ISSN:0012-8325    

DOI:10.1080/00128325.1996.11663288

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

ISSN:0012-8325    

DOI:10.1080/00128325.1996.11663289

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

ISSN:0012-8325    

DOI:10.1080/00128325.1996.11663290

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

ISSN:0012-8325    

DOI:10.1080/00128325.1996.11663291

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

The paper reviews the status of agroforestry research and development in Kenya over the past 2 decades, evolving from a simple rotational sequence of temporal agroforestry to intensive and complex multi-storey systems. In all these developments, the most distinctive element and point of focus is seen as the contribution of the multipurpose woody species (trees and shrubs). Agrofo estry during this period has undergone transformation from a mere descriptive study into one requiring a more scientific approach. Subsequent development in agroforestry research has focused on three key areas: characterisation and analysis of land use/farming systems, agroforestry technology development and systems improvement and assessment, screening, management and evaluation of MPT's. The paper examines major achievements in research as well as the constraints contributing to the slow rate in the development of research in agroforestry. The principal constraints identified include methodological difficulties coupled with the socio-economic and ecological complexity that are inherent in agroforestry systems. Particular attention is focused on participatory, analytical and multidisciplinary characterisation as a first step in agroforestry research. Finally, the paper stresses the need for additional research effort to be focused on key agroforestry technologies, in terms of adaptability with farmers, and to provide the basis for developing a decision support system package.

ISSN:0012-8325    

DOI:10.1080/00128325.1996.11663292

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

The paper begins by providing a context within which the Agroforestry Research Network for Africa—East and Central Africa has been functioning since 1989. It then proceeds to explain the structure and force on the organization in terms of current and future research activities. These include research on soil fertility, terrace management and erosion control, wood and fodder production. Research highlights selected from each of the participating countries are presented with respect to each theme. The paper concludes that when taken in total, results reported contribute to a general understanding of the reasons why fanners plant trees and prefer particular species. Understanding these reasons is important for planning new interventions that meet fanners' needs and fit their particular circumstances.

ISSN:0012-8325    

DOI:10.1080/00128325.1996.11663293

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

The Southern Africa AFRENA embraces four SADC countries, namely Malawi, Tanzania, Zambia and Zimbabwe which are characterised by the miombo vegetation and a unimodal rainfall regime. The research programme has focused on technology development to address small holder farmer problems of declining soil fertility, shortage of fodder and fuel wood, environment degradation through deforestation, overgrazing and soil erosion. After nearly a decade of research and capacity building, the network has developed several promising technologies, e.g sesbania improved fallows, sesbania/maizc relay cropping, maize/gliricidia intercropping, fodder banks, rotational wood lots for poles and fuel wood and indigenous fruits for human nutrition. Significant maize yield increases have been obtained following 2- to-3-year sesbania fallows or in relay cropping and gliricidia/maize intercropping systems. These technologies have advanced to farmers fields and currently the network has over 1000 experimenting farmers, most of whom are testing the sesbania improved fallows. Farmer enthusiasm and expections from these technologies are high throughout the network. In addition, several MPTs have proven themselves in terms of biomass production for fodder and positive effect on liveweight gains in goats. Further, the network has evaluated over 20 species of indigenous fruits, several of them have easily been propagated and have given fruits within 18–24 months of transplanting. Priority indigenous fruits in the region areUapaca kirkiana. andSclerocarrya birrea.Uapaka has been collected from five southern African countries for evaluation and improvement before distribution of planting materials to farmers. Future thrusts will focus mainly on extension and refining of the best teclinologies as well as research on strategic issues, such as nutrient dynamics in the systems being developed and implication on the sustainability of the systems under farm management.

ISSN:0012-8325    

DOI:10.1080/00128325.1996.11663294

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

The potential of short-duration improved fallow (6–12 months) with MPTs for crop production in the highlands of Western Kenya was investigated through a series of experiments comprising species screening, establishment methods and determination of optimum planting densities. In the first experiment, 12 multipurpose trees and shrubs were compared. The highest biomass productivity and nutrient yields (nitrogen and phosphorus) after one season's (6 months) growth were obtained fromCrotalaria grahamiana(300 kg N and 27 kg P/ha),Crotalaria mucronata(252 kg N and 16 kg P/ha) andCrotalaria striata(219 kg N and 16kgP/ha). In the second experiment, six herbaceous legumes were tested. The most productive species in terms of nutrient yields wereCalopogonium mucunoides, Desmodium uncinatum, Macroptilium atropurpureum and Glycine wightii(more than 150 kg of N and 19 kg of P/ha after 6 months). In a third experiment, an improved fallow system was tested with four species and two methods of planting over two seasons (12 months). The fastest growth was obtained withT. vogeliiandT. diversi foliawhich produced 100 kg of N each at 6 months.Sesbania sesbanwas more productive at 12 months (161 kg/ha) compared with 6 months (60–73 kg/ha). In terms of nutrient yields, direct seeded plants ofT. vogeliiwere as productive as transplanted seedlings. ForS. sesban, the fastest growth was obtained by seedlings, but at 12 months the productivity ofS. sesbanfrom seedlings and that from direct seeding was similar The highest maize grain yield following 12 months of fallow was obtained withS. sesban(3840–5089 kg/ha) andT. vogelii(4162–4849 kg/ha) compared to natural fallow (1968 kg/ha) which was not significantly different from continuous cropping (1854 kg/ha). In a fourth trial, seven densities (from 10,000 to 160,000 plants/ha) were tested. In terms of biomass and nutrient yields 2 months after planting the performance of the different densities were similar. Maize grain yields following 12 months of fallow were also similar and were not different from those obtained from continuous cropping and natural fallow treatments without inorganic P application. The difference in maize grain yield between improved fallow with sesbania (2875 to 3343 kg/ha) couch grass-infested natural fallow (1277 kg/ha) and continuous cropping (12017 kg/ha) were significant (P≤0.05) when inorganic P was applied.

ISSN:0012-8325    

DOI:10.1080/00128325.1996.11663295

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

The integration of trees with crops can influence both the supply and availability of nutrients in the soil. Trees can increase the supply of nutrients within the rooting zone of crops through (i) input of nitrogen (N) by biological N2 fixation, (ii) capture and “pumping up” of nutrients from below the rooting zone of crops and (iii) reduction in nutrient losses by leaching and erosion. Trees can increase the availability of nutrients through increased release of nutrients from soil organic matter (SOM) and recycled organic materials. Roots of trees frequently extend beyond the rooting depth of crops. The potential of deep-rooted trees to capture subsoil nutrients is (i) greatest when trees have a high demand for nutrients, (ii) greatest when high amounts of plant-available nutrient are present in the subsoil and (iii) greater for mobile nutrients, like nitrate, than for less mobile nutrients, like phosphate. Nitrate can accumulate below the rooting depth of annual crops when (i) production of the crops is limited by pests and nutrients other than N and (ii) subsoils contain anion exchange sites to sorb the nitrate. Recent research showed thatSesbania sesbanis very effective in taking up accumulated subsoil nitrate. Sesbania is also more effective than natural grass fallows in extracting subsoil water, which suggests that the potential for leaching loss of nutrients is less under sesbania than natural fallows. Other research showed that fast-growing trees with high N demand, such asCalliandra calothyrsus, S. sesbanandEucalyptus grandis, are much more effective in taking up subsoil nitrate than slower-growing trees, likeGrevillea robustaandMarkhamia lutea.The mineralization of SOM is a source of plant-available N and phosphorus (P). Nutrient release from SOM is normally more dependent on the portion of the SOM in biologically active fractions than on total quantity of SOM. Recent research indicated that the amount of N in the sand-associated fraction of SOM that floats in a dense liquid (referred to as light fraction N) is directly related to the release of N from SOM. Yield of unfertilized maize on a N-limiting soil has been shown to be strongly related to both inorganic soil N before maize planting and light fraction N. Inorganic soil N, N mineralization, and amount of light fraction N were higher after 2 and 3-yr tree fallows that continuous unfertilized maize in Zambia and Kenya. Among six tree fallows, inorganic N, N mineralization and light fraction N were (i) higher for the mean of the five N-fixing trees than the one non-fixing tree, (ii) higher for the mean of the two trees with lowest (lignin + polyphenol)/N ratios in leaf litter than the two trees with highest ratios in leaf litter, and (iii) higher forS sesbanthan the mean of the other trees. Some agroforestry trees have potential to provide sufficient N to sustain moderate crop yields through (i) increased N inputs from biological N fixation and deep capture of nitrate and (ii) effective recycling of N from plant residues and manures. Agroforestry trees, on the other hand, are not likely to provide sufficient P for sustained crop yields. Phosphorus is not fixed from the air like N, and the capture of P from subsoil is typically small. The recycling of P from organic materials is normally insufficient to meet the P requirements of crops because of the typically low P content of organic materials. Sustained crop production with agroforestry on P-deficient soils will normally require P fertilizer inputs.

ISSN:0012-8325    

DOI:10.1080/00128325.1996.11663296

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

Two long-term experiments were set up at the National Agricultural Research Centre, Muguga Kenya, to investigate the potential of several multipurpose trees in enhancing soil productivity and controlling soil erosion in the high and medium potential areas of Kenya. One experiment consisted ofSesbania sesban, Leucaena leucocephala, andLeucaena K28while the other hadCalliandra calothyrsusandLeucaena diversifoliagrown in alleys. Maize and beans were the test crops. The trees produced varying amounts of dry matter withSesbania sesbanhaving the fastest growth rate. Prunings constituted between 34 and 79% of the total tree biomass during the first year which accumulated to between 62 and 83% by the end of second year. Neither the trees nor the prunings showed positive effects on crop yield. Other aspects (for example analyses of soil physical and chemical properties) that might shed light on the effect of the trees and prunings on soil productivity have not been completed. Research is. however, still needed to establish quantitative measures for improved soil management under varying environments and assess its potential and limitations.

ISSN:0012-8325    

DOI:10.1080/00128325.1996.11663297

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor