Why soil facts are key to cassava production in Southeast Asia

1 November, 2013 by (comments)

By Tin Maung Aye, Keith Fahrney, Adrian Bolliger and Rod Lefroy

This post originally appeared on the CGIAR Research Program on Water, Land and Ecosystems (WLE) blog as part of a month-long focus on Restoring soils and landscapes.

cassava

Rumour has it that planting cassava is inherently bad for the soil. The crop is capable of widespread soil erosion, damaging the environment and reducing the productivity of other crops by removing too many nutrients from the soil, so the popular mantra goes. Yet at the same time, cassava can apparently grow well in poor, degraded soils with no or very little fertiliser application at all.

Cassava’s low demand for – and highly efficient use of – water and most nutrients has earned it a reputation as an ideal crop to cultivate on poor soil. But the association between degraded soil and the crop itself seems to have stuck, and the stigma is difficult to shake off.

As with most rumours, you have to dig a bit deeper to get to the roots of the truth.

We can quell the rumour if we can share the information that we as researchers have about how to prevent soil erosion and better manage cassava production systems with the people who need to know. Proper erosion control and soil fertility management is at the heart of sustainable cassava production, and has the potential to boot smallholder livelihoods.

The facts…

In Southeast Asia, cassava production has increased rapidly and many people want to be part of the boom. Rapid population growth and economic development have driven many people, especially the poorest, to grow cassava on sloping land. But farming on the slopes is usually deterred and sometimes banned – which does not stop farmers from planting cassava on slopes because it grows well, at least for a number of years. Consequently, harvests go unreported, and best soil management practices and adoption of tried and tested sustainable soil management techniques are not as broadly adopted as they should be.

Concerns that cassava exacerbates soil erosion arise from the fact that growing it on steep slopes without intercropping or contour planting will cause erosion. This is because cassava is a large plant that needs to be planted at wide spacing to get high root yields.  During the two to three-month period before cassava leaves grow enough to close the crop canopy, the soil between plants is left exposed to direct rainfall, which in turn results in soil run-off and loss. The steeper the slope, the greater the soil loss.

It is important to both protect the soil surface from the direct impact of raindrops and slow down the runoff and soil loss by reducing the length of the slope. The International Center for Tropical Agriculture’s (CIAT) research has highlighted great opportunities for mitigating soil erosion in Southeast Asia. Intercropping cassava with fast ground-covering, short-term crops like peanut is recommended because it protects the soil surface, provides a quick harvest and income, and helps control weeds. Mulching with crop residues or grass on the soil surface protects soil from direct raindrop impact, greatly improves water infiltration and can further reduce erosion.

Planting strips of forage grasses like Paspalum atratum or shrubs such as Tephrosia candida along slope contours will act as a barrier, breaking the slope length and preventing the loss of topsoil – the most fertile part of the soil – while inducing the formation of natural terraces to capture moisture, reduce the angle of the slope and increase yields. The forages can also feed animals in integrated crop-livestock smallholdings…

Read the full post on the WLE blog.

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Filed Under: Asia @en, Soils, Soils website