands in the states of Delaware, Maryland, and Virginia under con-servation tillage (Conservation Technology Information Center,2004). In such farming practices, poultry litter is spread on landsurfaces without soil incorporation. Crop residues on the soil sur-face further prevent poultry litter from contacting soil particles.Release of nutrients from the applied poultry litter is dependenton rainfall leaching and weathering. To minimize nutrient runofflosses, it is recommended that poultry litter be applied at ratesmatching crop requirements for P (NRCS, 1999), with additionalN applied from other sources to meet crop N needs (Harmelet al., 2004). To establish P-based agronomic application rates inconservation tillage systems, availability of nutrients in Delmarvapoultry litter after land application has to be determined. Objec-tives of this study were to investigate the release rate and kineticsof nutrients from PLT-amended phytase-diet poultry litter and toevaluate its nutrient supply capacity using long-term leachingtechniques. The results are expected to serve as a basis for develop-ing environmentally-sound agronomic rates for poultry litter landapplication on the Delmarva Peninsula.

2. Materials and methods

2.1. Leaching experiments

Poultry litter used in the experiments was obtained from a typ-ical broiler farm on the Delmarva Peninsula. The farm was oper-ated under standard industrial management. Birds were fed witha phytase-modified diet and the in-house bedding was treatedwith PLT. Shortly after being cleaned out of the poultry house, abucket of litter was delivered to the laboratory and passed througha 6-mm sieve for homogeneity. The sieved litter was placed in apolyethylene tank, covered with a layer of aluminum foil to reducewater evaporation, and settled at room temperature for 20 days.This was to simulate the litter storage operation in manure sheds.Selected physical and chemical attributes of the processed poultrylitter are given in Table 1.

The slightly-aged poultry litter was packed in PVC columns(15 cm i.d. � 25 cm height) to a depth of 5 cm. Triplicate columnswere prepared, each containing litter material equivalent to200 g of oven-dry mass. The columns, with their top open to theatmosphere, were placed in the laboratory at room temperature(23 ± 1 �C) and intermittently leached by 18 water-loading eventsin 190 days. In each ‘‘rain” event, 608 mL of deionized water wascontinuously pumped at 1.63 mL min�1 to each column evenlythrough the whole cross-section via a custom-made rain distribu-tor. The water-loading rate was 5.3 mm h�1, within the moderaterainfall intensity range of 2.5–7.6 mm h�1. To simulate the wet–dry cycles that occur in the field, water-loading was conducted at7-day intervals for the first 10 ‘‘rain” events, at 14-day intervals

for the 11–16th ‘‘rain” events, and at 21-day intervals for the lasttwo ‘‘rain” events. Considering that the annual average precipita-tion on the Delmarva Peninsula is approximately 1100 mm, a totalof 600 mm of water was fed through each of the three columns in190 days.

During each water-loading event, leachates from the poultry lit-ter columns were collected in individual 1000-mL glass beakers.The leachates were immediately recorded for volume and analyzedfor pH and electrical conductivity (EC). Aliquots of the leachateswere then centrifuged at 4000 rpm for 25 min., passed through a0.45-lm glass fiber filter to remove any particulate matter, andstored at 4 �C prior to further chemical analysis. Leachate sampleswere analyzed for concentrations of dissolved organic carbon(DOC), total dissolved nitrogen (TDN), total dissolved phosphorus(TDP), ammonium (NHþ4 ), nitrate (NO�3 ), nitrite (NO�2 ), orthophos-phate (PO3�

4 ), potassium (K+), sodium (Na+), calcium (Ca2+), magne-sium (Mg2+), chloride (Cl�), sulfate (SO2�

4 ), and iron (Fe).Cumulative release of various nutrients from weathering of poultrylitter was calculated and fitted against leaching time using avail-able mathematical models.

2.2. Analytical methods

The pH values of leachate samples were measured using an Acc-umet AB15 pH meter with an Accumet 3-in-1 pH/ATC combinationelectrode (Fisher Scientific, Swannee, GA). Electrical conductivitywas analyzed with an Oakton CON510 conductivity/TDS meter(Oakton Instruments, Vernon Hills, IL) with a CON510 conductancecell (cell constant = 1.0 cm�1) and a built-in ATC probe to normal-ized the reading to 25 �C. Dissolved organic carbon and TDN con-tents were determined with a Shimadzu TC/TN-5000A totalorganic carbon analyzer and an ASI-5000A auto sampler (Tokyo, Ja-pan). Total dissolved phosphorus contents were analyzed using thephosphomolybdate blue method of Murphy and Riley (1962) afterthe leachates were digested with H2SO4 and potassium persulfate

0 20 40 60 80 100 120 140 160 180 2000

5

10

15

20

25

30

35

Loaded water

Leac

hate

/Wat

er D

epth

(mm

)

Time (Day)

Fig. 1. Water loading (dashed line) and leachate flux time series measured frompoultry litter columns. Error bars represent standard deviations of triplicatemeasurements.

M. Guo et al. / Waste Management 29 (2009) 2151–2159 2153

in an autoclave. Inorganic anions Cl�, NO�2 , NO�3 , SO2�4 and HPO2�

4

and cations Na+, NHþ4 , K+, Ca2+ and Mg2+ were measured by ionchromatography (IC) using a Metrohm Personal IC 790 system(Metrohm Ltd., Herisau, Switzerland). Dissolved organic nitrogen(DON) concentrations were calculated by subtracting NH4–N,NO3–N and NO2–N from TDN. Dissolved organic phosphorus(DOP) was calculated as the difference between TDP and PO4–P.

2.3. Data analysis

Concentrations of nutrients in poultry litter leachates are re-ported as means of triplicate measurements. Mass release of nutri-ents from leaching of poultry litter in a specific water-loadingevent was calculated as follows:

Ma ¼13

X3

i¼1

ðCaiViÞ ð1Þ

where Ma is the total mass of nutrient a released in the water-load-ing event, Cai is the concentration of species a in sample i, and Vi isthe volume of sample i (i = 1, 2, 3), and 3 is the replicate number ofsamples.

The cumulative release of nutrients from the poultry litter col-umns was calculated by summing the mass of released solutes ineach water-loading event from the initiation of the experimentsas follows:

CRaj ¼Xj

j¼1

Maj

!,Mpl ð2Þ

where CRaj is the cumulatively released mass of nutrient a per unitmass of poultry litter from the onset of the experiments to after thejth water-loading event, Maj is the amount of released nutrient a inthe jth water-loading event, j is the number of water-loading events(j = 1, 2, . . .., 18), and Mpl is the mass of the poultry litter columns(Mpl = 0.2 kg).

Nutrient release kinetics were described by fitting the cumula-tive nutrient release data against the weathering/leaching timeusing computational models (SigmaPlot 10.0, Jandel Scientific,San Rafael, CA), employing the Marquardt-Levenberg algorithmin an iterative process. The best fit of kinetic models was deter-mined using paired t-tests, r2 values and the standard errors ofmodel parameters.

3. Results and discussion

3.1. Nutrient content of Delmarva poultry litter

As given in Table 1, the phytase-diet, PLT-amended Delmarvapoultry litter contained 75.0% of moisture and 25% of dry mass.Of the dry mass, 79.1% was organic matter and 20.9% was noncom-bustible ash. The organic matter was mainly wood chips and sawdust used as bedding materials in broiler houses. On the dry massbasis, the poultry litter contained 377 g kg�1 of organic carbon(OC), 40.4 g kg�1 of N, 15.1 g kg�1 of P, and 38.5 g kg�1 of K. The to-tal P was significantly lower than the previously reported average(22.5 g kg�1) for standard-diet poultry litter (Sims and Luka-McCafferty, 2002). The content of Fe was less than 0.8 g kg�1. Thelitter had a neutral pH of 7.1 and a high salinity of 25.1 dS m�1

(1:5 solid/water extracts). Water soluble OC, N, and P in the poultrylitter were 75.68, 15.52, and 1.77 g dry kg�1, respectively. Of thewater soluble N, 33.5% was in the NHþ4 form and 66.4% in the or-ganic form. Little NO�3 and no NO�2 was detected. The water solubleP, comprised of 75.1% inorganic P (PO4–P) and 24.9% organic P, wasclose to the previously reported average for standard-diet poultrylitter (1.59 g kg�1; Sims and Luka-McCafferty, 2002). Water soluble

K+, Ca2+, Mg2+, Na+, Cl�, and SO2�4 in the poultry litter were 33.04,

2.05, 1.19, 7.30, 11.43, and 11.27 g kg�1, respectively. The K, Ca,Mg, and Cl- in the poultry litter were from bird feed supplements,while Na and SO2�

4 were chiefly from the litter amendment PLT.Water soluble Fe (0.046 g kg�1) in the poultry litter was ratherlow, because most Fe existed in hydroxides and other forms of pre-cipitates at pH 7.1.

3.2. Leachate fluxes from poultry litter columns

A total of 600 mm of water were applied to each poultry littercolumn in 18 simulated rain events each at 33.3 mm during a per-iod of 190 days. Overall, 429 mm of leachate were received fromthe columns (Fig. 1). The balance was held by the litter materialand subsequently lost to the atmosphere via evaporation. Thepoultry litter initially exhibited a water holding capacity of2.04 g g�1 (oven-dry mass basis). The great water retention andthe resulting high moisture content would facilitate degradationof poultry litter and the corresponding nutrient release in fieldapplications. With leaching and decomposition of fine particles inthe litter profile, the amount of water retained in the columns aftereach water-loading kept decreasing. The water holding capacity ofthe test poultry litter stabilized at 1.52 g g�1 after 90 days of leach-ing. In the last six water-loading events nearly identical volumes ofleachate were collected from the columns (Fig. 1).

3.3. Nutrient concentrations in poultry litter leachate

The pH of leachates from the poultry litter columns ranged from7.2 to 8.7. The alkalinity may be attributed to carbonate salts suchas limestone, potassium carbonate, and sodium bicarbonate inchicken feed (Vadas et al., 2004). Electrical conductivity of leach-ates from the litter columns ranged from 0.3 to 24 dS m�1, decreas-ing as the leaching process progressed (data not shown). After 35days of weathering time or 5 ‘‘rainfall” events, the EC of poultry lit-ter leachate decreased to below 2 dS m�1. It is known that thegrowth of many plants will be restricted when soil EC exceeds4 dS m�1 (Plaster, 1992). The initially high leachate EC suggeststhat salinity toxicity may be introduced on seed germination andseedling development if poultry litter is applied at excessively highrates.

The poultry litter leachate contained high concentrations ofDOC (Fig. 2). Initially the DOC content was 11,800 mg L�1, corre-sponding to the high water extractable OC content in the poultrylitter (75.7 g kg�1, Table 1). It decreased abruptly to 2810 mg L�1

in the second ‘‘rain” event, gradually to 506 mg L�1 after 6 weeksof leaching, and then slowly to around 40 mg L�1 in the last phase

0 20 40 60 80 100 120 140 160 180 2000

200

400

600

800

2000400060008000

1000012000

DO

C (m

g L-1

)

Time (Day)

Fig. 2. Dissolved organic carbon (DOC) contents of poultry liter leachate. Error barsrepresent standard deviations of triplicate measurements.

0 20 40 60 80 100 120 140 160 180 2000

30

60

90

120

150

180

210

240

Phos

phor

us C

once

ntra

tion

(mg

L-1)

Time (Day)

Inorganic P Organic P

Fig. 4. Concentrations of inorganic (white bar) and organic (black bar) phosphorusin poultry litter leachate. The sum of inorganic and organic phosphorus is totaldissolved phosphorus (TDP). Error bars represent standard deviations of triplicatemeasurements.

2154 M. Guo et al. / Waste Management 29 (2009) 2151–2159

of the study (Fig. 2). Water extracts of agricultural soils (1:1 wt/wt)generally possess a DOC below 40 mg L�1 (Guo et al., 2001). Thelow DOC value of the poultry litter leachate at the late experimen-tal stage implies that readily-degradable organic components havebeen depleted after five months of weathering.

Concentrations of Na+, K+, Ca2+, Mg2+, Cl�, and SO2�4 in the poul-

try litter leachate ranged from 0.2to 68, 0.5 to 155, 0.3 to 7, 1.0 to 7,0.01 to 77, and 0.2 to 26 mmol L�1, respectively (Fig. 3). Consistentwith the EC trend, presence of these major inorganic ions wasabundant initially, decreased rapidly in the first 6 weeks of leach-ing, and became dilute afterwards. This suggests that release ofinorganic nutrients from weathering of poultry litter would occurpredominantly within the first two months following field applica-tion if adequate precipitation is provided. Also as indicated by thehigh water extractable concentrations (Table 1), these salt ions willsupply adequate macro nutrients for crops if poultry litter is land-applied at normal rates.

Concentrations of Fe in the poultry litter leachate were below11.7 mg L�1 (0.21 mmol L�1), decreasing with time. After the 12thwater-loading event, Fe became less than 0.1 mg L�1 (data not

0

20

40

60

80

100

120

140

160

0

10

20

30

40

50

60

70

80

Conc

entra

tion

(mM

)

0 20 40 60 80 100 120 140 160 180 2000

2

4

6

8

Conc

entra

tion

(mM

)

Time (Day)0 20 40 60 80 1

0

2

4

6

8

10

Time

Na+

Ca2+

Fig. 3. Concentrations of ionic nutrients in poultry litter leachate. Erro

shown). Iron in poultry litter originates from the additive ferroussulfate in broiler diet (Vadas et al., 2004). At pH above 7.0, leachedFe existed mainly in organic complexes and would be plant-available.

Total dissolved phosphorus (TDP) in the leachate ranged from47 to 223 mg L�1, of which 61–96% was in the form of inorganicorthophosphate (Fig. 4). Three concentration peaks of leachateTDP were observed during the 190-day leaching process. In addi-tion to the initial peak, another two occurred 40 and 120 days afterthe experiments started, respectively, implying different pools of Pin poultry liter. Phosphorus may exist in poultry litter in variousforms with different leachability. Dou et al. (2000) reported thatH2O, 0.5 M NaHCO3, 0.1 M NaOH, and 1.0 M HCl sequentially ex-tracted 49%, 19%, 5%, and 25% of the total P in layer feces (withno bedding material). The poultry litter (mainly bedding material)employed in the present trial contained water soluble P 11.7% ofthe total P (Table 1), in the range of 9.6–16.4% reported for otherphytase-diet broiler litters (McGrath et al., 2005); in standard-diet

0

10

20

30

40

50

60

70

80

00 120 140 160 180 200 (Day)

0 20 40 60 80 100 120 140 160 180 2000

5

10

15

20

25

30

Time (Day)

K+

Mg2+

Cl-

SO42-

r bars represent standard deviations of triplicate measurements.

0 20 40 60 80 100 120 140 160 180 2000

100200300400500600700

10001500200025003000

Nitro

gen

Conc

entra

tion

(mg

L-1)

Time (Day)

NH4-N NO3-N NO2-N Organic N

Fig. 5. Concentrations of ammonium – (NH4–N, white bar), nitrate – (NO3–N, fencebar), nitrite – (NO2–N, grey bar), and organic (black bar) nitrogen in poultry litterleachate. The sum of these forms of nitrogen is total dissolved nitrogen (TDN). Errorbars represent standard deviations of triplicate measurements.

M. Guo et al. / Waste Management 29 (2009) 2151–2159 2155

poultry litter without alum amendment, the fraction is roughly 7%(Sims and Luka-McCafferty, 2002). Release of P during the 190 daysof leaching was principally a result of poultry litter decompositionfrom biological and chemical reactions. This explains the remain-ing high concentration of TDP in the leachate (�60 mg L�1) at theend of the experiments (Fig. 4). It is expected that poultry litter willsupply P for plant growth even after one year of field weathering.Organic P initially accounted for 39% of the TDP, and decreasedto less than 4% (Fig. 4) as the DOC content in the leachate decreasedto below 50 mg L�1 (Fig. 2).

Total dissolved nitrogen (TDN) content in the leachate rangedfrom 6 to 2683 mg L�1, decreasing with time (Fig. 5). The majorforms of N were DON and NH4–N. Leaching of N mainly occurredin the beginning 120 days of the experiments, with TDN contentgreater than 55 mg L�1 in the leachate. Plants can directly absorbNH4–N and NO3–N. Dissolved organic nitrogen is subject to rapidmicrobial and chemical mineralization in the soil environment.Therefore, TDN released from poultry litter can be treated as theplant-available portion of nitrogen. The TDN was a result of bothmigration of water soluble N (accounting for 38.4% of total litterN, Table 1) and mineralization of recalcitrant N (61.6% of total litter

Cul

mul

ativ

e R

elea

se (g

kg-

1 )

05

101520253035404550

y=19.93 + 20.16 (1-e-0.0461t)r2 = 0.994

DOC

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

y =r2 =

T

Time (Day)0 20 40 60 80 100 120 140 160 180 200

Cul

mul

ativ

e R

elea

se (g

kg-

1 )

0

2

4

6

8

10

12

14

y = 4.18 + 3.04 (1-e-0.145t) + 4.51 (1-e-0.0246t)r2 = 0.998

TDN

Time0 20 40 60 80 1

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

y = 1r2 =

NH

Fig. 6. Release kinetics of dissolved organic carbon (DOC), total dissolved phosphorus (TDnitrogen (NH4–N), and nitrate–nitrogen (NO3–N) from poultry litter weathering. Curves

N) in the original poultry litter. In the environment, litter N is sub-ject to a number of processes including mineralization, immobiliza-tion, volatilization, nitrification, and denitrification (Brady andWeil, 2008). Microbial immobilization, ammonia volatilization,and anoxic denitrification may have caused a low recovery of min-eralized litter N in the leachate. Studies show that up to 60% of totalN in poultry litter may be lost via ammonia emission during storageand following application (Brinson et al., 1994; Sharpe et al., 2004).The prevalence of NHþ4 and absence of NO�3 in the leachate at theearly weathering stage (Fig. 5) entails the significance of ammoniavolatilization due to the anaerobic condition developed in litter col-umns by water saturation inhibiting nitrification. The presence ofNO�2 in the leachate (Fig. 5) further suggests that part of the releasedN might be lost to the atmosphere via denitrification. Field condi-tions are, however, mostly aerobic, which will promote nitrificationof NHþ4 to NO�3 and consequently reduce N losses via ammonia vol-atilization and denitrification, imparting more N for plant utiliza-tion. In aerobic soil-litter incubation studies simulating fieldapplications, NO�3 other than NHþ4 was found the predominant formof inorganic N in soil extracts (Preusch et al., 2002). Low concentra-tions (5–10 mg L�1, Fig. 5) of TDN were maintained in the leachatein the late stage of the experiments, suggesting slow yet continuousmineralization of poultry litter N. Supply of N from field-appliedpoultry litter occurred predominantly in the first crop season, butmay last longer than one year (Nicholson et al., 2003).

3.4. Nutrient release kinetics

Cumulative release of nutrients from the poultry litter columnswas calculated as a function of time. Release of DOC is described bya first order exponential rise to maximum (ERM) equation asfollows:

CRt ¼ CR0 þ CRminð1� e�ktÞ ð3Þwhere CRt is the cumulative mass of DOC released per unit mass ofpoultry litter in the columns, CR0 is the DOC that is resident andcould be initially leached out per unit mass of litter, CRmin is themass of DOC that could be potentially released as a result of decom-position per unit mass of poultry litter, k is a first order rate con-stant, and t is weathering/leaching time (day). The fitted curves

0.376 + 5.02 (1-e-0.0063t) 0.992

DP

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

y = 0.237 + 4.95 (1- e-0.0055t)r2 = 0.993

Inorganic P

(Day)00 120 140 160 180 200

.415 + 3.859t/(12.163 + t) 0.993

4+ - N

Time (Day)0 20 40 60 80 100 120 140 160 180 200

0.00

0.05

0.10

0.15

0.20NO3

- - N

y = 0.129/(1 + (t/115.17)-10.034)r2 = 0.999

P), inorganic phosphorus (Inorganic P), total dissolved nitrogen (TDN), ammonium–are obtained by fitting the data with mathematical models.

2156 M. Guo et al. / Waste Management 29 (2009) 2151–2159

precisely describe the cumulative release of DOC from the litter col-umns as a function of leaching time, with a coefficient of determi-nation (r2) of 0.994 (Fig. 6-DOC). Parameters CR0, CRmin, and k forEq. (3) are listed in Table 2. The models predict that under the de-scribed conditions, 40.1 g of DOC would potentially be releasedper kg of the Delmarva poultry litter, accounting for 11% of totalOC and for 53% of water extractable OC in the original litter (Table1). The release rate (indicated by the curve slope) decreased withtime, and more than 85% of the DOC was released within the first35 days. Considering that all poultry litter OC will be eventuallymineralized, while the leachate DOC became relatively constant(40 mg L�1) during the late stage of the 6-month experiments(Fig. 2), it is expected that release of DOC from poultry litter decom-position will last for years at a low rate. Other organic wastes, suchas spent mushroom substrate, exhibited DOC release pattern similarto poultry litter during weathering (Guo and Chorover, 2004).

Cumulative release of TDP also followed the ERM model:CRTDP ¼ 0:376þ 5:02ð1� e�0:0063 tÞ (Fig. 6-TDP). The small rate con-stant (0.0063, Table 2) suggests a long-lasting process for TP re-lease from poultry litter weathering. According to the releasekinetics, 5.40 g of TDP would be released per kg of the poultry lit-ter. The potential releases were 3.1 times higher than the waterextractable P in the original poultry litter, but 2.8 times lower thanthe total P (Table 1). Clearly, a portion of the total P existed in poul-try litter in unleachable forms such as Ca–P minerals (Seiter et al.,2008). Moreover, TDP release from poultry litter weathering was

Table 2Nutrient release model parameters and standard errors of poultry litter weathering. P-val

Nutrients Model

CRt ¼ CR0 þ CRminð1� e�ktÞDOC

CRt ¼ CR0 þ CRminð1� e�ktÞTP

CRt ¼ CR0 þ CRminð1� e�ktÞInorg. P

CRt ¼ CR0 þ CRminð1� e�ktÞK+

CRt ¼ CR0 þ CRminð1� e�ktÞNa+

CRt ¼ CR0 þ CRminð1� e�ktÞSO2�4

CRt ¼ CR0 þ CRminð1� e�ktÞCl�

CRt ¼ CR0 þ CRm1ð1� e�k1 tÞ þ CTN

CRt ¼ CR0 þ CRmin t=ðkþ tÞNH4–N

CRt ¼ CRmin=ð1þ ðt=t1=2ÞkÞNO3–N

CRt ¼ aþ k lnðt þ t0ÞCa2+

Mg2+ CRt ¼ aþ k lnðt þ t0Þ

CR0 is the amount of a nutrient that is resident and could be initially leached out per unCRmin is the mass of a nutrient that could be potentially released as a result of decompok is a first order release rate constant.* P = 0.0002–0.008.

much slower compared with the DOC release (Fig. 6). In 35 days,only 25% of the potentially leachable TDP was released from thepoultry litter. It would require 730 days for 99% of the potentiallyleachable TDP to be released from the litter material. The relativelyhigh TDP content (60 mg L�1, Fig. 4) in the leachate at the end ofthe experiments agrees that release and supply of P from poultrylitter decomposition would be a long process and might last overone year. It is calculated that merely 36% of the litter P was leach-able and would be released: Insoluble P minerals such as Ca3(PO4)2,Mg3(PO4)2, and FePO4 are basically not plant-available. Even the re-leased P would be subject to other chemical processes (e.g., formprecipitates) in soil and lose phytoavailability. For a specific grow-ing season, however, it may be reasonable to consider that soil fix-ation of leachate P would be compensated by the residual litter Prelease in the previous year and thus, TDP released from litterweathering during the crop season is plant-available. Because inor-ganic forms of P were dominant in poultry litter leachate (Fig. 4)and in the water extractable fraction (Table 1), the release kineticsof inorganic P from litter decomposition followed patterns similarto those of TDP (Fig. 6-Inorganic P). The fitted ERM equationsestimate that 5.19 g of inorganic P would be potentially releasedper kg of the litter. Overall, inorganic P accounted for 96% of thecumulatively released TDP.

Release kinetics of TDN from the poultry litter is best fittedby a Double ERM model: CRTDN ¼ 4:18þ 3:04ð1� e�0:145 tÞ þ 4:51ð1� e�0:0246 tÞ (Fig. 6-TDN). There were two apparent pools in poul-

ues from paired t test for these parameters are less than 0.0001 if not specified.

Coefficient ± std. error

CR0 19.93 ± 0.429CRmin 20.16 ± 0.429k 0.0461 ± 0.0020CR0 0.376 ± 0.063CRmin 5.02 ± 0.417k 0.0063 ± 0.0009CR0 0.237 ± 0.0556*

CRmin 4.95 ± 0.497k 0.0055 ± 0.0009CR0 9.27 ± 0.565CRmin 27.55 ± 0.564k 0.0495 ± 0.0020CR0 2.24 ± 0.092CRmin 6.14 ± 0.092k 0.0544 ± 0.0016CR0 3.55 ± 0.356CRmin 9.50 ± 0.354k 0.0767 ± 0.0056CR0 3.80 ± 0.212CRmin 9.83 ± 0.211k 0.0982 ± 0.0042

Rm2ð1� e�k2 tÞ

CR0 4.18 ± 0.133CRm1 3.04 ± 0.404k1 0.145 ± 0.0287*

CRm2 4.51 ± 0.390k2 0.0246 ± 0.0026CR0 1.41 ± 0.099CRmin 3.86 ± 0.093k 12.16 ± 1.035CRmin 0.129 ± 0.0015t1/2 115.17 ± 0.614k �10.03 ± 0.460a �0.644 ± 0.0835k 0.426 ± 0.0166t0 12.80 ± 1.688a �2.51 ± 0.196k 0.924 ± 0.0375t0 19.20 ± 2.267

it mass of litter.sition per unit mass of poultry litter.

M. Guo et al. / Waste Management 29 (2009) 2151–2159 2157

try litter that contributed water soluble N during weathering: Thereadily-degradable (e.g., water extractable) and slowly-degradable(e.g., water-unextractable in organic matter) N pools. The first poolwas relatively smaller (CRm1 3.04 < CRm2 4.51); but the N releasewas more rapid (k1 0.145 > k2 0.0246). As corroboration, waterextractable N (15.5 g kg�1) in the poultry litter only accountedfor 38.4% of the total N (40.4 g kg�1, Table 1). The TDN releasewas quick, of which 87% was realized within the initial 35 daysof the leaching experiments. The initially express release of N im-plies that to reduce nutrient runoff and leaching losses, a seasonalcrop or winter cover crop should be planted immediately followingpoultry litter application. Nevertheless, the potentially recoverableTDN in leachate was 11.7 g kg�1, lower than the water extractableN (15.5 g kg�1) and merely 29.0% of the total N (40.4 g kg�1) in theoriginal poultry litter. Although all litter N was mineralizable, a sig-nificant portion of the mineralized N had likely been lost to theatmosphere via ammonia volatilization and denitrification, causinga low N recovery in the leachate. Ammonium–N is a major form ofleachate TDN (Fig. 5). Accumulation of leachate NH4–N followed ahyperbola equation: CR ¼ 1:42þ 3:86t=ð12:16þ tÞ (Fig. 6-NHþ4 –N).The model estimates that 5.3 g of NH4–N would be potentiallyrecovered in leachate per kg of poultry litter during weathering.The leachate-recoverable NH4–N accounts for 45.3% of the11.7 g kg�1 leachable TDN, but is fairly close to the water extract-able NH4–N in the original litter (5.2 g kg�1, Table 1). Mineraliza-tion of organic N generates NHþ4 , which may be subsequentlyoxidized to NO�3 under aerobic conditions. Incubation studies showthat 42–64% of organic N in fresh poultry litter mixed with loamsoils was mineralized within 120 days at room temperature (Qafo-ku et al., 2001; Preusch et al., 2002). The little gain in leachateNH4–N from poultry litter decomposition confirmed the un-moni-tored ammonia volatilization. Decomposition of organic waste inan open environment always involves NH4–N losses (Eghballet al., 1997; Komilis and Ham, 2005). Laboratory and dynamicflow-through chamber studies demonstrate that ammonia volatil-ization ranges from 4% to 60% of the total N in poultry litter duringstorage and application (Brinson et al., 1994; Sharpe et al., 2004).Similar to TDN, NH4–N was released rapidly. More than 80% ofthe recoverable NH4–N was collected in the leachate within 35days. In contrast, release of NO�3 showed a pattern distinct fromother nutrients (Fig. 6-NO3–N). Since fresh poultry litter containednegligible NO�3 (Table 1), leachate NO�3 was essentially a product ofoxidation of NHþ4 by nitrifying microbes. Due to the anoxic condi-tions initially developed inside the poultry litter columns as a re-sult of high water holding (Fig. 1), the activity of nitrifyingbacteria (requiring O2 as an electron acceptor) was inhibited andlittle NHþ4 was oxidized, as indicated by the absence of NO�3 inleachates collected at the early experimental stage (Fig. 5). Drain-age of the poultry litter columns was improved with the decompo-sition of labile C and the leaching out of fine particles, allowingoxygen to diffuse into the columns at the middle stage of the leach-ing process. The best model to describe the cumulative release ofNO3–N is a first order sigmoidal logistic equation:

CRt ¼CRmax

1þ ð tt1=2Þk

ð4Þ

where CRmax is the maximum amount of releasable NO3–N in thepoultry litter columns, t1/2 is the length of time required to release50% of the CRmax, and k is the release rate constant. The fittedcurves, which have r2 > 0.99, suggests that if O2 and NHþ4 are avail-able, the activity of nitrifying bacteria increases sigmoidally withtime, resulting in a sigmoidal increase in NO3–N release. In fieldapplication with aerobic conditions, NHþ4 generated from minerali-zation of organic N will be rapidly nitrified to NO�3 . Soils mixed withfresh poultry litter at 7.9–8.7 g kg�1 showed predominance of NO3–

N over NH4–N in the water extracts after 14 days of 25 �C incuba-tion, although the mixtures initially contained >35 mg kg�1 ofNH4–N and <5 mg kg�1 NO3–N (Preusch et al., 2002). Conversionof NHþ4 to NO�3 helps reduce N losses via ammonia volatilizationof land-applied poultry litter.

Release of K+, Na+, Cl�, and SO2�4 from the poultry litter weath-

ering can also be described by models similar to those for DOC andP release (Fig. 7). Potentially leachable K+, Na+, Cl�, and SO2�

4 in thepoultry litter were 36.8, 8.4, 13.6, and 13.1 g kg�1, respectively. Theleachable contents of these nutrients were slightly higher thantheir corresponding water extractable fractions (Table 1), implyingthat these components existed in poultry litter predominantly aswater soluble salts. Release of these nutrients was rapid. Within35 days, 87–98% of the potentially leachable ions were released.

Releases of Ca2+ and Mg2+ from weathering of poultry litterwere unique and followed a logarithmic equation:

CRt ¼ aþ k lnðt þ t0Þ ð5Þ

where a, k, and t0 are constants. The model fits the experimentaldata well (r2 > 0.99, Fig. 7-Ca2+, Mg2+), and the values for a, k, andt0 are given in Table 2. As illustrated by the cumulative releasecurves (Fig. 7-Ca2+, Mg2+), the leaching rates of Ca2+ and Mg2+

decreased gradually with time, but still remained at a significant le-vel after 190 days of weathering. During the duration of this study(>6 months), 1.59 g of Ca2+ and 2.39 g of Mg2+ were cumulatively re-leased per kg of the poultry litter, close to the water extractablefractions yet far below the total contents in the material (Table 1).Likely, the majority of Ca2+ and Mg2+ existed in poultry litter inwater insoluble, unleachable forms as carbonate and phosphate pre-cipitates. It suggests that supply of Ca2+ and Mg2+ from poultry litterweathering is long-lasting and the water extractable content can beused to estimate the portion of the material available to plants.

3.5. Nutrient supply capacity of bisulfate-amended phytase-dietpoultry litter and land application implications

Masses of nutrients released from poultry litter over the 190-day weathering period were calculated from leachate flux and sol-ute concentration data and are reported in Table 3. For comparison,potentially releasable nutrients predicted by the release kineticsmodels are also included. Within 190 days under the describedleaching/weathering conditions, one Mg (ton) of the phytase-diet,bisulfate-amended poultry litter released 11.6 kg of N, 3.8 kg of P,and 37.2 kg of K+ as water soluble nutrients in leachate. The Nand P releases might be slightly underestimated as compared withfield litter applications, since field weathering conditions areharsher in terms of temperature variation, moisture change, andsolar irradiation; also aerobic conditions in the field would pro-mote nitrification, reducing losses of N via ammonia volatilizationand denitrification. Of the released and leachate-recoverable N,55.7% was DON, 42.8% was NH4–N, and 1.1% was NO3–N. Of the re-leased P, inorganic orthophosphate P accounted for 88.0%. Exceptfor P, Ca2+ and Mg2+, all test nutrients practically released duringthe leaching experiments agree well with the predicted releasableamounts in poultry litter (Table 3), suggesting that the nutrientreleasing process was nearly complete and the nutrient supplycapacity was reached. Release of P, however, would continueuntil the P supply capacity of 5.40 kg Mg�1 litter was fulfilled.Estimated from the release kinetics (Fig. 6-TDP), 730 days or 2years of weathering under the described conditions are requiredfor 99% of the releasable P to leach out of the poultry litter. It is evi-dent that P fertility of land-applied poultry litter will last longerthan one year and the residual release should be taken into accountin nutrient management.

Only a small portion of total N and P in land-applied poultry lit-ter is plant-available; the supply capacity cannot be predicted

Cul

mul

ativ

e R

elea

se (g

kg-

1 )

0

5

10

15

20

25

30

35

40

45

y = 9.27 + 27.55 (1-e-0.0495t)r2 = 0.995

K+

0

2

4

6

8

10

y = 2.24 + 6.14 (1-e-0.0544t)r2 = 0.997

Na+

0.0

0.5

1.0

1.5

2.0

y = -0.644 + 0.426 ln(t+12.80)r2 = 0.997

Ca2+

Time (Day)0 20 40 60 80 100 120 140 160 180 200

2

4

6

8

10

12

14

16

y = 3.80 + 9.83 (1- e-0.0982t)r2 = 0.995

Cl-

Time (Day)0 20 40 60 80 100 120 140 160 180 200

0

2

4

6

8

10

12

14

16

y = 3.55 + 9.50 (1-e-0.0767t)r2 = 0.984

SO42-

Time (Day)0 20 40 60 80 100 120 140 160 180 200

Cul

mul

ativ

e R

elea

se (g

kg-

1 )

0.0

0.5

1.0

1.5

2.0

2.5

3.0

y = -2.51 + 0.924ln(t+19.2)r2 = 0.996

Mg2+

Fig. 7. Release kinetics of potassium (K+), sodium (Na+), calcium (Ca2+), magnesium (Mg2+), chloride (Cl�), and sulfate (SO2�4 ) from poultry litter weathering. Curves are

obtained by fitting the data with mathematical models.

Table 3Nutrient release measured under simulated weathering after 190 days and predictednutrient release using kinetic models.

Nutrients Measured (kg Mg�1 litter) Predicted (kg Mg�1 litter)

DOC 40.56 ± 2.33 40.10 ± 0.86TDN 11.64 ± 0.59 11.73 ± 0.93NH4–N 4.98 ± 0.31 5.27 ± 0.19NO3–N 0.13 ± 0.01 0.13 ± 0.00NO2–N 0.045 ± 0.005 –TDP 3.82 ± 0.16 5.40 ± 0.48PO4–P 3.36 ± 0.062 5.18 ± 0.55Na+ 8.47 ± 0.27 8.38 ± 0.18K+ 37.21 ± 1.73 36.82 ± 1.13Ca2+ 1.59 ± 0.16 –Mg2+ 2.39 ± 0.14 –Cl� 13.59 ± 0.39 13.62 ± 0.42SO2�

4 13.45 ± 0.47 13.05 ± 0.71Fe 0.086 ± 0.006 –

DOC: dissolved organic carbon.TDN: total dissolved nitrogen.TDP: total dissolved phosphorus.

2158 M. Guo et al. / Waste Management 29 (2009) 2151–2159

based on the total contents of these nutrients. Laboratory and fieldtrials demonstrate that 21–64% of N in poultry manure is availableto crops (Bitzer and Sims, 1988; Preusch et al., 2002). Nicholsonet al. (2003) reported that on average, 33–43% of the total N in poul-try litter applied to sugar beet and potato fields at different rateswas utilized by crops. In a 4-yr field study with continuous annulapplication of poultry manure (15.6 g P kg�1) at 9.4–37.6 Mg ha�1

to pasture plots, Johnson et al. (2004) reported that less than 13%of the applied P was uptaken by forage plants. The present studysuggests that 28.7% of total N, 25.1% of total P, and 96.6% of totalK in the bisulfate-amended phytase-diet poultry litter would befurnished to support crop growth in one growing season, assumingall released nutrients in leachate are plant-available. Appropriateland application rates of poultry litter should be developed basedon the litter nutrient supply capacity, soil nutrient status, and cropnutrient requirements. In practice, it is usually estimated that 15%of total litter N is in NHþ4 and 85% in the organic form; the cropuse efficiency of litter NHþ4 –N is 50% if the fertilizer is applied with-

out soil incorporation and 60% of the organic N will be mineralizedin the first year following application (Marsh et al., 2003). If thecommon fertilization rates of 135 kg N ha�1 and 25 kg P ha�1 arefollowed on Delmarva, the present study suggests that applicationof bisulfate-amended phytase-diet poultry litter should be carriedout at a P-based agronomic rate of 6.6 dry Mg ha�1 shortly beforeplanting, with supplemental chemical N fertilization at58.4 kg N ha�1. Considering that the plant use efficiency of total Nin field-applied poultry litter ranges generally from 30% to 60% (Bit-zer and Sims, 1988; Marsh et al., 2003; Nicholson et al., 2003), if 40%of total N in poultry litter applied to cropland is assumed plant-available, the application rate of 6.6 dry Mg ha�1 would supply106 kg N ha�1 to crops and therefore, 29 kg ha�1 of chemical Nshould be supplemented. Simply because not all P recovered inleachate would be utilized by plants, this application rate shouldbe environmentally conservative. The rate is actually much lowerthan the currently practiced rate of 10 dry Mg ha�1 on Delmarva,but exceedingly coincides with the recommended poultry litterapplication rate of 6.7 Mg ha�1 for water quality protection in Texas(Acosta-Martínez and Harmel, 2006). In case poultry litter is ap-plied repeatedly each year to the same land as the sole P source,the application rate should decrease to 4.6 dry Mg ha�1, with chem-ical N supplement at 60.6 kg N ha�1. The P-based agronomic litterapplication rates will reduce P and N runoff losses and prevent soiltest P build-up while ensure adequate supply to meet crop nutrientdemands.

5. Conclusions

A variety of nutrients including OC, N, P, K, Ca, Mg, Cl, SO2�4 , and

Fe would be released from weathering of bisulfate-amendedphytase-diet Delmarva poultry litter. Intermittent leaching of 5-cm litter columns by 33-mm moderate rain events generatedleachate with pH 7.2–8.7 and EC of 0.3–24 dS m�1. Major inorganicsolutes in the leachate were K+, Na+, NHþ4 , Mg2+, Ca2+, Cl�, SO2�

4 , andHPO2�

4 . Concentrations of DOC, TDN, TDP, and K ranged from 35 to11,800 mg L�1, 5 to 2690 mg L�1, 45 to 225 mg L�1, and 20 to6060 mg L�1, respectively.

M. Guo et al. / Waste Management 29 (2009) 2151–2159 2159

Substantial masses of nutrients were released during poultrylitter weathering. In 190 days with 600 mm of water applied, re-leased DOC, TDN, TDP, and K per kg of poultry litter were 40.6,11.6, 3.8, and 37.2 g, respectively. The nutrient release occurredprimarily in the first 5 weeks, but for P it may last up to 2 years.Nitrogen recovered in leachate consisted of 55.7% DON, 42.8%NH4–N, and 1.1% NO3–N; released P was composed of 88.0% inor-ganic P and 12.0% organic P. Cumulative release of DOC, TDP,TDN, inorganic P, NH4–N, K+, Na+, Cl, and SO2�

4 followed a first orderExponential-Rise-to-Maximum model, while releases of Ca2+ andMg2+ were best described as a logarithmic process, and release ofNO3–N fitted a first order sigmoidal logistic equation. Approxi-mately 11.7 kg of N, 3.8 kg of P, and 36.8 kg of K would be suppliedto crops per Mg Delmarva poultry litter during one growing season.In field applications more litter N (e.g. 16–20 kg N Mg�1) may beavailable to seasonal plants. The supply capacity of P is5.4 kg Mg�1, but it may take two years for the plant-available Pto be released from poultry litter weathering. Environmentally-sound agronomic applications rates of poultry litter may be deter-mined according to the nutrient release kinetics and supply capac-ity of the organic material. For common practice, it isrecommended that Delmarva poultry litter be applied at 6.6 dryMg ha�1 shortly before planting, with supplemental chemical Nfertilization at 29 kg N ha�1. This will provide a fertilization of135 kg N ha�1, 25 kg P ha�1, and 245 kg K ha�1, with reasonableassumptions that 40% of total N and 25% of total P in poultry litterare plant-available and soil fixation of P released from litter weath-ering in one growing season can be compensated by residual Prelease.

Acknowledgements

This work was supported by a USDA 1890 Capacity BuildingGrant (No. DELX-2005-03548) and by the Delaware Water Re-sources Center.

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