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Technical Paper 8: Examples of Experimental Designs for Alley Farming Trials

Sagary Nokoe


8.0 Performance objective
8.1 Introduction
8.2 Examples of experimental designs
8.3 References


8.0 Performance objective

Technical paper 8 is intended to enable you to:

· Describe examples of experimental designs being followed in on-going alley farming field trials.

8.1 Introduction

This paper provides the interested reader with a set of examples of experimental designs for various types of alley farming trials. The examples are drawn from actual on-going or proposed field trials. They cover basic designs which appear to have universal acceptability for alley farming experiments.

The basic principles for the design and layout of alley farming trials are covered in the previous paper (Technical Paper 7). The standard design recommendations for AFNETA collaborative research projects are available from the network coordination unit.

8.2 Examples of experimental designs


Example 1: Fallow management in alley farming.
Example 2: Screening of multi-purpose trees in different intra-row spacings for alley farming.
Example 3: Screening of Gliricidia collections across a range of environmental and edaphic conditions in West Africa.
Example 4: Assessment of effects of feed supplementation from different legume trees.
Example 5: Comparison of the effectiveness of 3 leguminous tree crops in soil fertility maintenance and in sustainability of crop production.
Example 6: Efficiency of selected multipurpose tree species in alley farming on soil fertility regeneration and agricultural crop yield.
Example 7: Alley farming trials concerning both soil fertility and animal production.
Example 8: Evaluation of species mixture in alley trials.
Example 9: Effect of tree density on water relations of trees in alley farming systems in the dry areas.
Example 10: Evaluation of the negative effects of fodder uptake on agricultural crop yield.
Example 11: Light interception and its effect on crop yield in alley farms.
Example 12: Effect of lime and manure application on the growth of hedgerow species in strongly acidic (pH 3.5-5) soil.
Example 13: Integration of short grazed fallows in rotation within Leucaena alleys and their effects on soil fertility and crop yield.
Example 14: Pattern of N build-up in the pens of sheep receiving different feed supplementations of alley shrubs.
Example 15: Manurial value of manure dug out from pens receiving known levels of leguminous fodder supplements (Extension of example 14).
Example 16: Effect of hedgerow species on surface soil physical properties.
Example 17: Growth of alley shrubs in farmers' fields
Example 18: Evaluation of an alley cropping species, Calliandra calothyrsus (Meissn.) on an Oxic Paleustalf.
Example 19: Effect of alley crop combinations on sequentially cropped maize and cowpea.


Example 1: Fallow management in alley farming.

Treatment:

A - 4 year cropping/2 year unmanaged fallow
B - 4 year cropping/2 year managed fallow
C - 4 year alley cropping/2 year unmanaged fallow
D - 4 year alley cropping/2 year managed fallow

Intercrop: Maize

Notes:

(i) Treatment combinations will allow comparison of normal cropping with alley cropping at the end of or at any time during the 4-year period, as well as monitoring of the effect of fallow management and its interaction with cropping.

(ii) Design can be Randomized Complete Block (RCB) with a minimum of 3 replications.

(iii) Assessment can be in terms of changes in soil fertility status, crop yield/economic returns, etc.

(iv) Possible layout

A

C

D

B

A

D

C

B

B

A

C

D

(v) On farmers' plots, the design can be modified slightly as indicated in the layout below:

A

B

Normal Cropping

C

D

Alley Cropping

With each farmer as a replicate, this can be considered a split-plot arrangement, with type of cropping as the main-plot and management practice in the sub-plot.

Example 2: Screening of multi-purpose trees in different intra-row spacings for alley farming.

Treatments:

Two factors (Tree Species and Spacing) are involved:

Factor A Tree Species

A1: Acacia albida
A2: A. manginum
A3: Azadirachta indica
A4: Albizia lebbeck
AS: Leucaena leucocephala
A6: Gliricidia sepium

Factor B Intra-row spacing

B1: 50 cm
B2: 100 cm
B3: 150 cm
B4: 200 cm

Notes:

(i) Possible design: m a split plot (with species in main plots and intra-row espacement in sub-plots) in an RCB design with 3 replications. If the levels of Factor B differ from species to species (which is a possibility), this would lead to a nested design with intra-row spacing nested in the plots containing the trees.

(ii) A possible layout for one replicate could be:

REP 1:

Factor
B
within
A






Factor A:

B1






B2






B4






B3






A. manginum

Example 3: Screening of Gliricidia collections across a range of environmental and edaphic conditions in West Africa.

Treatments: 12 different accessions (ILG50 - ILG61)

Design: 3 x 4 rectangular lattice in three replicates, for 5 locations (triple rectangular lattice).

Possible layout at each location:

Block

Group X

Group Y

Group Z

(i)

5 4 6

2 5 12

4 3 11

(ii)

1 2 3

9 3 6

2 9 10

(iii)

10 11 12

4 7 10

6 8 12

(iv)

7 8 9

1 8 11

5 7 1

Example 4: Assessment of effects of feed supplementation from different legume trees.

Treatment: Four treatments corresponding to 4 feed rations formulated as follows:

1.

Normal ration (ALP)


2.

ALP + Gliricidia sepium

(800 gm DM/animal/day)

3.

ALP + Leucaena sp.

(800 gm DM/animal/day)

4.

ALP + Flemingia sp.

(800 gm DM/animal/day)

Procedure:

(a) Select 20 animals; usually they will be of different weights or ages. Divide animals into, for example, 5 weight groups of equal sizes, and ensure that each weight group receives all treatments. The design is thus identical to a block design with 5 replicates per treatment.

(b) Alternatively, allocate the 4 treatments randomly to the 20 animals, ensuring 5 replicates per treatment. This can then be considered as unrestricted randomized design. However, considering differences in weights and the possibility of unbalanced mean weight among treatment groups, the method of Covariance Analysis with initial animal weights as covariate should be used. The analysis of covariance is an extremely valuable statistical technique for increasing precision.

Example 5: Comparison of the effectiveness of 3 leguminous tree crops in soil fertility maintenance and in sustainability of crop production.

Treatments:

Two factors are involved in this example, namely, tree species and fertilization:
Tree species - Azadirachta indica, Leucaena sp., Gliricidia sp.
Fertilization - NPK 45 kg/ha, No fertilization

Design possibilities:

(i) For on-farm, farmer-managed trials, the ideal design is split-plot with fertilization in the main plot.

(ii) For research-plot trials, factorial arrangement in a block design allows equal evaluation of both factors. However, if interest lies more on one factor than the other, then the split-plot arrangement is recommended, with the more important factor in the split or smallest plot.

(iii) The factorial arrangement in a Randomized Complete Block (RCB) is used to demonstrate the analysis of variance outline.

Example 6: Efficiency of selected multipurpose tree species in alley farming on soil fertility regeneration and agricultural crop yield.

Treatments:

A. Alley farming with Species A
B. Alley farming with Species B
C. Alley farming with Species C
D. Non-alley farming

Notes:

(i) A Latin-Square arrangement is most suitable

(ii) Possible layout could be as follows:

A 50 *

B 12

C 18

D 92

B 63

C 4

D 52

A 8

C 12

D 72

A 35

B 83

D 21

A 25

B 32

C 62

* Numerical figures represent hypothetical data after 4 years of trial.

The data concerning treatment combinations could be observed from a known variable.

Example 7: Alley farming trials concerning both soil fertility and animal production.

Treatments: Three pruning regimes are planned, as follows:

1. Zero mulching/3 prunings for feeding.
2. 1 mulching/2 prunings for feeding.
3. 2 mulching/1 pruning for feeding.
4. 3 mulching/0 pruning for feeding

Assessment considerations:

(i) Dependent variables cover both the effects of mulching on soil and the effect of feeding animals with prunings, assuming the same amount of prunings are made on each occasion.

(ii) If soil fertility is assessed indirectly on the basis of agricultural crop yield, then an economic analysis (with revenue, for example, as the dependent variable) that combines both crop and animal productivity will be desirable. The analysis can also be performed separately for crop and livestock components. In the case of crop analysis, such separation will allow assessment of the effects on crop yield of removing prunings.

(iii) A block design is appropriate especially if trials are carried out on farmers plots, in which case a farmer's plot may be considered as a replicate. If several species are being evaluated a split-plot arrangement should be considered.

Example 8: Evaluation of species mixture in alley trials.

Treatment: This type of experiment could involve 3 species and 23 factorial arrangement in a block design.

Factors:

Species A at 0, 1 levels


Species B at 0, 1 levels


Species C at 0, 1 levels

Treatment Combinations:

A0B0C0

=

(1)

control

A1B0C0

=

(a)


A1B0C0

=

(ac)


A1B1C0

=

(ab)


A0B0C1

=

(c)


A0B1C1

=

(bc)


A0B1C0

=

(b)


A1B1C1

=

(abc)


Procedure: Randomize treatment combinations in blocks, and analyze results with 7 degrees of freedom (df) per treatment. The treatment source of variation is further split into:

Factors A, B. C, each with 1 df
Interactions AB, AC, BC, each with 1 df
Interaction ABC with 1 df

Example 9: Effect of tree density on water relations of trees in alley farming systems in the dry areas.

Treatments: A single tree species is investigated at different densities.

Tree density A
Tree density B
Tree density C
Tree density D
Tree density E

Design considerations are as for Example 6. Given more than one species, a split-plot may be considered.

Example 10: Evaluation of the negative effects of fodder uptake on agricultural crop yield.

Treatments:

A - No fodder removed
B - 20% fodder removed
C - 40% fodder removed
D - 60% fodder removed
E - 80% fodder removed
F - 100%. fodder removed

Design: Any of the basic designs may be used, depending on land availability.

Notes:

(i) Observe crop yield periodically and analyze according to design used. A block design or an ordinary randomized design could be appropriate.

(ii) Alternatively, the trend in the effect of fodder reduction on crop yield can be investigated using single degree of freedom orthogonal polynomials. The relevant data would be percentage losses in yield from the previous cropping season, during which no fodder was removed from any plot.

(iii) During analysis, check whether the trend in percentage losses over increasing removal of fodder is linear, quadratic, etc.

Example 11: Light interception and its effect on crop yield in alley farms.

Treatments: Three factors are involved:

Factor H- Hedgerow shrubs at 5 levels

H1: Acioa
H2: Alchornea
H3: Gliricidia
H4: Leucaena
H5: NIL (as control)

Factor S- Interhedgerow spacing at 2 levels

S1: Spacing 2m
S2: Spacing 4m

Factor F- Fertilization at 2 levels

F1: 45-20-20 N-P-K kg/ha
F2: 90-40-40 N-P-K kg/ha

Intercrop: Maize

Observations: Incident solar radiation of maize leaves at known height

(i) Height at which solar radiation values are taken (Hc)
(ii) Corresponding shrub height at time of solar observation (Hh)
(iii) Height/distance index ({Hh - Hc}/S)
(iv) Crop (maize) yield.

Design: Split-plot with Factor H in main plot, and a crossed (factorial) combination of Factor S and Factor F in the 4 sub-plots.

Analyses:

(i) Analysis of variance with the split-plot breakdown
(ii) Linear or non-linear regression relating:

- % incident light to height/distance index
- Crop yield to % incident light
- Crop yield to dry pruning biomas

Example 12: Effect of lime and manure application on the growth of hedgerow species in strongly acidic (pH 3.5-5) soil.

Treatments: Three factors are involved:

Factor S- Shrub species at 4 levels

S1: Sesbania
S2: Calliandra
S3: Leucaena
S4: Markhamia

Factor L- Liming at 2 levels

L1: 0 t/ha
L2: 10/ha

Factor M- Manure at 3 levels

M 1: 0 t/ha
M2: 5 t/ha and M3: 10t/ha

Design: Split-split plot arrangement. Factor S is the main plot, with each plots divided into 2 sub-plots. Three months after establishment the sub plots received the 2 levels of Factor L respectively. Each sub-plot is further divided into 3(sub-sub) plots to which levels of Factor M are allocated randomly.

Observations:

(i) Height growth of shrubs at predetermined intervals

(ii) A derived variable known as the Lime Response Index (LRI)

Definition:

Where HML (8) = the mean height of shrubs receiving liming at 8 months after planting (MAP)

HWL (8) = the mean height of shrubs without liming at 8 MAP

HWL (3) = the mean height of shrubs without liming at 3 MAP.

(Source: Yamoah, Grosz and Nizeyimana, 1989)

Example 13: Integration of short grazed fallows in rotation within Leucaena alleys and their effects on soil fertility and crop yield.

Treatments: Cropping systems at 5 levels:

C1: Continuous cropping without trees (control)
C2: Continuous cropping in Leucaena alleys
C3: Grazed tallow/cropping rotation in Leucaena alleys
C4: Cropping/grazed fallow rotation in Leucaena alleys
C5: Continuous alley grazing in Leucaena alleys
Duration of experiment is 4 years, with rotation in C3 and C4 effected every 2 years

Intercrop: Maize

Design: Randomized block design

Observations:

(i) Chemical analyses of soil samples at beginning of trial and before each first season crop

(ii) Dry matter and nitrogen content values from prunings of Leucaena hedgerows

(iii) Maize crop yield

(Source: Atta-Krah, 1990)

Example 14: Pattern of N build-up in the pens of sheep receiving different feed supplementations of alley shrubs.

Treatments: Diet supplement at 4 levels

D1: 200 g dry matter (DM)/head/day of mixed (1: 1 w/w ratio) of Leucaena and Gliricidia forage

D2: 400 g DM/head/day

D3: 800 g DM/head/day

D4: 1200 g DM/head/day

Design: Completely randomized, with 40 pregnant West African Dwarf sheep randomly allocated to the 4 diet supplementations (10 pens per diet treatment). All animals receive ad libitum chopped Panicum maximum grass plus 50 g of sun-dried cassava peel as basal diet Each pen also has 5 kg of wood shavings spread on top of litter at 4 weeks.

Observation: Random samples of wood shavings, analyzed for N at 2, 4, and 5 weeks after the sheep have been placed in the pens

(Source: Cobbina, Atta-Krah, and Kang, 1989)

Example 15: Manurial value of manure dug out from pens receiving known levels of leguminous fodder supplements (Extension of example 14).

Treatments: Two factors involved

Factor D- 5 levels of diet supplement (as in example 15) for 5 week-period.

D1: Pen with 200 g/DM/Head/day
D2: Pen with 400 g/DM/head/day
D3: Pen with 800 g/DM/head/day
D4: Pen with 1200 g/DM/head/day
D5: Control (raw wood shavings)

Factor S- Manure rates at 3 levels

S1: 4 g/kg soil
S2: 8 g/kg soil
S3: 12 g/kg soil

Design: Completely Randomized (CRD) or Randomized Complete Block (RCB) design with 5 x 3 factorial arrangment of treatments. Each treatment is replicated 3 times. The choice as to CRD or RCB depends on the arrangement of pots in the greenhouse. In each pot, maize is planted.

Observations:

(i) Maize shoot dry matter yield
(ii) Soil chemical analyses (pre- and post-trial)

(Source: Cobbina, Atta-Krah and Kang, 1989)

Example 16: Effect of hedgerow species on surface soil physical properties.

Treatment: Hedgerow species at 5 levels

S1: Leucaena leucocephala
S2: Gliricidia sepium
S3: Alchorneaa cordifolia
S4: Acioa barteri
S5: Control (no hedgerow species)

Intercrop: Sequential cropping of maize (main season crop) and cowpea (minor season crop)

Design: Randomised complete block with 3 replications (blocks). Inter hedgerow spacing is 4 m.

Observations:

(i) Crop yield
(ii) Soil physical properties (bulk density, pore size, water infiltration etc.) at predetermined intervals.

(Source: Hulugalle and Kang, 1990)

Example 17: Growth of alley shrubs in farmers' fields

Treatments: Alley shrubs at 3 levels

S1: Leucaena leucocephala var K28
S2: Gliricidia sepium local variety
S3: No alley shrub (control)

Design: Eight farmers plots are selected within a known area. Each farm constitutes a block, with 3 plots receiving randomly either S1, S2, or S3 This results in a completely randomized design with 8 replications (the replicates being the farmers)

Observations

(i) Soil chemical characters based on sample from each plot (before and during trial)
(ii) Shrub height growth at pre-determined periods.

(Source: Cobbina, Kang and Atta-Krah, 1989)

Example 18: Evaluation of an alley cropping species, Calliandra calothyrsus (Meissn.) on an Oxic Paleustalf.

Treatments: Treatments comprise combinations of two factors as follows:

Factor N - Rate of N applications at 3 levels

N1: 0 N
N2: 45 N in kg/ha
N3: 90 N in kg/ha

Factor P - Prunings management at 2 levels

P1: Prunings removed (-PR)
P2: Prunings retained (+PR)

Intercrop: Maize

Design:

(i) In Layout 1, randomization is such that all N levels are in each row. The +PR or -PR factor is randomly allocated such that in the third row no combination from the first row is repeated! This arrangement is not recommended.

(ii) In Layout 2, randomization of the N levels is made on row plots which have either +PR or -PR. This is a split-plot arrangement with PR in main plots and N in the sub-plots. This design is preferred to Layout 1.
(iii) In Layout 3, treatment arrangement is factorial (3 x 2). The design is simply the Randomized Block, and is much preferred to-Layout 1 and Layout 3 Its preference over Layout 2 is due to the fact that both PR and N levels can be evaluated equally.

(V = the middle row which is planted with same maize crop as in the alleys but receives no treatment)

Observations:

(i) Crop yield,
(ii) Soil chemical content

(Source: Gichuru and Kang, 1989)

Example 19: Effect of alley crop combinations on sequentially cropped maize and cowpea.

Treatment: Species combinations as follows:

Acioa barteri

Leucaena leucocephala

T1:

r

0%

T2:

0%

100%

T3:

25%

75%

T4:

50%

50%

T5:

75%

25%

T6:

100%

0%

Design: Randomized Complete Block plots are split at the cropping stage into 2 equal parts and receive 0 and 60 kg N/ha. This later modification changes the design to a split-plot.

(Source: Siaw, Kang, and Okali - In press).

8.3 References

Atta-Krah A.N. 1990. Alley farming with Leucaena: Effect of short grazed fallows on soil fertility and crop yields. Exp. Agric 26, 1-10.

Cobbina J., Atta-Krah A.N. and Kang B.T . 1989. Leguminous browse manure. supplementation effect on the agronomic value of sheep and goat Biological Agriculture and Horticulture, 6, 115-121.

Cobbina J., Kang B.T. and Atta-Krah A.N. 1989. Effect of soil fertility on early growth of Leucaena and Gliricidia in alley farms. Agroforestry Systems 8, 157-164.

Hulugale N.R. and Kang B.T. 1990. Effect of hedgerow species in alley cropping systems on surface soil physical properties of an Oxic Paleustalf in southwestern Nigeria. 301-307.

Gichuru M.P. and Kang B.T. 1989. Calliandra calothrysus (Meissn.) in an alley cropping system with sequentially cropped maize and cowpea in south-western Nigeria. Agroforestry Systems 9, 19 1 -203

Siaw D.E.K.A., Kang B.T. and Okali D.U.U. 1991. Alley cropping with Leucaena leucocephala and Acioa barteri. (In press).

Yamoah C., Grosz R. & Nizeyimana E. 1989. Early growth of alley shrubs in the highland region of Rwanda. Agroforestry Systems, 9, 171-184.


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