ABSTRACT
The impact of organic and inorganic fertilizers namely cow dung, poultry manure, NPK (15:15:15) and urea on soil microbial population and enzyme activities were analysed. The field experiment was laid out on an agricultural site in National Root Crops Research Institute (NRCRI), Umudike and soil samples collected at two weeks intervals for the period of twelve (12) weeks. The samples were analysed for chemical properties (pH, total nitrogen, available phosphorus, organic carbon and exchangeable potassium), microbial population (bacteria, fungi and actinomycetes) and soil enzymes (urease, phosphatase, cellulase and dehydrogenase activities). The experiment was laid in a Randomized Complete Block Design (RCBD) with each treatment replicated three times to give total of 15 plots. Chemical and microbial properties (pH, total nitrogen, available phosphorus, exchangeable potassium, organic carbon, bacterial and fungal counts) of the study site and organic fertilizers used in the experiment were analysed prior to treatments application using standard methods. The study site was moderately acidic (5.63), low in organic carbon (0.49%) and moderate in nitrogen, potassium and phosphorus content (0.16%, 0.22cmol/kg and 13.51mg/kg respectively). From the results, pH of the treated plots ranged from acidic to moderately acidic (5.22-6.01). The treated plots were high in nitrogen (0.23-0.74%). Organic carbon content ranged from low to moderate (1.43-2.94%). The plots were moderate in available phosphorus (12.92-15.98mg/kg) and high in exchangeable potassium (0.58-1.06cmol/kg). The fertilizers applied to the soil were also observed to have significant effects on the enzyme activities. Soil acid and alkaline phosphatase, urease, cellulase and dehydrogenase activities ranged between 48.23 and 132.77mg/p-nitrophenol/g, 27.53 and 87.33mg/p-nitrophenol/g, 24.07 and 56.30µgN-h-1g-1, 46.23 and 79.94µgG-g-1h-1, 37.70 and 83.91µgTPFg-1h-1 respectively. The mean total bacterial, fungal and actinomycetes counts ranged from 3.42 to 6.43cfu/g, 1.81 to 6.55cfu/g and 1.13 to 5.33cfu/g respectively. The results suggest the use of fertilizers in enhancing soil chemical and biological properties as revealed by the recorded values from the organic and inorganic treated plots when compared to the control. However, the use of organic over inorganic fertilizers is recommended due to their compositions and higher positive effects on the soil fertility parameters.
TABLE
OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of Contents vi
List of Tables ix
Abstract x
CHAPTER 1:
INTRODUCTION 1
1.1 Problem
Statement 3
1.2 Main
Objective 4
1.3 Specific
Objectives 4
CHAPTER 2:
LITERATURE REVIEW 5
2.1 Soil
Fertility Management: Use of Fertilizers 5
2.2 Soil
Amendments 6
2.2.1 Organic
amendments 7
2.2.2 Inorganic
amendments 8
2.3 Effects of Organic and Inorganic
Fertilizers on Soil Microbial
Community 9
2.4 Soil Enzyme Activities as Affected by
Application of Organic and
Inorganic Fertilizers 12
2.5
Effects of Organic and Inorganic
Fertilizers on Soil Physical and
Chemical
Properties 15
2.5.1
Physical properties 15
2.5.2 Chemical
properties 16
2.6 Adverse
Effects of Excessive and Consistent Applications of Inorganic
Fertilizers
on Soil Microbial Population and Enzyme Activities 17
CHAPTER 3:
MATERIALS AND METHODS
3.1 Study
Site 20
3.2 Land
Preparations, Experimental Design and Treatment Applications 20
3.3 Soil
Sampling and Collections 21
3.4 Soil
Chemical Analyses 21
3.4.1 Soil pH 21
3.4.2 Total
nitrogen 21
3.4.3 Organic
carbon 22
3.4.4 Available
phosphorus 23
3.4.5 Exchangeable
potassium 24
3.5 Cow
Dung and Poultry Manure Analyses 25
3.6 Isolation
and Enumeration of Microbial Isolates 25
3.6.1 Isolation
and enumeration of heterotrophic bacteria 25
3.6.2 Isolation
and enumeration of heterotrophic fungi 25
3.6.3 Isolation
and enumeration of actinomycetes 26
3.7 Soil
Microbial Respiration Rates 26
3.8 Soil
Enzyme Activities 27
3.8.1 Urease
activity 27
3.8.2 Phosphatase
activity 28
3.8.3 Cellulase activity 28
3.8.4 Dehydrogenase
activity 28
CHAPTER 4: RESULTS
AND DISCUSSION
4.1 Initial
Soil and Organic Fertilizers Used 30
4.2 Soil
Chemical Properties 32
4.2.1 Effect
of cow dung application on soil chemical properties 32
4.2.2 Effect
of poultry manure on soil chemical properties 35
4.2.3 Changes
in soil chemical properties of NPK fertilized soil 37
4.2.4 Effect
of urea fertilizer on soil chemical properties 39
4.3 Soil
Enzyme Activities 41
4.3.1 Effect
of cow dung treatment on soil enzyme activities 41
4.3.2 Effect
of poultry manure on soil enzyme activities 43
4.3.3 Effect
of NPK fertilizer on soil enzyme activities 45
4.3.4 Effect
of urea fertilizer on soil enzyme activities 47
4.4 Soil
Microbial Respiration Rates 49
4.5 Soil Microbial Population 51
4.5.1 Effect of cow dung treatment on soil
microbial population 51
4.5.2 Effect of poultry manure on soil microbial
population 53
4.5.3 Effect of NPK fertilizer on soil microbial
population 55
4.5.4 Effect of urea fertilizer on soil microbial
population 57
4.6 Discussion 59
4.6.1 Soil
chemical properties 59
4.6.2 Soil
enzyme activities 60
4.6.3 Soil
microbial population and respiration rates 62
CHAPTER
5: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 63
5.2 Recommendations 65
References 66
Appendices 77
LIST
OF TABLES
4.1: Basic
properties of the study site and the organic fertilizers 31
4.2: Changes
in chemical properties of cow dung fertilized soil with time 34
4.3: Effect
of poultry manure on soil chemical properties with time 36
4.4: Changes
in chemical properties of NPK fertilized soil with time 38
4.5: Effect
of urea fertilizer on soil chemical properties with time 40
4.6: Activities
of soil enzymes under cow dung treatment with time 42
4.7: Activities
of soil enzymes under poultry manure treatment with time 44
4.8: Activities
of soil enzymes under NPK treatment with time 46
4.9: Activities
of soil enzymes under urea treatment with time 48
4.10: Changes in
microbial respiration rates of organic and inorganic fertilized
soil with time 50
4.11: Effect
of cow dung treatment on soil microbial population with time 52
4.12: Effect of poultry manure on soil microbial
population with time 54
4.13: Effect of NPK fertilizer on soil microbial
population with time 56
4.14: Effect of urea fertilizer on soil microbial
population with time 58
CHAPTER
1
INTRODUCTION
Soil is a dynamic natural system that
lies at the interface between earth, air, water and life, providing critical
ecosystem service for the sustenance of humanity (Needelman, 2013). Soil is a
favourable habitat for microorganisms and is inhabited by a wide range of
microorganisms. These organisms are found in large number in soil usually
between one to ten million microorganisms per gram of soil with a dominant
number of bacteria and fungi (Basak et al., 2016).
In the quest for increasing food and
fibre production to meet the ever increasing demand, fertilizer has played a
crucial role. Fertilizer is any material of natural or synthetic origin that is
applied to soil or plant tissues to supply one or more plant nutrients
essential to the growth of plants. They can be classified according to whether
they provide a single nutrient or multi-nutrients. They are also classified as
organic or inorganic fertilizers (Savoy, 2015). The application of fertilizer
to soil is the most common management of agricultural soils. Organic and
inorganic fertilizers are primarily used to increase crop productivity (Singh
and Ryan, 2015). However, application of fertilizers may result to shifts in
the function and quality of soils by directly or indirectly changing the soil’s
physical, chemical and biological properties (Cinnadurai et al., 2013).
Organic fertilizers are natural
materials of either plant or animal origin which include livestock manure,
green manures, crop residues, household wastes, compost and wood litter.
Organic nutrient sources vary in quality and quantity. The quality is important
in determining the nutrient release potential of the organic fertilizer
(Mohanty et al., 2013). Organic soil
management can improve soil structure (Papadopoulos et al., 2014), help retain carbon in the surface soil and increase
crop yields (Bhattacharyya et al.,
2015). Application of organic materials such as farmyard manure, green manure
and straw can reduce the amounts of inorganic fertilizers used and augment for
soil carbon losses caused by land-use changes (Almagro and Martinez, 2014).
Inorganic fertilizers are those mined
from mineral deposits with little processing or industrially manufactured
through chemical processes. They vary
in appearance depending on the process of manufacture (Bilkisu
and Babatunde, 2015). The
particles can be of
different sizes and shapes (crystals, granules, dust, etc.) and the grades can
be straight fertilizers (containing one nutrient element), compound fertilizers
(containing two or more nutrients) and fertilizer blends (formed by physically
blending inorganic fertilizers to obtain desired nutrient rations). Application
of chemical fertilizers to soil is a common practice to increase crop
yields. Indiscriminate use of these fertilizers results to changes in the soil
physical, chemical and biological characteristics (Rivera-Becerril et al., 2017).
Biological properties such as soil microbial
population, community structures, functions and enzyme activities are the most
sensitive indicators of changes in soil quality under different agricultural
practices due to their rapid responses to environmental changes (Lima et al., 2013). Soil microorganisms are
very important to agroecosystems. They are involved in key roles such as soil
aggregate formation, organic matter decomposition, nutrient cycling and
sustenance of soil productivity (Luo et
al., 2015). Microorganisms are very sensitive to management practices such
as the use of mineral fertilizer and organic manure addition (Walsh et al., 2012). The use of fertilizer may
result to shifts in the population, community structure and functionality of
these soil microorganisms. Some microorganisms may proliferate and others may
be suppressed (Cinnadurai et al.,
2013).
Soil microbial enzymes are involved in various
biochemical processes such as soil organic matter decomposition and nutrient
cycling. Their activities are usually used as early indicators of soil quality.
Changes in the activities of these enzymes may reflect changes in soil quality
(Nedunchehiyan et al., 2013).
Different soil management practices including application of fertilizer affect
the activities of soil enzymes thereby, affecting the soil fertility
(Srinivasarao et al., 2018).
Therefore, this research work aims at evaluating the impact of soil management
with organic and inorganic fertilizers on soil microbial population and enzyme
activities.
1.1
PROBLEM
STATEMENT
Fertilizers are commonly added to
soil to provide one or more nutrients essential for the growth of plants and to
enhance the effectiveness of the soil. Soil properties are bound to change, positively
or negatively with the application of fertilizers to the soil. Soil management
through the use of fertilizers can affect the soil microbial population which
influences the stability, productivity and resilience of the ecosystem and as
well, quality. Soil enzyme activities are also affected by the application of
fertilizers which in turn affects soil activities.
Inorganic fertilized soil has less
microbial population which proves that some microbial species may not be able
to use the micronutrients as can be used by microbes found in organic
fertilized soil. Chemical fertilizers are water soluble and can easily travel
into the soil which may be a factor for quick leaching of soil nutrients.
Addition of these fertilizers has accumulative negative effects over time on
the soil as well as the inhabited organisms.
Organic materials increase the
abundance of soil organisms which include the microorganisms by providing
organic matter and micronutrients for these organisms. Organic fertilizers
contain microorganisms which are introduced into the soil on application of these
fertilizers. These microbes are found to be active. Hence, the need to study
the impact of organic and inorganic fertilizers on soil microbial population
and enzyme activities.
1.2
MAIN
OBJECTIVE
The study was aimed to assess the effects of
different fertilizer treatments, i.e. organic and inorganic, on soil microbial
population and enzyme activities.
1.3 SPECIFIC OBJECTIVES
·
To investigate the
effects of cow dung, poultry manure, NPK (15:15:15) and urea fertilizers on the
soil microbial population;
·
Determination of the soil
phosphatase, urease, cellulase and dehydrogenase activities as affected by the
application of the organic and inorganic fertilizers;
·
Determination of the soil
microbial respiration rates as affected by the application of organic and inorganic
fertilizers;
·
To determine the effects
of the applied organic and inorganic fertilizers on the soil chemical
properties.
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