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

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

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)

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

Crop - environment: mutual interaction Crop A

Facilitation: positive effect environment + crop Crop A Crop B

Facilitative production principle: insects

Competition: negative influence environment - crop Crop 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 …

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

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 - sequential cropping - relay intercropping 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 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? 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 species 1 species 2 mixture

Two basic designs Replacement design 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 k12=0.58 k21=1.93

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

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)?