Exante assessment of dual-purpose sweet potato in the crop–livestock system of western Kenya: A minimum-data approach

Mixed crop–livestock systems have a crucial role to play in meeting the agricultural production challenges of smallholder farmers in sub-Saharan Africa. Sweet potato is seen as a potential remedial crop for these farmers because of its high productivity and low input requirements, while its usefulness for both food and feed (dual-purpose) make it attractive in areas where land availability is declining. In this paper, we develop and apply a ‘minimum-data’ methodology to assess exante the economic viability of adopting dual-purpose sweet potato in Vihiga district, western Kenya. The methodology uses and integrates available socio-economic and bio-physical data on farmers’ land use allocation, production, and input and output use. Spatially heterogeneous characteristics of the current system regarding resources and productivity are analyzed to assess the profitability of substituting dual-purpose sweet potato for other crops currently grown for food and feed. Results indicate that a substantial number of farmers in the study area could benefit economically from adopting dual-purpose sweet potato. Depending on assumptions made, the adoption rate, expressed as the percentage of the total land under adopting farms, is between 55% and 80%. The analysis shows that the adoption rate is likely to vary positively with the average total yield of dual-purpose sweet potato, the harvest index (the ratio between tuber and fodder yields), the price of milk, and the nutritional value of available fodder. This study demonstrates the usefulness of the minimum-data methodology and provides evidence to support the hypothesis that dissemination of the dual-purpose sweet potato could help improve the livelihoods of smallholder farmers operating in mixed crop–livestock systems in east Africa.     

Impact of a no-till with mulch soil management strategy on soil macrofauna communities in a cotton cropping system

Systematic exportation, burning of crop residues and decreases in fallow periods have led to a large-scale depletion of soil organic matter and degradation of soil fertility in the cotton (Gossypium hirsutum L.) cropping systems of Cameroon. The present study tested whether soil management systems based on a no-till with mulch approach intercropped with cereals, which has been shown to restore cotton production, could boost the biological activity of soil macrofauna. The impacts of no tillage with grass mulch (Brachiaria ruziziensis Germain and Eward) (NTG) and no tillage with legume mulch (Crotalaria retusa L. or Mucuna pruriens Bak.) (NTL) on the abundance, diversity and functional role of soil invertebrates were evaluated during the third year of implementation in northern Cameroon (Windé and Zouana), compared to conventional tillage (CT) and no tillage (NT) without mulch. Macrofauna were sampled from two 30 cm × 30 cm soil cubes (including litter) at the seeding stage of cotton, and 30 days later. The collected organisms were grouped into detritivores, herbivores and predators. Examination of the soil macrofauna patterns revealed that the abundance and diversity of soil arthropods were significantly higher in NTG and NTL than in CT plots (+103 and +79%, respectively), while that of NT plots was in-between the no tillage groups and CT (+37%). Regarding major ecological functions, herbivores and predators were significantly more abundant in NTG and NTL plots than in CT plots at Windé (+168 and +180%, respectively), while detritivores, predators and herbivores were significantly more abundant in the NTG plots than in CT plots at Zouana (+92, +517 and +116%, respectively). Formicidae (53.6%), Termitidae (24.7%) and Lumbricidae (9.4%) were the most abundant detritivores while Julidae (46.1%), Coleoptera larvae (22.1%) and Pyrrhocoridae or Reduviidae (11.8%) were the dominant herbivores. The major constituents of the predatory group were Araneae (33.8%), Carabidae (24.6%), Staphylinidae (15.7%) and Scolopendridae (10.3%). Direct seeding mulch-based systems, NTG and NTL, favoured the establishment of diverse macrofaunal communities in the studied cotton cropping system.     

Phylogeography of North African Amietophrynus xeros estimated from mitochondrial DNA sequences

Amietophrynus xeros was sequenced for part of the 16S rRNA mitochondrial region to assess genetic diversity between populations from Niger, Mali, Senegal, Mauritania and Tanzania. Although populations are currently unconnected, diversity within the Sahel region was relatively low, indicating that the species only expanded into this region relatively recently, perhaps after the last glacial maximum. Diversity was higher between samples from Tanzania. Some individuals of two species from previously published studies, A. garmani and A. gutturalis, share haplotypes with A. xeros, but this is likely to be due to error, possibly misidentifica-tion. Similar errors appear to exist in published studies of other North African Amietophrynusspecies such as A. regularis.     

非洲藤(Palmae calamoideae)的两个新种

藤类广泛分布于非洲大陆热带森林的低地上,对区域林业经济发挥着重要作用。在非洲分布的20种之中有6种已被用于商业资源开发。尽管非洲藤类的经济价值很高,但至今对它们的分类仍不太确定。本文描述了单苞藤属和肿胀藤属的2个新种,分别从分类学、形态学、特征、生物学特性、保护和利用等方面做了研究。     

Mangrove species zonation and soil redox state,sulphide concentration and salinity in Gazi Bay (Kenya), a preliminary study

The relationship between soil redox state, sulphide concentration, salinity and spatial patterns of mangrove species distribution was investigated in the mangrove forest of Gazi Bay (Kenya). Field measurements were conducted to examine the relationship between species distribution along a band transect of 280m and soil redox potential (Eh) and sulphide patterns, as well as the indirectly related (through flooding regimes) soil salinity. Of the three major species Avicenniamarina, Ceriops tagal and Rhizophoramucronata present along the transect, only the distribution of the latter correlated with the measured soil variables, R. mucronata being absent from the lessreduced zone with high salinity. Bruguieragymnorhiza and Heritieralittoralis occur in minor populations, they are restricted to the saline, sulphidepoor and lessreduced substrates. From the results it is concluded that soil redox potential (Eh), sulphide concentration and salinity may contribute to structure mangroves through the distribution of dominant species, however in combination with other environmental conditions and processes of vegetation dynamics.     

Karité (Vitellaria paradoxa) and néré (Parkia biglobosa) associated with crops in South Mali

The effect of two tree species, karité (Vitellaria paradoxa) and néré (Parkia biglobosa) on soil condition, development and production of cotton, sorghum and pearl millet, main crops in South Mali, has been investigated.The soil under the trees is slightly richer (organic matter content and several cations) compared to adjacent tree-less sites. Also tree-specific effects exist.Soil enrichment, however, is mainly a matter of redistribution of locally available nutrient resources.Of the six associations studied, only karité-cotton shows no tree-induced reduction in crop production. All other associations suffer greatly from reduced crop outputs caused by the trees, usually in the order of 60%.There are at least two reasons that explain tree-induced yield reduction. Because of increased humidity in the immediate surroundings of trees, in both soil and air, lower numbers of crop plants survive up to maturity, presumably because plants are attacked by fungi. Secondly, crop plants that mature show reduced output because of inter-specific competition for light and nutrients.In case of néré, in order to minimize the trees' negative influence lopping is advised. Such practice, however, is less suitable in case of karité, because of its assumed lower potential to regenerate, as compared to néré.     

Root development in a Sesbania sesban fallow-maize system in Eastern Zambia

Roots of trees (Sesbania sesban) and crops (Zea mays) were quantified during two tree/crop cycles in a sequential tree — crop system at Chipata, Eastern Zambia. The experiment included one- and two-year fallows as well as fertilized and unfertilized controls. The roots of S. sesban represent a standing biomass in the soil of 3 Mg ha^t-1 in the top 1.5 m after two years, with 45–60% and 70–75% being in the top 25 and 50 cm respectively. S. sesban fallow improved early rooting and growth of the following maize crop. Increased soil infiltration was also observed in the two-year fallow treatment, as well as decreased bulk density and resistance to penetration in the soil. No differences between maize root parameters could be detected at tasselling, nor differences between nutrient status of the different treatments. Study results indicate that under the drought-prone conditions of Eastern Zambia, where improved soil physical conditions are important for early deep rooting of crops and access to water and nutrients, tree roots could play an important role in the fallow effect. Further studies are required to assess the relative importance of the improvement of soil chemical and physical properties.Submitted as ICRAF Journal Article # 95/28.     

Studies withGliricidia sepium for crop/livestock production systems in West Africa

This paper reports for progress of research onGliricidia sepium conducted by the Humid Zone Programme (HZP) of the International Livestock Centre for Africa (ILCA) at Ibadan in Southwest Nigeria in the period 1982–1986. It examines the biological characteristics of the species, with respect to growth, flowering and seed production, and analyses its potential for improving crop production (through soil fertility maintenance) and livestock production (through production of improved fodder). Integration ofGliricidia into cropping systems is necessary for optimum realisation of its crop improvement quality. The alley farming system is presented in the paper as one means of achieving sustainability in crop production through integration of trees, such asGliricidia, into cropping systems. The use ofGliricidia in Intensive Feed Gardens, for production of leguminous fodder is also described as an alternative production system. The paper finally reports on experiences with local farmers in on-farm research and development for the integration ofGliricidia andLeucaena into local farming systems. It ends with a suggestion for more research, targetted specifically at improvement of the species and its utilisation.     

Rooting systems of western and southern African Faidherbia albida (Del.) A. Chev. (syn. Acacia albida Del.) —a comparative analysis with biogeographic implications

Faidherbia albida is a well-known and widespread agroforestry species of the Sudano-Sahelian zone of West Africa. Recent collection and testing efforts have included attempts to introduce seed origins from eastern and southern Africa into the Sahel. These have generally met with failure. Despite superior early growth, mortality is severe by the first or second year. Trials conducted at the ICRISAT Sahelian Center in Niger have demonstrated that this is probably due to differences in rooting patterns between southern and western Africa origins. A separation of the species into two ecotypes, i.e., upland (western Africa) and riparian (eastern, southern and southwestern Africa) is proposed. Based on this argument, the Sudan/Ethiopia region is identified as a possible center of origin for the species. Submitted as ICRISAT Journal Article # JA-1107.