Tag: agroecosystems
Evaluating factors influencing heterogeneity in agroforestry adoption and practices within smallholder farms in Kenya
Rapid characterization of organic resource quality for soil and livestock management in tropical agroecosystems using near-infrared spectroscopy
Organic resources constitute a major source of nutrient inputs to both soils and livestock in smallholder tropical production systems. Determination of resource quality attributes using current laboratory methods is both timely and costly. This study tested visible and near-infrared (wavelengths from 0.35–2.50 m) reflectance spectroscopy (NIRS) for rapid prediction of quality attributes for a diverse range of organic resources. A spectral library was constructed for 319 samples of oven-dried, ground plant material originating from green leaf (186 samples), litter (33), root (25), and stem (21) samples from 83 species including tropical crops and trees used for agroforestry and manure samples (39). Organic resource attributes were calibrated to first-derivative reflectance using regression trees with stochastic gradient boosting, and screening tests were developed for separating various organic resource quality classes using classification trees. Validation r 2 values for actual vs. predicted values using a 25% holdout sample were 0.91 for N, 0.90 for total soluble polyphenol, and 0.64 for lignin concentration. Screening tests gave validation prediction efficiencies of 96% for detecting samples with high N concentration, 91% for low total soluble polyphenol, and 86% for low lignin concentration. The spectral screening tests were robust even at small (n = 48) calibrations sample sizes. Screening tests for detecting samples with low or high levels of P, K, Ca, and Mg gave prediction efficiencies of 74 to 92%. Near-infrared reflectance spectroscopy can be used to rapidly screen organic resource quality. Global spectral calibration libraries should be established for a range of resource quality attributes.
Agricultural intensification, soil biodiversity and agroecosystem function
Intensification of agriculture in the tropics has resulted from a shortage of farmland and insufficient food production to satisfy the needs of an expanding population. Many tropical farmers are challenged by the prospect of intensifying their production while sustaining or improving the fertility and productivity of soils with only locally available natural resources. The waste products of plant and animal production represent some of the most abundant natural resources available for use by tropical farmers to achieve these goals. The efficient use and management of these resources depends on understanding the role that decomposer biota play in regulating the structure and function of agricultural ecosystems. Furthermore, the development of agricultural management practices which promote the beneficial attributes of these organisms will be essential to sustaining the productivity and environmental integrity of tropical agriculture. Finally, understanding the role of biodiversity among decomposer biota in maintaining the functional properties of tropical agricultural ecosystems is critical to achieving this goal.The objective of this review is to further that understanding by describing the taxonomic and functional diversity of decomposer biota in the tropics and evaluating known links between their diversity and the function of agricultural ecosystems. We further describe the effects of changing land-use and agricultural intensification on the structure and diversity of decomposer communities in the tropics and suggest some priorities for future research
Global change and multi-species agroecosystems: Concepts and issues
Complex (multi-species) agroecosystems change rapidly as a result of farmers’ decisions based on their perception of opportunities and constraints. Overall, the major trend is still one of reducing complexity. This review addresses the driving forces as well as consequences of this change and discusses the hypothesis that complex agricultural systems are more dependable in production and more sustainable in terms of resource conservation than simple ones. Farmer decisions regarding planned diversity on the farm have consequences not only for the harvested produce, but also for associated diversity and non-harvested components which may contribute to ecological sustainability. Functional attributes of plants which can lead to complementarity in resource capture include root architecture and phenology. Three hypotheses on biodiversity and ecosystem function are formulated (ranging from weak negative to strong positive interactions) and discussed. Evidence is not yet conclusive
A novel decision analysis and risk assessment framework for improving agro-ecosystem interventions
Designing and implementing agro-ecosystem intervention decisions is a complex undertaking, outcomes are uncertain and risk of project failure and cost overruns are large.
Biodiversity and ecosystem services in agricultural landscapes—are we asking the right questions?
The assumed relationship between biodiversity or local richness and the persistence of ‘ecosystem services’ (that can sustain productivity on-site as well as off-site, e.g. through regulation of water flow and storage) in agricultural landscapes has generated considerable interest and a range of experimental approaches. The abstraction level aimed for, however, may be too high to yield meaningful results. Many of the experiments on which evidence in favour or otherwise are based are artificial and do not support the bold generalisations to other spatial and temporal scales that are often made. Future investigations should utilise co-evolved communities, be structured to investigate the distinct roles of clearly defined functional groups, separate the effects of between- and within-group diversity and be conducted over a range of stress and disturbance situations. An integral part of agricultural intensification at the plot level is the deliberate reduction of diversity. This does not necessarily result in impairment of ecosystem services of direct relevance to the land user unless the hypothesised diversity–function threshold is breached by elimination of a key functional group or species. Key functions may also be substituted with petro-chemical energy in order to achieve perceived efficiencies in the production of specific goods. This can result in the maintenance of ecosystem services of importance to agricultural production at levels of biodiversity below the assumed ‘functional threshold’. However, it can also result in impairment of other services and under some conditions the de-linking of the diversity–function relationship. Avoidance of these effects or attempts to restore non-essential ecosystem services are only likely to be made by land users at the plot scale if direct economic benefit can be thereby achieved. At the plot and farm scales biodiversity is unlikely to be maintained for purposes other than those of direct use or ‘utilitarian’ benefits and often at levels lower than those necessary for maintenance of many ecosystem services. The exceptions may be traditional systems where intrinsic values (social customs) continue to provide reasons for diversity maintenance. High levels of biodiversity in managed landscapes are more likely to be maintained for reasons of intrinsic, serependic (‘option’ or ‘bequest’) values or utilitarian (‘direct use’) than for functional or ecosystem service values. The major opportunity for both maintaining ecosystem services and biodiversity outside conservation areas lies in promoting diversity of land-use at the landscape and farm rather than field scale. This requires, however, an economic and policy climate that favours diversification in land uses and diversity among land users.
Historical land use evolution in a tropical acid upland agroecosystem
Understanding the historical evolution of land use in humid tropical agroecosystems may assist in developing more appropriate farming systems better able to sustain dense human populations, alleviate deforestation and regenerate degraded land resources. We analyzed land use change over a 40 year period for a key acid upland farming systems research site (8 km × 10 km) undergoing rapid transformation in Claveria, Mindanao, Philippines. The landscape is dominated by small-scale cereal cropping on gently to steeply rolling volcanic Oxisols. The six slope classes identified (ranging from 0–3% to more than 60%) each occupied between 9 and 19% of the study area. Aerial photographs (1:15000) taken in 1949 and 1967, and a ground survey in 1988, were used to map land use patterns at three points in time. Settlement by in-migration began early in the twentieth century. By 1949 9% of the land was cultivated, but grassland (59%) and forest (14%) were the dominant land uses. From 1949 to 1967 the cultivated area doubled to 20%, and the proportion of grassland decreased to less than 50% of the land. The forested area remained unchanged. Subsequently, settlement by small-scale farmers accelerated. Between 1967 and 1988 the area cropped annually doubled again to 41%. Forest land declined drastically during this period to 1%, while perennial cropland (mainly coffee) increased to 30%. Land use on the steeply sloping lands (more than 15%) was particularly affected during the 21 year period: 27% was converted to field crop production, and 43% to perennial crops. More than 33% of the food crop area is now on steep slopes. The analysis of the historical evolution of land use may guide research priorities for developing sustainable technologies on sloping land based on agroforestry.
Ant-mediated ecosystem services and disservices on marketable yield in cocoa agroforestry systems
The impact of complex direct and indirect interactions between multiple functional groups on plants is poorly documented. In tropical agroecosystems, ants interact with crop mutualists and antagonists, however, little is known about effects of dominants ant community properties on the consequence of such cascading interactions which can be measured through final ecosystem service, crop yield. Here, we present a replicated ant fauna manipulation experiment in cocoa agroecosystems, where we used ant exclusion treatments to test the economic importance of the presence of ants, and two additional treatments where we experimentally introduced one of two common dominant ant species which allowed comparing their effects with those of the naturally occurring ant fauna. The proximate aim was to assess the impact of ants Crematogaster sp., Camponotus brutus Auguste-Henri Forel and Oecophylla longinoda Latreille on cacao yield, which is known to depend on several, cascading intermediate ecosystem services (e.g. control of specific pests). Ants provided ecosystem services in term of reduced pest damage caused by Salhbergella singularis Hagh (Hemiptera: Miridae) and Characoma stictigrapta Hmps (Lepidoptera: Noctuidae) but also disservices such as increased pathogen disease caused by Phyphthora megakarya Brasier and Griffin dissemination and indirectly enhanced damage of other pest species. Yields were highest in non-manipulated and species-rich ant communities, whereas ant exclusion and communities dominated by a single species decreased yield by more than 30%. Associated ant communities between dominant and non-dominant species resulted in the same yields as in non-manipulated controls. Dominant ant communities maximized the control of a particular pest species, but not cacao yield. We show a positive relationship between ant species rich communities and financial performance and we postulate that complex agroecosystems can offer competitive business opportunities for small-scale farmers, while contributing to biodiversity conservation. However, more interdisciplinary studies are needed to quantify financial and biodiversity performance opportunities to allow up-scaling of these findings. © 2017 Elsevier B.V.
Carbon stock in planted woodlots at Kongowe, Kibaha, Tanzania
Forest degradation due to extraction of wood for fuelwood and charcoal production or agricultural expansion is one of the main sources of carbon dioxide (CO2) emissions in Africa. Woodlots can offset CO2 emissions while sustainably meeting the wood demand of local communities. However, the amount and dynamics of carbon (C) stored in soils in coastal area woodlots and the contribution of this practice to climate change mitigation is largely unexplored. This study evaluated wood biomass and C stocks in woodlots, forest reserves and farmland with Acacia crassicarpa Benth., Acacia mangium Wild., and Acacia auriculiformis Benth. to determine their ability to sequester soil C and offsetting CO2 emissions. Woodlots of fast-growing Acacia spp. produced wood (30 to 62 Mg C/ha), which may meet the household fuelwood demand for up to 10 to 20 years and offset up to 31 Mg C/ha of C emissions. Moreover, these species stored soil organic carbon (SOC) (58 Mg C/ha), which was similar to levels in the native forests; demonstrating climate change mitigation capacity. The effects of tree species on SOC was confined to the top 40 cm with native forest consistently recording the highest values. This improvement was attributed to litter and root turnover, C leaching and mixing of SOC by microorganisms, and increased recalcitrant form of SOC with depth. Because of the sandy soil texture in the study site, most of SOC stocks (up to 70% in the bulk soil and 50% in fractionated soils) were in the labile fractions and prone to degradation. Of the tested woodlot species, A. auriculiformis showed the highest promise to produce wood and improve SOC because of higher survival. Our results showed that woodlots systems utilizing the fast growing tree species hold high promise to mitigate atmospheric CO2 increase through on-farm wood supply to alleviate harvesting pressure and accumulation of SOC in the soil