Transcript Quantitative analysis of cropping systems

Sustainable low-input cereal production:
required varietal characteristics and crop
diversity
Working Group 4: plant-plant
interactions
About SUSVAR….
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System characteristics:
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Aims:
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Cereal production
Low-input conditions
Increased stability (yield and quality)
Increased resource use efficiency
Main means:
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Better use of crop genetic diversity
Better use of crop genetic diversity (1)
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Selection of suitable genotypes
Better use of available gene-pool for low-input systems
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Varieties that are well suited to low-input conditions in
general
Varieties that are well suited to specific conditions
(environmental conditions by definition more variable
than under high-input conditions)
Better use of crop genetic diversity (2)
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Use of mixtures
Utilize more genotypes simultaneously
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Heterogeneity contributes to stability (risk avoidance)
Generation of added value:
• Facilitation
• Competition
Crop - environment: mutual interaction
environment
Crop A
Facilitation: positive effect
environment
+
crop A
Crop
Crop B
Facilitative production principle: insects
Competition: negative influence
environment
crop A
Crop
Crop B
Competitive relations are important
Competition also the basis for over-yielding
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Competitive production principle
intra-specific competition > inter-specific
competition
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Niche-differentiation or complementarity
 better exploitation of available resources
Facilitative production principle: weeds
Facilitation
(the creation of a weed free environment)
is through
Competition
(suppression of weeds by other crop)
Challenge: avoid other crop from developing into a
weed.
Facilitative production principle: weeds
Working group plant-plant interaction
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Crop – weed interaction
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Weed suppression
Which traits
General or environment specific
Easy screening procedures
In case of mixtures
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Crop – crop interaction
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Yield stability
• Difference in stress-tolerance
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Productivity
• Niche differentiation
• Intra-specific competition > inter-specific competition
Weed suppression of mixtures
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Crop – crop – weed interaction
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How to maximize weed suppression?
• Combine most competitive cultivars
• Maximize complementarity
– Complementarity in resource use and acquisition
– Complementarity in weed suppression mechanism
Currently many different questions ….
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What do we want to obtain with mixtures?
(stability, productivity, weed suppression, others)
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How can added value of mixtures be obtained?
(what is the best strategy)
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How to select individual varieties for their
performance in mixtures?
Time to decide on where to go …
Organisation of activities and reciprocal benefits
WG 3
WG 4
Plant – Soil
Interactions
Plant – Plant
Interactions
WG 1
Genetics & Breeding
WG 6
WG 2
Variety testing &
certification
Biostatistics
WG 5
Plant Disease
Complex
Facilitative production principle: diseases
Plant-plant interaction
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Main issues:
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Productivity
Stability
Weed suppression
Learning-objectives
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To familiarise with options for evaluating:
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productivity
competitive relations
within intercropping systems
To be able to value the various methodologies
To learn the relationship between some indices of
relative competitive ability
Multiple cropping
Growing two or more crops on the same field in a year
- sequential cropping
- relay intercropping
- full intercropping
time
Reasons for intercropping
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Better use of available resources
(land, labour, light, water, nutrients)
Reduction in pest pressure + associated damage
(diseases, insects, weeds)
Socio-economic
(greater stability, risk avoidance, food/cash crops)
Sustainability
(erosion, soil fertility)
Facilitative production principle: diseases
Causal organism:
Magnaporthe grisea
two phases:
vegetative stage
Leaf blast
reproductive phase
Neck or panicle blast
Intercropping as weed management component
Leek monoculture
weed-free period
mechanical weeding
manual weeding
Weeds
Leek-Celery Intercrop
weed-free period
mechanical weeding
Weeds
Transplanting
Harvest
Competition the basis for over-yielding?
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Niche-differentiation
 better exploitation of available resources
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separation in time (relay)
separation in space (rooting depth)
different resource capture abilities
different growth requirements
Key to evaluation of intercrop productivity
Quantification of competitive relations
Example:
Two-species mixture (sp 1 - sp 2)
How many competition coefficients?
Key to evaluation of intercrop productivity
Quantification of competitive relations
Example:
Two-species mixture (sp 1 - sp 2)
How many competition coefficients?
2 intraspecific competition coefficients: b11, b22
2 interspecific competition coefficients: b12, b21
Intraspecific competition
Y=N/(b0+b1N)  W=Y/N=1/(b0+b1N)  1/W=b0+b1N
Measure of intraspecific competition
1/W1=b10+b11N1
b10
b11
b11/b10
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[plant/g]
[m2/g]
[m2/plant]
crowding coefficient (de Wit)
ecological neighbourhood area (Antonovics & Levin)
Intercropping: intra and interspecific
1/W1=b10+b11N1+ b12N2
b11/b12 relative competitive ability
What does this value learn us?
Intercrop productivity
1/W1=b10+b11N1+ b12N2
and
1/W2=b20+b22N2+ b21N1
b11/b12 and b22/b21
Niche differentiation index (NDI):
b11/b12 * b22/b21= (b11*b22)/(b12*b21)
NDI =1,<1,>1
How can we determine these indices?
Evaluation in practice
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Experiment with three treatments:
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Calculation of Relative Yield
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Monoculture of species 1 Y1,mono
Monoculture of species 2 Y2,mono
Mixture of species 1 and 2 Y1,mix, Y2,mix
RY1 =Y1,mix/Y1,mono
RY2 =Y2,mix/Y2,mono
Land Equivalent Ratio (LER)
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LER = RY1 + RY2
relative land area under sole crops required to produce the
yields achieved in intercropping
Two basic designs
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Additive design
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
species 1
x
x
x
x
x
x x x
x x x
x x x
x x x
x x x
species 2
0x0x0x0x
0x0x0x0x
0x0x0x0x
0x0x0x0x
0x0x0x0x
mixture
Two basic designs
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Replacement design
0 0 0 0
x x x
0 0 0 0
x x x
0 0 0 0
x x x
0 0 0 0
x x x
0 0 0 0
x x x
species 1
species 2
x
x
x
x
x
0
0
0
0
0
x 0
x 0
x 0
x 0
x 0
mixture
x
x
x
x
x
Replacement design
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Overall density constant
Results represented in a
replacement diagram
LER generally replaced by
Relative Yield Total (RYT)
Relative crowding coefficient
(k) to express competitive
relations:
k12=(1-z1)/(w11/w12-z1)
z1=fraction species 1
1.2
1.2
1.0
1.0
0.8
0.8
k21=1.93
0.6
0.6
0.4
0.4
k12=0.58
0.2
0.2
0.0
0.0
0
0.5
1
Replacement design
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k  intrasp/intersp comp.
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Similar to b11/b12?
k*k
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related to intercrop
productivity
=1, >1, <1
Similar to NDI?
1.2
1.2
1.0
1.0
0.8
0.8
k21=1.93
0.6
0.6
0.4
0.4
k12=0.58
0.2
0.2
k12=
0.58
0.0
0
0.0
0.5
1
Excercises
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Complete calculations on two intercrops
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grown at two different densities
in replacement and additive design
Focus on:
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What is the difference between outcomes from a
replacement and an additive design?
What is the difference between relative crowding
coefficient (k) and the ratio of competition coefficients
(e.g. b11/b12)?