Cassava, Manihot esculenta Crantz and wild relatives: Their relationships and evolution

About ninety eight species of Manihot arerecognized. All of them are native to the New world and areconcentrated in four regions of diversity in Brazil and CentralAmerica. All the Manihot species so far examinedhave 2n = 36 chromosomes. Interspecific hybrids betweencassava and its wild relatives show relatively regular meiosis, andfurther generations can be obtained. Electrophoresis shows affinityamong species of different sections, and between some of them andcassava. Both polyploidy and apomixis may have contributed tospeciation in this genus. Polyploidy offered genetic variabilitywhile apomixis is responsible for perpetuating new hybrid typesadapted to different environments. Cassava may have originated byhybridization between two wild Manihot speciesfollowed by vegetative reproduction of the hybrid.     

Applications of reduced tillage in hills of central Nepal

Conventional tillage practices on steep and fragile landscape of Himalayan hills result in significant loss of topsoil during rainy season. Soil erosion in Nepal mid-hills is the most critical during pre-monsoon season. Many reviews argue that reduced tillage could be an option to tackle this problem. However, very few field experiments to evaluate reduced tillage systems have to date been conducted in this region. Thus, a field experiment was initiated in factorial randomized complete block design on acidic sandy loam soil (Lithic Dystochrept) during the summer season of 2001 at Kathmandu University (1500 masl) to assess the effects of tillage and cropping patterns on soil and nutrient losses, crop yield and soil fertility. Two main treatments viz. conventional and reduced till, and two sub-treatments viz. sole maize (Zea mays) and maize + soybean (Glycine max) were considered. Soil organic carbon (OC), total nitrogen (N), plant available phosphorus (P) and exchangeable potassium (K) were determined for the original soil and eroded sediment using standard methods. Two years of data indicated annual soil and nutrient losses to be significantly lowered by reduced till as compared to conventional till. Total annual soil loss from conventional and reduced till was 16.6 and 11.1 Mg/ha, respectively. Similarly, annual nutrient losses associated with the eroded sediment were 188 kg OC/ha, 18.8 kg N/ha, <1 kg P/ha and 3.8 kg K/ha for conventional till and 126 kg OC/ha, 11.8 kg N/ha, <1 kg P/ha and 2.4 kg K/ha for reduced till. Soil OC and N losses were significantly higher in conventional till and this may be one of the major causes of fertility depletion in the Nepalese hills. Soil chemical properties did not differ due to tillage and cropping systems; however, over years pH, N and P were increased irrespective of treatments. Although treatments were at par for maize grain yield, conventional till + soybean produced highest grain yield (4.0 Mg/ha) followed by reduced till + soybean (3.9 Mg/ha) and conventional till sole maize (3.8 Mg/ha). Mixed cropping of legumes and maize do not help conserve soil and nutrient loss in hills of central Nepal. Thus, reduced till could be a viable option for minimizing soil and nutrient losses without sacrificing economic yields in central hills of Nepal.     

The soils of a typical slope in the Himalayas (Nepal): Their main characteristics and distribution

This study is based on a sequence of soils on a typical slope of the Himalayas in central Nepal from 2300 m to 4000 m. Above 2300 m the land is forested and at 4000 m forest gives way to alpine meadows.The soils have developed in silty loam materials derived from weathering of micaschists. They are humic, acid and strongly desaturated. Their spatial distribution is related to the bioclimatic zonation: acid brown soils and deep humic acid soils occur in the mountain zone and podzols and brown podzolic soils in the subalpine and alpine ones.Biological activity and “maturation” of humus decrease with increasing elevation. The podzolization process dominates. There is intense weathering of ferruginous phyllosilicates in eluvial horizons and accumulation of amorphous products in B horizons.     

珠江三角洲小流域地下水化学特征及演化规律

珠江三角洲地下水环境日益恶化,已成为制约经济社会发展的重要因素。以珠海市具有典型特征的闭合小流域作为研究对象,分旱、雨两季采集地下水分析主要离子及D、18O同位素,全面系统地研究了地下水水化学的时空变异特征与演变规律。结果表明：研究区内地下水主要受大气降水及附近地表水体渗透补给,以蒸发及地下水径流排泄,季节变化对区域内水化学空间变异性影响较小。沿地下水流方向（补给区-径流区-排泄区）,地下水化学类型主要从Ca-Na（Mg）-HCO3型向Na-Cl和Na-K-HCO3-CO3型演化,风化-溶滤、离子交换、海陆交互作用是控制当地地下水质演变的主要水文化学过程。     

Phases of soil erosion-derived colluviation in the loess hills of South Germany

In South Germany, soil erosion is as old as farming and dates back to Early Neolithic times. Its sedimentary products form thick colluvial and alluvial sediment bodies in all drainage basins. Numerous local studies exist but the extrapolation of findings from local case studies to a regional scale has been problematic. Here, a graphical approach is used for frequency analysis of existing data. A frequency distribution for optical dates on colluvial sediments from the beginning of agriculture until 1200 AD was constructed by: (1) representing the optical ages by Gaussian-distributions and (2) summing all the single curves. The resulting graph clearly shows phases of increased colluviation during periods of stronger human impact. A first significant increase occurred during the Bronze Age. During the Iron Age/Roman period and at around 800 AD, distinct maxima appear in the distribution, and highest frequencies are present towards the end of the analysed period at around 1100 AD. Conclusions that can be drawn from such an approach are limited by sampling bias and other factors, but for the analysed period, and on a regional and long-term scale, colluviation seems to have been mainly triggered by intensity of land use. Climatic fluctuations are of only secondary importance. Rainfall events that were sufficiently erosive to produce colluvial sediments occurred throughout the agricultural periods. The limiting factor for colluvium production was sensitivity of the landscape to erosion, and this is a result of land use.     

Bound water characteristics and microstructure evolution during uniaxial compression of mucky silty clay

Journal of Soils and Sediments - Compression studies can provide insights into evaluating the engineering potential and environmental impact of clay. The objective of this study was to...     

Obesity in South Africa: challenges for government and health professionals

OBJECTIVES: To review data on the prevalence, causes and health consequences of obesity in South Africa and propose interventions to prevent and treat obesity and related outcomes. METHODS: Data from existing literature were reviewed with an emphasis on changing eating and activity patterns, cultural factors, perceptions and beliefs, urbanisation and globalization. Results of studies on the health consequences of obesity in South Africans are also reviewed. RESULTS: Shifts in dietary intakes and activity patterns to higher fat intakes and lower physical activity are contributing to a higher prevalence of obesity. Few overweight black women view themselves as overweight, and some associate thinness with HIV/AIDS. Glucose and lipid toxicity, associated with insulin resistance, play roles in the pathogenesis of the co-morbid diseases of obesity. Elevated free fatty acids in the black population predispose obese black patients to type 2 diabetes. CONCLUSION AND RECOMMENDATIONS: Obesity prevention and treatment should be based on education, behaviour change, political support, intersectoral collaboration and community participation, local actions, wide inclusion of the population, adequately resourced programmes, infiltration of existing initiatives, evidence-based planning, and proper monitoring and evaluation. Interventions should have the following components: reasonable weight goals, healthful eating, physical activity and behavioural change. Genes and mutations affecting susceptibility to the development of co-morbidities of obesity and vulnerable periods of life for the development of obesity should be prioritized. Prevention should be managed in community services, identification of high-risk patients in primary healthcare services and treatment of co-morbid diseases in hospital services.     

Termite mounds in relation to the surrounding soils in the forest and derived savanna zones of southeastern Nigeria

Some physical and chemical properties of the two common termite mounds in southeastern Nigeria, Macrotermes (MM) and Cubitermes (CM) mounds, were compared and their relationships with the surrounding top and subsoils investigated. Percentage sand, silt, pH, calcium, magnesium, potassium, sodium, iron, and organic carbon were higher and clay and penetrometer resistance lower in the CM than the MM. Sand, silt, organic carbon, and calcium decreased and clay increased from the forest to the derived savanna in the CM, but no clear trend was shown with the other properties in both the CM and the MM. Most of the nutrients were higher in the CM than in the adjacent top or subsoil but the reverse was the case with the MM. More nutrients are associated with the inorganic fractions of the soil than with the organic carbon in the mounds and the soils surrounding them. The Ca:Mg ratio in the mounds and the top and subsoils adjacent to them was low for most crops but the K:Mg ratio was mostly adequate. Because of these differences in properties and sizes of the mounds, different management strategies are recommended for them and the soils around them.     

Population size,distribution, and symbiotic characteristics of indigenous Bradyrhizobium spp. that nodulate TGx soybean genotypes in Africa

Soils of many potential soybean fields in Africa are characterized by low levels of biological nitrogen fixation (BNF) activities and often cannot support high soybean yields without addition of inorganic N fertilizers or external application of soybean rhizobia. The most probable number (MPN) technique was used to determine the bradyrhizobial populations that nodulate TGx soybean genotypes (a cross between nonpromiscuous North American soybean genotypes and promiscuous Asian soybean genotypes), cowpea or North American soybean cv. Clark IV, in soils from 65 sites in 9 African countries. The symbiotic effectiveness of isolates from these soils was compared to that of Bradyrhizobium japonicum strain USDA110. The bradyrhizobial population sizes ranged from 0 to 10⁴ cells g⁻¹ soil. Bradyrhizobium sp. (TGx) populations were detected in 72% and B. japonicum (Clark) in 37% of the soil samples. Bradyrhizobium sp. (TGx) populations were generally low, and significantly less than that of the cowpea bradyrhizobial populations in 57% of the samples. Population sizes of less than 10 cells g⁻¹ soil were common as these were detected in at least 43% of the soil samples. B. japonicum (Clark) occurred in higher population densities in research sites compared to farmers’ fields. Bradyrhizobium sp. (TGx) populations were highly correlated with biotic but not abiotic factors. The frequent incidence of low Bradyrhizobium sp. (TGx) populations is unlikely to support optimum BNF enough for high soybean yields while the presence of B. japonicum (Clark) in research fields has the potential to compromise the selection pressure anticipated from the indigenous Bradyrhizobium spp. (Vigna) populations. Bradyrhizobium isolates could be placed in four symbiotic phenotype groups based on their effectiveness on a TGx soybean genotype and the North American cultivar Clark IV. Symbiotic phenotype group II isolates were as effective as B. japonicum strain USDA110 on both soybean genotypes while isolates of group IV were effective on the TGx soybean genotype but not on the Clark IV. The group IV isolates represent a unique subgroup of indigenous bradyrhizobia that can sustain high soybean yields when available in sufficient population densities.     

Grassland improvement in Africa

Of all the continents, Africa has the highest proportion of land fit for agriculture. The principal vegetative cover on this land is grass, which, when it is well managed, gives good protection against erosion. Unfortunately, much of this grassland, and especially that north of the Sahara desert, is so heavily overstocked that it produces far too little forage for livestock, and scarcely any cover remains for protection of the soil. The very low productivity of the livestock is a major factor in the poor nutrition of the people—especially of young children suffering from kwashiorkor. It is still a common practice to keep as many cattle as possible, as an indication of the owner's social status and wealth. Consequently in Africa the commonest problems include a shortage of forage and inefficient use of what is available. This condition needs to be alleviated by increasing the output from native grassland and producing more forage on arable land. Each country needs a competent organization to cope with these problems. Improved practices such as rotational grazing and culling unproductive animals may increase the yield of the livestock from two to ten times. All such practices can be gradually adopted by the pastoral people, and by those doing mixed farming, with the help of their own technically trained youth. By the use of these practices, along with family planning to hold the population near the present level, it will be possible for the people to have an adequate diet and for the soil and other natural resources to be maintained.     

Rare and vulnerable birds in South Africa

The paper summaries information obtained through an initial survey undertaken to identify those avian populations which qualify for inclusion in a South African Red Data Book, and whose conservation status is in need of special attention. One hundred and one species' populations are included in the preliminary list. Nine of the 101 species are endemic to South Africa. There is a predominance of forest and wetland species, of birds of prey, and of mainly tropical species occurring as intrusions in the north east of South Africa. Many of the species listed are peripheral to South Africa and are widespread and abundant extra-limitally. Twenty species' populations which require urgent conservation attention are listed. As far as is known, no avian species has become extinct during historical times in South Africa, but two are at present endangered, i.e. threatened with immediate extinction.     

Hopeaphenol: the first resveratrol tetramer in wines from North Africa

Grapes and wines are now known to constitute a rich source of phenolics such as stilbenes and flavonoids. These compounds have been shown to have cancer chemopreventive activity and potential beneficial effects on cardiovascular diseases thanks to their antioxidant and antiplatelet properties. However, because little is known about African wines and their phenolic compositions, we investigated wine samples from North Africa. A three-step method was used for the fractionation of the Merlot variety wine: column chromatography followed by centrifugal partition chromatography and reversed-phase semipreparative high-performance liquid chromatography (HPLC). Six polyphenolic compounds of the Merlot variety (from Algeria) were isolated and identified by NMR spectroscopy, five of which are known (trans-resveratrol, trans-piceid, trans-epsilon-viniferin, pallidol, and astilbin) and one that is reported for the first time in wine, (+)-hopeaphenol, a stilbene tetramer. Furthermore, these molecules were quantified in 10 commercial wines from North Africa by means of an analytical HPLC system coupled with diode array detection. Differences in concentrations were found ranging in mg/L from 4.6 to 45 (trans-piceid), 0.66 to 3.45 (trans-resveratrol), 0.2 to 1.2 (trans-epsilon-viniferin), 0.2 to 9.2 (pallidol), 0.3 to 3.8 (hopeaphenol), and 10.8 to 24.22 (astilbin). Such a high level of pallidol and astilbin has never been recorded in wine. North African wines may contribute to a significant proportion of dietary intake of stilbene and astilbin, which may have health benefits.     

Tillage systems and soil properties in West Africa

West African soil resources have high potentials for enhancing agricultural productivity, if well-managed and restored. In this context, the importance of tillage systems have not been fully appreciated as an integral part of good farming systems in order to tally with the peculiarities of the soil, crops and the environment. Most improved tillage systems are not widely used, although the relatively small-scale uncontrolled application of mechanical tillage has had untold adverse effects on properties and productivity of soils in the humid and subhumid regions.

In contrast, mechanical soil tillage involving deep plow-till and soil inversion has proven beneficial on compact soils of arid and semi-arid regions. The plow-based systems not only reduce soil bulk density and soil strength but also improve the efficiency of water and nutrient use.

The exposure of structurally unstable Alfisols and Ultisols predominant in the humid and sub-humid regions by mechanical tillage can cause more adverse effects than beneficial effects on soil properties and crop yields, especially on a long-term basis. On the other hand, the no-till system with crop residue mulch can maintain favorable soil properties. The conservation tillage system, however, requires more research to make it applicable to diverse soil types, crops and ecoregions.

Apart from the long-term effects of tillage on the level of soil organic matter and the attendant release of nutrients, the effects of tillage systems on the chemical properties of soil are often contradictory and are confounded by many other factors so that clear-cut cause and effect relationships are not obvious. The interactions between fertilizer application, liming, soil organic matter content and tillage systems, especially on acid soils, are such examples. More detailed studies on nutrient dynamics under different tillage systems are necessary. The interactions between the relatively new technologies of alley cropping and agroforestry which allow a more continuous use of the land should be investigated vis-à-vis tillage systems.

Long-term, well-designed, adequately equipped experiments (which are scanty in West Africa) should be encouraged to elucidate and confirm results of many short-term experiments.     

Collections of short-day onion germplasm in West Africa: a survey

Results are presented of a 1994 postal survey of holdings of local onion (Allium cepa L.) germplasm by institutions in West Africa. Data obtained from respondents included the number of accessions of onion or shallot held and the conditions in which onion seed was stored. Twenty-four replies were received and eighteen sites where collections were held were identified. The numbers of local A. cepa accessions in local collections varied in number from 38 down to nil, but many local collections were of less than five accessions. The largest number of national onion accessions was held at CERRA, Maradi, in Niger (16), and the largest regional collection was at the Station de Farako-bâ, Burkina Faso (38). Two sites held substantial shallot collections: CRA Bareng in Guinée and IDESSA, Bouaké, Côte d'Ivoire. Conditions under which onion seed was stored varied from low temperature, controlled storage in moisture-proof packs with desiccants, to storage in plastic envelopes under ambient laboratory conditions.     

Tillage systems and soil properties in east Africa

This paper defines tillage, indicating that as it is mostly a physical concern of the soil, it has not been studied as much as chemically related soil properties. Tillage in shifting cultivation is also reviewed. Different tillage systems in a number of east African Countries namely Tanzania, Malawi, Botswana, Kenya, Zambia and Uganda are reviewed. The types of tillage in their respective soils are discussed in each Country. Uganda's tillage practices for the main food crop (banana) are discussed, pointing out the crop's rooting system in relation to the heavy, relatively fertile soils, where the bananas are mostly grown. The paper distinguishes between tillage to avoid soil compaction and tillage to reduce soil crusting or hardening and concludes that more research should be carried out on tillage practices relating to heavy soils as it affects the different types of crops, as most of the previous tillage research had been carried out on relatively light soils. Soil crusting or hardening which may involve an understanding of the physical, chemical and biological properties of the soil, should also receive more attention.     

Science and elephant management decisions in South Africa

Most conservation practitioners rely on experience-based information for management decisions. In South Africa, government policy thus directs managers to base decisions for elephant management on the best available scientific information. The reliance of their management decisions on science, however, is unknown. We interviewed 30 managers from small to large protected areas in South Africa to evaluate whether science underpinned strategic and applied management decisions regarding elephants. We also evaluated their perspectives on limitations to, and opportunities for, greater reliance on science. Twenty-nine managers valued science as a platform for their decisions. However, most managers based decisions on experience-based information. Only 28%, 30% and 8% of managers respectively developed objectives, identified issues and selected management methods on science-based information. Furthermore, only 30% selected a desired number of elephants, and 5% selected a population control method, according to science-based information. The probability of managers basing decisions on science-based information differed with management area size, tenure, planning timeframes and manager experience. However, except for experience, these relationships were weak, and overall an implementation gap between science and elephant management existed. Limitations for science to inform decisions included lack of relevance and application of science findings to respective management areas, and scientists’ attitudes and credibility. Opportunities included more site specific studies, better communication of, and easier access to scientific material. These opportunities could enable scientists to contribute more effectively to elephant management decisions and improve the reliance on science among the wider community of conservation practitioners in Africa.