Dry matter production and nutrient cycling in agroforestry systems of mandarin grown in association with Albizia and mixed tree species

A study on dry matter production and nutrient cycling in agroforestry systems of mandarin grown in association with N₂-fixing Albizia and mixed tree species (non-N₂-fixing) was carried out in the Sikkim Himalaya. A site with Albizia was referred asAlbizia-mandarin stand and the other site with mixed tree species as mandarin stand. The stand total biomass, net primary productivity and mandarin fruit production was higher under the influence of Albizia. Agronomic yield of crops remained nearly the same in both the stands. Nitrogen and phosphorus concentrations of different components of Albizia were higher than those of mixed tree species, whereas their back translocation from leaf to branch before abscission was lower inAlbizia. The mandarin-based agroforestry is a highly nutrient-exhaustive system evaluated in terms of nutrient exit through the removal of agronomic yield. This system, under the influence of Albizia, was more productive with faster rates of nutrient cycling. Nutrient use efficiency increased under the influence of Albizia, in contrary to the hypothesis that efficiency should decrease with increasing rate of uptake. The poor nutrient conservation of Albizia, and malleability of nutrient cycling under its influence make it an excellent association which promotes higher availability and faster cycling of nutrients.Albizia should be utilised more extensively in the management of mandarin-based agroforestry systems.     

Cardamom, mandarin and nitrogen-fixing trees in agroforestry systems in India's Himalayan region. II. Soil nutrient dynamics

A study on seasonal soil nutrient dynamics was made in large cardamom (Amonum subulatum) and mandarin (Citrus reticulata) agroforestry systems in the Sikkim Himalaya, India. Alnus nepalensis was the N₂-fixing associate in the large cardamom system, and Albizia stipulata in the mandarin agroforestry system. Sites without N₂-fixing species in both agroforestry types comprised native non-symbiotic mixed tree species. Soil was acidic in the cardamom agroforestry and slightly acidic to neutral in the mandarin agroforestry system. Total-N in soils was the highest in the forest-cardamom stand and the lowest in the mandarin-based agroforestry systems. Soil ammonium-N and nitrate-N concentrations were highly seasonal, and the ratio of seasonal maximum and minimum varied up to six times. The C/N ratio was higher in cardamom agroforestry indicating lower N availability than in the mandarin agroforestry. Cardamom stand with Alnus showed a relatively narrower C/N ratio. N₂-fixing species help in maintenance of soil organic matter levels with higher N-mineralization rate as land use change from natural-forest system to agroforestry systems with sparse tree populations. Ratios of inorganic-P/total-P were lower in cardamom agroforestry than the mandarin agroforestry. Seasonal fluctuation in Ca-PO₄, Al-PO₄ and Fe-PO₄ contents regulated the availability of phosphates to some extent for plant uptake.     

Dry matter production and nutrient cycling in agroforestry systems of cardamom grown underAlnus and natural forest

A study on dry matter production and nutrient cycling in agroforestry systems of cardamom grown under N₂-fixingAlnus and mixed tree species (non-N₂-fixing) was carried out in the Sikkim Himalaya. The stand total biomass, and tiller number, basal area and biomass of cardamom crop was much higher under the influence ofAlnus. Annual net primary productivity ofAlnus trees was slightly higher than mixed tree species in spite of lower stand density ofAlnus. The agronomic yield of cardamom increased by 2.2 times under the canopy ofAlnus. Litter production and its disappearance rates were also higher in theAlnus-cardamom stand. Nitrogen and phosphorus concentrations of different components ofAlnus were higher than those of mixed tree species, whereas their back translocation from leaf before abscission was lower inAlnus. The cardamom based agroforestry system under the influence ofAlnus was more productive with faster rates of nutrient cycling. The poor nutrient conservation and low nutrient use efficiency ofAlnus, and malleability of nutrient cycling under its influence make it an excellent association which promotes higher availability and faster cycling of nutrients.     

Energy efficiency of large cardamom grown under Himalayan alder and natural forest

Energy efficiency of agroforestry systems of large cardamom grown under N₂-fixing Himalayan alder (alder-cardamom) and natural forest (forest-cardamom) was studied in the Sikkim Himalaya. Large cardamom (Amomum subulatum), the most important perennial cash crop of the region, is widely cultivated with Himalayan alder (Alnus nepalensis) as shade tree. Energy fixation, storage, net allocation in agronomic yield, and heat release and exit from the system were respectively 1.57, 1.44, 2.24 and 2.22 times higher in the alder-cardamom compared to the forest-cardamom system. Energy conversion efficiency and net ecosystem energy increment were also higher in the alder-cardamom than the forest-cardamom system. Energy fixation efficiency and energy conversion efficiency of large cardamom increased under the influence of Himalayan alder. Energy efficiency in N₂-fixation of Himalayan alder was also high (67.5 g N₂ fixed 10⁴ kJ^-1 energy). Quantum and flux of energy increased in the alder-cardamom compared to the forest-cardamom system that optimized the production potential of the cash crop under the influence of the Himalayan alder. Climatic sympatry of the large cardamom and Himalayan alder, and their synergetic energy efficiency makes this association ecologically and economically viable for the mountain regions.This revised version was published online in November 2005 with corrections to the Cover Date.     

Nutrient cycling under mixed-species tree systems in southeast Asia

Eucalyptus and Acacia are two tree genera that are commonly used in industrial plantations and as components of agroforestry systems in southeast Asia. These fast-growing trees are mostly grown in monocultures. However, questions are now being raised about the long-term sustainability of their growth as well as their effects on site quality. Losses of N and P from the site through biomass harvest and during site preparation constitute a major nutrient drain. As an alternative to monocultures, mixed-species cultures which include at least one N2-fixing tree species can improve plant productivity and soil N dynamics. Among the various aspects of N dynamics in such stands, export of N during biomass harvest and inputs by the N₂-fixing component are the most important. Reported estimates of the amount of N fixed by acacia and other N₂-fixing trees are highly variable, depending on inherited plant characteristics, tree age, site factors (e.g., drought), soil fertility (e.g., available P, metal toxicities) and unreliable methods of measuring N₂-fixation. Of the available techniques for assessing N₂-fixation by trees, the total N difference method (TND) is the simplest. The contribution of roots to assessments of N₂-fixation is recognized but rarely measured. For short-rotation mixed-species plantations, the amount and time of N transfer from N₂-fixing trees to non-N₂-fixing trees are important issues to consider when attempting to develop productive nutrient management strategies. Based on limited information from trials in southeast Asia, it appears that acacia fixes substantial amounts of N during the first few years of establishment and a significant amount of that N is transferred to adjacent eucalypts, thereby improving the growth and nutrition of the eucalypts. The presumed transfer of N from acacias to eucalypts during the early stages of plantation development probably results from belowground turnover of roots and nodules because aboveground litter decomposition is slight at this stage, and contributes little to the overall N dynamics. The available information on P cycling in mixed-species stands, during the early stages of stand growth, provides inconclusive evidence as to whether the availability of soil P increases, despite indications of higher levels of phosphatase activity in the fine roots of nitrogen-fixing trees. This would imply that additional inputs of P as fertilizer are required to remove any P deficiency in mixed-species stands. Long-term observations are required for better understanding of the nutritional and growth benefits of including N₂-fixing trees in mixed-species stands. This revised version was published online in June 2006 with corrections to the Cover Date.     

Agroforestry systems with Ilex paraguariensis (American holly or yerba mate) and native timber trees on small farms in Misiones, Argentina

In Misiones, in the northeast of Argentina, agroforestry systems of timber trees and perennial cash crops are becoming increasingly common. We evaluated the productivity of Ilex paraguariensis St Hill (South American holly or yerba mate, Aquifoliaceae) in association with indigenous trees: Enterolobium contortisiliquum (Vellozo) Morong. (timbó, Leguminosae, a N₂-fixing tree), and two timber species, Balfourodendron riedelianum (Engler) Engler (guatambú, Rutaceae) and Tabebuia heptaphylla (Vellozo) Toledo (lapacho negro, Bignoniaceae). Five years after planting, the tree species were 2.7 to 5.0 m high and 3 to 7 cm in diameter at breast height, and the yerba mate produced its first harvest. Additionally, the production of associated crops of subsistence covered the annual needs of the farmer. These systems are promising for sustainable use of deforested lands in the region.This revised version was published online in November 2005 with corrections to the Cover Date.     

Biomass and production of fine and coarse roots of trees under agrisilvicultural practices in north-east India

An understanding of the rooting pattern of tree species used in agroforestry systems is essential for the development and management of systems involving them. Seasonal variation, depth wise and lateral distribution of biomass in roots of different diameter classes and their annual production were studied using sequential core sampling. The investigations were carried out in four tree species under tree only and tree+crop situations at ICAR Research Farm, Barapani (Meghalya), India. The tree species were mandarin (Citrus reticulata), alder (Alnus nepalensis), cherry (Prunus cerasoides) and albizia (Paraserianthes falcataria). The contribution of fine roots to the total root biomass ranged from 87% in albizia to 77% in mandarin. The bulk of the fine roots (38% to 47%) in the four tree species was concentrated in the upper 10 cm soil layer, but the coarse roots were concentrated in 10–20 cm soil depth in alder (46%) and albizia (51%) and at 0–10 cm in cherry (41%) and mandarin (48%). In all the four tree species, biomass of both fine- and coarse-roots followed a unimodal growth curve by showing a gradual increase from spring (pre-rainy) season to autumn (post rainy) season. Biomass to necromass ratio varied between 2 to 3 in the four tree species. The maximum (3.2) ratio was observed during spring and the minimum (2) in the rainy season. In alder and albizia, the fine roots were distributed only up to 1 m distance from the tree trunk but in the other two species they were found at a distance up to 1.5 m from the tree trunk. The annual fine root production varied from 3.6 Mg ha^–1 to 6.2 Mg ha^–1 and total production from 4.2 to 8.4 Mg ha^–1 in albizia to mandarin, respectively. Cherry and mandarin had a large number of woody roots in the surface layers which pose physical hindrance during soil working and intercultural operations under agroforestry. But the high biomass of roots of these two species may be advantageous for sequential or spatially separated agroforestry systems. However, alder and albizia have the most desirable rooting characteristics for agroforestry systems.This revised version was published online in November 2005 with corrections to the Cover Date.     

Litterfall,litter decomposition and the use of mulch of four indigenous tree species in the Atlantic lowlands of Costa Rica

Litterfall, forest-floor litter biomass and nutrients, short-term litter decomposition and the effects of leaf mulches on initial growth of maize were studied for four indigenous tree species with agroforestry potential:Stryphnodendron microstachyum Poepp. et Endl.(S. excelsum), Vochysia ferruginea Mart,Vochysia guatemalensis Donn. Sm. (V. hondurensis) andHyeronima alchorneoides (O), growing in a young experimental plantation in the Atlantic humid lowlands of Costa Rica. Total annual leaf litterfall was higher inV. ferruginea plots, followed byS. microstachyum, V. guatemalensis andH. alchorneoides; all with values comparable to those reported for other tree species grown in agroforestry combinations in humid tropical regions. Forest-floor litter accumulation was highest underV. ferruginea andV. guatemalensis. Both litterfall and forest-floor litter material had similar patterns in nutrient concentrations: N was higher inS. microstachyum, Ca was higher inV. guatemalensis, K was higher inH. alchorneoides; Mg was higher inV. guatemalensis andH. alchorneoides; H. alchorneoides andV. guatemalensis had the highest P.V. ferruginea litter decomposed more slowly, whileS. microstachyum apparently decomposed faster than the other species. The twoVochysia species showed increases in N and P concentration in decomposing litter after seven weeks in the field,H. alchorneoides showed an increase in litter N and a decrease in litter P, andS. microstachyum showed a net decrease in both N and P over the same time period. The patterns found in the litter bag study were confirmed by results obtained in a tethered-leaves experiment.S. microstachyum andV. ferruginea litters lost more weight when mixed in a 11 proportion than either of them alone. Maize seedlings growing in plots mulched withS. microstachyum andH. alchorneoides leaves showed greatest initial growth, confirming patterns found in decomposition and nutrient release studies. The results show that these species could be used in agroforestry combinations with different advantages according to the specific objectives desired, whether these are soil protection, nutrient recycling, or enhancement of the growth of associated crops.     

Tropical leguminous species for acid soils: studies on plant form and growth in Costa Rica

Few studies of adaptability and growth of native legume species have been conducted on degraded acid soils. The lack of data for native species has often precluded their use in incentive-supported reforestation and international agroforestry schemes. A species screening trial that included 25 legume species was conducted at three abandoned pasture sites in the Atlantic Lowland of Costa Rica. Most of the leguminous species were of potential multipurpose value: 8% were exotic N₂-fixing trees, 60% (some of which were N₂-fixers) were indigenous to the region, and 32% (some of which were N₂-fixers) were native to other areas of Costa Rica. Survival (including damage indices), growth, tree form and N₂-fixing ability were used to evaluate species performance. Survival of the majority of the species after 3 years was high. Pithecellobium idiopodum, Inga edulis, Albizia guachapele, Pithecellobium elegans and Dalbergia retusa had greater than 90% survival at all sites. There were significant differences in growth measures among species. Across sites Acacia mangium, Stryphnodendron microstachyum and Inga edulis produced the greatest stem volume, and A. mangium, I. edulis, P. idiopodum and S. microstachyum had the highest crown volume. Inga edulis, P. idiopodum, I. coruscans and P. macroloba failed to form straight single stems. Acetylene reduction assay at Site 3 showed that I. edulis, A. mangium, A. guichapele, and I. coruscans had the highest nitrogenase activity among the best growing species. This trial indicates that there are native leguminous species with excellent potential for reforestation and agroforestry on acid soils high in aluminum and manganese.     

Large cardamom (Amomum subulatum Roxb.) plantation — An age old agroforestry system in Eastern Himalayas

Large cardamom (Amomum subulatum Roxb.) is a shade loving plant grown in the Indian hill states of Sikkim and Dargeeling district of West Bengal. About 30 important tree species are used to provide shade to the cardamom plants. Alnus nepalensis, a deciduous, nitrogen fixing and fast growing tree, is the species most commonly underplanted with cardamom. In addition to providing shade, it is also used for fuelwood. The old trees are cut and young plants coming up are allowed to grow in cyclic order. The quick decomposing leaf litter of A. nepalensis also fertilises the cardamom plants. The nitrogen added to the soil in this way has been found to be as high as 249 kg/ha. Large cardamom thrives well in a moist soil, which is maintained by water diverted from seasonal springs on the upper slopes. The system is well suited to conserving soil, water and tree cover of the characteristically steep slopes of the region. Moreover, the management inputs required for growing cardamom are low but the crop gives a higher financial return than rice or maize. The shade trees used in the system are also a major source of fuel, fodder and timber, especially as access to state owned forests is restricted by legislation. However, increasing incidence of viral chirkey and foorkey disease, panicle rot and capsule borer are reducing the cardamom productivity. It has been observed that integrating dairying and apiculture will further augment profitability from large cardamom agroforestry system.     

Decomposition and nutrient release from leaves,twigs and roots of three alley-cropped tree legumes in central Togo

The decomposition of leaves, twigs and roots of two diameter classes (<1.5 mm, 1.5–5 mm) were examined in an alley cropping experiment withGliricidia sepium, Calliandra calothyrsus andSenna sianea in the subhumid savanna of Central Togo using the litterbag technique. The effect of the application of leaves and twigs as mulch or green manure was examined. Gliricidia showed the most rapid mass loss. For all species, leaves decomposed faster than roots. Twigs had the lowest decomposition rate except forCalliandra. The two diameter classes of roots decomposed differently in the three species:Gliricidia fine roots decomposed faster than its coarser root fraction, the coarse roots ofSenna decomposed faster than the fine roots.Termites influenced the mass loss of twigs and roots to varying extents for the different species. In the case of twigs this was markedly influenced by the mode of application: green manure showed more termite frass than mulch.Nutrient release resembled the mass loss patterns of the prunings except for K, which was leached independently from mass loss. The release of the different nutrients was in the order CaGliricidia andSenna seemed to be best for mulch and green manure production at our site.     

Measuring nitrogen fixation by <Emphasis Type="Italic">Sesbania sesban</Emphasis> planted fallows using <Superscript>15</Superscript>N tracer technique in Kenya

A field experiment was performed in eastern Kenya to estimate N₂ fixation by Sesbania sesban over an 18-month period using the ¹⁵N dilution method. The influence of three reference species, Senna spectabilis, Eucalyptus saligna and Grevillea robusta, on the estimates of N₂ fixation was also assessed. Percentage Ndfa (nitrogen derived from the atmosphere) was calculated based on foliar atom excess (FAE), above-ground atom excess (AAE) or whole tree atom excess (WAE) data. The differences in atom% ¹⁵N excess values between species and plant parts are presented and discussed. We recommend the use of several reference species for estimating %Ndfa and that the different results obtained should be carefully considered in relation to the issues being addressed. In this study, Senna was the most suitable of the three reference species because its N uptake pattern and phenology were very similar to those of Sesbania. When well established, the amount of N fixed by Sesbania accounts for more than 80% of its total N content, according to FAE-based estimates. We estimated the Ndfa by Sesbania after 18 months to between 500 and 600 kg ha⁻¹ , depending on whether FAE, AAE or WAE data were used and on the choice of reference species. The substantial accumulation of N in planted Sesbania highlighted its potential to increase the sustainability of crop production on N-limited soils. We consider the ¹⁵N dilution method to be appropriate for quantifying N₂ fixation in improved fallows in studies, similar to this one, of young trees with high N₂-fixing ability.     

Insect herbivores and pathogens of Alnus species in Uganda

Published documentation of insect pests and pathogens associated with Alnus species in Africa is very scarce. We surveyed damaging insects and pathogens, and arthropod natural enemies on Alnus acuminata and A. nepalensis in Kabale and Mbale districts, Uganda between March 1999 and August 2000 in order to identify the range and relative abundance of arthropods and pathogens associated with the Alnus species. Frequently encountered damaging insects on the Alnus species included Apis mellifera, Apion globulipenne, a Systates sp. (Coleoptera: Curculionidae), Phymateus viridipes, a Lobotrachelus sp. (Coleoptera: Curculionidae), Coloborrtics corticina and some Chrysomelidae. Some species such as Aphis fabae, Parastictococcus multispinosus and a Cacopsylla sp. (Homoptera: Psyllidae) were observed feeding on other agroforestry tree species and/or crops although they generally occurred at low population intensities. Spiders and parasitic Hymenoptera were the most common natural enemies. Diseases were more severe in nurseries than in the field. Damping-off caused by Fusarium oxysporum, Septoria brown leaf spot and stem canker were the most serious diseases of Alnus. The array of damaging insects and pathogens indicates a potential danger to the cultivation of Alnus species in Uganda as adoption of the species for agroforestry continues to expand in the country. In view of the increasing demand for Alnus species for agroforestry in Uganda, regular pest monitoring and appropriate control strategies are necessary.This revised version was published online in November 2005 with corrections to the Cover Date.     

Influence of slope position, stand type and rhododendron (Rhododendron ponticum) on litter decomposition rates of Oriental beech (Fagus orientalis Lipsky.) and spruce [Picea orientalis (L.) Link]

Oriental beech (Fagus orientalis Lipsky.) and Oriental spruce [Picea orientalis (L.) Link] are the two most common tree species in northeast Turkey. Their distribution, stand type and understorey species are known to be influenced by topographical landforms. However, little information is available as to how these changes affect litter decomposition rates of these two species. Here, we investigated the effects of slope positions (top 1,800 m, middle 1,500 m and bottom 1,200 m), stand type (pure and mixed stands) and purple-flowered rhododendron (Rhododendron ponticum) on litter decomposition rates of Oriental beech and spruce for 4 years using the litterbag technique in the field. Among these three factors, stand type had the strongest influence on litter decomposition (P < 0.001, F = 58.8), followed by rhododendron (P < 0.001, F = 46.8) and slope position (P < 0.05, F = 11.6). Litter decomposition was highest under mixed beech/spruce forest, followed by pure beech and spruce forest. Beech and spruce litter decomposed much faster in mixed bags (beech–spruce) than they did separately under each stand type. Purple-flowered rhododendron significantly reduced litter decomposition of Oriental beech and spruce. Beech and spruce litter decomposed much slower at top slope position than at either bottom or middle position. Differential litter decomposition of Oriental beech and spruce was mainly due to adverse conditions in spruce forest and the presence of rhododendron on the ground which was associated with lower soil pH. Higher elevations (top slope position) slowed down litter decomposition by changing environmental conditions, most probably by decreasing temperature as also other factors are different (pH, precipitation) and no detailed investigations were made to differentiate these factors. The adverse conditions for litter decomposition in spruce forest can be effectively counteracted by admixture of beech to spruce monoculture and by using the clear-cutting method for controlling rhododendron.     

Agroforestry tree selection in central Chile: biological nitrogen fixation and early plant growth in six dryland species

Growth rate, resource partitioning, and several biological traits related to biological N₂ fixation for six native or non-native tree species were compared using ¹⁵N isotope dilution techniques. The trees were field grown for six years in a semiarid mediterranean-climate region with five to six months a year of absolute drought. Trees were tested as candidates for new agroforestry systems being developed in central Chile to improve soil fertility and land health, while also increasing productivity and profitability for landowners and animal breeders. Four nitrogen-fixing legume trees (NFTs) were tested: Acacia caven (Mol.) Mol.Prosopis alba Griseb., P. chilensis (Mol.) Steuntz. emend. Burk., and Tagasaste ( Chamaecytisus proliferus L.f. subsp. palmensis (Christ.)Kunkel). Additional, non-nitrogen-fixing trees were the slow-growing native Huingán (Schinus polygamus (Cav.) Caberera and the fast-growing European Ash (Fraxinus excelsior L.). Among the NFTs, highly contrasting patterns in biological nitrogen fixation (BNF) were detected, for N_dfa (proportion of N derived from atmosphere), nodule efficiency (NE = gN fixed g^–1 nodules), and N content in leaves, stems and roots. Tagasaste produced 2.5–25 times more biomass and fixed 4.5 to 30 times more atmospheric nitrogen than the South American Acacia and Prosopis species. N_dfa reached 250 g plant^–1 in Tagastaste, in the sixth year, with NE = maximum 2.68 in the 4th year, and 1.12 in the 6th year. In contrast, Acacia caven had by far the highest NE of the four NFTs – 12.13 in the 4th year and 6.6 in the 6th year. Whereas BNF in Tagasaste peaked in the fourth year, and declined thereafter, BNF in Acacia caven increased steadily over six years. Fraxinus excelsiorand Schinus polygamus had growth rates and biomass accumulation intermediate between that of Tagasaste and the South American NFTs.Results are discussed in relation to agroforestry, restoration of soil fertility, and ecological and economic rehabilitation of damaged ecosystems and landscapes.This revised version was published online in November 2005 with corrections to the Cover Date.     

Spice crops agroforestry systems in the East Usambara Mountains,Tanzania: growth analysis

A scarcity of cultivation land calls for more intensive and productive land use in the East Usambara Mountains in NE Tanzania. Spice crops could generate cash in higher parts of the mountains, but the present cultivation methods are depleting the valuable forest resources. The trial was established at the end of 2000 to find out how the two popular cash crops, cardamom (Elettaria cardamomum (L.) Maton.) and black pepper (Piper nigrum L.), normally grown under the natural forest, will produce in intensive agroforestry system with two multipurpose farm trees, Grevillea robusta A.Cunn. and nitrogen fixing Gliricidia sepium Jacq. Results from 6 years showed that cardamom produced better with grevillea than in natural forest; 5.5 times more in the fourth year than the average in the area. The Land Equivalent Ratios for black pepper and cardamom showed that pepper intercropped with grevillea produced 3.9 times more than in monoculture whereas cardamom intercropped with grevillea and pepper produced 2.3 times more than in monoculture. Gliricidia improved the nitrogen and organic matter content of the soil over the levels found in natural forest. Soil acidity was, however, preventing the plants from using the available mineral nutrients more effectively.     

Effect of four multipurpose tree species on soil amelioration during tree fallow in Central Togo

The effects of Cassia siamea, Albizia lebbek, Acacia auriculiformis, and Azadirachta indica on soil fertility have been studied on five-year-old fallows on Ferric Acrisols in Central Togo. Litter quality and soil fertility under the four species were significantly different. Topsoil pH increases significantly with increasing litter Ca levels. Cassia siamea and Azadirachta indica were superior in enriching the sandy-loamy topsoils with Calcium and in increasing soil pH. Under Acacia, which had the highest biomass production, litter accumulation appeared to be responsible for the low mineral soil Ca and P values. In addition, topsoil pH under Acacia was lower than under grass or bush fallow or the other species. Slow litter mineralization of Acacia auriculiformis was probably caused by the thick, leathery consistence and high tannin content of its litter. Due to its high biomass production supporting soil acidification pure Acacia auriculiformis stands seemed to be less favourable for improving soil fertility on planted fallows but more suited for firewood plantations and topsoil protection. The foliage as well as the litter and topsoil under Albizia showed narrow C/N- and C/P-ratios resulting in easily mineralizable organic matter. All tree species tested were superior to natural grass/herb fallow in building up surface soil fertility. However, differences with natural bush fallow were not significant.

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Résumé Au bout de cinq ans des differences fortement significative ont été trouvées quant aux caractères de la litière et de la fertilité des jachères arborées avec Cassia siamea, Albizia lebbek, Acacia auriculiformis et Azadirachta indica, respectivement. ll y a une corrélation positive entre le pH de l'horizon superficiel et la teneur en Ca dans la litière: l'enrichissement du sol sable-limoneux en Ca et le pH sont plus élevés sous Cassia siamea et Azadirachta indica que sous les autres espèces. Acacia se caractérise par la plus grande production en biomasse, donc une accumulation importante de litière sur le sol, ce qui entraîne les plus faibles teneurs en P et Ca dans l'horizon de surface. En plus, il semble qu'elle fait diminuer le pH parce que les valeurs trouvées sont inférieures à celles des parcelles témoin ou des autres espèces. La mineralisation retardée de la litière de Acacia auriculiformis depend probablement de la consistence des feuilles et du content élevé de tannine. Acacia est par consequent moins favorable à des jachères plantées mais plutôt efficace quant à la production du bois de feu et la protection du sol contre l'érosion. Vu les petits rapport C/N et C/P dans les feuilles, la litière et dans l'horizon superficiel d'Albizia, on peut supposer que sa matière organique soit plus facilement décomposable. Toutes les espèces d'arbre étudiées sont plus capables de lever la fertilité des sols que les herbes des parcelles témoin. La comparaison avec une jachère spontanée d'arbustes ne fait pas apparâitre d'effets significatifs.

     

Comparing genetic diversity in agroforestry systems with natural forest: a case study of the important timber tree Vitex fischeri in central Kenya

It is possible that current tree domestication practices undertaken by farmers reduce the genetic base of tree resources on farms, raising concerns regarding the productivity, sustainability and conservation value of agroforestry ecosystems. Here, we assessed possible changes in genetic variation during domestication in the important and heavily utilised timber species, Vitex fischeri Gürke (syn. Vitex keniensis), by comparing geographically proximate forest and farm material in central Kenya. Employing RAPD analysis, a total of 104 polymorphic markers revealed by five arbitrary primers were scored in a total of 65 individuals, 32 from forest and 33 from farmland. Despite concerns of possible genetic erosion, forest and farm stands did not differ significantly in levels of genetic variation, with H values of 0.278 and 0.269, respectively. However, Mantel tests did reveal greater geographically related associative genetic structure among individuals in farm rather than forest material, with r _M values of 0.217 and 0.114, respectively. A more detailed analysis of structure suggested this could be due to local variation in origin of some on-farm trees. Implications of data for the genetic management of V. fischeri stands during farmer-led tree domestication activities are discussed. At present, there appears little reason to reject on-farm V. fischeri as a source of germplasm for future on-farm planting or for conservation purposes, although this situation may change and will require monitoring.     

Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L., the baobab of continental Africa. The introduction potential of Adansonia species from the center of diversity in Madagascar and from Australia remains untapped. To assess this potential, the mineral contents and B₁ and B₂ vitamin levels of dried baobab leaves were determined for five-year old trees of A. digitata, A. gibbosa (A. Cunn.) Guymer ex D. Baum, A. rubrostipa Jum. & H. Perrier (syn. A. fony Baill.), A. perrieri Capuron and A. za Baill. grown in an introduction trial in Mali. Nutritional data were evaluated against survival and vigor to identify promising germplasm. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa (B₁ 88 mg 100 g⁻¹, B₂ 187 mg 100 g⁻¹, protein 20.7% dry weight). However, the local species far outperformed the introductions in survival, tree height, basal diameter and resistance to termites. We suggest grafting as a way of harnessing the vigor of well-adapted local baobab varieties to the superior nutritional profiles of A. rubrostipa and others. Cross-species grafting tests in Adansonia were successful, thus creating new agroforestry possibilities with different scion/rootstock combinations.     

Litter dynamics and soil properties under different tree species in a semi-arid region of Rajasthan,India

Litterfall and decomposition are the two main processes accounting for soil enrichment in agroforestry. The extent of enrichment in soil properties depends on the tree species, management practices and the quantity and quality of litter. A field investigation was carried out to study litterfall production, decay rates, release of nutrients and consequent changes in soil physicochemical properties under crowns of four multipurpose tree species (MPTs) in irrigated conditions in farm fields. The species were Prosopis cineraria (L.), Dalbergia sissoo (Roxb.) ex DC, Acacia nilotica (L.) Del. and Acacia leucophloea (Roxb.) Willd. Annual accretion of litter ranged from 36 to 54 kg tree⁻¹ year⁻¹ and was highest under D. sissoo and lowest under A. nilotica. Total litterfall production was in the order: P. cineraria > A. leucophloea > A. nilotica > D. sissoo. P. cineraria showed the highest NPK concentration in litter. For all MPTs, a large pulse of litterfall coincided with the winter season (November to February). Litter of P. cineraria decomposed fastest while that of A. nilotica was slowest. More than 95% of the leaf litter of P. cineraria decomposed in 6 months, of D. sissoo in 7 months and A. leucophloea and A. nilotica in 9 months. Decomposition rate of litter was highly correlated with neutral detergent fibre (NDF) (r = −0.94) and P (r = −0.91) concentration. N, P and K release were best correlated with NDF, acid detergent fibre (ADF), P, lignin, lignin/N and C/P ratios and NDF alone explained 88% to 94% of the variability in litter decomposition and nutrient release rates. There was significant build up of soil organic carbon and available NPK in the agrisilvicultural systems but also a decrease in soil pH. Build up in soil fertility was significantly correlated with litterfall and soil improvement was greatest under P. cineraria.