Design Of Agroforestry Systems Research Articles

The role of spatial self-organization in the design of agroforestry systems.

The development of sustainable agricultural systems in drylands is currently a crucial issue in the context of mitigating the outcomes of population growth under the conditions of climatic changes. The need to meet the growing demand for food, fodder, and fuel, together with the hazards due to climate change, requires cross-disciplinary studies of ways to increase livelihood while minimizing the impact on the environment. Practices of agroforestry systems, in which herbaceous species are intercropped between rows of woody species plantations, have been shown to mitigate several of the predicaments of climatic changes. Focusing on agroforestry in drylands, we address the question of how we can improve the performance of agroforestry systems in those areas. As vegetation in drylands tends to self-organize in various patterns, it seems essential to explore the various patterns that agroforestry systems tend to form and their impact on the performance of these systems in terms of biomass production, resilience to droughts, and water use efficiency. We use a two-soil-layers vegetation model to study the relationship between deep-rooted woody vegetation and shallow herbaceous vegetation, and explore how self-organization in different spatial patterns influences the performance of agroforestry systems. We focus on three generic classes of patterns, spots, gaps, and stripes, assess these patterns using common metrics for agroforestry systems, and examine their resilience to droughts. We show that in contrast to the widespread practice of planting the woody and herbaceous species in alternating rows, that is, in a stripe pattern, planting the woody species in hexagonal spot patterns may increase the system’s resilience to droughts. Furthermore, hexagonal spot patterns reduce the suppression of herbs growth by the woody vegetation, therefore maintaining higher crop yields. We conclude by discussing some limitations of this study and their significance.

Fresh root decomposition pattern of two contrasting tree species from temperate agroforestry systems: effects of root diameter and nitrogen enrichment of soil

Fresh tree root decomposition induced by tillage is an important source of soil nutrients in agroforestry systems. Here we examined the effects of tree species, root size and soil N enrichment on fresh root decomposition under laboratory conditions. Fresh roots with two diameters (<2 and 2- 5m m) ofPopulus euramericana cv. 'N3016' (poplar) and Pinus tabu- laeformis (pine) collected from agroforestry systems in Northeast China were used in the experiment. For each root treatment, four N levels (0, 50, 100 and 150 μ gN g �1 soil) were added. We recognized N concentration and C/N ratio as the root quality variables, and determined decomposition rates as cumulative CO2 production and mass loss. Poplar roots had higher N concentration and lower C/N ratio and decomposed faster than pine roots, and smaller roots decomposed faster than the corresponding larger roots. The effect of N addition on root decomposition varied from positive to negligible to negative, and depended on root quality and N addition rates. Increased N availability did not accelerate and even suppressed poplar root decompo- sition, whereas generally stimulated pine root decom- position. Our results suggest that root quality should be incorporated into the design of agroforestry systems. Moreover, the differential responses of N addition on decomposition of fresh roots with different quality provide insights into soil nutrient management in agroforestry practices.

Deep-drainage control and yield: the trade-off between trees and crops in agroforestry systems in the medium to low rainfall areas of Australia

In the dryland cropping areas of southern Australia, at risk from dryland salinity, tree belts can improve water management by taking up water unused by crops, with the risk that crop yield will be reduced through competition. As there are few direct markets for tree products grown in the medium to low rainfall areas, the design of agroforestry systems becomes important in reducing the trade-off in crop yield. This study examined some factors that influence the trade-off between crop yield and deep-drainage control in order to develop design guidelines for medium to low rainfall agroforestry. Twenty-one sites in the grain-growing region of Western Australia and southern New South Wales were surveyed over 2 years for crop yields, tree leaf area index, and estimated recharge, providing data from 32 tree–crop interfaces on the relative influence of environmental factors and farming system characteristics on the trade-off between water management and crop yield. The factors most strongly correlated with higher yields were water-gaining sites, orientation that provided shelter from southerly to north-westerly (S, SW, W, NW) winds, and tree age (&lt;10 years). The factors most strongly correlated with the area of cropped land protected against deep drainage were tree age (&gt;10 years), lighter soil types, and low rainfall (&lt;400 mm). Economic analysis of the trade-off required to produce a particular deep-drainage reduction target produced 3 groups of sites: (1) those where trees resulted in a gross margin increase of $15/ha and an estimated deep-drainage reduction of 52% (n = 3), (2) those with a gross margin loss of $49/ha and estimated deep-drainage reduction of 47% (n = 11), and (3) those with a gross margin loss of $163/ha and a deep-drainage reduction of 37% (n = 18). None of the 3 sites in the first group were in the most favourable class in both years, highlighting the vulnerability of a relatively fixed farming system to climate variability.

PARTICIPATORY EVALUATION OF TEPHROSIA SPECIES AND PROVENANCES FOR SOIL FERTILITY IMPROVEMENT AND OTHER USES USING FARMER CRITERIA IN EASTERN ZAMBIA

In eastern Zambia, farmers prefer direct seeded improved fallow species like Tephrosia vogelii to other species because of the reduced labour requirement for establishment. Since relying on two locally available provenances of T. vogelii could become ecologically unsustainable, due to pest and disease outbreaks, a wider range of usable direct seeded Tephrosia provenance material is desirable. A farmer participatory evaluation of Tephrosia candida provenances for their effectiveness as improved fallows and provision of construction materials and fuel wood was conducted. Using an indigenous board game called bao, 68 farmers rated the four provenances and five control species/provenances for these benefits. The T. candida provenances were rated high for soil fertility improvement. First year T. candida post-fallow performance showed that maize yields could be obtained that were comparable with yields following Tephrosia vogelii provenances. According to farmers' ratings, T. candida provenances could provide better fuel wood and light construction materials than T. vogelii, although they were not considered to be as good as Sesbania sesban and Senna siamea. Tephrosia candida provenances have the potential to be tested by many farmers on-farm. Farmers' methods of screening trees can complement scientific predictors, and their early integration into the selection and design of agro-forestry systems can improve relevance and adoption.

Hydraulic lift and its influence on the water content of the rhizosphere: an example from sugar maple, Acer saccharum.

Hydraulic lift, the transport of water from deep in the soil through plant root systems into the drier upper soil layers, has been demonstrated in several woody plant species. Here the volume of water involved in hydraulic lift by a mature sugar maple tree is estimated. Twenty-four intact soil cores were collected from the vicinity of a sugar maple tree at the same positions at which thermocouple psychrometers had been placed. Desorption measurements were made on the soil cores and the data were fitted to the Campbell relation for soil matric potential ψ versus soil water content θ. The psychrometer data were filtered to obtain the diurnal component contributed by hydraulic lift. The diurnal component in ψ was combined with the Campbell relation for each soil core to obtain the increase in soil water content Δθ due to hydraulic lift. The additional water contents Δθ were numerically integrated to obtain a volume of 102±54 1 of water which was hydraulically lifted each night. The volume of hydraulically lifted water (HLW) is sufficiently great that in ecosystems where hydraulic lift occurs it should be included in models for calculating the water balance. However, a previous analysis of the stable hydrogen isotope composition (δD) of water in understory plants around trees conducting hydraulic lift implies a much greater volume of HLW than that calculated from the analysis performed above. To reconcile these differences, it is hypothesized that some understory plants preferentially extract HLW due to its higher matric potential and that the proportion of this water source within the xylem sap of at least some understory plants that use HLW was so great that the roots of these plants must therefore be in close proximity to the tree roots from which the HLW comes. The results of this study have implications for studies of plant competition where positive associations may exist as well as for ion uptake, nutrient cycling and the design of agroforestry systems.

Tree root characteristics as criteria for species selection and systems design in agroforestry

This literature review presents information about the role of tree root systems for the functioning of agroforestry associations and rotations and attempts to identify root-related criteria for the selection of agroforestry tree species and the design of agroforestry systems. Tree roots are expected to enrich soil with organic matter, feed soil biomass, reduce nutrient leaching, recycle nutrients from the subsoil below the crop rooting zone and improve soil physical properties, among other functions. On the other hand, they can depress crop yields in tree-crop associations through root competition. After a brief review of favourable tree root effects in agroforestry, four strategies are discussed as potential solutions to the dilemma of the simultaneous occurrence of desirable and undesirable tree root functions: 1) the selection of tree species with low root competitiveness, eventually supplemented by shoot pruning; 2) the identification of trees with a root distribution complementary to that of the crops; 3) the reduction of tree root length density by trenching or tillage; and 4) the use of agroforestry rotations instead of tree-crop associations. The potential and limitations of these strategies are discussed, and deficits in current understanding of tree root ecology in agroforestry are identified. In addition to the selection of tree species and provenances according to root-related criteria, the development of management techniques that allow the manipulation of tree root systems to maximize benefit and minimize competition are proposed as important tasks for future agroforestry research.

Design of agroforestry systems: Some examples and lessons from Bangladesh

As traditional land-use systems, agroforestry has been practiced by farmers for centuries. Only recently, however, has it been employed as a development strategy to alleviate rural poverty and ecological degradation. The design of agroforestry systems is often the determinant factor of success or failure. To date, project and research design has focused largely on maximizing biological productivity, usually through the introduction of external agroforestry models. The experience in Bangladesh indicates that local participation in the design process is crucial. Two examples from Bangladesh contrast design approaches and levels of participation and offer lessons that should be valuable for agroforestry design efforts.

Agroforestry, attitude towards risk and nutrient availability: a case study of south Indian farming systems

Introduction of two systems of agroforestry to the farmers portfolio is evaluated for their changes in cropping pattern, input use, income generation, farmers attitude towards risk and nutrient availability. Two different types of farmers are studied under both irrigated and dryland farming systems. Farm survey data collected from south Indian villages have been used with a mean-variance framework to identify the risk aversion levels of farmers. The results indicate that the risk-taking preferences of farmers should be given consideration in evaluating the impact of agroforestry systems. Among the two agroforestry systems analyzed, the one with drumstick is shown to increase the risk of crop production while the one with leucaena reduces the risk and enables farmers to invest in more risky cash crops. The impact of agroforestry on crop allocation, input use and income differs due to the differences in resource availability of farmers. The influence of agroforestry on nutrient availability of the farm households also differs based on the components of agroforestry, orientation of farming and the nature of farming systems. It is argued that design of agroforestry systems should consider differences in resource constraints in farming systems and risk attitudes of farmers towards their allocation decisions and that such considerations would largely enhance the successful adoption of agroforestry in developing countries.

A knowledge-based expert system for planning and design of agroforestry systems

Computer-based Expert Systems that use knowledge, facts, and reasoning techniques to solve problems, normally requiring the abilities of human experts, are increasingly being used in many activities. The United Nations University (UNU) Agroforestry Expert System (AES) is a first attempt to apply this technique to agroforestry. UNU-AES is a prototype Knowledge-Based Expert System (KBES) designed to support land-use (agricultural, forestry, etc.) officials, research scientists, farmers, and individuals interested in maximizing benefits gained from applying agroforestry management techniques in developing countries. This prototype addresses the options for alley cropping, a promising agroforestry technology which has potential applicability when used under defined conditions in the tropics and subtropics. Alley cropping involves the planting of crops in alleys or interspaces between repeatedly pruned hedgerows of fast-growing, preferably leguminous, woody perennials. The primary benefits from this technique include nutrient enrichment, soil improvement, and erosion control. UNU-AES, which is the first known attempt at the application of expert system procedures in the field of agroforestry, uses a total of 235 decision rules to develop its recommendations. With the inclusion of more climatic and socio-economic data and improved advisory recommendations, UNU-AES can be expanded to provide advice on alley cropping in more diverse geographical and ecological conditions and eventually address other agroforestry techniques.

The state of the art of agroforestry diagnosis and design

Seven years ago the International Council for Research in Agroforestry set out to develop a methodology for the diagnosis of land management problems and design of agroforestry systems. Since then over 60 documents (articles, conference papers and manuals) relating to the D & D methodology have been published by ICRAF and the methodology has been used to develop agroforestry plans and identify research priorities for a wide range of ecological and cultural conditions throughout the tropical regions of Africa, Latin America and Asia. This article reviews the evolution of the D & D methodology and suggests directions for its future development.