Effects of mulching with multipurpose-tree prunings on soil and water run-off under semi-arid conditions in Kenya

The effect of adding leaf mulches ofGrevillea robusta, Cassia siamea andGliricidia sepium on the rate of soil and water run-off from a crop field were studied during two cropping seasons in an alfisol under semi-arid conditions at Machakos, Kenya. The experiment was conducted in a randomized complete block design with three replications; two rates of mulch of each species (2.24 t and 4.48 t, on dry matter basis, per ha) and a no-mulch control constituted the seven treatments. Soil and water run-off losses after each major rainfall event and the changes in ground and crop cover were measured. Rainfall erosivity and changes in soil bulk density and infiltration rate were also determined.Soil losses from the plots with mulches ofCassia siamea, Gliricidia sepium andGrevillea robusta were significantly lower than those from the control (p=0.10). Over the two seasons, the cumulative soil losses from plots mulched with cassia, gliricidia and grevillea were 11%, 57% and 81% lower than that of the control plot. Similarly, water run-off losses from cassia, gliricidia and grevillea mulch plots were 28%, 48% and 58%, respectively, lower than that of the control plot. Thus, cassia was found to be better than gliricidia and grevillea in reducing both soil and water run-off losses.Soil bulk density did not change while infiltration rate at the end of the experiment was significantly more than in the beginning; however, there were no significant differences in these soil physical properties among the treatments.     

Intercropping under coconuts in Sri Lanka

Coconut is a major commercial crop of Sri Lanka. Growing a number of other crops in association with coconuts is a widespread practice in all coconut-growing areas of the country. The rationale for the practice is that other crops can profitably be grown between or under the coconuts during the different growth stages of the palms and thus the overall productivity of the land under this long-duration crop can substantially be increased. The paper gives a concise account of the practice in Sri Lanka indicating the crops most commonly grown as intercrops, arrangement of different crops and early research results on the productivity of the intercrops and their effect on coconuts. Adequate supplies of water and labour are the two major inputs needed for the success of the system. Drought, lack of funds, price instability, lack of technical know-how on intercrop management and problems of timely availability of inputs are the major constraints experienced by farmers in expanding intercropping. Research on both biological and socio-economic aspects is needed to overcome these constraints and extend this potentially attractive system.     

Silvopastoral research and adoption in Central America: recent findings and recommendations for future directions

Human population growth in Central America during the last thirty years has lead to encroachment of forests for food production and resulted in the replacement of forests with pastureland. Deforestation and degradation of productive soils have prompted researchers to investigate agroforestry as an alternative approach to land management. Silvopastoral systems in particular have been studied and their capacity to augment nutrient cycling, enhance soil processes, supply forage for livestock, and provide habitat for flora and fauna have been documented. Despite conclusive research findings, Central American producers are reluctant to integrate well-researched silvopastoral systems into their farming systems. Thus, it is imperative that researchers investigate the reasons for scant adoption, and that adoption is given precedence. We suggest that adoption research be made a priority on local, national, and regional silvopastoral research agendas. To explore incidence of low adoption, research should identify specific barriers, assess the technology generation process, examine the risks that silvopastoral adoption presents, and evaluate the potential for the integration of silvopastoral technologies on-farm. In addition, we recommend that the future Central American silvopastoral research agenda include the development of a clear understanding of the process of adoption specific to potential silvopastoral adopters in the region. This revised version was published online in June 2006 with corrections to the Cover Date.     

Trees outside forests: agro-, community,and urban forestry

Planted forests are often considered to consist of tree plantings at a scale large enough to satisfy such objectives as commercial production of timber and fiber, protection of watersheds, and preservation of natural habitats. However, trees are planted also at greatly reduced scales in agroforestry systems or as community woodlots to provide a mixture of products and services to resident households, local communities, and regional cultures.Agroforestry systems represent a major form of small-scale tree planting, where trees are grown in purposeful combinations with agricultural crops and/or livestock in order to take advantage of tree-crop interactions, and thereby enhance crop production, diversify farm output, stabilize or improve soils, or ameliorate harsh environmental conditions. Some important examples of these systems in tropical countries include homegardens, alley cropping, improved fallows, intercropped trees for shade and fodder production, and trees planted in hedgerows and along fence lines. Throughout the tropics, there is a large variety of indigenous practices and species mixtures that represent adaptations of these systems to meet localized needs and opportunities. Research and development programs have supported the expansion and refinement of many of these systems during the last 20 years, but substantial constraints on tree planting still exist in the form of land-tenure practices, population pressures that relegate agroforestry practices to degraded lands, subsistence needs that prevent extended periods of tree growth, and insufficient technical information or technology dissemination.Agroforestry systems in temperate, industrialized countries include combinations of trees, pasture, and livestock; fruit or nut trees interplanted with vegetable or grain crops; windbreaks and shelterbelts; multispecies riparian buffer strips; and forest farming systems for specialty crops. Compared to the tropics, however, temperate-zone systems tend to focus on one or two high-value crops, often involve some level of mechanization, and frequently represent an opportunistic approach to improving the economic profitability of farms rather than meeting subsistence needs. In both tropical and temperate regions, agroforestry systems and community woodlots will be an important component of new sustainable agriculture and environmental protection programs.Although species diversity is an essential feature of all agroforestry systems, community forests generally involve planting only a few species in small woodlots near farms, around villages, along roads, and as riparian buffers. Provincial or state governments and the local populace are often involved in landownership and plantation establishment. Major objectives of these forests are production of fuelwood for local consumption and of other tree products for market; soil stabilization, reclamation, or improvement; and protection of water quality. As with many other planted forests, the number of species widely used in community forests has been relatively small, with the genera Eucalyptus, Pinus, and Acacia providing the bulk of the species. Major issues with these planted forests focus on rights for use of the products, tending responsibilities once trees are established, protection until trees are large enough for their designated use, increasing interest in using native species, and greater community involvement in planning and management.Trees planted along streets and waterways, or as woodlots in parks and other public places, represent a major group of planted forests in many urban and periurban landscapes. In addition to providing many of the same environmental services that agroforests and community forests do, these urban plantings have unique aesthetic and recreational value. For much of the world's ever-increasing urban population, these may be the only tangible reference points for understanding planted forests.These relatively little-recognized forms of planted forests -- planted trees, to be more appropriate -- are now receiving much greater attention. There are, however, some serious technical and sociopolitico-institutional constraints to their development as more widely adopted systems in both tropical and temperate regions.     

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.     

Multipurposes tree prunings as a source of nitrogen to maize under semiarid conditions in Zimbabwe

Time of pruning application and mixing prunings of varying qualities could be important management options to increase the rate of nitrogen recovery from multipurpose-tree prunings that are used as a source of nitrogen to crops. A field experiment was conducted in the semiarid zone of Zimbabwe to test this hypothesis, using prunings of calliandra (Calliandra calothyrsus) and leucaena (Leucaena leucocephala), alone and in mixtures, and maize (Zea mays) as the test crop. Time of pruning application significantly improved N uptake, N recovery, and grain yield of maize. Applying prunings of calliandra at maize planting was significantly better in terms of N uptake, N recovery, and grain yield than applying them four weeks after planting. However, with leucaena, time of prunings application had no significant effects on N recovery. Mixing prunings of leucaena and calliandra had no effect on maize N uptake, N recovery, and grain yield. Split application of available prunings during the crop growth cycle had no effect on N recovery compared to one-time application of entire amounts of prunings at planting.     

Dynamics of Particulate Organic Matter following biomass addition from fallow-improvement species in southern Mali

Knowledge about the nature and turnover rates of soil organic matter (SOM) is a key to soil fertility maintenance, especially in traditional farming systems. Particulate organic matter (POM), rather than total SOM content, is now considered a better measure of the soil's fertility. Fractionation of SOM, based on particle-size distribution after dispersion, was carried out on soil samples collected from a field experiment at N'Tarla, Mali (12.25° N latitude, 5.42° W longitude, Typic Plinthustalf). Biomass of off-site grown Gliricidia sepium (Jacq.) Walp. (gliricidia), Pterocarpus erinaceus Poir.(pterocarpus), and Stylosanthes hamata (L.) Taub.(stylosanthes) was applied to a maize (Zea mays L.) crop for two consecutive years. A significant decrease was noted in the soil's POM and POM-N contents after harvest of maize in both years as compared with the initial value measured at the beginning of the experiment. Small POM fraction (0.053 to 0.250 mm, POM₅₃) contributed more to total POM than large POM fraction (0.250 to 2.000 mm, POM₂₅₀). The POM N content was better correlated with maize grain yield than POM total weight, and the N content of POM₅₃ was better related to maize grain yield (R² = 0.55) than that of POM₂₅₀ (R² = 0.20). Total SOM was poorly correlated with maize grain yield (R² = 0.14). The results indicate that the quality of the applied biomass is of greater value than its quantity in sustaining maize grain yield, and POM₅₃ might be a better indicator of soil fertility status than POM₂₅₀ and total POM. This revised version was published online in June 2006 with corrections to the Cover Date.