Christian Nolte

Biomass production and N fixation of five Mucuna pruriens varieties and their effect on maize yields in the forest zone of Cameroon

Mucuna has been tested intensively in past years as green manure for intensive maize production in West Africa. However, information is missing about the yield effect of different existing mucuna varieties. Five Mucuna pruriens varieties were grown for 40 weeks followed by sole maize (Zea mays L.) in order to determine differences in biomass production, nitrogen fixation, and effects on maize yield. Mucuna varieties differed in length of growing period, total biomass production (5.9—8.8 Mg ha—1), seed production (0.65—1.3 Mg ha—1), nitrogen (N) uptake (147—222 kg ha—1), N fixation (87—171 kg ha—1), and the amount of N retained in residues (138—218 kg ha—1). The grain yield of maize grown immediately after the short mucuna fallow was significantly higher after mucuna vars. jaspaeda (4.60 Mg ha—1), utilis (3.49 Mg ha—1), and cochinchinensis (3.44 Mg ha—1), compared with a non-fertilized control (1.93 Mg ha—1) which had a maize crop and vegetation regrowth before. After mucuna vars. ghana and veracruz, 2.90 and 2.65 Mg ha—1 of maize grain were produced, respectively. No significant correlation between mucuna biomass and its N uptake and maize grain yield was found, whereas maize stover yield showed a significant positive correlation. Application of 30, 60, and 90 kg ha—1 N as urea on sub-plots of the control yielded 2.20, 3.19, and 3.46 Mg ha—1 of maize grain in the first year. Only the difference between 0 and 90 kg ha—1 N was significant. Fertilizer N equivalent values for mucuna varieties ranged from 41 to 148 kg ha—1. The yield advantage of vars. jaspaeda, utilis, and cochinchinensis versus the control without N fertilizer application was confirmed in the following year, with no significant difference in maize grain yield between mucuna and the control with N fertilizer application. Biomasseproduktion und N-Fixierung von funf Mucuna pruriens-Varietaten und ihr Einfluss auf die Maisertrage in den Waldgebieten Kameruns Kurzzeit-Grundungung mit Mucuna fur intensive Maisanbausysteme ist in den letzten Jahren vielfach in Westafrika getestet worden. Allerdings fehlen Informationen uber die Ertragseffekte der verschiedenen vorhandenen Mucuna-Varietaten. Funf Mucuna pruriens-Varietaten wurden 40 Wochen lang als Grundungung zu Mais (Zea mays L.) angebaut, um Unterschiede in ihrer Biomasseproduktion, Stickstofffixierung und Ertragseffekte auf Mais zu testen. Die Mucuna-Varietaten unterschieden sich in Anbauperiode, Gesamt-Biomasseproduktion (5,9—8,8 Mg ha—1), Samenproduktion (0.65—1.3 Mg ha—1), Stickstoffaufnahme (147—222 kg ha—1), Stickstofffixierung (88—171 kg ha—1) und im Anteil Stickstoff, der fur die Folgefrucht im System erhalten blieb (138—218 kg ha—1). Der Kornertrag von Mais, angebaut direkt nach der Mucuna-Grundungung, war signifikant hoher nach var. jaspaeda, utilis und cochinchinensis als in der ungedungten Kontrolle, deren Vorfrucht naturliche Kurzgrunbrache war. Die Maisertrage nach var. ghana und var. veracruz betrugen 2,90 und 2,65 Mg ha—1. Es wurden keine signifikanten Korrelationen zwischen Mucuna-Biomasse sowie ihrem N-Gehalt und dem Kornertrag von Mais gefunden, der Strohertrag von Mais zeigte hingegegen eine signifikant positive Korrelation. Die Dungung von 30, 60 und 90 kg N ha—1 als Harnstoff nach Kurzgrunbrache mit naturlicher Vegetation resultierte in 2,20, 3,29 und 3,46 Mg ha—1 Kornertrag im ersten Jahr des Maisanbaus. Nur die Differenz zwischen 0 und 90 kg ha—1 N-Dungung war signifikant. Der Maiskornertrag nach den Mucuna-Varietaten entsprach einer N-Dungung von 41 bis 148 kg ha—1. Der Kornmehrertrag der Varietaten jaspaeda, utilis und cochinchinensis gegenuber der ungedungten Kontrolle wurde im zweiten Anbaujahr bestatigt, allerdings wurde kein signifikanter Unterschied im Kornertrag zwischen Mucuna-Grundungung und Harnstoffdungung gefunden.

Deforestation, hunting and the ecology of microbial emergence

Infectious agents represent a significant risk to humans, their domestic crops and animals, and the planet’s wildlife. The past century was punctuated by the emergence of a variety of infectious diseases. Perhaps most notable of the completely novel diseases emerging into the human population during this period was HIV-1, which will have a serious demographic impact on human populations. While recently emerged and reemerging pathogens has attracted substantial attention during the past decade, an understanding of the factors which influence microbial emergence remains elusive. Understanding the processes by which humans, or other organisms, acquire new diseases has practical implications for maintaining the health of communities as well as fundamental implications for understanding the functioning of ecosystems. Historically, approaches to the study of infectious agents have focused largely on the impact of these agents on morbidity and mortality, or on the development of medicines to treat them. These approaches have yielded significant progress in human and animal medicine. Nevertheless, these approaches have not generally placed infectious agents in the context of ecosystems or examined the general factors contributing to the emergence of such microbes. An ecological framework for examining emerging infectious diseases has a number of potential benefits. Such a framework will help to determine the impact of environmental factors on the changing prevalence of infectious diseases. It may also provide insights into the impact of human activities on the emergence of new disease. More generally, an ecological approach is likely to contribute to the well sought after goal of a predictive science of emerging infectious diseases. The problems of defining an ‘emerging infectious disease’ have been discussed considerably elsewhere. One set of emerging diseases are those that are completely novel, or thought never to have gained a foothold within a given species or population before. The goal of this paper is to examine factors which influence human acquisition of completely novel microbes. We approach this problem from three directions. The first examines the underlying diversity of potentially emerging microbes. The second explores the impact of human activities on contact with this microbial diversity. The final direction investigates the influence of environmental change on the frequency of human contact. To demonstrate how such phenomena might be approached empirically, we present a case study of hunting and deforestation in Cameroon. Among the conclusions drawn from this study is that certain synergies, for example between logging activities, hunting of nonhuman primates, and international travel are likely to increase the frequency at which novel microbes successfully enter into the global human population.

Relationships of intercropped maize, stem borer damage to maize yield and land-use efficiency in the humid forest of Cameroon.

Stem borers are the most important maize pests in the humid forest zone of Cameroon. Field trials were conducted in the long and short rainy seasons of 2002 and 2003 to assess the level of damage and yield reductions caused by stem borers in monocropped maize and in maize intercropped with non-host plants such as cassava, cowpea and soybean. The intercrops were planted in two spatial arrangements, i.e. alternating hills or alternating rows. All intercrops and the maize monocrop were grown with and without insecticide treatment for assessment of maize yield loss due to borer attacks. The land-use efficiency of each mixed cropping system was evaluated by comparing it with the monocrop. The temporal fluctuation of larval infestations followed the same pattern in all cropping systems, but at the early stage of plant growth, larval densities were 21.3-48.1% higher in the monocrops than in intercrops, and they tended to be higher in alternating rows than alternating hills arrangements. At harvest, however, pest densities did not significantly vary between treatments. Maize monocrops had 3.0-8.8 times more stems tunnelled and 1.3-3.1 times more cob damage than intercrops. Each percentage increase in stem tunnelling lowered maize grain yield by 1.10 and 1.84 g per plant, respectively, during the long and short rainy season in 2002, and by 5.39 and 1.41 g per plant, respectively, in 2003. Maize yield losses due to stem borer were 1.8-3.0 times higher in monocrops than in intercrops. Intercrops had generally a higher land-use efficiency than monocrops, as indicated by land-equivalent-ratios and area-time-equivalent-ratios of >1.0. Land-use efficiency was similar in both spatial arrangements. At current price levels, the net production of mixed cropping systems was economically superior to controlling stem borers with insecticide in monocropped maize. The maize-cassava intercrop yielded the highest land equivalent ratios and the highest replacement value of the intercrop. At medium intensity cropping this system is thus recommended for land-constrained poor farmers who do not use external inputs such as fertilizer and insecticides.

Abundance, dispersion and parasitism of the stem borer Busseola fusca (Lepidoptera: Noctuidae) in maize in the humid forest zone of southern Cameroon.

This study was conducted in the humid forest zone of Cameroon, in 2002 and 2003. The main objective was to investigate the effects of intercropping on infestation levels and parasitism of the noctuid maize stem borer Busseola fusca Fuller. Two trials were planted per year, one during the long and one during the short rainy season. Maize monocrops were compared with maize/legume or maize/cassava intercrops in two spatial arrangements: maize on alternate hills or in alternate rows. Spatial analyses showed that the stemborer egg batches were regularly dispersed in the maize monocrop and aggregated in the intercrops, as indicated by b, the index of dispersion of Taylors power law. Depending on the crop association and planting pattern, intercrops reduced the percentage of plants with stem borer eggs by 47.4-58.4% and egg densities by 41.2-54.5% compared to monocropped maize. Consequently, larval densities were 44.4-61.5% lower in intercrops compared to monocrops. Intercropping maize with non-host plants did not affect larval parasitism. Up to two-fold higher levels of egg parasitism by scelionid Telenomus spp. were recorded in inter- compared to monocrops during the short rainy seasons of 2002 and 2003. No differences were found among the mixed cropping treatments and parasitism was lower during the long compared to the short rainy seasons. It was proposed that differences in levels of parasitism were due to density dependence effects rather than the effect of the presence of non-host plants in the system.

The effect of grassy field margins and fertilizer on soil water, plant nutrient levels, stem borer attacks and yield of maize in the humid forest zone of Cameroon

Abstract Two field experiments, planted in a split plot design, were conducted during 2002 in the forest zone of Cameroon, to investigate the effect of border rows with Pennisetum purpureum (Poaceae) or with Panicum maximum (Poaceae) on soil water, plant nitrogen (N), phosphorus (P) and potassium (K), borer infestations, parasitism and maize yield. The grassy boundaries were the main plots and fertilizer treatment the sub plots. Soil humidity was significantly higher under the grass borders than in maize plots. Nitrogen uptake by maize tended to be highest in plots surrounded by P. purpureum but the differences were significant during the second season only. Busseola fusca (Fuller) (Lepidoptera: Noctuidae) was the predominant borer species followed by Eldana saccharina (Walker) (Lepidoptera: Pyralidae). The predominant parasitoid species was the scelionid egg parasitoid Telenomus busseolae Gahan (Hymenoptera: Scelionidae). During both seasons, plant nitrogen, B. fusca infestation, plant damage and yield were significantly higher in maize sub-plots that received fertilizer The interaction between the grassy margin effect and the fertilization was significant only for B. fusca infestations, during the second season with maize + P. purpureum having a significantly lower number of borers in the fertilized than the unfertilized sub-plots. The grassy borders had no effect on B. fusca egg parasitism variables except in the first season, when maize with P. purpureum had a significantly higher percentage of egg batches parasitized. During both seasons, there were some significant differences in yield variables between main plots but the trends were not clear. Multiple regression showed that B. fusca infestation, plant damage, egg parasitism, plant N, P and K affected yield, with plant nutrients explaining most of the variability. The implication of the findings for the feasibilty of this habitat management technology to farmers in southern Cameroon is discussed.

Relationships of soil fertility and stem borers damage to yield in maize-based cropping system in Cameroon

Abstract Field trials were designed to investigate the effect of direct nitrate fertilisation and mucuna fallow on maize yield and borer attacks in the humid forest zone of Cameroon. A traditional maizecassava- groundnut system (farmers’ practice) was compared with a maize-cassava + 120 Kg N ha-1, a rotation system in which maize-cassava followed a mucuna fallow as well as with a maize monocrop grown after mucuna fallow and with a maize monocrop grown with 120 Kg N ha-1. Average egg batch densities of Busseola fusca (Lepidoptera: Noctuidae) were lower by 35–55% in inter- than monocrops but the effect of nitrogen on B. fusca oviposition was not different from that of mucuna fallow. Highest larval infestations were found in sole maize with nitrogen and sole maize after mucuna. Yield losses were 4–10 times higher in the farmers’ practice compared to maize-cassava after mucuna and maizecassava with nitrogen. Mixed cropping systems including farmers’ practice yielded higher total gross and net benefits compared to sole maize crops. But, they were higher in maize-cassava intercrop + N than for farmer’s practice.

Role of Inland Valleys in the Management of Stem Borers and Their Natural Enemies in Upland Maize Fields in the Humid Forest Zone of Cameroon

Abstract During the dry season in the humid forest zone of Cameroon, maize is the most important off-season cash crop grown in hydromorphic inland valleys (IVs), which may also be reservoirs for pests such as the stemborer Busseola fusca Fuller and its natural enemies. Pest and parasitoids were monitored in IVs and close-by upland maize fields from January 2002 through December 2004. Trap catches and oviposition data showed that B. fusca was active throughout the dry season and long and short rainy seasons of 2004. Egg batch densities were considerably lower in the dry than in the rainy seasons. Important natural enemies were the scelionid egg parasitoids Telenomus busseolae Gahan and T. isis Polaszek. B. fusca was the predominant borer species in all seasons in maize in IVs as well as in upland fields, followed by Sesamia calamistis Hampson and Eldana saccharina Walker. B. fusca larval densities were lowest in the IVs and increased in the course of the year in the upland fields. In contrast, S. calamistis densities were higher in IVs than in upland maize fields. At harvest of the IV maize, B. fusca and E. saccharina larval densities were 47.3 and 15.5 times higher, respectively, than on old maize stubbles in upland fields planted during the previous year. Grain yields as well as the marketable ear index were 1.1–2 times higher in the dry season than in the long and short rainy seasons, indicating the importance of IVs for dry season maize production in Cameroon.

Groundnut, maize and cassava yields in mixed-food crop fields after Calliandra tree fallow in southern Cameroon

Shortened fallow periods lead to a decline in crop yields in traditional mixed-food crop fields in southern Cameroon. Farmers use no inputs such as fertilizers for crop production in these field types. Planted fallows with adapted tree species might sustain or increase crop production under those conditions, as found in other parts of Africa. Two-year-old calliandra three fallows, with trees planted in alleys, clusters, equidistantly or around plot borders, were compared with two- and four to five-year-old natural fallows for their effect on groundnut, maize and cassava yields on eighteen farmer fields in southern Cameroon. Trial fields covered a wide range of soil and environmental conditions. The tree fallows had no significant effects on the yields of maize and cassava with the exception of the border planting, in which trees were not rigorously pruned back prior to cropping. Here, cassava tuber yields were reduced. Cassava tuber yields declined generally with decreasing planting distance to trees. The yield of groundnut, the most important crop in this field type, wa.s adversely affected. However, maize graft yields were positively related to biomass produced by calliandra trees, notably on soils with pH seer about 5.3. The data indicated that yields of all crops could be increased with higher plant densities, irrespective of fallow type. The tree fallows, with the exception of border planting, showed less adaptability than four to five-year-old natural fallows to sites with low crop yields, whereas no difference compared with hvo-year-ald natural hallows was found.

Urban Farming Systems in Yaoundé – Building a Mosaic

Urban agriculture is prevalent in Cameroon, the first country examined in this book of case studies, yet its role in urban life was little studied until the 1990s. At that time researchers began to look at some aspects of this complex phenomenon, such as the role of traditional leafy vegetables in the diet and incomes of the urban poor (Gockowski & Ndoumbe 1999). Following their attendance at a regional stakeholder meeting organized by Urban Harvest in late 2000, scientists from different institutions came together in 2001 to move forward work they were pursuing independently on different topics related to urban agriculture in Yaounde. This interdisciplinary collaboration produced the original empirical studies contained in this chapter and the two that follow, which aim at a deeper understanding of some of the complexities of urban farming in the country and indicate directions for further work, both in research and the development of public policy.

Crop–Livestock Integration in the Urban Farming Systems of Yaoundé

As a result of rapid rates of urban growth, especially in the larger centres of Douala and the capital, Yaounde, about half the Cameroon’s population lives in urban areas (World Bank 2003). Yaounde’s population increased at the rate of about 10 percent per annum from 0.64 million in 1987 to 1.5 million in 2000 (DSCN 2000), and is projected to be as much as 4 million by the year 2020. The city’s population faces enormous problems of poverty, with unemployment registering around 25 percent (DRSP 2003). To sustain themselves, households resort to urban agriculture (UA), which also provides some income. Statistics taken from just one aspect of UA show that at least 32 000 households sell traditional leafy vegetables, most of which are produced by the women in those households, using extensive mixed crop-farming systems (Gockowski et al. 2003).