ABSTRACT
Field experiments were conducted between 2016 and 2018 at Forestry Research Institute of Nigeria, Humid Forest Research Station, Umuahia, South east Nigeria, to study litter production, decomposition and nutrient release dynamics in Allanblackia floribunda (oliv) agroforestry system and espacement interaction on growth and yield of maize and mungbean. The experiments were all laid out in a randomized complete block design with three replications for the experiment on litter production, decomposition and nutrient release, and four replications for the alley cropping experiments. Litter trays were used for monthly collection of leaf litter while the litter bag method was employed for the decomposition study. In the first espacement experiment, there were four treatments comprising 2 maize spatial arrangements (single and double rows) between Allanblackia hedge rows and a no-tree control (maize monocrop in single and double rows) In the second espacement experiment, treatments were four and comprised 2 mungbean plant spacings (20cm x 20cm and 30cmx 20cm) between Allanblackia rows and a no-tree control (mungbean monocrop 20cm x 20cm and 30cm x 20cm spacing). Results indicated that the dry season months of November, December, January and February gave significantly higher leaf litterfall (23.76 – 43.50 kg/ha in 2016/17 and 34.75 – 151.22kg/ha in 2017/18) than the rainy season months (4.96 – 14.53 kg/ha in 2016/17 and 8.81 – 17.96 kg/ha in 2017/18). Leaf litter production positively and significantly correlated with maximum temperature and negatively correlated with rainfall and relative humidity, with a bimodal pattern showing leaf litter peak production in January and December. The C:N ratio was 10.6:1. The cumulative mean leaf litter decomposition at 48 WALP was 91.0%, with a biphasic mode of decay, having an initial rapid phase of mass loss (4 – 24 WALP) and a later slower phase (28 – 48WALP). Leaf litter half-life was obtained at 8 WALP while the turn over coefficient k (decay constant) was 4.62/year. The percentage cumulative mean nutrient release for N, P, K, Ca and Mg increased up to 24 or 28 WALP and thereafter stabilized up to 40 WALP, after which a slight decline in P, K, Ca and Mg and a significant drop in nitrogen. However, Organic carbon increased significantly up to 32 WALP, beyond which no significant changes occurred in the cumulative release from the leaf litter. At 10 and 12 WAP, maize double row regardless of cropping system produced significantly taller plants and higher leaf area index than maize single row. However, maize double row under sole cropping had significantly higher seed yield than maize under alley cropping, irrespective of maize spatial arrangement. Alley cropping and mungbean spacing did not significantly affect mungbean stem diameter and leaf area index. In contrast, mungbean spacings 20 x 20cm and 30 x 20cm under sole cropping produced comparable high seed yields (2.7 – 3.1t/ha) as the closer spacing of 20 x 20cm in alley cropping (2.6 t/ha) but significantly higher yields than the wider spacing of 30 x 20cm in alley cropping with Allanblackia floribunda tree species. The continuous leaf litter production throughout the year, the high rate of litter decomposition and subsequent release of nutrient make A. floribunda leaf litter a good source of organic manure for soil fertility restoration and improved growth and yield of arable crops (maize and mungbean). The early yield reductions observed in the A. floribunda agroforestry system could be substantially minimised if the trees are planted at wider spacing and pruning of tree branches and crown management are done regularly.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table
of Contents vii
List of Tables xii
List of Plates xiv
Abstract xv
CHAPTER 1:
INTRODUCTION 1
CHAPTER 2: LITERATURE REVIEW 6
2.1 Agroforestry
6
2.1.1. Definitions of Agroforestry 6
2.1.2 Types
of Agroforestry systems and practices 7
2.1.3 Benefits of Agroforestry 14
2.2 Litterfall
19
2.3 Litter
Decomposition and Nutrient Release 22
2.4 Methods of Evaluating Litter Decomposition
24
2.4.1.
Mass balance 24
2.4.2. Litterbags 25
2.4.3. Tethered leaves 28
2.4.4.
Cohort layered screen 29
2.5. Rate of Litter Decomposition and Nutrient
Release 30
2.6. Factors Influencing Litter Decomposition
Rates 32
2.6.1 Climatic condition. 32
2.6.2 Substrate quality 33
2.6.3 Microbial activities 35
2.7. Benefits of Litterfall and Decomposition in Agroforestry System 36
2.7.1. Soil
protection and erosion control 36
2.7.2. Nutrient
cycling 37
2.7.3 Growth
and yield of crops 38
2.8 Crop
Yield in Agroforestry 39
2.8.1. Effects of alley cropping on crops 40
2.9 Species Description 43
2.9.1. Allanblackia floribunda 43
2.9.2 The
maize plant 45
2.9.3 Mungbean 48
CHAPTER 3: MATERIALS AND
METHODS 52
3.1 Study Area 52
3.2. Soil Sampling 53
3.2.1 Particle
size distribution 53
3.2.2 Determination
of soil pH 53
3.2.3 Determination
of organic carbon 53
3.2.4
Determination
of total nitrogen 53
3.2.5 Determination
of available phosphorus 54
3,2.6 Determination
of exchangeable cations 54
3.3. Experiment 1: Leaf
Litter Production of Allanblackia
floribunda 54
3.4. Experiment
2: Leaf Litter Decomposition and Nutrient
Release
Dynamics of Allanblackia
floribunda Leaf Litter 55
3.5. Computational Procedures 56
3.5.1.
Cumulative leaf litter decomposition (%) per sampling interval. 56
3.5.2. Leaf litter half – life and full-life
estimations 56
3.5.3. Turnover coefficient 57
3.5.4. Relative
leaf litter disappearance/decay rates
(% day-1
sampling interval-1) 61
3.5.5. Nutrient release of the decomposing leaf
litter 61
3.6 Physical and Chemical Analysis of Leaf Litter Samples 62
3.7. Experiment
3: Espacement Interaction with Allanblackia on
Growth and Yield
of Maize 62
3.7.1. Planting materials 62
3.7.2. Land preparation and soil sampling 62
3.7.3. Experimental design, treatments and
treatment allocation 63
3.7.4. Planting and field maintenance 63
3.7.5. Records of agronomic measurements 64
3.8 Experiment 4: Espacement Interaction with Allanblackia
on
Growth and Yield
of Mungbean 71
3.8.1. Planting materials 72
3.8.2. Land preparation 72
3.8.3. Experimental design, treatments and
treatment allocation. 72
3.8.4. Planting and field maintenance 72
3.8.5. Records of agronomic measurements 72
3.9. Statistical Analysis 73
CHAPTER 4: RESULTS AND
DISCUSSION 80
4.1. Soil Physico-Chemical Properties and Meteorological 80
Data of Experimental Sites
4.2. Experiment 1: Leaf Litter Production
of Allanblackia
floribunda 84
4.2.1.. Leaf litterfall of A. floribunda. 84
4.2.2 Correlation
of leaf litterfall of A. floribunda
with some
climatic variables 84
4.2.3. Discussion 88
4.3 Experiment
2: Litter Decomposition and Nutrient Release
Dynamics of Allanblackia
Floribunda Leaf Litter. 90
4.3.1 Cumulative
leaf litter decomposition (%) per sampling
interval of
A. Floribunda 90
4.3.2. Relative
leaf litter disappearance/decay rates
(% day-1
sampling interval-1) 90
4.3.3 Turnover
Coefficient (k1), leaf litter Half – life and
full-life
of A. Floribunnda. 93
4.3.4 Regression
equation parameters, observed and expected
mass losses (% decomposition) of A. Floribunda leaf litter 93
4.3.5 Nutrient release of A. floribunda leaf litter 93
4.3.6 Correlation between decomposition rate
and nutrient release 98
4.4 Discussion 100
4.4.1 Leaf
litter decomposition of A. floribunda 100
4.4.2 Relative decay/disappearance rate 101
4.4.3 Turnover
coefficient (K1), leaf litter half – life
and
full-life of A. Floribunnda. 102
4.4.4 Nutrient release A. floribunda leaf
litter 103
4.5. Experiment
3: Espacement Interaction with Allanblackia on
Growth and Yield of Maize 105
4.5.1. Soil moisture and
interception of photosynthetically active
radiation (PAR) by Maize. 105
4.5.2. Maize growth and seed yield 105
4.5.3 Discussion 113
4.6 Experiment
4: Espacement Interaction with Allanblackia
on
Growth and Yield of Mungbean 115
4.6.1. Interception
of photosynthetically active radiation (PAR)
and
mungbean growth. 115
4.6.2. Mungbean seed yield and yield components 117
4.6.3. Discussion 122
CHAPTER 5: CONCLUSION AND
RECOMMENDATIONS 125
5.1 Conclusion
125
5.2 Recommendations 128
References
Appendices
LIST OF TABLES
PAGE
4.1: Some physical and chemical
properties of the agroforestry site
at Forestry Research Institute 0f
Nigeria, Umuahia, in 2016 and 2017. 81
4.2: Some physical and chemical
properties of the Non-agroforestry
site at Forestry Research Institute
of Nigeria, Umuahia, in 2016 and 2017. 82
4.3: Meteorological data of
experimental site at Forestry Research
Institute of Nigeria, Umuahia. 83
4.4: Mean monthly leaf litter production of Allanblackia
floribunda 85
4.5: Seasonal variation of leaf litter production
of Allanblackia floribunda 86
4.6: Correlation of leaf litter production of A. floribundawith some
climatic
variables. 87
4.7: Cumulative
leaf litter decomposition (%) of A.
floribunda
per
sampling interval. 91
4.8:
Relative leaf litter disappearance/decay rates of A. floribunda
(%
day-1 sampling interval-1). 92
4.9: Turnover
Coefficient (K1), Leaf Litter Half – life and Full-life of
A.
floribunnda. 94
4.10: Regression equation parameters observed and
expected mass losses
(decomposition)
of A. floribunda leaf litter. 95
4. 11: Initial Nutrient Content of A. floribunda Leaf
Litter 96
4.12:
Cumulative nutrient release of leaf litter of A. floribunda 97
4.13: Correlation between
decomposition rate and nutrient release 99
4.14: Soil
moisture and interception of photosynthetically active radiation
by maize in the agroforestry and non-agroforestry sites 106
4.15: Effect
of alley cropping with Allanblackia
floribunda and maize spatial
arrangement on maize plant height
(cm) in 2016 and 2017 cropping
seasons. 108
4.16: Effect
of alley cropping with Allanblackia
floribunda and maize spatial
arrangement on maize stem girth (cm) in 2016 and
2017 cropping seasons. 109
4.17: Effect
of alley cropping with Allanblackia
floribunda and maize spatial
arrangement on maize stem girth (cm) in 2016 and
2017 cropping seasons 110
4.18:
Effect of alley cropping with Allanblackia
floribunda and maize spatial arrangement
on maize seed yield and yield components 112
4.19:
Photosynthetically active radiation intercepted by mungbean in the agroforestry and non-agroforestry sites 116
4.20:
Effects of alley cropping and mungbean spacing on mungbean plant
height (cm). 118
4.21: Effects of alley cropping
and mungbean spacing on mungbean stem
girth (cm). 119
4.22: Effects of alley cropping
and mungbean spacing on mungbean leaf
area index. 120
4.23: Effect
of Alley cropping with Allanblackia
floribunda and
mungbean
plant spacing on mungbean seed yield. 121
LIST OF PLATES
PAGE
3.1a Litter trays in
the field 58
3.1b Burying the
litter bag 59
3.1c Burying the
litter bag 60
3.2a PAR measurement
at 6WAP 65
3.2b Maize double
row at 12WAP 66
3.2c Maize single
row at 16WAP 67
3.3a Double maize
row + Allanblackia 68
3.3b Single maize
row + Allanblackia 69
3.3c Allanblackia
plot 70
3.4a: Mungbean growth
in sole cropping 74
3.4b: Harvesting of
mungbean 75
3.4c: Mungbean pods
in sole cropping 76
3.5: PAR measurement in mungbean 77
3.6a: Mungbean
pods in alley cropping 78
3.6b: Mungbean
in alley cropping 79
CHAPTER 1
INTRODUCTION
Native fruit trees in agroforestry systems
play notable role in rural communities especially in the areas of poverty
alleviation, food security, wealth creation, health and environmental
management, mainly in tropical Africa and mostly with women (Asaah et al., 2011). Trees,
when intercropped in farm land, are often able to control soil erosion, enhance
water and nutrient cycling and improve both soil organic carbon and the
abundance of activities of useful soil organisms (Barrios et al., 2012). Trees can also have
negative effects on crops in terms of water and nutrients competition. The land
area available for the crops on the field is also reduced, so that the total
influence of agroforestry on crops field over time will be based on features
and interactions of the trees, crops, soil type, climatic condition and
management (Bayala et al., 2012).
Agroforestry
systems that integrate perennial trees with sustainable agriculture can be a
vital element of both biodiversity conservation, socio-ecological resilience
and socio-economic gains (Sistla, 2016). Though agroforestry
systems are less diverse and less dense than natural forests but they are vital
tools for sustainable biodiversity conservation (Oke and Odebiyi, 2007; McNeely
and Schroth, 2006). It has been reported that
conventional agroforestry practices help in biodiversity conservation through in
situ conservation of tree species on farms thereby reducing pressure on
remnant forests (Fifanou et al.,
2011).
Allanblackia
floribunda is a dioecious multipurpose tree which belongs to the family Clusiaceae or Guttiferae. It is an evergreen tree that grows mainly in tropical rainforests but
is also found in cultivated farmland areas (Buss and Tissari, 2010). The genus Allanblackia
consists of nine species found in the equatorial rainforests of West, East and
Central African regions extending from Tanzania to Sierra Leone (Pye-Smith,
2009). Three of the nine species (A. stuhlmannii, A. floribunda and A.
parviflora) have known importance in food (margarine) and cosmetic (soap
and detergent) industries. Out of the three species of importance A. floribunda is grown in Nigeria. The seed of A. floribunda is rich in
edible oil and has some healthy physicochemical characteristics in food
production that gives it an edge over other oils (Folarin et al 2017; Crockett, 2015). When dried, the
kernel contains about 67-73% of solid white fat comprising 52
58
% stearic acid and 39
45
% oleic acid (Fobane et al., 2014;
Pye- Smith 2009). The oil when used as vegetable-based dairy
products such as ice cream, margarine and spreads, requires less chemical
processing as compared to others. It solidifies at room temperature (SDN, 2016;
Crockett, 2015) and the fatty acid composition (Stearic and oleic) of the
oil has been reported to lower plasma cholesterol levels and thereby reduce the
risk of heart attacks unlike other oils used for food manufacturing that
contain higher levels of lauric, myristic, and/or palmitic acids with health
risks (Folarin et al 2017; Crockett,
2015; Sefah, 2006). The oil is also used for pharmaceutical preparations due to
the presence of stearic acid (Folarin et
al 2017).
A new agro-business based on the sales of
the seed is being established in Ghana, Nigeria, Cameroon and Tanzania. The
seed oil is of prime importance as a foreign exchange earner and is being
developed as a rural-based enterprise for its application in the manufacture of
margarine (Buss and Tissari, 2010). There is a huge market for Allanblackia spp oil and it has already
received European Union certification as safe in food products. The demand for Allanblackia spp seeds is about
100,000 tons annually.
However, only 200 tons are supplied annually on average from Ghana (40 tons of A.
parviflora), Nigeria (20 tons of A. floribunda) and Tanzania (150
tons of A. stuhlmannii) (Oppong, 2008; Kattah, 2010). The
present rate of seed supply implies that collection of seeds from the wild
would not sustain the Allanblackia spp business. Since the demand
for Allanblackia spp oil is greater than the supply from the natural
forest and remnants on farms, the risk is that wild seed collection of Allanblackia
spp may lead to over-exploitation of this resource in such a manner that
will impair natural regeneration as well as biodiversity conservation (Oppong,
2008; Kattah, 2010). Consequently,
some species of Allanblackia are on
International Union for the Conservation of Nature’s (IUCN) red list of
endangered species (SDN, 2016; Cheek, 2004).
To address the challenges
of over-exploitation and decreasing A. floribunda abundance in the
forests, there is need for A. floribunda to be introduced into our
farming systems through agroforestry in homestead farms and on- farm
conservation. A. floribunda-based
agroforestry will not only serve as an alternative source of income to farmers,
but also contribute to the maintenance of soil nutrient pool through litter
production and its subsequent decomposition. Agroforestry being a
dynamic, ecologically based, natural resource management system not only
integrates trees in farm and rangeland, diversifies and sustains smallholder
production for increased social, economic and environmental benefits (Leakey,
1996) but also has great potentials for enhancing the protection status of
forest tree species which are heavily harvested by dependent communities. Such
tree species can be integrated into farming systems around the forest to
provide alternative sources for the associated products and services (Kasolo
and Temu, 2008; Ruark, 1999).
Litterfall from plants especially trees, is
an important channel for organic matter and energy into the soil and is necessary
for nutrient cycling in ecosystem (Triadiati et al., 2011). Hence, litterfall, decomposition and nutrient cycle
in terrestrial ecosystem play important role in turnover of nutrient and
maintenance of soil fertility and productivity (Saha et al., 2016). Bisht et al.,
(2014) noted that litterfall and decomposition are key processes in
biogeochemical process of agroforestry system. Plant litterfall and
decomposition is therefore a crucial ecosystem process that defines and
maintains the plant-soil relationships by regulating the nutrient turnover and
the build-up of soil organic matter. In fact, the release of nutrients through
decomposition is the main source of available nutrients for plants in most unmanaged
terrestrial ecosystems (Chandraa et al., 2015). A
thorough understanding of litter production, decomposition and nutrient release
dynamics of plant litter is essential in understanding the functioning of
agroforestry ecosystems, since it is central to many ecosystem functions such
as soil formation and nutrient cycling (Rawat et al., 2010; Yu et al.,
2004). Integrating Allanblackia
floribunda into our farm lands will not only help in conserving the species
but also improve the soil quality and nutrient status of the farm land through
leaf litter accumulation and decomposition of A. floribunda. The tree species could also serve as an alternative
source of income for resource poor farmers and help in ameliorating some of the
environmental concerns associated with conventional farming systems.
Despite
its importance, little is known about intercropping A. floribunda tree with arable crops like maize and mungbean under
an alley cropping arrangement in South Eastern Nigeria. Maize (Zea mays) is a crop that features prominently in the cropping
systems of South Eastern Nigeria (Okpara, 2000) while mungbean (Vigna radiata) is a new crop which
is gradually being grown in Nigeria (Onuh
et al., 2011). Maize is
not only a staple food but a leading agricultural crop
which is used as food, feed, fuel and fibre (Scott, 2015). On the other hand,
mungbean is reported to be an excellent food owing to its significant amount of
proteins, carbohydrate and a range of micronutrients in diets and invaluable
source of lysine and digestible protein for humans (Anwar et al., 2007; AVRDC, 2012; Khan et al.,
2012; Mondal et al., 2012). Mungbean protein and
carbohydrates are freely digested and cause less flatulence than that from
other legumes (Waniale et al., 2014).
The popularity of systems
involving cereals and legumes stems from the fact that cereals provide staple
food and are high yielding (Willey, 1979), while legumes
offer a lot of dietary proteins and improve nutrient status of soils through
nitrogen fixation (Okpara and Omaliko, 1995, Anjum et al., 2006). There is a dearth of
research information on intercropping of grain crops with hedgerow species such
as Allanblackia floribunda under
alley cropping in South Eastern Nigeria.
Objectives of the study were to:
1.
evaluate the rate of A. floribunda leaf litterfall and quality
2.
determine the
decomposition and nutrient release pattern of A. floribunda leaf litter
3.
examine the effect of A.
floribunda tree and maize spatial arrangement on growth and yield of maize
under alley cropping.
4.
ascertain the effect of A.
floribunda tree and mungbean spacing on growth and yield of mungbean.
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