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Abstract
An ethnobotanical study in lowland rice areas in East Africa was undertaken to assess farmers' knowledge on the usage of non-cultivated plants occurring in paddy fields, and to understand what rice farmers in this region do with useful species once they encounter them in their crop. Inventories of weed species in 19 rice schemes in Tanzania and Kenya were followed by interviews among 380 experienced rice farmers, community elders and traditional healers, grouped into 19 informant groups. Among informant groups, a high degree of consensus about uses of weeds growing in rice paddies was observed. From a total of 222 observed rice weed species, the informant groups identified 67 species with usages described in 1300 use reports. Among these 67 species, 20 are among the most commonly cited weed species in rice paddies in sub-Saharan Africa. Only in 42 cases (3% of the total use reports) did the farmers indicate that they collected (13 species) or spared (four species) these weeds during weeding. In all other cases, such plants were removed or killed during weeding, irrespective of their usefulness. Non-cultivated plants that are spared are those of which the putative agronomic qualities (i.e. for crop protection or soil improvement) are considered more important than their crop competition effects (i.e. Azolla filiculoides and Marsilea crenata) and those that are found in the field margins, which do not compete with the crop. Non-cultivated plants that are collected during weeding have food, fodder or medicinal purposes or a combination of purposes. The most cited species that are collected or spared during weeding were Bidens pilosa, Ipomoea aquatica, Corchorus olitorius and Stachytarpheta jamaicensis. This study revealed that lowland rice farmers in East Africa generally have a high level of understanding and consensus on the usefulness of the non-cultivated plants growing in lowland rice schemes. When they occur in their crop however, the vast majority of these species are primarily seen as weeds and consequently removed or killed.
Highlights
Among the numerous production challenges African rice farmers are facing, competition from weeds is considered as one of the most common and serious (Waddington et al, 2010)
The specific objectives of the study were (1) to assess farmers' ethnobotanic knowledge on rice weeds in East Africa and (2) to understand what rice farmers in this sub-region do with useful species once they encounter them in their crop
The facilitator asked the same three questions to the group: (1) Do you know this weed and does this weed have a use? (2) If yes, what can it be used for, which parts are used and how? (3) What do you do with this weed when you encounter it during a weeding intervention? In addition, the informants were asked about the main weed management methods in their rice schemes
Summary
Among the numerous production challenges African rice farmers are facing, competition from weeds is considered as one of the most common and serious (Waddington et al, 2010). Rice is a volatile crop that can be grown under a range of hydrological conditions ranging from free-draining rain-fed uplands to continuous flooded lowlands (Andriesse and Fresco, 1991). Much of the rice is grown in the temporary or continuous flooded lowlands (either rain-fed or irrigated) of Africa, covering an estimated 64% of the total area under rice and producing about 73% of the total annual paddy production of the region (Diagne et al, 2013). Rice production in lowlands is estimated to lose 15% (irrigated lowlands) to 23% (rain-fed lowlands) due to competition from weeds under current weed management practices (Becker and Johnson, 2001; Becker et al, 2003). Conservative estimates show that weeds account for annual rice yield losses of 2.2 million tons equating to US$1.45 billion in SSA (Rodenburg and Johnson, 2009)
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