Integrated Soil Fertility Management in cassava-legume systemsPieter Pypers (TSBF-CIAT), Jean-Marie Sanginga (CIAT), Kasereka Bishikwabo (CIAT), Sylvain Mapatano (DIOBASS), Adrien Chifizi (DIOBASS), Masamba Walungululu (UCB), Wivine Munyahali (UCB), Janvier Bashagaluke (UCB), Willy Tatahangy (INERA), Nkonko Mbikayi (INERA) and Bernard Vanlauwe (TSBF-CIAT).
Contact: [email protected]
Improved germplasm
Cassava affected by mosaic disease
CMD-resistant cassava
Viral diseases are a major constraint for cassava production, particularly cassava mosaic disease (CMD). Cassava brown streak virus disease (CBSD) is threatening cassava production in eastern and southern Africa.
Disease-resistant cassava germplasm is essential to increase productivity and stimulate investment in the cropping system.
Use of germplasm tolerant to abiotic stresses can aid overcoming specific crop constraints, and stimulate investment in nutrient inputs. In legumes, tolerance to drought, soil acidity and low soil P are important traits.
Improved germplasm should be responsive to nutrient application and have a high yield potential, to maximize returns to investment in mineral fertilizer or organic inputs.
Cassava and legumes are compatible in terms of water and nutrient demands. Choosing cassava varieties with a tall, slow-closing canopy can allow integrating legumes during two consecutive seasons.
Mineral fertilizer application
Control (no inputs)
NPK applied at 2 bags ha-1
Cassava is often considered as a crop with low nutrient demands that can be grown in poor or degraded soils.
Cassava exports high amounts of nutrients, particularly N (up to 70 kg N ha-1, mostly through aboveground biomass) and K (up to 160 kg K ha-1, mainly through the tubers).
Cassava is highly responsive to fertilizer application. Observed tuber yield responses to fertilizer (2-3 bags of NPK 17:17:17 ha-1) varied between 30 and 160 %.
Legumes are most responsive to P-containing fertilizers. P application enhances nodulation and N fixation. Observed grain yield responses in beans varied between 20 and 150%.
Appropriate fertilizer management (banding P-fertilizer in the legume line, split application of N and K to the cassava) and timely planting and weeding are essential to maximize fertilizer use efficiency.
Compound NPK-fertilizer is suitable because it matches the nutrient requirements of both crops.
Activities are on-going to formulate site-specific fertilizer recommendations, based on local soil conditions and crop requirements.
Adapted agronomy (crop spacing)
1st legume: groundnut (2 months after planting cassava)
2nd legume: climbing bean (6 months after planting cassava)
Cassava is commonly planted at a spacing of 1m x 1m (10,000 plants ha-1).
Spacing the cassava at 2m between rows and 0.5m within the row allows intercropping with legumes during two consecutive seasons. Adapted agronomy can increase legume production by 40%, without affecting cassava production.
Crop rotation is important to reduce pest and disease pressure. The cassava intercropping system is sufficiently versatile to accommodate different legumes (beans, soybean or groundnut).
Combining improved germplasm, fertilizer application, organic matter management and adapted agronomy can double net revenue of the system.
This system has been positively evaluated by farmer groups. Farmers are currently using the system for multiplication of planting material, and experimenting in a large number of adaptation trials.
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System productivity
cassava spacing
integration of a 2nd legume
fertilizer application
legume grain yield cassava tuber yield cassava stem yield
Notes: Cassava spaced at 1m x 1m was intercropped with 2 legume lines between the cassava lines, and does not allow intercropping of a 2nd legume. Cassava spaced at 2m (between rows) x 0.5m (within row) was intercropped with 4 legume lines between the cassava lines in the 1st season (equal crop density as in the 1m x 1m system), and allows integration of another legume in the 2nd season (2 lines intercropped between the cassava lines).
In treatments with integration of a 2nd legume, a bush bean was grown in the 1st season, followed by a climbing bean in the 2nd season (5 months after cassava planting); the legume yield presented is the sum for the 1st and 2nd legume.
All treatments received a basal manure application of 2.5 t ha-1. Fertilizer was applied at 2 bags of NPK (17:17:17) ha-1 at planting (equally distributed to the cassava and the legume, and applied in the planting holes/lines). In the treatment with fertilizer application and integration of a 2nd legume, additional fertilizer (1 bag ha-1) was applied at planting of the 2nd legume.
net revenue
0
1000
2000
3000
- - - NPK NPK
- - 2ndlegume
- 2ndlegume
1x1 2x0.5 2x0.5 2x0.5 2x0.5
bean
gra
in y
ield
(kg
ha-1
)
0
10
20
30
- - - NPK NPK
- - 2ndlegume
- 2ndlegume
1x1 2x0.5 2x0.5 2x0.5 2x0.5
cass
ava
tube
r yie
ld (t
ha-1
)
0
5
10
15
20
- - - NPK NPK
- - 2ndlegume
- 2ndlegume
1x1 2x0.5 2x0.5 2x0.5 2x0.5
cass
ava
stem
yie
ld (
t ha-1
)
B/C = 6.7B/C = 6.6
B/C = 6.8B/C = 6.3
B/C = 4.8
0
2000
4000
6000
- - - NPK NPK
- - 2ndlegume
- 2ndlegume
1x1 2x0.5 2x0.5 2x0.5 2x0.5
net b
enef
its (U
S$
ha-1
)
Productivity and net revenue in cassava-legume systems can be maximized using Integrated Soil Fertility Management (ISFM). ISFM combines (i) improved germplasm, (ii) mineral fertilizer application, (iii) organic matter management and (iv) adapted agronomy.This was demonstrated in on-farm trials with farmer groups in Sud-Kivu, Democratic Republic of Congo.
Organic matter management
Dual purpose soybean
Soil organic matter enhances nutrient cycling and availability, performs important biological functions and improves soil physical conditions.
Organic matter application is often crucial to generate yield increases. Degraded soils with low organic matter content are commonly unresponsive to mineral fertilizer, but can be rehabilitated by adding organic inputs. Recent findings suggest that such unresponsive soils can be identified using local soil classification knowledge. In Sud-Kivu, farmers distinguish red soils (Kalongo) and black soils (Civu).
Organic matter can be produced in situ, using promiscuous dual-purpose soybean or climbing beans.
N fixation by legumes may increase above-ground biomass yield in cassava, which is important for food (leafs) and planting material (stem cuttings).
Interactions between organic matter and mineral fertilizer remain poorly understood in cassava-based systems.
0
500
1000
1500
2000
control NPK manure manure+NPK
bean
gra
in y
ield
(kg
ha-1
)
Civu (rich in organic matter, responsive)
Kalongo (poor in organic matter, often degraded)
