False beliefs on the socio-economic drivers of cassava cropping

General belief has it that cassava is (i) a subsistence crop, grown to avoid hunger (ii) by poor farmers, (iii) predominantly as an intercrop, (iv) requiring less labour than other crops and (v) no inputs. These beliefs influence policy, project development and implementation, and if wrong, may have far-reaching consequences for the success and sustainability of interventions. This study examines five beliefs about cassava and discusses consequences for interventions targeting cassava. From 2004 to 2006, 120 detailed farm surveys were carried out with smallholder farmers in 6 sites in central/eastern Uganda and western Kenya, whereby households were categorised in three wealth categories by local key informants. Through structured interviews and field visits, details on the importance of cassava, socio-economic indicators, food security, crop management and labour aspects were obtained. Our results show that cassava does ensure food security, but that the other beliefs are either myths or half truths. Besides supplying 27–41% of starchy staple food consumption, cassava also provided significant income (84 US$yr-1), similar to that of maize (90 US$ yr-1). It is too simplistic to classify cassava as a ‘poor man’s crop’ as in Uganda wealthier households marketed more (+16%), but in Kenya consumed less (–11%) cassava than poorer farmers. Cassava is not predominantly intercropped (30% of acreage in Uganda and 51% in Kenya), farmers do use inputs on cassava (36% of the households hire labour) and total labour requirements (287 mandays ha-1) were higher than for most crops. Contrary to expectations, we conclude that increasing cassava production will not improve food security – unless a disease epidemic is present – but instead will improve the scope for commercialisation of cassava. To ensure that projects designed to enhance cassava production benefit poor and/or labour deficit households, specific provisions are needed, including development of labour saving technologie

False beliefs on the socio-economic drivers of cassava cropping

General belief has it that cassava is (i) a subsistence crop, grown to avoid hunger (ii) by poor farmers, (iii) predominantly as an intercrop, (iv) requiring less labour than other crops and (v) no inputs. These beliefs influence policy, project development and implementation, and if wrong, may have far-reaching consequences for the success and sustainability of interventions. This study examines five beliefs about cassava and discusses consequences for interventions targeting cassava. From 2004 to 2006, 120 detailed farm surveys were carried out with smallholder farmers in 6 sites in central/eastern Uganda and western Kenya, whereby households were categorised in three wealth categories by local key informants. Through structured interviews and field visits, details on the importance of cassava, socio-economic indicators, food security, crop management and labour aspects were obtained. Our results show that cassava does ensure food security, but that the other beliefs are either myths or half truths. Besides supplying 27–41% of starchy staple food consumption, cassava also provided significant income (84 US$yr-1), similar to that of maize (90 US$ yr-1). It is too simplistic to classify cassava as a ‘poor man’s crop’ as in Uganda wealthier households marketed more (+16%), but in Kenya consumed less (–11%) cassava than poorer farmers. Cassava is not predominantly intercropped (30% of acreage in Uganda and 51% in Kenya), farmers do use inputs on cassava (36% of the households hire labour) and total labour requirements (287 mandays ha-1) were higher than for most crops. Contrary to expectations, we conclude that increasing cassava production will not improve food security – unless a disease epidemic is present – but instead will improve the scope for commercialisation of cassava. To ensure that projects designed to enhance cassava production benefit poor and/or labour deficit households, specific provisions are needed, including development of labour saving technologie

Improved cassava varieties increase the risk of soil nutrient mining: an exante analysis for western Kenya and Uganda

Cassava production in Uganda and western Kenya has been hit hard by the cassava mosaic disease (CMD) epidemic. In response, CMD resistant cassava varieties are currently released on a wide scale. The new varieties yield up to 3 times more than the local varieties. These high yield levels will put major pressure on soil nutrient stocks. Using a local variety, an average farmer will harvest about 10 t ha-1 fresh roots, thereby removing 26 kg N, 3 kg P and 19 kg K per hectare. Using a good CMD-resistant variety, the same farmer can harvest a 30 t ha-1, thereby removing 83 kg N, 10 kg P and 47 kg K per hectare. If stems are used for planting material and/or firewood, then removal increases to 216 kg of N, 22 kg of P and 102 kg of K per ha for CMD-resistant varieties. Soils in western Kenya and Uganda are predominantly Ferrasols, Acrisols and Nitisols; old weathered soils with small nutrient stocks. Without the use of fertilizers, the rapid depletion of soil nutrient stocks seems unavoidable with the new varieties. This will eventually result in yield decline of cassava and rotational crops. The question arises if traditional cropping systems are suitable for cultivating crops with high nutrient demand. However, production levels of banana, the other important food crop in Uganda, have been sustained for over half a century in several parts of the country, despite K requirements (142 kg ha-1yr-1) of good yielding bananas (25 t ha-1yr-1) being similar to that of good-yielding cassava varieties. But, in contrast to cassava fields, traditional banana fields maintain their soil fertility through large amounts of organic inputs, on the expense of annual cropped fields and grassland. Due to the position of cassava in the farming system, it is unlikely that soil management strategies in banana can be successfully adopted by cassava farmers. However, rotating the improved cassava varieties with fertilized cash crops and introducing promiscuous leguminous inter- and relay crops in cassava fields are potential management options to improve the sustainability of the system. Nonetheless, the development of K deficits will remain a serious concern. The high yield levels of the new cassava varieties have already triggered its promotion as a cash crop. Provided that there is a good (industrial) market outlet, farmers can be motivated to use targeted organic & inorganic fertilizer to prevent soil fertility depletion

Comparing the regional epidemiology of the cassava mosaic and cassava brown streak virus pandemics in Africa

The rapid geographical expansion of the cassava mosaic disease (CMD) pandemic, caused by cassava mosaic geminiviruses, has devastated cassava crops in twelve countries of East and Central Africa and is well documented. Region-level epidemiological studies continue to reveal a more-or-less regular pattern of annual spread along a contiguous ‘front’. More recently, outbreaks of cassava brown streak disease (CBSD) were reported from Uganda and other parts of East Africa that had been hitherto unaffected. Recent survey data reveal several significant contrasts between the regional epidemiology of the two pandemics: i) severe CMD spreads in an ‘expanding concentric rings’-like manner, whilst CBSD seems to be spreading from independent hot-spots; ii) the severe CMD pandemic has arisen from virus recombination and inter-species synergy, whilst current knowledge suggests that the CBSD pandemic is a ‘new encounter’ situation; iii) CMD pandemic spread has been tightly linked with the appearance of super-abundant B. tabaci whitefly populations, in contrast to CBSD, where outbreaks have occurred 3-12 years after whitefly population increases; iv) the cassava mosaic geminiviruses (CMGs) causing CMD are transmitted in a persistent manner, whilst cassava brown streak viruses (CBSVs) appear to be semi-persistently transmitted; and v) different patterns of symptom expression mean that phytosanitary measures are easy to implement for CMD but have limited effectiveness whilst the same measures are hard to do for CBSD but potentially very effective. One important similarity between these two cassava virus pandemics is that the viruses occurring in pandemic-affected areas are also found elsewhere, indicating that contrary to earlier published information, the viruses per se are unlikely to be the key factors driving the two pandemics. A model is proposed for the temporal relationship between B. tabaci abundance and changing incidences of both CMD and CBSD in the Great Lakes region. This emphasizes the pivotal role played by the vector in both pandemics and highlights the urgent need to identify effective and sustainable strategies for controlling whiteflies on cassava