Effects of Pineapple Peel (PP) Composts on Soil Microbial Structure and

Enzyme Activities

*1Inyang C.U, 2Nwaugo, V.O. and 3Ntukidem, E.

1Dept of Microbiology, University of Uyo, Nigeria

2Dept of Microbiology, Abia State University, Uturu, Nigeria

ABSTRACT

The effects of Pineapple peel (PP) composts on soil microbial community structure

and enzyme activities were evaluated in Uyo, Southern Nigeria . Two types of

composts were produced, one pineapple peel (PP) compost and the other, PP

supplemented with poultry droppings (PD). During the composting process,

analysis of the composts showed that N03 had a range of 1.32-3.17 mg/g, PO4 had

2.84-3.91 mg/g and TOC 13.31-16.8 mg/g. pH was 8.41-9.2 while temperature was

30.4-30.8oC. Water content was 36.7-28.4%. Except for water content, all other

parameters had higher value in the PD supplemented PP compost. Amendment

of soil with these composts, showed higher microbial populations in PD

supplemented PP compost. The bacterial groups estimated were total

heterotrophic (THB), phosphate solubilizing (PSB), cellulose utilizing (CUB),

nitrifying (NB) and coliform bacteria (CB). THB was the highest while CB was the

least. Soil enzyme activities showed that dehydrogenase had the highest range of

activity (18.62-28.31), followed by cellulase (10.71-22.31). Urease was more active

in the PD supplemented PP compost (19.7) than the control soil (3.1). Alkaline

1

phosphatase followed the urease trend which increased in activity with increase in

pH. Acid phosphatase did not show significant change in neither composts nor

compost-amended soil. Results obtained suggest that addition of PD improved the

PP compost quality for agricultural purposes.

Key words: compost; soil quality, bacterial groups, enzymes , pineapple peel.

* Corresponding author DR V.O Nwaugo

Email, vonwaugo @ yahoo.com Phone: 238063494654.

INTRODUCTION

The fertility of a soil depends extensively on the microbial community

structure of that soil ecosystem. Soil microorganisms and their enzymes not only

play active roles in soil fertility, as a result of their involvement in the recycling of

nutrients but are also, sensitive biological indicators for soil quality evaluation

(Shantikhsar et al, 2008: Nwaugo et al 2008a). Haran et al, (2006) and Karin

(2006) stated that both the enzymes and the producing microorganisms are very

sensitive to slight changes in the soil environmental conditions.

Following the abuse, use and re-use of the soil for food production, soil

easily loses its quality. It quickly becomes depleted in nutrients, resulting in the

application of both organic and inorganic fertilizers to improve its quality (Nwaugo

et al., 2008b, Nattipong and Alissara, 2006). Some of these additions to soil,

affect the soil physicochemical parameters as well as the soil microbial

community structure and functions, thereby improving or adversely affecting soil

quality with time (Karin, 2006 Haran et al, 2008).

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For sometime, the assessment of soil quality had been mainly by the use

of physicochemical parameters. The nature of soil microbial community structure

was a later addition (Nannipieri et al, 2002). Very recently, the use of soil

enzymes functions in soil quality assessment has shown the soil situation more

vividly as these enzymes are very sensitive to slight changes (Cookson, 1996:

Nwaugo et al, (2008). The involvement of these enzymes in soil quality

assessment gives an indication of all forms of microbial community structure

involving both culturable and unculturable micro-organisms. This becomes very

important as Pelczar et al., (2003) and Humphries (2002) stated that only 3-5%

of all microbial species are culturable in the laboratory. Many types of enzymes

have been used as indicators of soil stress or changes. However, while some are

produced by all microorganisms, a few are specific to particular organisms or

induced by the presence of certain substances in the environment.

In most developing countries, the use of compost as the main enhancer of

soil fertility is still low. Where such exists, data concerning the effects on soil

microbial community structure and enzyme functions are very scanty. Again, the

sources and types of composting materials determine the quality of the compost

produced. This study therefore was designed to assess the quality of pineapple

peel compost and its effects on soil after amendment using soil microbial

community structure and enzyme activities as parameters.

Materials and methods;

The study area was Uyo, a metropolitan community in southern Nigeria. It has

tropical rainforest climate and lies between latitude 4o33”and 5o33 N and

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longitude 5o . Pineapple peels used in the study were

obtained from both orchards and market places where the fruits are processed

for sale.

The peels were composted using the pit method with regular turning for

twelve (12) weeks. Two types of pineapple peel composts were produced; one

was pineapple peel alone and the other was pineapple peel (PP) supplemented

with poultry droppings (PD). Amendment of the soil was done according to

Nattipong and Alissara (2006) at the rate of 1kg of the compost type to 10m2 of

the farmland soil. The compost was evenly spread and mixed with the 0-10cm of

the top soil using hand operated (manual) plough.

Soil sampling

After soil amendment, the soil was allowed to set for two weeks before

sampling for analysis. The top 5-10cm of each soil type amended with each

compost type were sampled using shipreck augar and sterile universal sample

bottles. All samples were analyzed within 2hr of collection for biological

parameters and 2-3 days for physicochemical parameters.Soil samples for

physicochemical analysis were stored in the refrigerator (4oC) until required for

use.

Physicochemical parameters analysis;

A few physicochemical properties of the composts and soil samples were

determined using various standard methods. These were pH, temperature,

organic carbon, nitrate and phosphate contents which were assessed according

4

to AOAC (2005). The moisture content was determined by drying to constant

weight method according to the same AOAC (2005).

Microbiological analysis;

Prevalence of various bacterial species in the soil was determined by the use of

various culture media, specific for the group. This was done after ten-fold serial

dilution according to Chesebrough (2002) using the spread plate technique. Five

bacterial groups were assessed. These were total heterotrophic (THB), coliform

(CB), phosphate solubilizing (PSB) cellulose utilizing (CUB) and nitrifying

bacteria (NB). Tryptone Soy Agar was used for THB, McConkey Agar for CB.

Phosphate medium (US Patent, 2003) and modified mineral salt Agar were used

for PSB and NB respectively. Cellulose agar was used for CUB.

Soil enzyme activities;

The activities of the soil enzymes were determined using soil samples

sieved with 0.5 sieves after drying at room temperature for 24 hours. The

enzymes whose activities were determined include dehydrogenase, urease,

cellulase and the phosphatases (acid and alkaline). Dehydrogenase was

determined as described by Alef (1995) which involved the use of 0.25%

aqueous triphenyl tetrazolum chloride (TTC). The formed triphenyl formazon was

measured at 485nm. The urease activity was estimated according to Nannipieri

et al (1997) using the colorimetric method involving urea amendment of soil. The

result was expressed as mg NH4-Ng-1 dry soil 24 h-1. The activity of the cellulase

was determined according to Deng and Tabatabai (1994) involving the carboxyl

methyl cellulose (CMC) amendment of soil.

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Both acid and alkaline phosphatases activities were determined using the

methods of Tabatabai (1997) in which p-nitrophenyl phosphate was used in the

soil amendment. The reactions were stopped and read at 410nm at pH of 6.8

(acid) and 11.5 (alkaline). The results were expressed as umol-p-nitrophethol

Results;

Results of the physicochemical properties are shown in Table 1. In the

compost, temperature was above 30.0 C while in soil (both compost amended

and control) it was below 30.00C. The difference was only significant (P = 0.05)

in control soil which had 28.70C. pH had its highest value in PD supplemented

PP compost (9.2), followed by the PP + PD compost amended soil (8.4) while

the least was in the control soil which was acidic (6.3) (Table 1). The difference

observed in the pH values was quite significant ( P = 0.05).

P04, N03 and TOC, ranged from 2.41-3.91 mg/g, 0,21-1.34 mg/g and 9.72-

16.86 mg/g respectively with the highest values in the PP+PD compost.

Statistical analysis showed significant difference (P = 0.05). In terms of C/N ratio,

the PP+PD compost had the best ratio of 10.79 while the least was in contrl soil

(26.77), followed by the soil amended with the PP compost (20.08). Lowest

values were in soil (control) (10.71).

The acid phosphatase enzyme was the least effected as it remained fairly

the same in all the samples (soil and compost) analyzed with a range of 3.12-

3.59 umol.p-nitrophenol. On the other hand, alkaline phosphatase showed

statistically significant variation in its activities (P = 0.05). Its activities correlated

positively with the observed increase in pH. Alkaline phosphatase had its highest

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activity in PP +PD compost with the highest pH of 9.2 and least activity in control

soil (2.77) with the least pH (6.3).

Table 2 shows the bioloads of the various compost types and soil samples

according to the amendments made. The THB was the most abundant group in

all the samples assessed with PP+PD compost having the highest (3.9x107cfu/g)

followed by PP+PD compost amended soil (3.7xcfu/g). The least occurring

bacterial group was the coliform bacterial, which had a range of 1.2x102cfu/g (pp

compost)- of 3.4x104 and 2.9 x 102 – 3.3 x 103 cfu/g (soil control). CUB and PSB

which ranged from 2.7x104-3.9 x104 (control soil – PP+PD compost) respectively

were not statistically different from each other in all the samples analyzed (P

=0.05).

NB was lowest in PP compost (1.1x102cfu/g0 but increased to

2.4x102cfu/g in the PP +PD compost amended soil. Other sample had values

between there figure.

Generally, higher bacterial prevalence were observed in the soil amended

with the two compost types, but the PP+PD compost caused higher increase

than PP compost. Values are shown in Table 2.

The results of the enzyme activities shown in Table 3 followed the pattern

of THB except the urease. Dehydrohenase had its highest activity in soil

amended with PP+Pd COMPOST (31.86) which had the highest THB. Its lowest

activity was in the control soil (16.72). Urease activity was highest in the PP+PD

compost (9.7), followed by PP compost (7.24) but lowest in control soil (3.74).

Cellulose activity was statistically high in the PP+PD compost (22.31), followed

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by the soil amended with the PP+PD compost (19.62) while the least was in test

soil (10.71) (P=0.05).

DISCUSSIONS AND CONCLUSION

Results obtained in this study indicated that all the parameters determined in the

physicochemical section were significantly increased by soil compost

amendment. The high TOC and PO4 observed in compost, which reflected in the

amended soil, occurred as a result of the release of these nutrients from the

composted material - pineapple peels. Chrost and Siuda (2006) and Karin (2006)

had earlier reported similar increase in soil following organic matter incorporation.

Nwaugo et al., (2008a) also observed that soil impacted with Palm Oil Mill

Effluent (POME) had an increased nutrient content.

In the same vein, the significant change in pH of both compost and

compost amended soil could have been caused by the metabolism of the little

protein in the pineapple peel or from the poultry droppings. This metabolism

resulted in the release of NH3 which then dissolved in the available moisture to

cause the increase in pH values. Nwaugo et al, (2008c) and Karin (2006) also

reported that soil impaction with organic materials caused increase in pH values.

This study therefore agrees with these researchers that composting releases

plant nutrients from the composted materials which when incorporated into the

soil, caused corresponding increase in the soil nutrients.

Analysis of the physical and chemical parameters measured showed

some significant differences in the effects of composting pineapple peel alone

and incorporating poultry droppings into it. All the parameters showed higher

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values in the poultry droppings amended pineapple peel compost. A similar

observation had earlier been reported by Nattipong and Alissara (2006) and Tam

and Wong (1995). Pineapple peel contained mainly carbohydrates while

incorporation of poultry droppings added the much needed nitrogen source to

have a more balanced medium in favour of better C/N ratio. The moisture content

which showed highest values in the PP compost decreased in the amended soil

samples. Pineapple fruit is a high moisture fruit (HMF) hence its waste had high

moisture too. However this moisture was taken up by the impacted soil to

decrease the observed soil moisture.

Observation in the bioloads of the various bacterial groups analyzed

showed increase of all groups except the coliforms. The coliforms were adversely

affected by high temperature and pH. Nattipong and Alisssara (2006) reported

that during composting, temperature could rise up to 60-70oC which could kill

non-thermophiles, like the coliforms. Similarly, these coliforms survive more

under slightly acidic or neutral pH values (Chessbrough, 2003) but in the study

the pH became alkaline hence the change in coliform prevalence.

The increase in PSB and CUB above the soil (control) values could be

attributed to the compost effect. The composting process caused the release of

microbial utilizable nutrients, resulting in their proliferation. The bacterial

proliferation was more pronounced in the PD amended PP compost. This

observation buttresses the earlier one in the physicochemical parameters and

agrees well with Nattipong and Allissara (2006) who reported that swine manure

encouraged higher bacterial growth in cassava pulp compost. Nwaugo et al,

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(2008c) also reported a similar situation in cattle market waste impacted soil in

Okigwe.

Generally the THB were predominantly higher in all cases both in the

composts and amended soil types. Nwaugo et al, (2008b) and Pelczar et al,

(2003) agreed that THB is a group of all culturable bacteria while the other

groups are only fractions of this THB. Again, these other bacterial groups, equally

constitute part of the THB. hence will be smaller than the THB. However, the

similarity between CUB and PSB could be attributed to the pineapple peel

content. The major source of soil cellulose is plant material and pineapple peel is

a plant material. In addition, pineapple has considerable phosphate content,

hence could encourage PSB growth.

. In this study, all the enzymes assessed showed highest activities in the

poultry droppings (PD) supplemented pineapple peel (PP) compost impacted

soil. Similarly the pineapple peel compost supplemented with poultry dropping

had higher enzyme activities than the PP compost.. PP+PD compost amended

soil also had higher soil enzyme activities while PP compost amended soil had

lower values.

Dehydrogenase activity was closely tied to the values of the bioload of the

THB. This enzyme is an integral part of the living bacterial cells and is involved in

the oxidation of organic matter (Makoi and Ndakidemi, 2008). It is produced by all

microorganisms hence a good indicator of changes in soil. In this study,

dehydrogenase had the highest activity in all the compost and compost

amended soil types. The conditions in the PD supplemented PP compost

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favoured more bacterial growth which then reflected in the dehydrogenase

production and activities. The PP compost also caused higher dehydrogenase

activities in soil amended with it above the control soil.

Urease activity was observed to be higher in the compost with poultry

droppings. This observation agrees well with Saliha et al, (2005) and

Shahinrokhsar et al, (2008) who stated that there was high urease activity in soil

with high urine (NH3) odour as observed during the composting process. This

was more in the poultry dropping supplemented compost than the pineapple peel

compost. Urease is responsible for the hydrolysis of urea with consequent

release of NH3. This observation further explains the high pH change observed in

the PP + PD compost and compost impacted soil. Nwaugo et al, (2008c) had

earlier reported high urease activities in cattle market waste and POME impacted

soil types.

Cellulase activities closely followed the trends in bioloads of THB and

CUB. Results indicated that high bacterial load samples showed high cellulase

activities indicating more oxidation of the cellulose contained in the compost

materials. However, higher cellulose per gram could be found in the pineapple

peel compost but this did not induce higher cellulose activities above the poultry

dropping supplemented compost. This is because increase in carbon utilization

is accompanied by increase in Nitrogen consumption too (Pelczar et al, 2003).

The utilization of carbon and Nitrogen results in the proliferation of the microbial

cells observed in PP +D compost and compost amended soil. This observation

agrees with Prescott et al (2003) that higher C/N ratio encourages better

11

microbial proliferation. The increased proliferation is synonymous with increased

metabolic activities.

The least affected enzymes are the phosphatases which are important in

the hydrolysis of esters and anhydride of phosphoric acid (Makoi and Ndakidemi,

2008). Since these are both phosphatases (acid and alkaline), they operate in

both conditions to metabolize the phosphates. However, observations in this

study agree well with Nwaugo et al (2008a) Ndakidemi, (2006) and Wright and

Reddy (2001) that pH is an important factor in phosphatase activities. The

alkaline phosphatase showed increased activities with the increase in pH values

while that of the acid phosphatase did not show much change. This suggests that

alkaline phosphatase is more sensitive to pH change within the range observed

in this study. The presence of uric acid in the PD, in addition to the acidic nature

of the composting material – PP could have accounted for the observations in the

acid phosphatase.

In conclusion, observations in this study suggest that supplementing plant

material in composting process with animal/poultry wastes has better effects on

soil microbial and enzyme activities than composting plant materials alone. This

means that increased biogeochemical transformations favourable to agricultural

activities will be experienced in the amended soil.

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TABLE 1: Physicochemical parameters of the compost and soil amended with

these composts

Parameters Pp compost PP + DD

compost

Soil + PP

compost

Soil PP + PD Soil alone

Temp oC 30.4 30.8 29.6 29.8 28.7

TOC mg/g 13.31 16.8 9.7 12.8 12.28

NO3 mg/g 1.32 3.17 1.24 2.21 1.4

PO4 mg/g 2.84 3.91 2.76 3.28 2.41

Moisture

content %

28.4 26.74 26.2 24.11 10.42

pH 8.4 9.2 7.2 8.1 6.3

C/N Ratio 10.08 5.31 7.82 5.79 8.77

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TABLE 2: Values of enzymes activities determined in the compost study

Bacteria

group

Pp compost PP+PD

compost

Soil alone Soil PP+DP

compost

Soil +PP+PD

THB 3.2X105 + 0.10a 3.9X107 + 0.3b 4.7X106+ 0.5C 8.7X105+ 0.7d 3.7X107 + 0.9e

CB 1.2X102 + 0.2a 1.5X102 + 0.3a 3.4X104+ 0.5b 1.0X103+ 0.7c 1.6X103 + 0.9e

CUB 2.7X 104 + 0.2a 3.9X104 +0.4b 2.2X104+ 0.6C 3.1X104+ 0.8b 3.6X104 + 0.0e

PSB 2.7X102 + 0.2a 3.1X103 + 0.4b 2.7X103+ 0.7C 2.4X103+ 0.8c 3.3X103 + 0.9d

NB 1.1X102 + 0.2a 1.8X103 +0.3b 2.1X103+ 0.4C 1.7X103+ 0.3b 2.4X103 + 0.9e

Key

THB - Total Heterotrophic Bacteria

CB - Coliform Bacteria

CUB - Cellulose Utilizing Bacteria

NB - Nitrifying Bacteria

PP - Pineapple Peel PD - Poultry Dropping

Figures followed by the same alphabets are not significantly different but those

followed by different alphabets are significantly different.

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TABLE 3: Bioloads of various bacterial groups in composts and composts

amended soil sample (cfu/g)

Enzyme PP

compost

PP+ PD

compost

Soil alone Soil+PP

compost

Soil +PP+PD

Dehydrogenase 18.62 28.31 16.72 23.91 31.86

Urease 7.24 9.7 3.74 4.58 5.74

Acid phosphatase 3.12 3.59 3.27 3.31 3.43

Alkaline phasphatase 3.10 4.62 2.97 3.67 4.12

cellulase 19.24 22.31 10.71 14.41 16.62

Values are means of three times sampling

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