Temporal changes in VAM fungi in the cocoa agroforestry systems of central Cameroon

In Cameroon, cocoa trees are mostly grown in forests and without fertilization. Our aim was to learn more about the temporal dynamics of soils in cocoa agroforests by comparing young (1–4 years old) and old (over 25 years old) cocoa agroforests. Short fallow and secondary forest were used as treeless and forest references. The numbers and diversities of soil vesicular arbuscular mycorrhizal (VAM) fungi on 60 cocoa producing farms in the Central province of Cameroon were assessed based on the classical morphotyping of spore morphology. We also observed the soil organic matter, nitrogen and major soil nutrients. VAM spore density was significantly lower in the young cocoa agroforests (16 spores g⁻¹ dry soil) than in the old cocoa agroforests (36 spores g⁻¹ dry soil). Levels in the nearby secondary forest (46 spores g⁻¹ dry soil) were not significantly different from old cocoa. The spore density was significantly highest in the short fallow (98 spores g⁻¹ dry soil). The Shannon–Weaver index also showed significantly lower biodiversity in young cocoa (0.39) than in old cocoa agroforests (0.48), secondary forest (0.49) and short fallow (0.47). These observations were supported by significant differences in the C:N ratio, Ca, Mg, and cation exchange capacity between young and old cocoa agroforests. We concluded that unfertilized cocoa agroforests could be sustainable, despite a decrease in some soil characteristics at a young stage, due to traditional land-conversion practices based on selective clearing and burning of secondary forest.     

Afforestation of savannah with cocoa agroforestry systems: a small-farmer innovation in central Cameroon

Cocoa cultivation is generally considered to foster deforestation. Contrary to this view, in the forest–savannah interface area in Cameroon, farmers have planted cocoa agroforestry systems on Imperata cylindrica grasslands, a soil-climate zone generally considered unsuitable for cocoa cultivation. We undertook a survey to understand the agricultural and ecological bases of this innovation. Age, cropping history and marketable cocoa yield were assessed in a sample of 157 cocoa plantations established on grasslands and 182 cocoa plantations established in gallery forests. In a sub-sample of 47 grassland cocoa plantations, we inventoried tree species associated with cocoa trees and measured soil organic matter levels. Marketable cocoa yields were similar for the two types of cocoa plantations, regardless of their age: 321?kg?ha^?1 in cocoa plantations on grasslands and 354?kg?ha^?1 in cocoa plantations in gallery forests. Two strategies were used by farmers to eliminate I. cylindrica prior to the establishment of cocoa plantations, i.e., cropping oil palms in dense stands and planting annual crops. Farmers then planted cocoa trees and fruit tree species, while preserving specific forest trees. The fruit tree and forest tree densities respectively averaged 223 and 68 trees?ha^?1 in plantations under 10?years old, and 44 and 27 trees?ha^?1 in plantations over 40?years old, whereas the cocoa tree density remained stable at 1,315 trees?ha^?1. The Shannon–Weaver index increased from 1.97 to 2.26 over the same period although the difference was not statistically significant. The soil organic matter level was 3.13?% in old cocoa plantations, as compared to 1.7?% in grasslands. In conclusion, our results show that the occupation of grasslands by cocoa agroforestry systems is both an important example of ecological intensification and a significant farmer innovation in the history of cocoa growing.     

Factors affecting the adoption of agroforestry practices by farmers in Cameroon

This paper presents empirical evidence on the impact of socio-economic factors on the adoption of agroforestry practices in Cameroon. The analysis uses primary farm-level data collected from June to December 1996. Three major provinces of the country were covered, namely Centre, Southwest and Northwest Several agroforestry technologies have been promoted among farmers in the zone, including alley farming, improved fallow, live fencing, cut-and-carry fodder and apiculture. The status of adoption of each agroforestry practice is described and factors that affect adoption identified. These are gender of farmer, household family size, level of education, farmer’s experience, membership within farmers’ associations, contact with research and extension, security of land tenure, agroecological zone, distance of the village from nearest town, village accessibility and income from livestock. Research findings indicate that since factors affecting farmers’ adoption of agroforestry practices differ across techniques, generalisation is to be avoided.     

农林复合生态系统游猎型蜘蛛种群动态及影响因素的研究

蜘蛛是华北农区的主要天敌种群之一,本文研究了农田蜘蛛种群结构及优势种在林带-田埂-农田环境的分布动态。结果表明:(1)研究地区游猎型蜘蛛的优势种为中华狼蛛(Lycosa sinensis Schenkel)和中华平腹蛛(Gnaphosa sinensis Simon);(2)林带和田埂在农作物栽种前和成熟后是蜘蛛栖息和获取食物的主要场所,是农林复合系统中蜘蛛种群的重要种库;(3)耕作活动对蜘蛛种群有较强的负面影响,林带环境具有维持蜘蛛种群稳定性的作用;(4)蜘蛛密度与距林带距离呈负相关性,且在距林带一定范围内密度变化极其显著(P=0.001,α=0.05),表现出明显的林带效应。     

Weed dynamics during the change of a degraded pasture to agroforestry system

This study evaluates weed dynamics during the first 4 years (2008–2011) of the implementation of an agroforestry system in the municipality of Tomé-açu in the state of Pará, Brazil. The study was conducted in a degraded pasture of Brachiaria humidicola, and treatments (T) included mixed plantations of oil palm with short-cycle leguminous species (T1) with the inclusion of manioc in T2 and forest species and palm trees in T3. In 2008, a floristic survey was conducted in 12 plots of 2 × 2 m per treatment. In 2009, herbicide was applied to one half of the area in each treatment. A total of 19,367 individuals of height <1.5 m were surveyed, of which 51 % were B. humidicola and 21 % were leguminous species that had been planted. Overall, an increase in plant density was observed between 2009 and 2010, followed by a decrease over the following year in areas without herbicide and a tendency for high densities to persist in areas with herbicide. Species richness increased over the study period in all areas (with or without herbicide), which might be related to habitat availability resulting from the reduced density of B. humidicola due to the effects of the herbicide, the leguminous species planted and the development of the agroforestry system. The association of short-cycle leguminous plants with afforestation appears to be an effective method for controlling weeds in the absence of herbicides.     

Acacia nilotica trees in rice fields: A traditional agroforestry system in central India

Time-tested, indigenous land-use systems can provide valuable information for the design of ecologically sustainable and socially acceptable agroforestry systems. One such traditional system is the growing of Acacia nilotica (L.) Willd. Ex Delile trees, locally known as babul, in rice fields of smallholder farmers in Madhya Pradesh State of Central India, an area with subhumid monsoon climate and hot summer. The functional characteristics of the system were collected through participatory rural appraisal involving intensive interactions with farmers in the region during six years, and through a structured-questionnaire survey in 25 villages, involving a total of 200 farm families. The farms had an average of 20 babul trees, ranging in age from <1 to 12 years, per hectare in upland rice fields, the tree-stand density being greater on smaller than on larger farms (>8 ha). Over a ten year rotation period, the trees provide a variety of products such as fuelwood (30 kg/tree), brushwood for fencing (4 kg/tree), small timber for farm implements and furniture (0.2 cu.m), and non-timber products such as gum and seeds. The babul + rice system was estimated to have a benefit/cost (B/C) ratio of 1.47 and an internal rate of return (IRR) of 33% at 12% annual discount rate during a ten-year period, though at a low level of income. Babul trees account for nearly 10% of the annual farm income of smallholder farmers (<2 ha). By practising the agroforestry (rice + babul) system, farmers get higher cash returns on a short-term (10-year) harvest cycle of trees, and the labour input (both family- and hired) on farms was distributed more uniformly throughout the year than in rice monoculture. Purchased inputs are seldom used in the system. The ease of management of the system, the self-generating and robust nature of the tree and the multiple products and services it provides, and easy marketability of the products are the major factors that encourage farmers to adopt the system. Furthermore, the farmers have secure ownership rights to their land, so that they are interested in long-term measures such as tree plantings on their farms. In spite of its long history and tradition as a sustainable approach to land use, the system has not attracted the attention of development agencies. More detailed investigations on its social, economic, and cultural attributes are warranted to not only improve this system, but provide insights into farmer adoption of agroforestry innovations.This revised version was published online in November 2005 with corrections to the Cover Date.     

Soil properties under Acacia nilotica trees in a traditional agroforestry system in central India

Acacia nilotica (L.) Willd. ex Del is an important multipurpose tree of traditional agroforestry system in the central belt of the Indian sub-continent. The tree is reported to reduce crop yields under its canopy. However, information is lacking on the spatial variation in soil physical characters, nutrient pool sizes and their availability to crops under its canopy. The present study reports influence of three tree canopy positions, viz. mid canopy, canopy edge and canopy gap, of Acacia nilotica (≥ 12 years) on texture, organic C, total and mineral N and P, and soil pH, in 0 to 10, 10 to 20 and 20 to 30 cm depth of the soil at ten sites in a traditional agroforestry system. Sand particles declined by 10% and 9% whereas clay particles increased by 14% and 10% under mid canopy and canopy edge, respectively, compared to that under canopy gap. Clay particles did not decline significantly with soil depth under all canopy positions. Proportion of silt particles was not influenced by the canopy position. Soil organic C, total N, total P, mineral N (NO₃ ⁻-N and NH₄ ⁺-N) and P were greater under mid canopy and canopy edge positions compared to canopy gap. Soil organic C and N pool sizes were maximum in 0 to 10 cm and declined with the depth of soil. Total and mineral P contents were nearly uniform across the depths. C/N ratio tended to increase with the soil depth whereas C/P ratio declined. This revised version was published online in June 2006 with corrections to the Cover Date.     

Integrated indicators for performance assessment of traditional agroforestry systems in South West Cameroon

Farming Systems developed in Humid Tropical Zones are frequently characterized by a combination of perennial and annual plants, intermixed in complex tree-crop associations. The productive functioning, the agronomic and economic performances, and the sustainability of these crop associations remain poorly understood. To improve the management capacity of these complex agroforestry systems, adequate indicators must be developed and integrated in assessment systems. These may then be used to aid farmers, assisted by their extension agents, in making decisions regarding management practices. The present study focused on the agroforestry systems developed by 38 farmers in the South West Region of Cameroon, which were surveyed for a large set of variables, aiming at formulating a Traditional Agroforestry Performance Indicators System (TAPIS). Analyses of the relationships among indicators in TAPIS allowed an improved understanding of agro-ecological and agro-economic performances in the studied plots, revealed tradeoffs regarding plant stand, income generation, food production, input demands and work requirements; and may contribute to the sustainability assessment of agroforestry systems.     

Plant species in the Kilimanjaro agroforestry system

An inventory of plant species was conducted on farms, farm boundaries and homesteads in the Kilimanjaro agroforestry system. The survey covered 30 farms in 6 villages in Hai District on the slopes of Mount Kilimanjaro, Tanzania. Over 100 plant species spread over 40 families were identified and their uses obtained through interviews with farmers. The species identified include 53 tree species, 29 food crop species, 21 non-woody plants of economic value and 8 weed species. The food crops, trees and other economically useful plants are carefully chosen by the local farmers and intimately intercropped on the same unit of land. In most cases, the plants had two or more uses of which food, fuelwood, medicine, poles, timber and fodder were the most important.     

Nitrogen and fine root length dynamics in a tropical agroforestry system with periodically pruned Erythrina poeppigiana

The effect of pruning all branches (complete pruning) or retaining one branch (partial pruning) on the dynamics of nitrogen cycling in aboveground biomass, nitrogen supplying power of an amended Eutric Cambisol, and fine root length, was studied in an Erythrina poeppigiana (Walp.) O.F. Cook—tomato (Lycopersicon esculentum Mill.) alley cropping practice in Turrialba, Costa Rica during 1999–2000. Over the 1 year pruning cycle, in which trees were completely or partially pruned four times, respective aboveground biomass production was 4.4 Mg or 7 Mg ha⁻¹ (2-year-old trees) and 5.5 Mg or 9 Mg ha⁻¹ (8-year-old trees); N cycled in aboveground biomass was 123 kg or 187 kg ha⁻¹ (2-year-old trees) and 160 kg or 256 kg N ha⁻¹ (8-year-old trees); mean fine root length was 489 or 821 m (2-year-old-trees), 184 or 364 m per tree (8-year-old-trees). Pruning intensity did not significantly affect net N mineralisation and net nitrification rates during the tomato-cropping season. For the tomato crop, pre-plant mean net N mineralisation rate of 2.5 mg N kg⁻¹ soil day⁻¹ was significantly lower than 16.7 or 11.6 mg N kg⁻¹ soil day⁻¹ at the end of vegetative development and flowering, respectively. Mean net nitrification rates of 3.5, and 4.3 mg N kg⁻¹ soil day⁻¹, at pre-plant and end of vegetative development, respectively, were significantly higher than 0.3 mg N kg⁻¹ soil day⁻¹ at end of flowering. In humid tropical low-input agroforestry practices that depend on organic inputs from trees for crop nutrition, retention of a branch on the pruned tree stump appears to be a good alternative to removal of all branches for reducing N losses through higher N cycling in aboveground biomass, and for conserving fine root length for higher N uptake, although it might enhance competition for associated crops.     

Carbon and nutrient stocks in the litter layer of agroforestry systems in central Amazonia,Brazil

Both second-growth and agroforestry systems (AFs) have the potential for recovering thousands of abandoned pasturelands in Amazon. The AFs may do it faster and, at the same time, produce direct economic benefits for farmers. Improved nutrient recycling may be expected due to distinctive litter production in AFs, but lacks experimental data yet. The stocks of carbon and nutrients of the litter layer under different agroforestry systems (AFs) were investigated at an abandoned pasture site, 60 km north of Manaus. The experimental design consisted of three blocks, with five treatments: four different types of 5-year-old AFs and a secondary forest (CAP). Litter layer was sampled in the wet and dry seasons, sorted according to the predominant plant species and analysed for carbon and nutrient concentrations. The litter layer in the control plots was much larger than in the AFs, and thus, the carbon stocks in the litter layer of the control (wet = 489 g m²; dry = 783 g m²) were larger than in the AFs. However, due to a clearly higher concentration of nutrients in the litter from the AFs, some nutrient stocks were similar or even greater than in the control. The planted timber species and the green manures were important sources of K and Ca to the litter layer while the peach-palm was an important source of Mg. In general, the litter of AFs had lower C:nutrient ratios than the litter in the secondary forest control, indicating a faster nutrient recycling in the AFs.     

Leaf litter and its nutrient contribution in the cacao agroforestry system

Cacao agroforestry systems (cacao-AFS) produce abundant litter. After decomposing, litter releases nutrients into the soil. The aim of this research was to estimate litter production and its nutrient content in 35- and 55-year-old cacao-AFS. The research was conducted in three cacao-AFS of each age, in Cardenas, Tabasco, México. Four traps per cacao-AFS were used to collect litter. Litter was collected every 15 days for one year. It was then fractioned into cacao leaves, shade tree leaves, petioles, branches and stems, and cacao flowers and fruits. To determine nutrient content of litter, samples were composited by age of cacao-AFS and by season of the year. Then chemical analysis was done in triplicate. Data were subjected to analysis of variance, orthogonal contrasts, and Student t and Duncan tests. Cacao-AFS produce litter all year. Thirty-five-year-old cacao-AFS produced more litter than 55-year-old cacao-AFS (2042 vs 1570 kg DM ha^?1 year^?1). Except for the shade tree leaf fraction (559.5 vs 642 kg DM ha^?1), 35-year-old cacao-AFS were superior to 55-year-old cacao-AFS in all the other litter fractions. Cacao leaf fraction was the main source of litter in cacao-AFS of both ages. Neither age of cacao-AFS nor the season of the year affected N, K, Zn or S content in litter. Orthogonal contrasts indicated statistical differences between ages of cacao-AFS for P, Ca, and Fe content in litter. Both N–P–K–Ca–Mg contents in litter of 35-year-old cacao-AFS (1.2–0.4–1.2–1.7–0.4%) and in litter of 55-year-old cacao-AFS (1.1–0.6–1.2–1.4–0.4%) are enough to recover the nutrients extracted by the cacao crop.     

Unexpected lack of influence of tree rows on the dynamics of wheat aphids and their natural enemies in a temperate agroforestry system

Trees at low density and cereals may be combined in silvoarable agroforestry systems: tree rows and their companion vegetation introduce an heterogeneity in the cropped field that may modify the dynamics of insects crop pests and their predators. This hypothesis was tested in tree-wheat systems by monitoring aphids and their predators for two years in southern France, in two fields in 2006 and one in 2007. Tree row vegetation diversity was either suppressed by weeding or stimulated by seeding flowering species that could attract adult predators of aphids. The dynamics of aphids and predators were recorded by tiller sampling and yellow trap monitoring. Between 3500 and 5000 aphids were collected from each studied field. Surprisingly, no differences could be evidenced on the dynamics of both aphids and their predators between agroforestry and monocropping plots, nor between weeded and flowered plots. The heterogeneity induced by the tree row in the cropped field was probably not strong enough to alter the populations dynamics. A high landscape diversity in the area due to nearby forest patches and fallows may have blurred the impact of the tree lines. Different results may be expected in areas with lower biodiversity like cereal monocropping zones.     

树木-水稻农林系统中害虫的侵害

本文比较研究了10种水稻害虫在3个树种(Akashmoni,Jhau和Albida)与稻子混栽的农-林复合生态系统中的发生情况,通过3个树种的冠幅大小、透光率以及害虫发生程度相比较,提出农-林复合生态系统中,水稻害虫的发生与树冠的透光率呈密切的负相关关系。     

Modelling species and spacing effects on root zone water dynamics using Hydrus-2D in an Amazonian agroforestry system

Modelling the root zone water dynamics in a tree crop agroforestry system is a useful approach to understanding small-scale effects in tree crop systems and may be helpful for optimizing tree spacing in agroforestry system planning. The agroforestry system in this study consists of the species Theobroma grandiflorum (Willd ex Spreng) Schum (Cupuaçu), Bactris gasipaes H.B.K. (peach palm) and the cover crop Pueraria phaseoloides (Roxb.) Benth (Pueraria). The soiltype is an oxisol. Calibration was conducted for each of the three species separately. Calibration results show good conformity between simulated and measured data. Simulated scenarios examine the influence of different spacing between trees on root water uptake, evaporation and drainage. Mean interception and crop factors of the whole flow region vary with spacing or are held constant to examine below-ground effects only. Also a fictitious scenario of an older agroforestry system with deeper roots is calculated. In order to overcome restrictions of the computer program Hydrus-2D, correction factors in the root zone were introduced and a calculation scheme for root water uptake of a flow subregion was developped. Below-ground effects of spacing between trees are not or almost not present, but the depth of the tree roots has a significant influence on root water uptake, evaporation and drainage. When mean interception and crop factor vary, drainage increases and root water uptake decreases slightly with spacing. The modelling approach has been found promising for optimizing agroforestry systems although it can only be seen as a first beginning. In an agroforestry systems under drier conditions differences in results will probably be larger.     

Streuobst: a traditional agroforestry system as a model for agroforestry development in temperate Europe

The development of agroforestry for industrialised countries can be furthered by an understanding of the history and present functioning of traditional systems. In temperate Europe, fruit trees were traditionally grown on agricultural land undersown with crops or managed grassland (Streuobst). The historical evolution of this agroforestry system has been driven by the interaction of technical progress, market development and intervention by public authorities. Streuobst reached its peak in the 1930s, but has since been in continuous decline due to the development of intensively managed dwarf-tree orchards. However, even today, it still occupies approximately one million hectares in 11European countries and has a strong impact on the European fruit market. The profitability of streuobst is relatively poor due to its low labour productivity, but it has advantageous ecological and socio-cultural features, particularly in terms of biological diversity and landscape aesthetics. Accordingly, it finds strong acceptance among the general public, such that subsidised eradication programs have been abandoned and, in a number of countries, streuobst is now supported by non-governmental organisations and by state conservation policies. Modern agroforestry in temperate, industrialised countries should be oriented towards the creation of similar ecological and socio-cultural benefits in order to receive public support as a land-use system. This revised version was published online in June 2006 with corrections to the Cover Date.     

Rehabilitation practices that shape cocoa agroforestry systems in Central Cameroon: key management strategies for long-term exploitation

In Africa’s main cocoa producing countries, rehabilitation of old cocoa orchards is increasingly debated but rarely adopted. In Central Cameroon, rehabilitation practices are regularly set up in old cocoa-based agroforestry systems (cAFS). To better understand the impact of such practices we built a chronosequence of 40 cAFS. We carried out specific surveys with farmers on each plot in order to check for rehabilitation effects on cocoa stands and associated woody species (AWS). We found that cocoa trees represented on average 88.2% of woody individuals and increased with age (from 84.7 to 91.5%). The cocoa stand basal area (BA) share significantly increased with age and reached up to 40.2% in the oldest systems. Cocoa, fruit and forest trees mean BA increased with aging. They were on average of 6.5, 5.7 and 10.7 m² ha^?1 respectively. Six different architectural types, different from the theoretical architectural evolution of cocoa trees over time, were identified. Among them, type 4 characterized by several orthotropic suckers of differing ages, was found typical of farmers’ cutting back practices. Type 4 cocoa trees density increased over time and its BA represented on average 60% of cocoa stand BA in the oldest systems. Concomitantly, farmer’s management of AWS led to continuous evolution of the systems both in terms of density and species composition. Our results show that (i) permanent densification and cutting back practices (type 4) allow the rejuvenation of cocoa stands while increasing cocoa stands BA share; (ii) the continuous management of AWS by farmers is undertaken to favour cocoa trees share over time by limiting inter-specific competition and promoting complementarity between cocoa trees and AWS. We argue that such practices explain a fair part of the long-term sustainability observed in cAFS from Central Cameroon and represent a model from which new rehabilitation schemes could be inspired.