Enhancing CropSyst for intercropping modeling

Bryan Carlson, Rolf Sommer*, Birthe Paul, Mirriam Muli and Claudio Stöckle r.sommer@cgiar.org

iCropM, 15-17 March 2016, Berlin

• Definition: Growing two (or more) plant species simultaneously overlapping in space and time.

• Benefits: • better use of the acreage of land • better nutrient use (efficiency) • commensalism/allelopathy (e.g. Push-Pull systems) • diversification (improved diet, reduction

of production risk, improved soil protection/health)

• Costs: • competition • increased complexity • allelopathy

• Some definitions: • (effective) land equivalent ratio (LER) • relative yield totals (RYT) • …

"The whole is greater than the sum of its parts!" 2

Intercropping

The importance of intercropping in sub-Saharan Africa • Intercropping dominates in smallholder farming systems of SSA!

3 Napier-Desmodium, Tanzania

Maize-Cowpea, Zambia

Maize-Pigeon pea, Tanzania

The importance of intercropping in sub-Saharan Africa

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Push-Pull System, Kenya Maize-Bean, Kenya

Intercropping in CropSyst "As simple as possible, but not any simpler."

• 1D

• 2 crops with no distinct row arrangement (no alley cropping or wide bed&furrow systems with distinct 2D pattern)

• different planting dates possible (relay cropping)

• dominance of one species over the other may change over time (e.g. maize pigeon pea system)

• simulate the growth of these two species and the influence of competition for • light, • water, • nitrogen

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Light interception (I )

Three cases to consider: 1. Interception by the taller (T)

species above the shorter species

2. Interception by the taller species within/below the shorter species

3. Interception of the shorter (S) species 6

𝐼 = 𝑓 ∗ 𝑃𝐴𝑅 Upper canopy

(U)

Lower canopy

(L)

𝑓 = 1 − 𝑒−𝑘∗𝐿𝐴𝐼

Light interception (I )

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The PAR fraction intercepted by the upper canopy is:

𝑓𝑈 = 1 − 𝑒−𝑘𝑇∗𝐿𝐴𝐼𝑈 eq. 3

The PAR fraction intercepted by the taller species at the lower

canopy is:

𝑓𝐿_𝑇 =𝐿𝐴𝐼𝐿𝑇

∗𝑘𝑇

𝐿𝐴𝐼𝐿𝑇∗𝑘𝑇+𝐿𝐴𝐼𝐿𝑆

∗𝑘𝑆(1 − 𝑒

−𝐿𝐴𝐼𝐿𝑇∗𝑘𝑇 − 𝐿𝐴𝐼𝐿𝑆

∗𝑘𝑆 ) eq. 4

and that of the shorter species:

𝑓𝐿_𝑆 =𝐿𝐴𝐼𝐿_𝑆∗𝑘𝑆

𝐿𝐴𝐼𝐿_𝑇∗𝑘𝑇+𝐿𝐴𝐼𝐿_𝑆∗𝑘𝑆∗ (1 − 𝑒

−𝐿𝐴𝐼𝐿𝑇∗𝑘𝑇 − 𝐿𝐴𝐼𝐿𝑆

∗𝑘𝑆 ) eq. 5

Light interception (I )

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The PAR intercepted at the upper canopy is:

𝐼𝑈 = 𝑓𝑈 ∗ 𝑃𝐴𝑅 eq. 6

The available PAR reaching the lower canopy must be reduced by

this intercepted radiation.

Thus, the radiation intercepted by the two species at the lower

canopy is:

𝐼𝐿_𝑇 = 𝑓𝐿_𝑇 ∗ (𝑃𝐴𝑅 − 𝐼𝑈) eq. 7

𝐼𝐿_𝑆 = 𝑓𝐿_𝑆 ∗ (𝑃𝐴𝑅 − 𝐼𝑈) eq. 8

Transpiration and evaporative demand • Partitioning of evaporative demand between the upper and lower canopy

and between species done using actual radiation interceptions as scaling factors.

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Water and N-uptake • Non limited conditions:

• uptake is calculated for each species as if it was growing alone using either the evaporative demand or crop-specific N-uptake boundaries as "sink".

• Limited conditions:

• demand/uptake of each species is reduced based on root prevalence and root length density in each soil layer, so as to allow the sum of both demands to be equal to the available water or N.

Maize-Bean intercropping trial – Wote, Kenya

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Maize-Bean intercropping trial – Wote, Kenya

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50 yr. annual average rainfall sum: 600 mm

Maize-Bean intercropping trial – Wote, Kenya

• Planting • 20 October 2015

• 60 cm row spacing

• Fertilizer application • 1.5 t/ha manure (maize and beans), incorporated before 5 day before planting

• 25 kg/ha DAP at planting (maize only)

• 50 kg/ha CAN topdressing of maize (16 Dec.)

• Maize phenology • 50% tasseling: 14 Dec.

• 50% silking: 25 Dec.

• maturity: 5 Feb. 2016

• harvest: 16 Feb. 12

• Bean phenology • start flowering: 13 Dec.

• start grain filling: 22 Dec.

• maturity: 3 Jan. 2016

• harvest: 21 Jan. 2016

Maize-bean intercropping trial – Wote, Kenya

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13 November 4 December 15 December

8 January

Results – leaf area index and aboveground biomass

Maize

dots = observed (± SD); lines = simulations 14

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Results – Aboveground biomass inter- vs. mono-cropping

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Maize

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mono-cropping

intercropping

inter-cropping

mono-cropping

Results – Yield inter- vs. mono-cropping

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Intercr. Monocrop. Intercr. Monocrop.

Bean Maize

Yie

ld (

t/h

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32 %

Intercropping out-competes mono-cropping!

68 %

Outlooks

• some debugging

• implement simplified way of accommodating differences in plant species density/spacing

• move from VBA to C++ version of CropSyst

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Thank you!