1. Working Group 4: plant-plant interactions
Sustainable low-input cereal production: required varietal characteristics and crop diversity
Working Group 4: plant-plant interactions

2. About SUSVAR…. System characteristics: Aims: Main means:
Cereal production
Low-input conditions
Aims:
Increased stability (yield and quality)
Increased resource use efficiency
Main means:
Better use of crop genetic diversity

3. Better use of crop genetic diversity (1)
Selection of suitable genotypes
Better use of available gene-pool for low-input systems
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)

4. Better use of crop genetic diversity (2)
Use of mixtures
Utilize more genotypes simultaneously
Heterogeneity contributes to stability (risk avoidance)
Generation of added value:
Facilitation
Competition

5. Crop - environment: mutual interaction
Crop A

6. Facilitation: positive effect
environment +
crop
Crop A
Crop B

7. Facilitative production principle: insects

8. Competition: negative influence
environment -
crop
Crop A
Crop B

9. Competitive relations are important

10. Competition also the basis for over-yielding
Competitive production principle
intra-specific competition > inter-specific competition
Niche-differentiation or complementarity
 better exploitation of available resources

11. 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.

12. Facilitative production principle: weeds

13. Working group plant-plant interaction
Crop – weed interaction
Weed suppression
Which traits
General or environment specific
Easy screening procedures

14. In case of mixtures Crop – crop interaction Yield stability
Difference in stress-tolerance
Productivity
Niche differentiation
Intra-specific competition > inter-specific competition

15. Weed suppression of mixtures
Crop – crop – weed interaction
How to maximize weed suppression?
Combine most competitive cultivars
Maximize complementarity
Complementarity in resource use and acquisition
Complementarity in weed suppression mechanism

16. Currently many different questions ….
What do we want to obtain with mixtures?
(stability, productivity, weed suppression, others)
How can added value of mixtures be obtained?
(what is the best strategy)
How to select individual varieties for their performance in mixtures?

17. Time to decide on where to go …

19. Organisation of activities and reciprocal benefits
WG 3
Plant – Soil
Interactions
WG 4
Plant – Plant
Interactions
WG 1
Genetics & Breeding
WG 6
Variety testing &
certification
WG 2
Biostatistics
WG 5
Plant Disease
Complex

20. Facilitative production principle: diseases

21. Plant-plant interaction
Main issues:
Productivity
Stability
Weed suppression

22. Learning-objectives To familiarise with options for evaluating:
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

23. Multiple cropping - sequential cropping - relay intercropping
Growing two or more crops on the same field in a year
- sequential cropping
- relay intercropping
- full intercropping
time

24. Reasons for intercropping
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)

25. Facilitative production principle: diseases
Causal organism:
Magnaporthe grisea
two phases:
vegetative stage
Leaf blast
reproductive phase
Neck or panicle blast

26. 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

27. Competition the basis for over-yielding?
Niche-differentiation
 better exploitation of available resources
separation in time (relay)
separation in space (rooting depth)
different resource capture abilities
different growth requirements

28. Key to evaluation of intercrop productivity
Quantification of competitive relations
Example:
Two-species mixture (sp 1 - sp 2)
How many competition coefficients?

29. 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

30. Intraspecific competition
Y=N/(b0+b1N)  W=Y/N=1/(b0+b1N)  1/W=b0+b1N

31. Measure of intraspecific competition
1/W1=b10+b11N1
b10 [plant/g]
b11 [m2/g]
b11/b10 [m2/plant]
crowding coefficient (de Wit)
ecological neighbourhood area (Antonovics & Levin)

32. Intercropping: intra and interspecific
1/W1=b10+b11N1+ b12N2
b11/b12 relative competitive ability
What does this value learn us?

33. 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

34. How can we determine these indices?

35. Evaluation in practice
Experiment with three treatments:
Monoculture of species 1 Y1,mono
Monoculture of species 2 Y2,mono
Mixture of species 1 and 2 Y1,mix, Y2,mix
Calculation of Relative Yield
RY1 =Y1,mix/Y1,mono
RY2 =Y2,mix/Y2,mono
Land Equivalent Ratio (LER)
LER = RY1 + RY2
relative land area under sole crops required to produce the yields achieved in intercropping

36. Two basic designs Additive design 0 0 0 0 x x x x 0 x 0 x 0 x 0 x
species species mixture

37. Two basic designs Replacement design 0 0 0 0 x x x x 0 x 0 x
species species mixture

38. Replacement design 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
k12=0.58
k21=1.93

39. Replacement design k  intrasp/intersp comp. k*k Similar to b11/b12?
related to intercrop productivity
=1, >1, <1
Similar to NDI?
k12=0.58k12=0.58
k21=1.93

40. Excercises Complete calculations on two intercrops Focus on:
grown at two different densities
in replacement and additive design
Focus on:
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)?