Soil & Tillage Research 146 (2015) 279–285

Aggregation and clay dispersion of an oxisol treated with swine andpoultry manures

Graziela Moraes de Cesare Barbosa a,*, José Francirlei de Oliveira a,b, Mario Miyazawa a,Danilo Bernardino Ruiz a, João Tavares Filho b

aAgronomic Research Institute of Paraná State, Soil Department Londrina, Paraná, Brazilb State University of Londrina, Center of Agricultural Sciences, Department of Agronomy, Londrina, Paraná, Brazil

A R T I C L E I N F O

Article history:Received 2 September 2013Received in revised form 28 August 2014Accepted 27 September 2014

Keywords:No tillOrganic matterMicroaggregate

A B S T R A C T

Fertilisation using animal manure can improve soil structure. However, the positive and negative effectsof this practice remain inconclusive, and manure application can change the superficial electric potential,thereby increasing the dispersible clay content, disaggregation and susceptibility of soil to erosion andcontamination of surface water. The objective of this study was to evaluate a water-dispersible clay andthe aggregation of an oxisol over time with the application of different doses of swine and poultrymanure. The experiment was conducted in a very clayey dystroferric red latosol, and the treatmentsconsisted of the superficial application of 33 and 66 m3ha�1 swine manure and 1920 and 3840 kg ha�1

poultry manure for corn production. A treatment without fertiliser (mineral or organic) was used as areference. Soil samples from 0.00 to 0.10 m layer were collected at 0, 15, 30 and 60 days after manureapplication to determine the soil aggregate classes, weighted mean diameter (WMD), aggregate stabilityindex, dispersible clay content, pHH2O and pHKCl. The DpH was also determined. The application of swinemanure led to rapid and dynamic changes in the dispersible clay content as well as the aggregationprocess compared to the application of poultry manure. The effects of the application of 33 or 66 m3ha�1

swine manure can be divided into three phases: (i) immediate increases in the pHH2O resulting in anincrease in dispersible clay content and the mass of aggregates <0.250 mm immediately after theapplication of the manure at 0 days after application (DAA); (ii) a decrease in the pHH2O as well asflocculation and restructuring of the soil between 15 and 30 DAA; and (iii) a further increase in the massof aggregates <0.250 mm between 30 and 60 DAA. In contrast to the swine manure applications, acementation effect of organic carbon was observed in the poultry manure applications, and clayflocculation and soil aggregation occurred after the application of 1920 kg ha�1 or 3840 kg ha�1 poultrymanure, thereby increasing the WMD at 15 DAA. However, the aggregation effect was ephemeral, and at30 and 60 DAA, decreases in the WMD and aggregates >2.00 mm were observed independent of the dosesof applied poultry manure.

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1. Introduction

The growing demand for food of animal origin has prompted pigand poultry farming systems to increase productivity, which isaccompanied by risks concerning environmental pollution. There-fore, there is a trend towards shifting the production chain fromdeveloped to developing countries, mainly due to their lessrestrictive environmental policies (Kunz et al., 2009; Knox, 2014;Ramachandran, 2014). Swine and poultry manures are mainly

* Corresponding author. Tel.: +55 4333762391.E-mail address: graziela_barbosa@iapar.br (G.M.d.C. Barbosa).

http://dx.doi.org/10.1016/j.still.2014.09.0220167-1987/ã 2014 Elsevier B.V. All rights reserved.

disposed by application to soil, and in Brazil, there are no strictregulations regarding this type of disposal, increasing the potentialfor soil and water contamination (Kunz et al., 2009).

Soil aggregates are used as indicators of soil quality (Vrdoljakand Sposito, 2002) and can therefore be used to evaluate the effectsof manure and sewage sludge disposal on soil quality (Hati et al.,2006; Lee et al., 2009; Bandyopadhyay et al., 2010; Tavares Filhoet al., 2010; Watteau and Villemin, 2011 Watteau et al., 2012). Overtime, soil fertilisation with manure or sewage sludge can improvethe physical properties of soil (Hati et al., 2006; Bandyopadhyayet al., 2010). Zhou et al. (2013) observed that animal manureapplied with mineral fertiliser was more effective at changing themicrostructure dynamics and increasing soil aggregation than was

280 G.M.C. Barbosa et al. / Soil & Tillage Research 146 (2015) 279–285

the use of mineral fertiliser alone in an ultisol after 20 years. Inaddition to increasing the stability of the aggregates, thisfertilisation can also increase the porosity, water-use efficiencyand grain productivity (Hati et al., 2006; Bandyopadhyay et al.,2010). However, soil chemical alterations that occur due to theapplication of swine and poultry manures are strongly influencedby the soil type, precipitation, quantity and time betweenapplication and sampling (Choudhary et al., 1996 Zhou et al.,2013). Therefore, the relationship between the temporal stabilityof aggregation and carbon inputs to the soil immediately afterapplication remains poorly understood.

Benites and Mendonça (1998) observed that the addition ofmore than 15 Mg ha�1 of non-humified organic matter (manure) tosoil changed the superficial electric potential and increased thedispersible clay content. In addition, Tavares Filho et al. (2010)observed that doses of up to 48 Mg ha�1 sewage sludge increasedthe DpH (pHH2O–pHKCl), indicating a change in the superficialelectric potential, while not demonstrating an increase in claydispersion compared to no application of sewage sludge.

Soon after soil application, swine and poultry manure canpromote rapid changes in the superficial electric potential, therebyincreasing the clay dispersion and reducing the aggregation of thesoil due to the effect of the large amount of carboxyls per atom ofcarbon (17.2–22.7 (R-COO�) COOH/mmol(�) g�1 C) in these types ofmanures (Ohno et al., 2007). However, this effect is ephemeralbecause these carboxyls are easily decomposed (Gerzabek et al.,1997).

The negative charge and salts in swine and poultry manures canalter the superficial electric potential of the soil and cause claydispersion, such as that observed by Benites and Mendonça (1998).The dispersion process caused by swine and poultry manures, evenwithin a short time period, increases the susceptibility of the soil toerosion and surface water contamination due to the increasinglevels of salts in the soil solution (Munodawafa, 2007; Chen et al.,2012; Hahn et al., 2012).

The dispersible clay content and aggregate stability revealsstructural modifications caused by soil management. Analysis ofthe potential soil disaggregation, even within a short period of time(Watteau et al., 2012), can indicate the correct management of theapplication of swine and poultry manures. Therefore, the objectiveof this study was to evaluate the water-dispersible clay content andaggregation of an oxisol over time following the application ofdifferent doses of swine and poultry manures.

2. Material and methods

2.1. Experimental design

The experiment was conducted at the experimental station ofthe Agricultural Research Institute of Paraná State (23�22 0S and51�10 0W), Brazil. The altitude of this location is 585 m, and thearea receives an average annual rainfall of 1588 mm. The climateis humid and subtropical, with temperatures between 16 and27 �C.

The soil is a very clayey dystroferric red latosol (Santos et al.,2006) or Ferralsol (IUSS, 2006), originating from weathered basalt.The main characteristics of the soil are its advanced degree ofweathering and high contents of iron oxides (greater than

Table 1Physical and chemical characteristics of the soil study.

Layer Clay Sil Sand P C pHH2OAl

m g kg�1 Mg kg�1 g kg�1 cmol k

0–0.10 83 14 3 18.30 17.23 4.97 0.05

180 g kg�1), aluminium, 1:1 clay minerals (kaolinite) and quartz(Reatto et al., 2008), which are characterised by low-activity clay,little differentiation among horizons, and a strong and welldeveloped microgranular structure comprising angular and sub-angular microaggregates (Reatto et al., 2009; Brossard et al., 2012).These microaggregates are organised into micropeds that aresmaller than 1 mm, with a porous massive structure according toVolland-Tuduri et al. (2005). The physical and chemical character-istics of the soil are shown in Table 1.

The experimental area was managed using a disk plough(0.30 m depth) followed by a disk harrow (0.15 m depth) until2007. Since 2008, the site has been under no-till, withsoybean and corn grown in the summer and oat and wheatgrown in the winter. Lime was applied using dolomitic limestoneat 3 Mg ha�1 without incorporation prior to the initiation of theno-till system.

For corn, oat and wheat, the manure doses were calculatedbased on the nitrogen levels; for soybean, the doses were based onthe phosphorous levels. Corn was grown during the assessmentyear of this study, and 150 kg N ha�1 nitrogen was applied usingmineral fertiliser and swine and poultry manures.

The following treatments were established: no application ofmineral or organic fertiliser (reference, T1), the application of 33(T2) and 66 m3ha�1 (T3) swine manure, and the application of1920 (T4) and 3840 kg ha�1 (T5) poultry manure. Treatments T2and T4 are equivalent to 150 kg N ha�1, and T3 and T5 correspond to300 kg N ha�1.

The experimental design used a complete randomised blockwith four replications in 50 m2 (5 �10 m) plots. The manures wereapplied to the soil surface without incorporation on 03 November2011. The temperature and rainfall data for the period arepresented in Fig. 1. The chemical properties of the swine andpoultry manures are presented in Table 2.

2.2. Procedures for soil sampling and analysis

The soil samples were collected using a straight shovel from 0 to0.10 m depth. The samples were collected on 04 and 19 November2011, 04 December 2011 and 04 January 2012 at 0, 15, 30 and 60days after manure application (DAA). Four points were collectedper each plot that comprised a sample.

The distribution of the aggregate size classes was determinedthrough wet sieving according to the method of Yoder (1936) asadapted by Castro Filho et al. (1998) using 8.0, 4.0, 2.0, 1.0, 0.5and 0.25 mm diameter sieves. The corresponding aggregatesize classes were >2.00, 2.00–1.00, 1.00–0.50, 0.50–0.25 and<0.25 mm.

The weighted mean diameter (WMD) was calculated accordingto Kemper and Rosenau (1986), and the aggregate stability index(ASI) was calculated according to Castro Filho et al. (1998) with thefollowing equations:

WMD ¼Xn

i¼1ðxi�wiÞ

ASI ¼ weightofdrysample � wp25 � sandweightofdrysample � sand

� ��100

H + Al Ca Mg K S T V Al

g�1 (%)

6.05 4.37 2.25 0.55 7.17 13.22 54.01 0.86

Fig. 1. Daily rainfall in the field during the sample collection period 0, 15, 30 and 60 days after application of swine and poultry manure correspondent to: 1 – application on03 November 2011; 2 and 3 – soil samples collected on 04 and 19 November 2011; 4 – 04 December 2011; 5 – 04 January 2012.

Table 3Classes of aggregates of a dystroferric red latosol at 0, 15, 30 and 60 days afterapplication (DAA) of 33 (T2) and 66 m3ha�1 (T3) of swine manure and 1920 (T4) and3840 kg ha�1 (T5) of poultry manure. Treatment without fertilizer (mineral ororganic) was used with reference (T1).

Treatments 0 DAA 15 DAA 30 DAA 60 DAA

0.50–0.25 mm (g)T1 5.63 a2 5.40 a 5.25 a 5.11 aT21 4.50 a 4.44 a 4.64 a 5.31 aT3 3.99 ab 2.89 b 3.60 ab 5.16 aT4 4.80 ab 3.77 b 5.46 a 5.58 aT5 4.83 a 4.13 a 4.74 a a1.00–0.50 mm (g)T1 9.36 a 8.27 a 9.52 a 8.87 aT2 6.32 a 7.02 a 8.33 a 8.16 aT3 5.65 a 5.33 a 7.42 a 8.52 aT4 8.19 ab 5.93 b 10.07 a 9.82 aT5 7.01 a 5.62 a 7.93 a 7.76 a2.00–1.00 mm (g)T1 9.75 a 8.38 a 9.94 a 8.46 aT2 6.43 a 7.02 a 8.26 a 7.72 aT3 5.70 b 6.12 b 9.34 a 8.13 aT4 8.32 a 5.77 b 9.64 a 9.29 aT5 7.79 ab 6.61 b 10.41a 8.42 ab

G.M.C. Barbosa et al. / Soil & Tillage Research 146 (2015) 279–285 281

where wi = mass proportion of each aggregate class in relationto the total mass; wp = weight of the aggregates for each class (g);xi = mean diameter for each class (mm); wp25 = weight of theaggregates in the <0.25 mm class.

Sand particles refer to concretions >2.00 mm and wereconsidered to have a mass of 1.02 g (Castro Filho et al., 1998).

Water-dispersible clay was determined using the pipettemethod using slow reciprocating agitation (180 rpm) for 16 haccording to Donagema et al. (2011).

The pHH2O and pHKCl (1 mol L�1) values were determinedaccording to Donagema et al. (2011), and D pH (DpH = pHKCl–

pHH2O) was calculated according to Mekaru and Uehara (1972).

2.3. Statistical analysis

The measured data were tested for normality (Shapiro–Wilk)and homogeneity (Levene) and subjected to an analysis of variance.Those datasets lacking normality or homoscedasticity were ln-transformed. In the case of significant F-tests, the mean valueswere compared using Tukey’s test with a significance level of 5%.

Linear correlations (Pearson, p < 0.05) between the aggregateclasses (>2.00, 2.00–1.00, 1.00–0.50, 0.50–0.25 and <0.25 mm),WMD and ASI and DpH, pHKCl and pHH2O were determined.

3. Results

The effects of the different doses of swine and poultry manureson the aggregate classes (>2.00, 2.00–1.00, 1.00–0.50, 0.50–0.25and <0.25 mm) over time are shown in Table 3. For T1, there was nosignificant difference in the aggregate classes over time (Table 3).

Immediately after application (0 DAA), the mass of aggregates<0.25 mm in T2 and T3 were higher than in T1 (Fig. 2a). During theperiod between 15 and 30 DAA, soil restructuring occurred with areduction of the <0.250 mm class in T2 and T3 to a level that wassignificantly lower than in T1 at 30 DAA. A renewed increase inaggregates <0.250 mm occurred at 60 DAA in the swine manuretreatments independent of the applied dose.

Aggregation promoted by swine manure at 30 DAA wasobserved with a significant increase in aggregates >2.00 mm inT2 and an increase in 1.00–2.00 mm aggregates in T3, which

Table 2Chemical properties of the swine and poultry manure (on a dry basis).

Parameters Liquid swine manure Poultry litter

pH 7.90 8.58Total Kjeldahl N (g kg�1) 24.9 24.4Total organic carbon (g kg�1) 91 231C:N ratio 3.65 9.47Ca (g kg�1) 0.84 2.29Total K (Mg kg�1) 35.70 10.5Total P (g kg�1) 15.45 8.4Mg (g kg�1) 0.38 0.69Total Na (Mg kg�1) 9.12 5.3

showed a mass increase from 6.12 g at 15 DAA to 9.34 g at 30 DAA(Table 3).

Unlike swine manure, the poultry manure applications did notpromote an immediate increase in the <0.25 mm class, and the soilhad a better structure than in the reference treatment, with asignificantly smaller mass of aggregates <0.250 mm in T4 and T5than T1 at 15 DAA (Fig. 2b).

The application of 1920 kg ha�1 poultry manure (T4) promotedaggregation in the soil at 15 DAA, with significant increases in theaggregates >2.00 mm and WMD and a decrease in aggregatesbetween 0.25 and 2.00 mm during this period. From 30 to 60 DAA,the WMD and the aggregates >2.00 mm were significantly reduced,whereas the aggregates between 0.25 and 2.00 mm increased(Table 3).

Aggregation in T5 was evident based on the increase in theWMD at 15 DAA. During the period between 30 and 60 DAA, theWMD was significantly reduced, and the aggregate mass of the2.00–1.00-mm class increased (Table 3).

>2.00 mm (g)T1 30.93 a 30.82 a 35.14 a 34.12 aT2 33.62 b 34.70 ab 39.56 a 36.35 abT3 28.67 a 36.69 a 38.96 a 32.35 aT4 33.91 b 39.37 a 32.73 b 31.56 bT5 33.04 a 33.85 a 34.85 a 32.43 aWMD (g)T1 5.25 a 4.99 a 5.48 a 5.73 aT2 5.90 a 6.22 a 6.29 a 6.00 aT3 5.81 a 6.74 a 6.67 a 5.49 aT4 5.67 ab 6.67 a 5.29 b 4.95 bT5 6.04 ab 6.65 a 5.06 b 5.83 ab

1 T2 and T4 are equivalent to 150 kg N ha�1 and T3 and T5 corresponds to300 kg N ha�1.

2 Different lowercase letters in row indicate significant difference by Tukey’s test(p < 0.05)

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

0 1 2 3 4 5

Agg

rega

tes

< 0

.25

mm

(g) T1

T2T3

(a)aa

b

a

a

a

a

b

b

aaa

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

Agg

rega

tes

< 0

.25

mm

(g) T1

T4T5

(b)

aaa

a

a a

a

a a

a

a

a

0 DAA 15 DA A 30 DAA 60 DAA

Fig. 2. Aggregates mass <2.00 mm of a dystroferric red latosol as a function ofexposure time to no application and application of swine (a) and poultry (b)manure. T1, control; T2 and T3, application of 33 and 66 m3ha�1 of swine manure;T4 and T5, application of 1920 and 3840 kg ha�1 of poultry manure. Different letterrepresent difference significant by Tukey test (p < 0.05)

Table 5Linear correlation coefficients of the DpH, pHKCl and pHH2O with aggregate classes,weighted mean diameter (WMD) and aggregate stability index (ASI) in swine(n = 32) and poultry (n = 32) manures.

DpH pHKCl pHH2O

Swine<0.25 mm �0.76* 0.44* 0.62*

0.25–0.50 mm �0.02 �0.15 �0.090.50–1.00 mm 0.35* �0.37* �0.40*

1.00–2.00 mm 0.49* �0.27 �0.39*

>2.00 mm 0.31 �0.26 �0.31WMD 0.25 �0.05 �0.14ASI% 0.74* �0.44* �0.62*

Poultry< 0.25 mm �0.02 0.06 0.060.25–0.50 mm 0.17 �0.10 �0.190.50–1.00 mm 0.19 �0.29 �0.37*

1.00–2.00 mm 0.14 �0.16 �0.22>2 mm 0.11 0.18 0.10WMD �0.13 0.29 0.34ASI% 0.06 �0.05 �0.08

* p < 0.05.

282 G.M.C. Barbosa et al. / Soil & Tillage Research 146 (2015) 279–285

3.1. Water-dispersible clay, pHH2O and pHKCl

The water dispersible clay contents over time in the soils thatreceived swine and poultry manure applications are presented inTable 4. For T1, the dispersible clay did not change over time.

After the application of swine manure, disaggregation of thesoil and an increase in the dispersible clay content were observed,with a maximum dispersion at 15 DAA for T2 and T3 (Table 4). ForT2, the dispersible clay content was significantly lower than that ofthe reference (T1) at 30 DAA and increased again at 60 DAA. For T3,the clay dispersion decreased significantly relative to T1 at 30 and60 DAA.

With poultry manure application, the dispersible clay contentdecreased over time in T4, with a lower dispersion at 30 and 60DAA, whereas for T5, the dispersible clay content remainedconstant over time (Table 4).

The linear correlation coefficients of pHCaCl, pHH2O and DpHwith the aggregate classes, WMD and ASI are presented in Table 5.With the application of swine manure (T2 and T3), an increase inthe soil pHH2O resulted in a more negative DpH, decreasing the ASIand increasing the mass of aggregates <0.25 mm. Despite thelower coefficients, the reduction of pHH2O resulted in a more

Table 4Water dispersible-clay (%) in a dystroferric red latosol at 0, 15, 30 and 60 days afterapplication (DAA) of poultry and swine manure equivalent to 100% and 200% of thedose of mineral fertilizer.

Treatments 0 DAA 15 DAA 30 DAA 60 DAA

Water dispersible clay (%)

T1 77 a1 75 a 73 a 74 aT2 76 ab 77 a 70 b 73 abT3 75 ab 77 a 72 b 72 bT4 77 a 76 ab 73 c 74 bcT5 77 a 77 a 76 a 75 a

1 Different lowercase letters in row indicate significant difference by Tukey’s test(p < 0.05)

positive DpH and an increase in the ASI and aggregate classesbetween 0.50 and 2.00 mm.

The aggregation promoted by the application of poultry manure(T4 and T5) was not related to the changes in pHKCl, pHH2O and DpH(Table 5).

Immediately after the application of swine manure (0 DAA), thepHH2O increased from 5.65 (T1) to 6.05 in T2 and to 6.13 in T3. ThepHH2O decreased significantly at 15 DAA in both T2 and T3, and at30 DAA, the pHH2O increased in the order T2 � T3 � T1 (p < 0.05). At60 DAA, the pHH2O values in T2 and T3 were similar to that in T1(Fig. 3a).

The poultry manure applications in T4 and T5 did not changethe pHH2O over time relative to that in T1 (Fig. 3b).

4. Discussion

There was no change in the dispersible clay contents or soilaggregation parameters over time in T1 (Table 3), indicating thatthe changes observed in the other treatments were caused by theapplication of different doses of swine and poultry manure.

4.1. Application of swine manure and the distribution of aggregateclasses

The effect of the application of swine manure (T2 and T3) can bedivided into three phases: (i) an increase in the mass of aggregates<0.250 mm immediately after the application of manure at 0 DAA;(ii) soil aggregation between 15 and 30 DAA with a significantreduction in the mass of aggregates <0.250 mm; and (iii) arenewed increase in aggregates <0.250 mm between 30 and 60DAA (Fig. 2a).

The increase the mass of aggregates <0.250 mm immediatelyafter swine manure application (T2 and T3) can be explained byincreases in the clay dispersion during the first 15 DAA, with themaximum dispersion occurring during this period (Table 4).Considering that an alteration of the electrolyte concentration by0.001 mmol L�1 is sufficient to change the thickness of the doublelayer and change the effect of short-range attractive forces(Nguetnkam and Dultz, 2011), 15 days after the application ofswine manure (independent of the dose) was sufficient to increasethe pHH2O (Fig. 3), resulting in a more negative DpH (varying from�0.80 in T1 to �0.88 in T2 and �0.85 in T3) by saturating the clayswith a negative charge and consequently increasing the dispersibleclay content.

4.00

4.50

5.00

5.50

6.00

6.50

0 1 2 3 4 5

pHH

2O T1

T2

T3

(a)aa

b

a

b

b

a

ab

b

a

aa

4.00

4.50

5.00

5.50

6.00

6.50

7.00

pHH

2O T1

T4

T5

(b)

aa

aa

a a

a

a a

a

a a

0 DAA 15 DA A 30 DAA 60 DAA

Fig. 3. pHH2O of a dystroferric red latosol at 0, 15, 30 and 60 days afterapplication (DAA) of swine (a) and poultry (b) manures. T1, control; T2 andT3, application of 33 and 66 m3ha�1 of swine manure; T4 and T5, applicationof 1920 and 3840 kg ha�1 of poultry manure. Different letter representdifference significant by Tukey test (p < 0.05).

G.M.C. Barbosa et al. / Soil & Tillage Research 146 (2015) 279–285 283

Dispersion occurs mainly as a result of electrostatic phenomenaand is closely related to the interaction between exchangeable ionsand clay surfaces (Tisdall and Oades, 1982). Swine manure ispredominantly negatively charged due to the presence of carboxylradicals (Gerzabek et al.,1997; Ohno et al., 2007), occurring at up to22.7 COOH mmol(�) g�1, and may present higher concentrations ofcarboxylic groups than fulvic acids (Ohno et al., 2007). Inaccordance with Benites and Mendonça (1998), the increase inthese carboxyl groups is associated with the low net charge on thesurfaces of iron and aluminium oxy-hydroxides and phyllosilicates(Uehara et al., 1972), thus promoting soil dispersion by blockingpositive sites on the surface of oxides and the oxygen sheet inkaolinite or through the complexation of polyvalent cationswithin the solution (Tisdall and Oades, 1982; Wuddivira andCamps-Roach, 2007).

In addition to blocking sites, hydroxyls can interact with eachother through hydrogen bridges and expand the diffuse doublelayer, thereby hindering the formation of electrochemical saltbridges and provoking electrochemical repulsion and the removalof soil colloids. The results indicate that doses greater than33 m3ha�1 swine manure can promote clay dispersion and soildisaggregation soon after application.

These results are consistent with those reported byTavares Filho et al. (2010), who observed that the addition of24 t ha�1 sewage sludge resulted in a pHH2O that was higher thanthe pHKCl, resulting in a DpH value that is consistently negativeand confirming the predominance of hydroxyls in the organicmaterial and their effects on the dispersion of soil colloids.Wuddivira and Camps-Roach (2007) also observed short-termclay dispersion and soil disaggregation with the addition ofcured manure.

The reduction in the mass of aggregates <0.250 mm and theincrease in the masses of aggregates >2.00 mm in T2 andaggregates 1.00–2.00 mm in T3 between 15 and 30 DAA (Table 3)occurred due the significant reduction in the pHH2O during thisperiod (Table 5, Fig. 3).

The reduction in the pHH2O and the re-aggregation of the soilbetween 15 and 30 DAA occurred due to the short half-life of theswine manure (Gerzabek et al., 1997) and the rapid rate ofdecomposition (Magid et al., 2010). This decomposition led to areduction in the excess negative charge, and the increasedavailability of positive sites led to a pH reduction and re-aggregation of the soil between 15 and 30 DAA. A reduction inthe excess negative charge reduced the number of carboxyl groupsthat were interlinked via hydrogen bridges and therefore led to anexpansion of the diffuse double layer, allowing for the restabilisa-tion of the electric potential at the surface as well as theelectrochemical bridges formed by polyvalent cations.

The dispersion and immediate disaggregation of the soil at 0 DAAand the subsequent reduction in the dispersion and re-aggregation15 DAA indicate that the organic matter in the manure is labile andrapidly oxidised by microorganisms (Tisdall and Oades, 1982;Gerzabek et al.,1997). Polysaccharides produced during saprophyticactivity are an important group within this type of organic matter.These compounds are formed soon after the manure is applied to thesoil (Balota et al., 2014) but have a short half-life (Gerzabek et al.,1997) and decompose quickly (within weeks) (Tisdall and Oades,1982). Balota et al. (2014) observed that in no-till systems thatreceive applications of swine manure, polysaccharides representapproximately 43% of the organic carbon, approximately 75% ofwhich is represented by labile polysaccharides with a strongrelationship with microbial biomass carbon.

In the swine manure applications (T2 and T3), changes in themass of aggregates <0.250 mm over time demonstrated thetransient effect of these polysaccharides formed by the additionof organic matter, which increased the clay flocculation andaggregate stability between 15 and 30 DAA (Fig. 2a). Tisdall andOades (1982) reported the transient effect of polysaccharides in thesoil based on results that were consistent with immediate claydispersion followed by flocculation and re-aggregation over time.

For T2, the increase in the pHH2O from 4.98 at 30 DAA to 5.23 at60 DAA, despite the value of 5.60 in T1 (Fig. 3a), may have beensufficient to increase the contents of dispersible clay andaggregates <0.250 mm at 60 DAA. For T3, the increase inaggregates <0.250 mm at 60 DAA cannot be explained by changesin the pHH2O and dispersible clay content because the pHH2Odecreased from 5.43 to 5.10 at 30 to 60 DAA, and the dispersibleclay was constant during this period (Fig. 2a and Table 4). Theseresults are not consistent with the findings of Wortmann andShapiro (2007), who observed an increase of up to 200% foraggregates >2.0 mm at 15 DAA following the application of50 Mg ha�1 feedlot manure; this effect persisted for up to sevenmonths after application.

The increase of aggregates <0.25 mm at 60 DAA in T2 andparticularly in T3 may have been the result of an indirect effectcaused by swine manure. The increase in the concentration of freesodium ions during the decomposition of swine manure and theabsorption of calcium by corn throughout the crop cycle may havereduced the Ca:Na ratio. In addition, 63.2 mm of rain fell during thethree days before the collection of soil samples at 60 DAA, whichmay have intensified the reduction of the Ca:Na ratio.

Rainfall tends to leach soluble salts and minerals, including Ca2+, reducing its cementing effect on aggregate stability (Bagarelloet al., 2006) and increasing the exchangeable sodium content(Abu-Sharar et al., 1987).

Sodium causes clay dispersion because of its ionic radius andcharge density, with values between 5 and 100 mol m�3 for

284 G.M.C. Barbosa et al. / Soil & Tillage Research 146 (2015) 279–285

monovalent cations, such as sodium, compared to 0.1–2.0 mol m�3

for bivalent cations, such as calcium (Sposito, 2008). These factorspromote an increase in the hydrated radius of soil colloids witha subsequent dilation of the diffuse double layer and a reductionin the electrostatic force between them, resulting in the slakingof aggregates and swelling and dispersion of clay particles(Abu-Sharar et al., 1987).

4.1.1. Application of swine manure and aggregates <0.25 mmThe fact that carboxyl radicals in oxisols with 7 years of no-till

are found mainly in the fraction of aggregates between 53 and212 mm (Verchot et al., 2011) and the fact that the swine manurecan consist of up to 22.7 COOH/mmol(�) g�1C (Wuddivira andCamps-Roach, 2007) indicate rapid decomposition, clay dispersionand an increase in aggregates <0.25 mm caused by the poly-saccharides that were added to the soil with the different doses ofswine manure.

Swine manure may affect aggregates <0.25 mm because it isapplied in liquid form to the soil. When swine manure penetratesinto the soil meso- and micropores, the swine manure solution canchange the ionicity indices of cations in the clay–cation bonds andalter the clay behaviour, such as the dispersibility. The degree ofionicity in these bonds dictates the interaction with watermolecules, leading to the separation of clay particles fromaggregated clay domains and the exposure of the surface charge(Marchuk and Rengasamy, 2011). Although this effect has not beenobserved for swine manure, according to Watteau et al. (2012), theapplication of urban sludge for 6 years can promote a reduction inthe structural stability of organo-mineral associations, an increasein the water dispersibility and an increase in particles in the 0–2 mm fraction.

4.2. Application of poultry manure and distribution of aggregateclasses

The effect of poultry manure on soil aggregates was differentcompared to that of swine manure. In contrast to swine manure,poultry manure did not change the mass of aggregates <0.25 mm.In T4 and T5, there was a decrease in aggregates between 0.25 and2.00 mm, an increase in aggregates <2.00 mm and an increase inthe WMD during the first 15 DAA (Fig. 2b and Table 3). Changes inthe aggregation process promoted by poultry manure could not beexplained by changes in the pHH2O, pHKCl or DpH (Table 5).

The different effects on the aggregation and dispersible claycontents caused by swine and poultry manure, as well as theaggregationpromotedbypoultrymanureat15DAA,canbeexplainedby the quality of organic matter in poultry manure compared tothat of swine manure, as demonstrated by Ohno et al. (2007).

The decomposition of poultry manure in soil is slow to relativeto the decomposition of swine manure, and the changes in soilpHH2O are not as drastic compared the application of swine manure(Fig. 3b). Poultry manure is applied in solid form and is less reactivein soil relative to swine manure, with a lower humification indexand proportion of carboxylic acids per carbon atom (17.2COOH/mmol(g)�1 in poultry manure compared to 22.7COOH/mmol(g)�1

in swine manure) and a higher capacity to be adsorbed by goethite(Ohno et al., 2007), one of the main minerals in oxisols (Reattoet al., 2008). In addition, poultry manure has a higher carboncontent and C:N ratio and a lower Na content than does swinemanure (Table 2).

The slow decomposition of the organic matter in poultrymanure causes a cementing effect on organic matter, which ismainly based on polysaccharide production (Oades 1967; Kouakouaet al., 1997; Gerzabek et al., 1997; Balota et al., 2014), andsubsequently increases the stability and diameter of the soilaggregates (Tisdall and Oades, 1982; Watteau et al., 2012).

These results are consistent with those of Hati et al. (2006),Bandyopadhyay et al. (2010), Rauber et al. (2012) and Balota et al.(2014), who reported an increase in dissociated and reactivecarboxylic groups, producing a negative charge in the soil after theapplication of manure and causing a subsequent increase in thebiological activity and soil aggregation.

Aggregates >2.00 mm consist of aggregated connections andparticles that are linked together mainly by fine roots and fungalhyphae, which are mainly composed of particles between 0.02 and0.25 mm; the stability of these aggregates is mainly determined byagricultural management (Tisdall and Oades 1982). Aggregates<0.25 mm were not altered by the application of poultry manure(Fig. 2b). Thus, in addition to the decomposition of polysaccharides,other processes, such as shrinkage due to the drying of aggregates<0.25 mm of oxisol (Volland-Tuduri et al., 2004) and the dynamicgrowth of corn roots, may have reduced the WMD and mass ofaggregates >2.00 mm in T4 and T5 at 30 and 60 DAA (Table 3).

5. Conclusions

Swine manure application resulted in rapid and dynamicmodifications of the dispersible clay contents and aggregationprocesses compared to the application of poultry manure. Doses ofswine manure greater than 33 m3ha�1 increased the dispersibleclay content and mass of aggregates smaller than 0.250 mm in adystroferric red latosol soon after application, with maximumdispersion occurring at 15 DAA. Despite the clay flocculation andrestructuring of the soil between 15 and 30 DAA, furtherdisaggregation was observed at 60 DAA for the 33 m3ha�1 dosesof swine manure.

The changes in the balance loads of the soil with poultrymanure applications were not as drastic over time compared to theswine manure applications, and a cementation effect of organiccarbon was observed. The application of 1920 kg ha�1 or 3840 kgha�1 poultry manure promoted clay flocculation and soilaggregation after application, increasing the WMD at 15 DAA.The reduction of the WMD at 30 and 60 DAA was influenced byother factors in addition to the application of poultry manure. Inthis study, changes in the dispersible clay contents and aggregationprocesses with poultry manure applications were not explained bytemporal variations in the electrochemical attributes (pHH2O,pHKCl, and DpH).

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