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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).
2
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
3
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.
5
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
6
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
7
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
8
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,
9
(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
10
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
16
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.
17
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
18
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