Growth of ten multipurpose tree species on acid soils in Sangmelima,Cameroon

Ten multipurpose tree species were planted both in monoculture and intercropped withArachis hypogea (groundnut) in a randomized complete block with three replications. The vigrou, biomass, nutrient content, and coppicing percentage of the trees were evaluated. Intercropping with groundnuts during the establishment phase did not affect subsequent growth and development of the species.Acacia mangium, Acacia auriculiformis, Cassia siamea, Calliandra calothyrsus andParaserianthes falcataria established well, when compared toGliricidia sepium, Leucaena leucocephala, Dialum guineense, Dubocia macrocarpa andMilicia excelsa. A. mangium, A. auriculiformis, C. calothyrsus, C. siamea andP. falcataria produced the highest leaf (4 to 20 t ha^–1) and wood (12 to 37 t ha^–1) biomass yield (primary growth) at one to three years after planting. Coppicing percentage ofA. mangium A. auriculiformis andP. falcataria were relatively low (35 to 50%).C. calothyrsus andC. siamea showed the highest coppicing percentage (95 to 100%) and produced the greatest coppice biomass (9 to 13 t ha^–1). Total nitrogen and organic matter percentage of soils from under the stands of these two species were also significantly higher than that of the rest. The two species may thus be considered for use in agroforestry technologies for soil improvement on acid soils, which are typical of the moist tropics.     

Productivity and nutrient cycling in young Acacia senegal farming systems on Vertisol in the Blue Nile region, Sudan

Acacia senegal, the gum arabic-producing tree, is the most important component of traditional dryland agroforestry systems in the␣Sudan. The spatial arrangement of trees and the type of agricultural crop used influence the interaction between trees and crops. Tree and crop growth, gum and crop yields and nutrient cycling were investigated over a period of 4 years. Trees were grown at 5 × 5 m and 10 × 10 m spacing alone or in mixtures with sorghum or sesame. No statistically significant differences in sorghum or sesame yields between the intercropping and control treatments were observed (mean values were 1.54 and 1.54 t ha⁻¹ for sorghum grain and 0.36 and 0.42 t ha⁻¹ for sesame seed in the mixed and mono-crop plots, respectively). At an early stage of agroforestry system management, A. senegal had no detrimental effect on crop yield; however, the pattern of resource capture by trees and crops may change as the system matures. A significant positive relationship existed between the second gum picking and the total gum yield. The second gum picking seems to be a decisive factor in gum production and could be used as an indicator for the prediction of the total gum yield. Soil organic carbon, N, P and K contents were not increased by agroforestry as compared to the initial levels. Soil OC was not increased by agroforestry as compared to sole cropping. There was no evidence that P increased in the topsoil as the agroforestry plantations aged. At a stocking density of 400 trees ha⁻¹ (5 × 5 m spacing), A. senegal accumulated in its biomass a total of 18.0, 1.21, 7.8 and 972 kg ha⁻¹ of N, P, K and OC, respectively. Agroforestry contributed ca. 217 and 1500 kg ha⁻¹ of K and OC, respectively, to the top 25-cm of soil during the first four years of intercropping.     

Influence of Acacia senegal agroforestry system on growth and yield of sorghum, sesame, roselle and gum in north Kordofan State, Sudan

We examined the effects of intercropping with Acacia senegal (L.) Willd on growth and yield of sorghum (Sorghum bicolor L.), sesame (Sesamum indicum L.) and roselle (Hibiscus sabdariffa). Field experiments were conducted in El-Obeid Research farm (13°10’ N; 30°12’ E), North Kordofan State, Sudan, during 2002 2003 in an 11-year-old A. senegal plantation. The experimental design was randomized complete block design (RCBD) with four replications. Data were recorded for plant height (cm), fresh weight (kg ha -1 ), dry weight (kg ha -1 ), crop yield (kg ha -1 ), and gum yield (kg ha -1 ). We used Land Equivalent Ratios (LER) and simple financial analyses of gross surpluses to evaluate the productivity and profitability of the different treatments. The results indicated that A. senegal trees had a beneficial effect on crop performance and yield as well as gum yield. Significant differences (p<0.05) were obtained for plant height, fresh weight, dry weight and crop yield. Therefore, yield of sorghum, sesame and roselle under intercropping system were 13.7%, 23.8% and 20.9% higher than that obtained in the sole cropping system respectively. The highest yield increase was observed with sesame (23.8%). Gum yield (g/tree/picking) was signifi- cantly (p<0.05) increased for sorghum, sesame and roslle under inter-cropping system. The highest yield of (298g/tree/picking) was obtained when roselle was intercropped with A. senegal, while the least gum yield of (239 g tree-1 ) was recorded in pure A. senegal plot. All the treatments gave land equivalent ratio (LER) of more than one-indicating the superiority of growing the field crops in intercropping over the sole cropping systems. The highest LER of 3.8 was obtained for sesame intercropped with A. senegal (Hashab), followed by 3.7, when sorghum was intercropped with A. senegal and 3.3 when roselle intercropped with A. senegal. All the treatments gave positive net revenues, the highest being for intercropped sorghum (558 SDG ha -1 ) (SDG=Sudanese gienh). The intercropping of roselle gave the second net revenue (518 SDG ha -1 ),while the sole sorghum gave the lowest net revenue (501 SDG ha -1 ).     

Crop yields of rice and wheat grown in rotation as intercrops with three tree species in the outer hills of Western Himalaya

Studies on tree crop interaction under rainfed condition in Dehradun valley were conducted for 13 years during 1977 to 1990. Grewia optiva (Bhimal), Morus alba (Mulbery) and Eucalyptus hybrid were tried along with rice (CV: Akashi) — wheat (CV: RR-21) rotation. One-year-old tree seedlings of the above tree species were planted in line, 5 m apart in N-S direction, in July 1977, in the middle of the plot (size 20 m × 20 m). Eucalyptus was first harvested in 1987. Grewia optiva, Morus alba and coppice of Eucalyptus were harvested in 1990. All tree species had depressing effect on crop yields. Eucalyptus had maximum effect in depressing crop yield till the first harvest and had least effect thereafter. From 1987 onwards, Morus alba affected rice most, while wheat was mostly affected by Grewia optiva. The depressing effect on an average varied from 28 to 34% depending upon the species.Distance of tree line from the crop significantly affected the crop yield upto a distance of 5 m and there was 39% decrease in crop yield upto 1 m, 33% from 1–2 m, 25% from 2–3 m and 12% from 3–5 m distance. Annual removal of lops and tops from trees partly compensated the deficit. Grewia optiva could produce 1.08 t ha^–1 yr^–1 of branches and 0.26 t ha^–1 yr^–1 of leaves (air dry) and 1.28 t ha^–1 yr^–1 of branches and 0.28 t ha^–1 yr^–1 of leaves were obtained from Morus alba. Wood (ADT) produced by the trees was 33.6 t ha^–1 from Eucalyptus, 9.5 t ha^–1 from Grewia optiva and 11.6 t ha^–1 from Morus alba.     

The agronomic and economic performance of banana,bean and tree intercropping in the highlands of Burundi: an interim assessment

To meet their wood, fodder and fruit needs, resource-poor farmers with only small land holdings are forced to mix trees in their food crop plots. An experiment was conducted to study the effect of nine tree species planted at 312.5 trees ha^–1 (4×8 m) on the yield of bananas planted at 625 stools ha^–1 (4×4 m) and beans (80000 plants ha^–1) as well as the wood production of the trees when intercropped. In addition, an economic analysis was done to compare the different tree/banana/bean associations.After three and one-half years, wood volume (in m³ ha^–1) ofGrevillea robusta (18.1), was highest and that ofErythrina poeppigiana (2.7),Cedrela odorata (2.4) orMarkhamia lutea (0.8) was the lowest. Volume ofCedrela serrata (13.7) was not significantly different from that ofAlbizia chinensis (12.8) but was significantly higher than that ofLeucaena diversifolia (6.8),Acrocarpus fraxinifolius (6.7) orCalliandra calothyrsus (6.0).None of the tree species had a significant influence on the yields of the bananas and none affected the yield of the bean crops until the seventh cropping season, three years after the trees were planted. In that year, Grevillea reduced bean yield by 29%, Albizia by 34% and Leucaena by 36%. From the economic analyses, all the treatments except Leucaena and Markhamia had positive net benefits relative to the control (banana/bean) but the results were highly variable.C. serrata was found to be the best tree to be intercropped in a banana/bean system.     

A comparison of agrisilvicultural systems with plantation forestry in the Atlantic Lowlands of Costa Rica

Survival and growth data (ages 0–5 years) are presented for two timber species (Acacia mangium, Cordia alliodora) planted in monocultures or in association with a sequence of agricultural cropsZea mays, Zingiber officinale andEugenia stipitata (a fruit shrub) in the tropical humid Caribbean lowlands of Costa Rica. Average annual height and diameter growth rates were 3.2 m and 4.0 cm (C. alliodora), 3.5 m and 3.8 cm (A. mangium).C. alliodora associated with crops gave the greatest productivity with an average total stem volume increment of 19 m³ ha^–1 yr^–1. Root rot ofA. mangium (mainlyRosellinia sp.), leading to tree mortality, was greater in pure plots compared to associated plots.A. mangium can not be recommended for similar sites because of this problem.     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica II. Cacao and wood production,litter production and decomposition

During 7 years (1979–1985) cacao harvests (beans and husks) have been recorded for the agroforestry systems ofTheobroma cacao underCordia alliodora andErythrina poeppigiana shade trees. The mean oven dry cacao yields were 626 and 712 kg.ha^–1.a^–1 cocoa beans underC. alliodora andE. poeppigiana respectively. Harvests have gradually increased over the years and the plantation has now reached maturity.Annual extraction of N, P, K, Ca and Mg in fruits, which is relatively small, was calculated on the basis of chemical analyses. The following average values were found (kg.ha^–1.a^–1): At the age of 8 years, theC. alliodora trees have reached 26.7 cm diameter (DBH) and 14.0 m in height. Mean annual growth (from age 5 to 7) is 14.6 m³.ha^–1.a^–1.Natural plant residue production has been measured for 4 years (Nov. 1981–Oct. 1985). UnderE. poeppigiana it has reached a value of 8.91 t.ha^–1.a^–1 and underC. alliodora 7.07 t.ha^–1.a^–1. The shade trees have contributed 57 and 47% respectively. Transference and decomposition rates are high and important in the nutrient cycles.The nutrient content of the litter was analysed and corresponding average yearly transfers were (kg.ha^–1.a^–1): For part I see Vol. 4, No. 3, 1986.Agroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesselschaft für Technische Zusammenarbeit), Turrialba, Costa Rica     

Agroforestry systems for soil and water conservation and sustainable production from foothill areas of north India

Some conservation based agroforestry systems (AFS) were developed for possible adoption in place of high risk rainfed farming on land capability classes Ito IV of a typical topo-sequence of foothill north India. The agri-silvi-horticulture system integrating leucaena, lemon, papaya and turmeric on class I irrigated land provided sustainable mean net returns of Rs. 17066 against Rs. 7852 ha.^–1 yr.^–1 from double cropped agricultural system. The intercropping of cluster beans with leucaena gave the highest net returns of Rs. 3540 ha.^–1 yr.^–1 in the agri-silvicultural system adopted on class II land. Eucalyptus terettcornis (Smith) in top and Bhabbar grass (Eulaliopsis binata Retz) in the understorey on a sandy loam class III land gave four years (1985–1988) mean air dry grass yield of 4.2 (used for paper pulp) from October and 1.19 t. ha^–1 yr.^–1 (used for fodder) from June cut. The net returns from grass alone were Rs. 4672 against Rs. 1679 ha.^–1 yr.^–1 from rainfed field crops raised on an adjoining plot. The returns from trees would be additional. Bhabbar grass raised under Acacia species on a 25 to 30% sloping gravelly class IV land provided yield varying from 2.18 to 4.31 from October cut and 0.50 to 1.1 t. ha.^–1 yr.^–1 from June cut with 6 years mean of 3.9 t. ha.^–1 yr.^–1 which at 1988 prices provided net returns of Rs. 2402 ha^–1. These AFS proved superior to traditional farming on each land capability class.     

Estimates of above-ground biomass and nutrient accumulation in Mimosa scabrella fallows in southern Brazil

Naturally regenerated stands of bracatinga (Mimosa scabrella Bentham) are harvested for firewood after six to eight years of unregulated growth, debris burnt and the area planted to one cycle of intercropped maize (Zea mays L.) and beans (Phaseoulus vulgaris L.). Burning breaks dormancy of bracatinga seed (> 80% germination) marking the onset of a new fallow-crop cycle. This production system has been practiced for nearly 100 years in Southern Brazil, covering some 60,000 ha in 3,000 small farms. An estimation of above-ground biomass and nutrient accumulation was made using literature data on stand age, population numbers, tree sizes, tree biomass partitioning and concentration of major nutrients in tree tissues. A simple simulation model, used to quantify above-ground nutrient pathways and their temporal dynamics, confirmed that six to eight years is the optimal rotation length. Biomass and nutrients deposited onto the soil, peak at stand age six years, which may result in significant soil fertility improvement prior to crop planting. At year six, estimated total above-ground biomass amounts to 83 Mg ha^–1; 44 Mg ha^–1 available as firewood and 39 Mg ha^–1 to be returned to the soil. Roughly half the amount of nutrients fixed in the above-ground bracatinga biomass would be exported in firewood and subsequent grain crops.     

Nitrogen mineralization and maize yields following application of tree prunings to a sandy soil in Zimbabwe

Despite the promotion of prunings as sources of nitrogen for crops, lack of synchronization between N mineralization from prunings and plant uptake remains a major limitation to the impact of prunings on crop yields. A laboratory and a field experiment were therefore carried out to determine the mineralization patterns of selected prunings and assess the potential that exists to improve synchrony by mixing prunings of different quality. The laboratory incubation experiment was conducted for 84 days to determine the C and N release patterns of prunings of different quality and the manipulation of the C and N mineralization trends by mixing prunings of different quality. High quality prunings were considered to be those with high CO₂ evolution rates and mineralize N rapidly. The % C and % N released in 84 days were highest for the high quality prunings of Tithonia diversifolia (70% and 30% respectively) and least for the low quality prunings of Flemingia macrophylla (25% and –5% respectively). The medium quality prunings of Acacia angustissima and Calliandra calothyrsus had similar proportions of released C and N (about 40% C and 10% N). Different mixtures of T. diversifolia with other species showed contrasting influence on C release and N mineralization. Most mixtures released less C than that predicted, but in contrast most mixtures released N at a rate either matching or above the predicted. The % N released was strongly correlated with the polyphenol protein binding capacity (r² = 0.53) and also with the % C released (r² = 0.62). The field experiment was done for two cropping seasons to determine the effects of the prunings of these species and their mixtures on maize grain yield. The prunings were added at 5 t ha^–1 and incorporated into the top 15 cm by hand hoeing in the first season and their residual effects were monitored in the second season. Medium and low quality prunings produced significantly (p < 0.05) higher maize grain yields in the first season ranging between 2.4 t ha^–1 and 3.4 t ha^–1 compared with T. diversifolia which produced 1.7 t ha^–1. This suggested better synchrony in N release and uptake by maize with medium and low quality prunings compared with high quality prunings. The only mixture that indicated improved synchrony was the mixture of T. diversifolia and C. calothyrsus. This study showed that mixing prunings of different quality produce different patterns of N mineralization, some of which were unexpected and had a potential for improving N synchrony.This revised version was published online in November 2005 with corrections to the Cover Date.     

Tree species composition,structure and utilisation in Maruzi Hills Forest Reserve in Uganda

The study investigated the tree species composition, vegetation structure and harvesting pattern to guide management of the Maruzi Hills Forest Reserve. Stratified random sampling was used to site six (100 m × 100 m) permanent sample plots in the woodland, bushland and grassland vegetation types identified in the reserve. Rényi diversity profiles indicated that bushland vegetation had a lower Shannon diversity index (H = 2.054) than grassland (H = 2.38) and woodland vegetation (H = 2.319). Grassland and woodland vegetation also had lower proportions of the dominant species (α_∞ = 1.15 and 1.66, respectively) than bushland vegetation (α_∞ = 3.25). However, the mean stem density of the woodland, bushland and grassland vegetation was 214 stems ha^?1, 191 stems ha^?1 and 114 stems ha^?1, respectively. Bray-Curtis and Jaccard ecological distance matrices showed that, although the three vegetation types shared some common species, the ecological distances were relatively high suggesting significant species composition variation between the vegetation types, particularly between the bushland and the other vegetation types. The species with the highest proportional abundance in the survey were Combretum molle (23%), Acacia hockii (17.7%), Combretum collinum (16.1%), Grewia mollis (6.5%) and Lannea barteri (6.5%). Diameter size-class distribution of woody perennials and tree stumps indicated higher frequencies of the smaller-diameter size classes. The stump records were indicative of charcoal burning and firewood collection as major causes of tree/shrub harvesting. The Maruzi Hills woodland conservation strategy should consider the differences in species composition between vegetation types if the highest number of species is to be conserved.     

Litter and biomass production from planted and natural fallows on a degraded soil in southwestern Nigeria

To rehabilitate a degraded Alfisol at Ibadan, southwestern Nigeria, Senna siamea (non-N-fixing legume tree), Leucaena leucocephala, and Acacia leptocarpa (N-fixing legume trees) were planted in 1989, and Acacia auriculiformis (N-fixing legume tree) in 1990. Pueraria phaseoloides (a cover crop) and natural fallow were included as treatments. Litterfall and climatic variables were measured in 1992/1993 and 1996/1997 while biomass production and nutrient concentrations were measured in 1993 and 1995. Total litter production from the natural and planted fallows was similar, with means ranging from 10.0 (L. leucocephala) to 13.6 t ha⁻¹ y⁻¹ (natural fallow) during the 1996/1997 collection. Leaves constituted 73% (L. leucocephala) to 96% (A. auriculiformis) of total litterfall. Acacia auriculiformis grew most quickly but S. siamea produced the highest aboveground biomass which was 127 t ha⁻¹ accumulated over four years, and 156 t ha⁻¹ accumulated over six years of establishment. The aboveground biomass of P. phaseoloides and natural fallow was only 6 to 9 t ha⁻¹ at six years after planting. Nitrogen concentration in the leaves/twigs of was 2.5% for L. leucocephala, and 2% for other planted species and natural fallow. Pueraria phaseoloides had concentrations of P, K, Ca and Mg comparable to levels in the leaves/twigs of the tree species. Through PATH analysis, it was found that maximum temperature and minimum relative humidity had pronounced direct and indirect effects on litterfall. The effects of these climatic variables in triggering litterfall were enhanced by other variables, such as evaporation, wind, radiation, and minimum temperature. Improvement in chemical properties by fallows was observed in the degraded soil. This revised version was published online in June 2006 with corrections to the Cover Date.     

Assessing the Potential of Trees for Afforestation of Degraded Landscapes in the Aral Sea Basin of Uzbekistan

Land degradation is a serious hindrance to agricultural development in Uzbekistan, a country striving to rebuild its agricultural sector for self-sustained production. The potential of multipurpose trees for upgrading degraded land is enormous. However, knowledge is lacking about the establishment and growth characteristics of different species, the energy content of firewood and the nutritive value of fodder. This study presents such data for 10 selected local multipurpose species grown on gleyic solonchak soil. Elaeagnus angustifolia L. and Tamarix androssowii showed superior biomass growth, respectively producing up to 11.0 and 10.4 t ha⁻¹ of utilizable aboveground dry matter (DM). E. angustifolia showed high potential for rapid establishment evidenced by root elongation of over 100 m tree⁻¹ at the age of 3 years. T. androssowii, Prunus armeniaca L. and Populus nigra var. pyramidalis Spach exhibited the greatest fuelwood characteristics, showing calorific values in the range of 14.4 – 16.2 MJ DM kg⁻¹. E. angustifolia and Morus alba L. demonstrated superior fodder potential given by the crude protein content of 216 and 117 g DM kg⁻¹. Recommendations on species selection are proposed based on various species characteristics. In assessing the potential of trees for afforestation of degraded land a reliable economic analysis of these aspects must be taken into account. When considering all characteristics concurrently, a mixture of species instead of monocrop cultivation seems to provide the best solution for improving degraded land.     

Alley cropping on an Ultisol in subhumid Benin. Part 1: Long-term effect on maize, cassava and tree productivity

In southern Benin, West Africa, two alley cropping systems were studied from 1986 to 1992. Yield development was followed in a maize and cassava crop rotation vs. intercropping system, with alleys of Leucaena leucocephala (Lam.) de Wit and Cajanus cajan (L.) Millsp. vs. a no-tree control, with and without NPK fertiliser. Without alleys, NPK fertilisation maintained high yield levels of 2–3 t maize dry grain plus 4–6 t ha^–1 cassava root DM in intercropping, 3–4 t ha^–1 maize and 6–10 t ha^–1 cassava in solercropping. Without NPK, final yields seemed to stabilise at about 1 t maize plus 2 t cassava in intercropping and twice as much in each solecrop. Alley cropping induced significant yield increases by about 50% with both tree species in unfertilised, intercropped maize, and with Cajanus in fertilised, solecropped cassava. In monetary terms, the NPK-fertiliser response of stabilised yields was significant for all treatments except the solecropped Leucaena alleys. It is concluded that on Ultisols with low nutrient status in the upper rooting zone, alley cropping with low-competitive tree species may improve food crop yields but the greatest monetary output is achieved by intercropping with mineral fertiliser independent of the presence or absence of an agroforestry component.     

Evaluation of fuelwood quality of indigenous and exotic tree species of India's semiarid region

The fuelwood potential of indigenous (Acacia nilotica, Azadirachta indica, Casuarina equisetifolia, Dalbergia sissoo, Prosopis cineraria andZizyphus mauritiana) and exotics (Acacia auriculiformis, A. tortilis, Eucalyptus camaldulensis andE. tereticornis) trees were studied. Calorific value variations for components, such as, stump, main stem, treetop, branches, foliage and bark, were determined. Tree components differed highly significantly (P<0.01) among groups (indigenous and exotics) and within species. The calorific means ranged from 18.7 to 20.8 MJ/kg for indigenous tree species and 17.3 to 19.3 MJ/kg for exotics. Besides calorific values, other fuelwood characteristics, such as, density, ash, biomass/ash ratio, moisture and nitrogen content were also studied. It was observed that indigenous tree species are better suited as fuelwood species as they contain high density wood, low ash content and low N percentage. The fuelwood value index (FVI) was found to be high of indigenous tree species and was maximum forCasuarina equisetifolia (2815). The most promising tree species were in the order ofC. equisetifolia, A. nilotica andZ. mauritiana.     

Management of windbreaks in the Sahel: the strategic implications of tree water use

At sites in the Sahel where windbreaks are used to control wind erosion, management strategies are required to minimise competition for water between trees and crops. Uptake of water by windbreak trees was therefore studied in experiments designed to compare water use among tree species, assess which variables exert most control over transpiration and determine the source of water transpired by windbreak trees. Transpiration and soil-water extraction by Acacia nilotica, Acacia holosericea and Azadirachta indica trees in windbreaks were measured at the ICRISAT Sahelian Centre, Niger. Coupling of windbreaks to the atmosphere was evaluated and a stable isotope technique was used to compare utilisation of groundwater by windbreaks and crops at two sites in Niger with different water table levels. Azadirachta indica used least water, probably as a result of lower stomatal conductances, since windbreaks exhibited good physiological control over transpiration. The potential for competition for water was most severe with Acacia nilotica and Acacia holosericea, as they extracted large quantities of water through lateral roots, and at the location where trees could not access groundwater. At such sites, the effects of competition on crop productivity should be minimised by planting tree species with low water requirements and by using pruning to limit tree transpiration.This revised version was published online in November 2005 with corrections to the Cover Date.     

Species Selection for Afforestation of Sub-Standard Soil Sites with Particular Reference to Biomass Production and Soil Rehabilitation

Abstract

Performance of three, evenaged leguminous tree species (Acacia nilotica, A. auriculiformis and Pithecellobium duke) was evaluated on sodic soil sites (pH 9.6) at Biomass Research Centre, Banthra, Lucknow (north India). Species differed significantly in respect to plant survival, growth and productivity since beginning of its growth as observed at the age of five, 10 and, 15 years. Acacia nilotica had highest average girth at breast height (60.5 cm) and stand biomass (161 Mg ha^-1) in spite of its lowest plants survival after 15 years of growth. A. auriculiformis ranked next to it with 131 Mg ha^-1 productivity. Basal area ranged from 12.8 to 23 m² ha^-1 in different species. P. duke performed poorly as it had only 71 Mg ha^-1 of biomass. Average leaf area per hectare in different species ranged from4,129 m² ha^-1 to 16,090 m² ha^-1 after 15 years of growth. A. nilotica also showed superiority in respect to energy content in woody biomass (2,467 GJ ha^-1) and fuel wood value index (1694) as compared to the other two species. At the age of 15 years, litter accumulation over the soil surface resulted in marked reductions in soil pH, electrical conductivity, bulk density and sodium content, and increase in soil porosity, organic carbon and nitrogen content, particularly in the uppermost layer of the mineral soil (0-5 cm). A. nilotica exhibited greater efficiency in terms of soil amelioration followed by A. auriculiformis. The relative ranking of three species was A. nilotica > A. auriculiformis > P. duke, respectively. This indicated greater promise of A. nilotica for biomass production, energy harvest, and soil amelioration on degraded soil sites. Matching tree species to soil conditions needs serious considerations in order to expand site specific afforestation programs and to ameliorate vast tracts of degraded soil sites.     

The population dynamics and productivity of <Emphasis Type="Italic">Acacia pennatula</Emphasis> in the pasturelands of the Nature Reserve Mesas de Moropotente,Estelí, Nicaragua

Acacia pennatula trees are the most conspicuous woody species in the pasturelands of the Nature Reserve Mesas de Moropotente, Estelí, Nicaragua. Cattle ranchers keep A. pennatula because it produces fence posts, forage (pods) and firewood. A population projection matrix model was developed to: (1) estimate the sustainable harvest (H) of fence posts at different tree population densities, (2) explore the range of recruitment (R), and survival and growth of both saplings and small poles compatible with current population density, and (3) determine how much carbon is stored in the soil-pasture-tree system. Acacia pennatula trees take 40 years to reach H size (D₃₀ ≥ 30 cm). Estimated sustainable H from current tree population density is 1.8l7 trees ha⁻¹ year⁻¹, yielding 2.8 large and 11.2 regular size fence posts ha⁻¹ year⁻¹. This annual output easily satisfies the needs of a typical 100 ha cattle ranch in the study area. Current population density is congruent with very low R (<100 saplings ha⁻¹ year⁻¹), very low survival rates (<0.30%) and/or retarded D₃₀ growth of saplings and small poles. Total carbon in tree biomass was only 37 Mg ha⁻¹. Cattle ranchers have learned to harness the invasive nature of the species to obtain valuable tree products for farm use or sale.     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) or poro (Erythrina poeppigiana) in Costa Rica

Predictive models were developed for Cordia alliodora branch and Theobroma cacao branch or leaf biomass,based on branch basal areas (r² 0.79) but the model of C. alliodora leaf biomass, although significant, was of very low accuracy (r² = 0.09) due to annual leaf fall. At age 10 years, shade tree stem biomass accounted for 80% of the total above-ground biomass of either tree. However, between the ages of 6 and 10 years, the biomass increment of T. cacao branches (3–4t.ha^–1.a^–1) was similar to that of the shade tree stems. During the same period, the net primary productivity was 35 and 28 t.ha^–1.a^–1, for the Erythrina poepigiana and and C. alliodora systems, respectively.Cocoa production under either of the shade trees C. alliodora or E. poeppigiana was 1000 kg.ha^–1.a^–1 (oven-dry; ages 6–10 yr). During the same period, C. alliodora timber production was 9 m³.ha^–1.a^–1 whilst the leguminous shade tree E. poeppigiana does not produce timber. Litterfall over the same 5 years, including crop and/or shade tree pruning residues, averages 11 and 23 t.ha^–1.a^–1, respectively. The main difference was due to E. poeppigiana pruning residues (10t.ha^–1.a^–1).Soil organic material reserves (0–45 cm) increased over 10 years from 198 to 240 t.ha^–1 in the E. poeppigiana plots and from 168–184 t.ha^–1 in the C. alliodora plots. These values, together with the productivity indices presented, provide evidence that the systems are sustainable.For economic reasons, the use of C. alliodora is recommended under the experimental conditions. however, on less fertile soils without fertilization, the greater biomass and hence nutrient return to the soil surface under E. poeppigiana, might make this the preferable shade tree.     

Symbiotic properties and Rhizobium requirements for effective nodulation of five tropical dry zone acacias

Five tropical dry zone acacias were inoculated with three fast-growing Rhizobium strains and four slow-growing Bradyrhizobium strains. After two months of growth in the greenhouse, the plants were harvested and their shoot height and dry weight, nodule number and dry weight, acetylene reduction activity, and total shoot nitrogen were determined. The results showed that: (1) Acacia polyacantha (being evaluated for the first time) was promiscuous, nodulating indiscriminately with Rhizobium and Bradyrhizobium strains. (2) Faidherbia albida and Acacia holosericea (that were previously known to nodulate with Bradyhizobium strains only) nodulated with Rhizobium strains as well and (3) Acacia senegal and Acacia nilotica that were previously known to be nodulated exclusively by Rhizobium strains only were nodulated with both genera.

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Resumé Cinq espèces d'acacias de zone tropicale séche ont été inoculées avec trois souches de Rhizobium à croissance rapide et quatre souches de Bradyrhizobium à croissance lente. Aprés deux mois de croissance en serre, les plants ont été récoltés et lahauteur et le poids sec de parties aériennes, le nombre et le poids sec de nodules, l'activité réductrice de l'acétylène et la quantité d'azote total contenue dans les parties aériennes ont été déterminés. Les résultats ont montrés que: (1) Acacia polyacantha (étudié, pour la prémière fois) est une espèce qui nodule indifféremment avec des souches de Rhizobium et de Bradyrhizobium. (2) Faidherbia albida et Acacia holosericea nodulaient également indifféremment avec des souches de Rhizobium et de Bradyrhizobium, contrairement à des études antérieures qui montraient que ces espèces nodulaient exclusivement avec des souches de Bradyrhizobium. (3) De même, Acacia senegal et Acacia nilotica nodulent avec les deux types de souches alors qu'elles étaient connues pour être nodulées exclusivement par des souches de Rhizobium.