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1.
Integration of shrubs into the smallholder crop-rangeland-livestock farming systems in non-tropical dry areas could reduce feed gaps, rangeland degradation and desertification, but data on yield and fodder quality of most native and exotic shrubs are scanty. The study aimed at identifying shrubs for dryland agroforestry based on agronomic and fodder quality attributes. Fodder and wood yield, percent fodder (FBR) and fodder quality of 26 non-legume shrubs were determined from 6 to 8 months regrowth in north-west Syria. Seed yield was estimated from plants that were not cut. Fodder (31–87 Mg DM ha−1), wood (16-2064 Mg DM ha−1) and seed (0-132 Mg DM ha−1) yield, FBR (24–87%), fodder concentrations of crude protein (69–195 g kg−1.), acid detergent lignin (ADL) (24–109 g kg−1), acid detergent fiber (ADF) (102–267 g kg−1), neutral detergent fiber (NDF) (214–526 g kg−1), in vitro organic matter digestibility (IVOMD) (391–526 g kg−1), and in vitro gas production after 24 h of incubation (25–39 ml 200 mg−1 DM) varied (P < 0.05) among the shrubs. Atriplex halimus-halimus and A. herba-alba from Spain, A. canescens, A. ploycarpa and A. lentiformis from USA, A. halimus and A. herba-alba from Syria and A. nummularia from Australia and South Africa had greater potential for development of dryland agroforestry technologies. The promising shrubs could be integrated into the rangeland-crop-livestock systems in non-tropical dryland environs to provide fodder, fuel-wood, shade, medicine, stabilize sand-dunes, and sequester carbon; thereby contributing to mitigation of rangeland degradation and global warming; if major constraints to adoption of fodder trees such as agronomic problems, low multipurpose value, land shortage and quality seed supply could be overcome.  相似文献   

2.
Fine root and nodule production and turnover in pruned 2- and 8-yr-old Erythrina poeppigiana (Walp.) O.F. Cook trees were estimated under humid tropical conditions by applying the compartment flow model (CFM) to fine root and nodule biomass and necromass measured in sequentially taken core samples. Shoot pruning intensities compared were complete pruning (i.e., complete removal of shoots) and partial pruning (i.e., retention of one branch on the pruned stump). The CFM provided reasonable estimates of nodule dynamics but did not apply to fine root data. Over a five-month observation period, nodule production in completely and partially pruned 2-yr-old trees was 58.2 and 115 g tree–1, respectively, and the corresponding values in 8-yr-old trees were 26.8 and 26.4 g tree–1. Senescent nodules and fine roots pass to soil organic matter via decomposition. Partially and completely pruned 2-yr-old trees added 95.4 and 50.4 g tree–1 decomposed nodules to soil, respectively. The respective value for 8-yr-old trees were 26.7 and 36.5g tree–1. Nodule and fine root turnover was compensated for by new production at 10–14 weeks after pruning. The retention of a branch on the pruned E. poeppigiana tree stump allows better fine root and nodule survival, and enhances tree biomass production.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

3.
We investigated variation in forage production, in sacco dry matter (DM) and nitrogen (N) degradations, and in vitro gas production characteristics of four Albizia (A. lebbeck N 864, A. procera N 865, A. saman N 825) and Paraserianthes falcataria (N 783) provenances obtained from The Nitrogen Fixing Tree Association. After one year of establishment forage production was assessed by harvesting trees at 0.5 m above ground in the main wet (April–August) minor-wet (September–November) and dry (December–March) seasons at Ibadan, southwestern Nigeria. Forage samples from the main-wet and dry seasons were incubated for 6, 12, 48, 72 and 96 h in rumen-fistulated cattle to estimate in sacco DM and N degradation characteristics. In vitro gas production was estimated over 3, 6, 12, 24, 48, 72 and 96 h of incubation. Forage production of A. procera was significantly higher than the other species in all seasons. Cell-wall components were comparatively higher in A. procera than the other species. Potential DM and N degradations of A. lebbeck and A. saman were significantly higher than P. falcataria and A. procera. The results suggest that A. lebbeck and A. saman provenances used in this study have relatively higher feed value than A. procera and P. falcataria.  相似文献   

4.
Little information is available on soil respiration and microbial biomass in soils under agroforestry systems. We measured soil respiration rate and microbial biomass under two age classes (young and old) of a pecan (Carya illinoinensis) — cotton (Gossypium hirsutum) alley cropping system, two age classes of pecan orchards, and a cotton monoculture on a well-drained, Redbay sandy loam (a fine-loamy, siliceous, thermic Rhodic Paleudult) in southern USA. Soil respiration was quantified monthly during the growing season from May to November 2001 using the soda-lime technique and was corrected based on infrared gas analyzer (IRGA) measurements. The overall soil respiration rates ranged from 177 to 776 mg CO2 m–2 h–1. During the growing season, soil respiration was higher in the old alley cropping system than in the young alley cropping system, the old pecan orchard, the young pecan orchard, and the monoculture. Microbial biomass C was higher in the old alley cropping system (375 mg C kg–1) and in the old pecan orchard (376 mg C kg–1) compared to the young alley cropping system (118 mg C kg–1), young pecan orchard (88 mg C kg–1), and the cotton monoculture (163 mg C kg–1). Soil respiration was correlated positively with soil temperature, microbial biomass, organic matter, and fine root biomass. The effect of alley cropping on soil properties during the brief history of alley cropping was not significant except in the old systems, where there was a trend of increasing soil respiration with short-term alley cropping. Over time, different land use and management practices influenced soil properties such as soil temperature, moisture, microbial biomass, organic matter, and fine root biomass, which in turn affected the magnitude of soil respiration. Our results suggest that trees in agroforestry systems have the potential to enhance soil fertility and sustainability of farmlands by improving soil microbial activity and accreting residual soil carbon.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

5.
Three browse species, Afzelia africana Sm., Khaya senegalensis (Desv.) A. Juss., and Pterocarpus erinaceus Poir. were investigated as agroforestry system components in a subhumid zone of West Africa. The foliation, flowering and fruiting of ten trees per species were recorded every 15 days for 2 years. The total foliage biomass at maximum availability was determined by complete pruning of 75 trees. The chemical composition of the foliage and the proportion of trees pruned on the pasture were determined. The phenological phases of the species began in the dry season and ended at the end of the rainy season. Afzelia africana and Pterocarpus erinaceus were totally defoliated during 2–6 weeks while K. senegalensis replaced the foliage progressively and earlier. The crude protein content was significantly different (123 g, 102 g and 92 g kg−1 dry matter (DM) for Afzelia africana, Pterocarpus erinaceus and K. senegalensis, respectively). The foliage biomass per tree of K. senegalensis, Pterocarpus erinaceus and Afzelia africana differed significantly (41 kg, 30 kg and 21 kg DM ha−1, respectively) while Pterocarpus erinaceus had the highest available foliage biomass per ha. The trees of Afzelia africana were intensively pruned. There was a significant relationship found between foliage biomass and circumference of the crown for Afzelia africana (R 2 = 82%) and Pterocarpus erinaceus (R 2 = 81%). Relationships were also found between circumference of the branches and foliage biomass. In conclusion, the trees are important potential fodder and nitrogen sources for animals in the agrosilvopastoral system and the phenological differences make the fodder available during a long period of time.  相似文献   

6.
Besides aboveground interactions, pruning of trees may also modify their rooting pattern for which a better understanding is needed for the optimisation of agroforestry systems. Thus, variation in fine root (d 2 mm) distribution of pruned trees and crops were assessed during three cropping seasons by sampling soil layers at 10 cm intervals up to 50 cm and at four distances from tree trunk. Three crown pruning treatments (totally-pruning, half-pruning and no-pruning) were applied to karité (Vitellaria paradoxa) and néré (Parkia biglobosa). In 1999, 59% (0.477 cm cm–3) and 69% (0.447 cm cm–3) of fine roots for karité and néré respectively occurred in the upper 20 cm with a significant decrease in root length density with soil depth. However, in 2000, totally-pruned trees of néré and karité showed 32% (0.051 cm cm–3) and 34% (0.078 cm cm–3) of their density in the upper 20 cm whereas root distribution in 2001 was similar to that of 1999. Thus, pruning to reduce belowground competition for the benefit of associated crops can be recommended in the light of the temporary reduction of root density in crop rooting zone and consequently the increase in crop production.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

7.
Tree pruning is a common management practice in agroforestry for mulching and reducing competition between the annual and perennial crop. The below-ground effects of pruning, however, are poorly understood. Therefore, nutrient dynamics and root distribution were assessed in hedgerow plantings of Acacia saligna (Labill.) H.L. Wendl. after tree pruning. Pruning to a height of 1.5 m was carried out in March and September 1996. In July and October 1996, the fine root distribution (< 2 mm) and their carbohydrate contents were determined at three distances to the tree row by soil coring. At the same time, foliar nutrient contents were assessed, whereas nutrient leaching was measured continuously. The highest root length density (RLD) was always found in the topsoil (0–0.15 m) directly under the hedgerow (0–0.25 m distance to trees). Pruning diminished the RLD in the acacia plots at all depths and positions. The relative vertical distribution of total roots did not differ between trees with or without pruning, but live root abundance in the subsoil was comparatively lower when trees were pruned than without pruning. In the dry season, the proportion of dead roots of pruned acacias was higher than of unpruned ones, while the fine roots of unpruned trees contained more glucose than those of pruned trees. Pruning effectively reduced root development and may decrease potential below-ground competition with intercropped plants, but the reduction in subsoil roots also increased the danger of nutrient losses by leaching. Leaching losses of such mobile nutrients as NO3– were likely to occur especially in the alley between pruned hedgerows and tended to be higher after pruning. The reduced size of the root system of pruned acacias negatively affected their P and Mn nutrition. Pruning also reduced the function of the trees as a safety net against the leaching of nutrients for both NO3– and Mn, though not for other studied elements. If nutrient capture is an important aim of an agroforestry system, the concept of alley cropping with pruning should be revised for a more efficient nutrient recycling in the system described here.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

8.
Latin American pastures usually include trees that may be important in sustaining productivity and conserving resources and biodiversity. A participatory survey of trees in seasonally dry pastures of 54 farms in the Caribbean region of Colombia, followed by cluster and correlation analyses, revealed a multistrata configuration. Trees of large stature (e.g., Tabebuia rosea, Albizia caribaea and Sterculia apelata) provided shade and produced timber. The most important fodder trees were those of medium stature (Albizia saman, Guazuma ulmifolia, and Cassia grandis) that produced fruits or pods, while other species were managed as shrubs producing green leaf fodder (e.g., Crescentia cujete and Gliricidia sepium, which was also ubiquitous as living fence posts). Trees were present on between 26 and 69% of the pastures on each farm, at densities varying from less than 3 to more than 50 trees ha−1. There were more trees in drier areas, of lower fertility, with extensive grazing, where milk as well as meat was produced. Most farmers planted timber trees, encouraged regeneration of fodder trees, and knew about fodder species preferences of cattle and the effects of trees on pasture and animal productivity. Their knowledge of tree phenology was less certain and varied even amongst farmers in similar locations. There is scope to develop silvopastoral systems with woody species familiar to farmers, but it is critical to determine how important different vegetation strata are for sustainability of cattle production. An experiment has been established to achieve this, with treatments based on an analysis of how trees are presently used on farms in the region. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

9.
The effect of pruning all branches (complete pruning) or retaining one branch (partial pruning) on the dynamics of nitrogen cycling in aboveground biomass, nitrogen supplying power of an amended Eutric Cambisol, and fine root length, was studied in an Erythrina poeppigiana (Walp.) O.F. Cook—tomato (Lycopersicon esculentum Mill.) alley cropping practice in Turrialba, Costa Rica during 1999–2000. Over the 1 year pruning cycle, in which trees were completely or partially pruned four times, respective aboveground biomass production was 4.4 Mg or 7 Mg ha−1 (2-year-old trees) and 5.5 Mg or 9 Mg ha−1 (8-year-old trees); N cycled in aboveground biomass was 123 kg or 187 kg ha−1 (2-year-old trees) and 160 kg or 256 kg N ha−1 (8-year-old trees); mean fine root length was 489 or 821 m (2-year-old-trees), 184 or 364 m per tree (8-year-old-trees). Pruning intensity did not significantly affect net N mineralisation and net nitrification rates during the tomato-cropping season. For the tomato crop, pre-plant mean net N mineralisation rate of 2.5 mg N kg−1 soil day−1 was significantly lower than 16.7 or 11.6 mg N kg−1 soil day−1 at the end of vegetative development and flowering, respectively. Mean net nitrification rates of 3.5, and 4.3 mg N kg−1 soil day−1, at pre-plant and end of vegetative development, respectively, were significantly higher than 0.3 mg N kg−1 soil day−1 at end of flowering. In humid tropical low-input agroforestry practices that depend on organic inputs from trees for crop nutrition, retention of a branch on the pruned tree stump appears to be a good alternative to removal of all branches for reducing N losses through higher N cycling in aboveground biomass, and for conserving fine root length for higher N uptake, although it might enhance competition for associated crops.  相似文献   

10.
Water is the most limiting factor for plant production in arid to semiarid regions. In order to overcome this limitation surface runoff water can be used to supplement seasonal rainfall. During 1996 we conducted a runoff irrigated agroforestry field trial in the Turkana district of Northern Kenya. The effects of two different Acacia saligna (Labill.) H. Wendl. tree planting densities (2500 and 833 trees per ha), tree pruning (no pruning vs. pruning) and annual intercrops (no intercrop vs. intercrop: Sorghum bicolor (L.) Moench during the first season and Vigna unguiculata (L.) Walp. during the second season) on water use were investigated. The annual crops were also grown as monocrops. Water consumption ranged from 585 to 840 mm during the first season (only treatments including trees). During the second season, which was shorter and the plants relied solely on stored water in the soil profile, water consumption was less than half of that during the first season. Highest water consumptions were found for non-pruned trees at high density and the lowest were found for the annual crops grown as monocrops. Tree pruning decreased water uptake compared to non-pruned trees but soil moisture depletion pattern showed complementarity in water uptake between pruned trees and annual intercrops. The highest values of water use efficiency for an individual treatment were achieved when the pruned trees at high density were intercropped with sorghum (1.59 kg m–3) and cowpea (1.21 kg m–3). Intercropping and high tree density increased water use efficiency in our runoff agroforestry trial. We ascribe the observed improvement in water use efficiency to the reduction of unproductive water loss from the bare soil.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

11.
Green leaf biomass of Tithonia diversifolia is high in nutrients and recognised as a potential source of nutrients for crops. We conducted a field survey in western Kenya to determine the variation in leaf nutrient concentrations in tithonia grown in naturalised hedges and agricultural fields, and to examine whether leaf nutrient concentrations were related to soil nutrient status. Leaf P and K concentrations were higher in naturalised hedges (3.2 g P kg–1 and 35 g K kg–1) than in unfertilised fields (2.2 g P kg–1 and 23 g K kg–1). The critical level of 2.5 g P kg–1 for net P mineralisation was exceeded by > 90% of the leaves from hedges, but by only 14% from unfertilised fields. Leaf P and K concentration increased linearly with increasing natural logarithm of anion resin extractable soil P and exchangeable soil K, respectively. However, at the same levels of soil available P and K, field-grown tithonia consistently produced lower leaf P and K concentrations than that grown in hedges. This study indicates that biomass from tithonia planted on nutrient-depleted soils would be a less effective source of P and K, via biomass transfer, than tithonia from naturalised hedges.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

12.
Tree and windbreak species considered for the Southern Sahelian Zone (SSZ) of West Africa have to be evaluated following multiple criteria such as fast establishment, shelter efficiency, production of feed for livestock, and firewood. An on-station experiment was conducted on a sandy soil in southwest Niger between 1988 and 1993 to assess the establishment, growth, nutritive, and calorific values of seven species considered for windbreaks:Andropogon gayanus, Bauhinia rufescens, Acacia holosericea, Acacia nilotica, Acacia senegal, Faidherbia albida, andAzadirachta indica. Mortality and stem diameter were monitored twice a year. From 20 months after planting (MAP) onwards, species were annually trimmed to 2 m height and to 1 m sidewards of the main stem. Fresh and dry weight of leaves, twigs, wood, and fruits were recorded. Leaves were analyzed for crude protein (CP) and metabolizable energy (ME) content. Wood was analyzed for its gross calorific value and its ash content. At 56 MAP, all species had less than 5% morality, except forA. holosericea, which had a mortality rate of 15.9%.A. indica andA. holosericea showed the highest stem diameter among species with 12.2 and 11.8 cm, respectively, at 56 MAP.A. senegal had the highest dry matter production with 22.3 t ha–1 at 56 MAP, followed byA. indica (12.0 t ha–1),A. holosericea (11.7 t ha–1) andB. rufescens (11.2 t ha–1), butA. holosericea was most productive at earlier harvests. OnlyA. senegal (6.4 t ha–1) andA. indica (5.1 t ha–1) had a significant wood production, whereasA. holosericea (5.7 t ha–1) had the highest phyllodes production. Leaves ofA. senegal andA. indica had highest CP contents of 258 and 214 g kg–1, respectively. The leaves of all species exceptA. gayanus had a higher CP:ME ratio than natural pasture in the region. The calorific values of firewood did not differ significantly among the species.A. nilotica, the species with one of the lowest firewood production, had the highest Fuelwood Value Index of 6.6. The choice of species for planting trees and windbreaks in the SSZ must be oriented along these criteria. Further research should be directed towards cost-benefit analyses, land tenure and property rights in combination with surveys on local knowledge of rural people.  相似文献   

13.
Fine root dynamics of shaded cacao plantations in Costa Rica   总被引：1，自引：0，他引：1  
Root turnover may contribute a significant proportion of recycled nutrients in agroforestry systems and competition between trees and crops for nutrients and water may depend on temporal fine root regrowth patterns. Fine root biomass ( 2 mm) and fine root productivity were measured during one year in plantations of cacao (Theobroma cacao) shaded by Erythrina poeppigiana or Cordia alliodora planted on a deep alluvial soil in Turrialba, Costa Rica. Fine root biomass of approximately 1.0 Mg ha–1 varied little during the year with maximum values at the beginning of the rainy season of 1.85 Mg ha–1 in the cacao-C. alliodora system compared to 1.20 Mg ha–1 for cacao-E. poeppigiana. Fine root productivity of C. alliodora and E. poeppigiana (maximum of 205 and 120 kg ha–1 4 week–1, respectively) was greatest at the end of the rainy season, while for cacao it was greatest at the beginning of the rainy season (34–68 kg ha–1 4 week–1), which suggests that if nutrient competition occurs between the shade trees and the cacao, it could be minimized by early fertilization during the beginning of the rains immediately after pruning the shade trees. Annual fine root turnover was close to 1.0 in both systems. Assuming that fine root biomass in these mature plantations was constant on an annual basis, nutrient inputs from fine root turnover were estimated as 23–24 (N), 2 (P), 14–16 (K), 7–11 (Ca) and 3–10 (Mg) kg ha–1 year–1, representing 6–13% and 3–6% of total nutrient input in organic matter in the C. alliodora and E. poeppigiana systems, respectively.  相似文献   

14.
The effects of spacings between hedgerows (alley widths) and the spacings of trees within hedgerows ofGliricidia sepium on growth and grain yield of maize were investigated at Senehun in southern Sierra Leone. Four between-row spacings (2, 4, 6 and 8 m) were combined with three within-row spacings (0.25, 0.50 and 1.00 m) in a split block design. Maize, at densities of 20,000, 40,000 and 53,333 plants ha–1, was established in the alleys and also as pure crops. N, P and K fertilizers were applied to all plots before pruning of the trees began. When pruning started, only the pure maize plots received fertilizer; prunings from the hedgerows were returned to the appropriate alleys in the other plots.Plots with the highest maize populations consistently gave the best yields before pruning started, but lower populations gave improved yields after pruning. Yields of maize increased with increasing alley widths before the start of pruning, after which the narrower alleys of 2 and 4 m outyielded the wider ones by almost double, probably because of the large amount of nutrients applied in prunings. Lack of light limited grain yields before the start of pruning, when there was some shading by the hedgerows. Alleys of 2–4 m wide, planted no closer than 0.50 m within rows, resulted in more than twice the yields of maize than in the 8-m alleys planted at 0.25 m within rows, once the hedgerows were well established and were being managed.  相似文献   

15.
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.  相似文献   

16.
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.  相似文献   

17.
To quantify the nitrogen (N) use by Pinus densiflora trees growing on an infertile lava surface, N pools, N requirement and N uptake through fine roots and N deposition from the atmosphere were estimated. The N requirement and the N uptake of fine roots were 55.5kgNha–1year–1 and 39.7kgNha–1, respectively. Thus, the ratio of N uptake to N requirement of the fine roots was 71.5%. Including fine-root contribution, the total N requirement of the P. densiflora trees was 98.6kgNha–1year–1, and the total N uptake was 64.2kgNha–1year–1. Thus, the N uptake of the P. densiflora trees was 64.1% of the N requirement, indicating that P. densiflora trees growing on an infertile lava surface obtain some of their N from below-ground organic material layers every year and the contribution of N storage in trees for their growth is not any higher than indicated in previous reports that excluded fine-roots contribution. The wet N deposition of our research forest was only 5.8% of the N requirement of the P. densiflora trees and only 8.9% of the N uptake. Movement of the below-ground organic material layer N concentrations in the F- and L-layers coincides with needle development and fine-root growth, suggesting the possibility that P. densiflora trees extract N from the organic N of those layers for growth.  相似文献   

18.
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.  相似文献   

19.
The consumption of the pine needles and the stripping of bark by sheep grazing annual pastures in three open stands of P. radiata and one of P. pinaster were measured. The P. radiata were four years old and the densities were 250, 500 and 750 trees ha-1. The P. pinaster included two, three and four year-old trees and the density was 440 trees ha–1.Needles were eaten immediately after the sheep were admitted and this continued throughout the year. Within ten weeks of the start of winter grazing, sheep stocked at 7–10 ha–1 had eaten about half of the accessible needles on both species where densities were less than500 trees ha–1. The estimated consumption was about 260 g sheep–1 day–1 for the P. radiata. Bark stripping then commenced and continued throughout spring and summer on most plots. In some plots at low tree density, bark was stripped from more than 35% of the trees. In denser stands, needle consumption per tree was less and bark was stripped from less than 5% of the trees.Bark damage was most common on the smaller trees, and severity of stripping was negatively correlated with tree size. Of all the trees with bark damage, 22% of the P. pinaster and 14% of the P. radiata had more than half of the stem circumference stripped. A number of these will probably suffer both stem distortion and growth retardation, and some may die.Methods of reducing the incidence of bark damage are discussed.  相似文献   

20.
We tested the hypothesis that shallow-rooted crops and deep-rooted trees will share the available water in a complementary manner, when grown together, in a field trail in the Turkana district of northern Kenya during 1994 to 1996. Such studies have been few in dryland agroforestry. The effects of two different Acacia saligna (Labill.) H. Wendl. tree planting densities (2500 and 833 trees per ha), tree pruning (no pruning vs. pruning) and annual intercrops (no intercrop vs. intercrop) on total biomass production and their interactions were tested. In 1996 Sorghum bicolor (L.) Moench was used during the first vegetation period and Vigna unguiculata (L.) Walp. during the second. We used naturally generated runoff water for irrigation to supplement low rainfall amounts typical for the area. High biomass production (> 13 t ha–1 over a two year period) was observed irrespective of intercropping of pruned trees or sole tree stands. Although the pruning treatment reduced total tree biomass yields by a quarter, the introduction of annual intercrops after the pruning of trees outweighed this loss. The yields of the intercrops in the pruned tree treatments were similar to their yields when grown as monocrops. The calculation of land equivalent ratios showed overyielding for intercropped, pruned systems. The high values for LER (1.36 at low and 1.47 at high density of trees) indicate that there is complementarity in resource use between the different species.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

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