Sustainable low-input cereal production:

required varietal characteristics and crop

diversity

Working Group 4: plant-plant interactions

About SUSVAR….

System characteristics: Cereal production Low-input conditions

Aims: Increased stability (yield and quality) Increased resource use efficiency

Main means: Better use of crop genetic diversity

Better use of crop genetic diversity (1)

Selection of suitable genotypesBetter 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)

Better use of crop genetic diversity (2)

Use of mixturesUtilize more genotypes simultaneously

Heterogeneity contributes to stability (risk avoidance) Generation of added value:

• Facilitation• Competition

Crop - environment: mutual interaction

environment

Crop A

Facilitation: positive effect

environment

cropCrop A Crop B

+

Facilitative production principle: insects

Competition: negative influence

environment

cropCrop A Crop B

-

Competitive relations are important

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

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

Crop – weed interaction Weed suppression Which traits General or environment specific Easy screening procedures

In case of mixtures

Crop – crop interaction Yield stability

• Difference in stress-tolerance

Productivity• Niche differentiation• Intra-specific competition > inter-specific competition

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

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?

Time to decide on where to go …

WG 1Genetics & Breeding

WG 3Plant – Soil Interactions

WG 4Plant – PlantInteractions

WG 5Plant Disease

Complex

WG 6Variety testing &

certification

Organisation of activities and reciprocal benefits

WG 2Biostatistics

Facilitative production principle: diseases

Plant-plant interaction

Main issues: Productivity Stability Weed suppression

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

Multiple cropping

Growing two or more crops on the same field in a year

- sequential cropping

- relay intercropping

- full intercropping

time

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)

Facilitative production principle: diseases

Causal organism:Magnaporthe grisea

two phases:vegetative stageLeaf blast

reproductive phaseNeck or panicle blast

Intercropping as weed management component

manual weeding

Transplanting Harvest

weed-free period

Leek monoculture

Leek-Celery Intercrop

Weeds

Weeds

weed-free period

mechanical weeding

mechanical weeding

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

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 [plant/g]

b11 [m2/g]

b11/b10 [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 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

Two basic designs

Additive design

0 0 0 0 x x x x 0 x 0 x 0 x 0 x

0 0 0 0 x x x x 0 x 0 x 0 x 0 x

0 0 0 0 x x x x 0 x 0 x 0 x 0 x

0 0 0 0 x x x x 0 x 0 x 0 x 0 x

0 0 0 0 x x x x 0 x 0 x 0 x 0 x

species 1 species 2 mixture

Two basic designs

Replacement design

0 0 0 0 x x x x 0 x 0 x

0 0 0 0 x x x x 0 x 0 x

0 0 0 0 x x x x 0 x 0 x

0 0 0 0 x x x x 0 x 0 x

0 0 0 0 x x x x 0 x 0 x

species 1 species 2 mixture

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 0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 0.5 1

0.0

0.2

0.4

0.6

0.8

1.0

1.2

k12=0.58

k21=1.93

Replacement design

k intrasp/intersp comp. Similar to b11/b12?

k*k related to intercrop

productivity =1, >1, <1 Similar to NDI? 0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 0.5 1

0.0

0.2

0.4

0.6

0.8

1.0

1.2

k12=0.58

k12=0.58

k21=1.93

Excercises

Complete calculations on two intercrops 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)?