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1.
The sustainability of cocoa growing systems in the humid tropics is debatable. Socio-economic and technical data were obtained
from 1,171 cocoa farmers and 1,638 cocoa plantations to assess the long-term dynamics of cocoa agroforests in central Cameroon
since the beginning of the twentieth century. On-site, we estimated the age of the cocoa trees and measured their density
in a sub-sample of 402 cocoa plantations. We inventoried associated woody species in 45 cocoa plantations from this sub-sample.
Our results revealed a high Shannon index for the cocoa plantations (2.6) and showed that an average of 25 tree species per
cocoa plantation had been planted with the cocoa trees at a density of 120 trees ha−1. Surveys indicated that there had been no mineral fertilization. Nearly 70% of the cocoa agroforests were over 40 years old,
and all farmers continuously regenerated their cocoa tree stands. Irrespective of the cocoa plantation age, the cocoa tree
density remained over 1,000 plants ha−1, and fermented dried cocoa yields were 255 kg ha−1 on average. Cocoa agroforests occupied 60% of the cultivated area on farms and cocoa sales accounted for 75% of total farm
income. Almost a third of the farmers were from the area and under 40 years old. In conclusion, our results show that the
farmers’ agroforestry practices, in addition to the fact that the cocoa tree stands were continuously regenerated and passed
down between generations of farmers, could explain the long-term dynamics of cocoa agroforests in central Cameroon. 相似文献
2.
This study examined the hypothesis that incorporation of Gliricidia sepium (Jacq.) Walp.) (gliricidia), a fast-growing, nitrogen-fixing tree, into agroforestry systems in southern Malawi may be used
to increase the input of organic fertilizer and reduce the need for expensive inorganic fertilizers. The productivity of maize
(Zea mays L.), pigeonpea (Cajanus cajan L.) and gliricidia grown as sole stands or in mixed cropping systems was examined at Makoka Research Station (latitude 15°
30′ S, longitude 35° 15′ E) and a nearby farm site at Nazombe between 1996 and 2000. Treatments included gliricidia intercropped
with maize, with or without pigeonpea, and sole stands of gliricidia, maize and pigeonpea. Trees in the agroforestry systems
were pruned before and during the cropping season to provide green leaf manure. Maize yields and biomass production by each
component were determined and fractional light interception was measured during the reproductive stage of maize. Substantial
quantities of green leaf manure (2.4 to 9.0 Mg ha−1 year−1) were produced from the second or third year after tree establishment. Green leaf manure and fuelwood production were greatest
when gliricidia was grown as unpruned sole woodlots (c. 8.0 and 22 Mg ha−1 year−1 respectively). Improvements in maize yield in the tree-based systems also became significant in the third year, when c. 3.0 Mg ha−1 of grain was obtained. Tree-based cropping systems were most productive and exhibited greater fractional light interception
(c. 0.6 to 0.7) than cropping systems without trees (0.1 to 0.4). No beneficial influence of pigeonpea on maize performance
was apparent either in the presence or absence of gliricidia at either site in most seasons. However, as unpruned gliricidia
provided the greatest interception of incident solar radiation (>0.9), coppicing may be required to reduce shading when gliricidia
is grown together with maize. As pigeonpea production was unaffected by the presence of gliricidia, agroforestry systems containing
gliricidia might be used to replace traditional maize + pigeonpea systems in southern Malawi.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
The importance of agroforestry systems in CO2 mitigation has become recognized worldwide in recent years. However, little is known about carbon (C) sequestered in poplar
intercropping systems. The main objective of this study is to compare the effects of three poplar intercropping designs (configuration
A: 250 trees ha−1; configuration B: 167 trees ha−1 and configuration C: 94 trees ha−1) and two intercropping systems (wheat–corn cropping system and wheat–soybean cropping system) on biomass production and C
stocks in poplar intercropping systems. The experiment was conducted at Suqian Ecological Demonstration Garden of fast-growing
poplar plantations in northwestern Jiangsu. A significant difference in C concentration was observed among the poplar biomass
components investigated (P ≤ 0.05), with the highest value in stemwood and the lowest in fine roots, ranging from 459.9 to 526.7 g kg−1. There was also a significant difference in C concentration among the different crop components (P ≤ 0.05), and the highest concentration was observed in the corn ear. Over the 5-year period, the total poplar biomass increased
with increasing tree density, ranging from 8.77 to 15.12 t ha−1, while annual biomass production among the crops ranged from 4.69 to 16.58 t ha−1 in the three configurations. Overall, total C stock in the poplar intercropping system was affected by configurations and
cropping systems, and configuration A obtained the largest total C stock, reaching 16.7 t C ha−1 for the wheat–soybean cropping system and 18.9 t C ha−1 for the wheat–corn cropping system. Results from this case study suggest that configuration A was a relative optimum poplar
intercropping system both for economic benefits and for C sequestration. 相似文献
4.
The conversion of forests to agroecosystems or agroforests comes with many changes in biological and chemical processes. Agroforestry,
a tree based agroecosystem, has shown promise with respect to enhanced system nutrient accumulation after land conversion
as compared to sole cropping systems. Previous research on tropical agroforestry systems has revealed increases in soil organic
matter and total organic nitrogen in the short term. However, research is lacking on long-term system level sustainability
of nutrient cycles and storage, specifically in traditional multi-strata agroforestry systems, as data on both the scope and
duration of nutrient instability are inconclusive and often conflicting. This study, conducted in Ghana, West Africa, focused
on carbon and nitrogen dynamics in a twenty-five year chronosequence of cacao (Theobroma cacao Linn.) plantations. Three treatments were selected as on-farm research sites: 2, 15 and 25-year-old plantations. Soil carbon
(C, to a depth of 15 cm) varied between treatments (2 years: 22.6 Mg C ha−1; 15 years: 17.6 Mg C ha−1; 25 years: 18.2 Mg C ha−1) with a significant difference between the 2- and 15- and the 2- and 25-year-old treatments (p < 0.05). Total soil nitrogen in the top 15 cm varied between 1.09 and 1.25 Mg N ha−1 but no significant differences were noted between treatments. Soil nitrification rates and litter fall increased significantly
with treatment age. However, photosynthetically active radiation (PAR) and soil temperature showed a significant decrease
with age. No difference was found between decay rates of litter at each treatment age. By 25 years, system carbon sequestration
rates were 3 Mg C ha−1 y−1, although results suggest that even by 15 years, system-level attributes were progressing towards those of a natural system. 相似文献
5.
Homegardens are one of the oldest forms of managed land use systems characterised by high diversity and complexity of their
species structure which in turn contribute to efficient nutrient cycling. Litterfall and decomposition are the two major processes
that replenish the soil nutrient pools and endow sustainability to these agroforests. A study was carried out in the village
Dargakona, Barak Valley, northeast India to understand the pattern of litter production and litter decomposition in the traditional
homegardens. Annual litter production was 6.27 Mg ha−1 with a bimodal distribution pattern and the nitrogen input through litterfall accounted for 48.17 kg ha−1 year−1. Litter decomposition studies for ten multipurpose trees revealed Sapium baccatum and Toona ciliata to be the most labile litter species and the decay rate coefficients varied among the species with differing rates of nutrient
release pattern. Such studies can provide information regarding the litter quality of indigenous tree species and help validate
farmers planting and management of multiple species which allows for efficient nutrient cycling of the system. 相似文献
6.
Sumatra’s Rubber Agroforests: Advent, Rise and Fall of a Sustainable Cropping System 总被引:2,自引:1,他引:1
Until the end of the nineteenth century primary forests covered nearly all the island of Sumatra. The first valorisation of
this natural resource was hunting and gathering activities, followed by and later associated with swidden cultivation of upland
rice. The industrial revolution in Europe and North America in the 1950s created increasing demand for rubber. Answering this
new market opportunity, farmers introduced rubber seedlings in their swiddens amidst the upland rice. By doing so, they invented
a new cropping system, i.e. rubber agroforests. Thanks to the continuously increasing demand for rubber by the developing
industry, rubber agroforests spread over Sumatra’s eastern peneplains until the 1990s. Forest conversion to rubber agroforests
conserves a high level of forest biodiversity and the agroforests act as a buffer zone around national parks. But with growing
demographic pressure, market integration and household monetary needs, agroforests are increasingly endangered. New cropping
systems have appeared and challenge agroforests’ dominance in the landscape. Since the mid-twentieth century, rubber monospecific
plantations have been competing for land, with an undoubtedly higher profitability than agroforests. More recently, oil palm
plantations have spread over the island, quickly becoming the new challenger to rubber agroforestry. Nevertheless, the international
community shows more and more interest in forest and biodiversity conservation. Forest cover in Jambi province has nearly
disappeared over the past 30 years. The only way to save the remnants of forests and agroforests seems to be the creation
of market incentives through conservation programs such as reducing emissions from deforestation and degradation. 相似文献
7.
Coffee (Coffea canephora var robusta) is grown in Southwestern Togo under shade of native Albizia adianthifolia as a low input cropping system. However, there is no information on carbon and nutrient cycling in these shaded coffee systems.
Hence, a study was conducted in a mature coffee plantation in Southwestern Togo to determine carbon and nutrient stocks in
shaded versus open-grown coffee systems. Biomass of Albizia trees was predicted by allometry, whereas biomass of coffee bushes was estimated through destructive sampling. Above- and
belowground biomass estimates were respectively, 140 Mg ha−1 and 32 Mg ha−1 in the coffee–Albizia association, and 29.7 Mg ha−1 and 18.7 Mg ha−1 in the open-grown system. Albizia trees contributed 87% of total aboveground biomass and 55% of total root biomass in the shaded coffee system. Individual
coffee bushes consistently had higher biomass in the open-grown than in the shaded coffee system. Total C stock was 81 Mg ha−1 in the shaded coffee system and only 22.9 Mg ha−1 for coffee grown in the open. Apart from P and Mg, considerable amounts of major nutrients were stored in the shade tree
biomass in non-easily recyclable fractions. Plant tissues in the shaded coffee system had higher N concentration, suggesting
possible N fixation. Given the potential for competition between the shade trees and coffee for nutrients, particularly in
low soil fertility conditions, it is suggested that the shade trees be periodically pruned in order to increase organic matter
addition and nutrient return to the soil.
An erratum to this article can be found at 相似文献
8.
The potential contribution of agroforestry systems to the management and genetic resources conservation in iroko (Milicia excelsa), an important and valuable timber tree species in sub-Saharan Africa, is addressed in this paper. The structure and dynamics
of traditional agroforestry systems and the ecological structure of Milicia excelsa populations in farmlands were studied through a survey carried out in 100 farmlands covering the natural range of iroko in
Benin. Forty-five species belonging to 24 plant families were recorded in traditional agroforestry systems. Average tree density
varied from 1 to 7 stems ha−1 with diversity index ranging from 2.6 to 2.9. Milicia excelsa occurred sparsely in agroforestry systems in all regions, with density ranging from 1 to 4 stems ha−1; stand basal area varying from 33.10−4 to 129.10−4 m2 ha−1, and negligible seedling regeneration. However, male and female trees were apparently evenly distributed on farmlands in
all regions (F/M > 0). Iroko trees produced viable seeds with moderate germination rate and early growth (germination rate
22% and height 7.29 cm after 3 months). Suggestions are made regarding optimal densities for iroko conservation in farmlands,
according to farmers’ socioeconomic conditions in different regions, in order to improve traditional agroforestry systems
and their use as biological corridors in conservation of Milicia excelsa genetic resources. 相似文献
9.
E. Y. Raddad O. Luukkanen A. A. Salih V. Kaarakka M. A. Elfadl 《Agroforestry Systems》2006,68(3):193-207
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. 相似文献
10.
Yoshiyuki Kiyono Yukihito Ochiai Yukihiro Chiba Hidetoshi Asai Kazuki Saito Tatsuhiko Shiraiwa Takeshi Horie Visone Songnoukhai Viengmany Navongxai Yoshio Inoue 《Journal of Forest Research》2007,12(5):371-383
In northern Lao People’s Democratic Republic, rising human population has drastically reduced the fallow period of slash-and-burn
agriculture which has led to a considerable decrease in the carbon stock in these communities. We estimated chronosequential
changes in the communities' carbon stocks, and established the relationship between the fallow period and fallow-period-average
carbon stocks in three carbon pools of bamboo-dominated communities in hilly areas of the Luang Prabang Province, northern
Lao People’s Democratic Republic. Based on measurements by destructive sampling, we devised a model and root-to-shoot ratios
for estimating bamboo biomass. In six secondary plant communities established after slash-and-burn cropping, we estimated
community biomass using the above model and others, and measured deadwood and litter stocks. The communities’ biomass and
deadwood significantly increased with time after the last cropping and the former reached about 100 Mg ha−1 after 15 years, whereas litter stocks did not show significant trends over time. Extending the fallow period from 2 to 5 years
would increase fallow-period-average carbon stock from 14.2 to 25.1 Mg C ha−1. The overstory height was significantly correlated with biomass, deadwood, and litter carbon stocks of these communities.
Based on our findings, changes in a community’s carbon stocks can be estimated using the changes in overstory height, which
should be taken into account in future studies to reduce uncertainty in estimating carbon stocks in tropical ecosystems. 相似文献
11.
Land management practices that simultaneously improve soil properties are crucial to high crop production and minimize detrimental
impact on the environment. We examined the effects of crop residues on crop performance, the fluxes of soil N2O and CO2 under wheat-maize (WM) and/or faba bean-maize (FM) rotations in Amorpha fruticosa (A) and Vetiveria zizanioides (V) intercropping systems on a loamy clay soil, in subtropical China. Crop performance, soil N2O and CO2 as well as some potential factors such as soil water content, soil carbon, soil nitrogen, microbial biomass and N mineralization
were recorded during 2006 maize crop cultivation. Soil N2O and CO2 fluxes are determined using a closed-based chamber. Maize yield was greater after faba bean than after wheat may be due to
differences in supply of N from residues. The presence of hedgerow significantly improved maize grain yields. N2O emissions from soils with maize were considerably greater after faba bean (345 g N2O–N ha−1) than after wheat (289 g N2O–N ha−1). However, the cumulated N2O emissions did not differ significantly between WM and FM. The difference in N2O emissions between WM and FM was mostly due to the amounts of crop residues. Hedgerow alley cropping tended to emit more
N2O than WM and FM, in particular A. fruticosa intercropping systems. Over the entire 118 days of measurement, the N2O fluxes represented 534 g N2O–N ha−1 (AWM) and 512 g N2O–N ha−1 (AFM) under A. fruticosa species, 403 g N2O–N ha−1 (VWM) and 423 g N2O–N ha−1 (VFM) under Vetiver grass. We observed significantly higher CO2 emission in AFM (5,335 kg CO2–C ha−1) from June to October, whereas no significant difference was observed among WM (3,480 kg CO2–C ha−1), FM (3,302 kg CO2–C ha−1), AWM (3,877 kg CO2–C ha−1), VWM (3,124 kg CO2–C ha−1) and VFM (3,309 kg CO2–C ha−1), indicating the importance of A. fruticosa along with faba bean residue on CO2 fluxes. As a result, crop residues and land conversion from agricultural to agroforestry can, in turn, influence microbial
biomass, N mineralization, soil C and N content, which can further alter the magnitude of crop growth, soil N2O and CO2 emissions in the present environmental conditions. 相似文献
12.
This long term experiment provides production data for evaluation of combined forestry and livestock systems. Five systems
were established in Pinus radiata planted in 1981 (620 mm average annual rainfall). Sheep were introduced in 1984 and trees were pruned in several lifts. Adjusted
tree stockings were (1) 60 widely spaced trees ha−1, (2) 200 widely spaced trees ha−1, (3) 200 trees ha−1 in five-row belts, (4) 1,090 trees ha−1 (unpruned) and 815 trees ha−1, and (5) no trees (open pasture). Tree growth, wool production, liveweight gain and pasture production were measured. At
year 25, tree diameter under bark at 1.3 m (DBHUB) in Systems 1, 2, 3 and 4 (unpruned) was 46.0, 39.2, 33.5 and 24.1 cm, while
volume of bark-free 6-m butt-logs was 49, 117, 86 and 233 m3 ha−1. Inner rows of System 3 belts contained smaller trees than outer rows. Pruned System 4 trees had slightly greater diameter
than unpruned trees. Pasture production declined with tree stocking and time, due to shading and competition. Wool production
(WP ha−1) and liveweight gain (LWG ha−1) declined linearly from year 9 to 17 with increasing disparity among systems. In 1998 (year 17) WP ha−1 in Systems 1, 2 and 3 was 64, 16 and 43% of that in open pasture. Further analysis is needed to evaluate the financial costs
and returns of various systems under particular rotation lengths and market prices. 相似文献
13.
In Cameroon, cocoa trees are mostly grown in forests and without fertilization. Our aim was to learn more about the temporal
dynamics of soils in cocoa agroforests by comparing young (1–4 years old) and old (over 25 years old) cocoa agroforests. Short
fallow and secondary forest were used as treeless and forest references. The numbers and diversities of soil vesicular arbuscular
mycorrhizal (VAM) fungi on 60 cocoa producing farms in the Central province of Cameroon were assessed based on the classical
morphotyping of spore morphology. We also observed the soil organic matter, nitrogen and major soil nutrients. VAM spore density
was significantly lower in the young cocoa agroforests (16 spores g−1 dry soil) than in the old cocoa agroforests (36 spores g−1 dry soil). Levels in the nearby secondary forest (46 spores g−1 dry soil) were not significantly different from old cocoa. The spore density was significantly highest in the short fallow
(98 spores g−1 dry soil). The Shannon–Weaver index also showed significantly lower biodiversity in young cocoa (0.39) than in old cocoa
agroforests (0.48), secondary forest (0.49) and short fallow (0.47). These observations were supported by significant differences
in the C:N ratio, Ca, Mg, and cation exchange capacity between young and old cocoa agroforests. We concluded that unfertilized
cocoa agroforests could be sustainable, despite a decrease in some soil characteristics at a young stage, due to traditional
land-conversion practices based on selective clearing and burning of secondary forest. 相似文献
14.
Competition for light between hedgerows and maize in an alley cropping system in Hawaii, USA 总被引:4,自引:0,他引:4
Successful agroforestry systems depend on minimizing tree-cropcompetition. In this study, field experiments and a simulation
model were usedto distinguish between tree-crop competition for light and belowgroundcompetition in an alley cropping system.
Maize (Zea maysL.) was harvested periodically in three treatments: between vertical barriers ofshade cloth, hedgerows of Flemingia macrophylla (Willd.)Merr., and sole maize. Radiation intercepted by the maize was calculated using asimulation model based on measured
values for direct and diffuse light, hedgerowdimensions and leaf area, and solar trajectory. Radiation use efficiency wascalculated
as biomass production per unit of intercepted radiation. Maizebiomass and yield in both the alley crop and the shade cloth
treatment weregreatest in the center of the alleys. Grain yield between hedgerows was 3.5Mg ha−1 (averaged across the alley), significantlyless than in the shade cloth (7.4 Mg ha−1) or thesole maize (7.7 Mg ha−1) treatments. Lightintercepted by the maize in the alley crop was about half that intercepted bythe maize in the sole crop.
The shade cloth intercepted less light than thehedgerows because it did not have an appreciable width. Radiation use efficiencyin
the three treatments was 0.75 g mol−1 PAR anddid not differ significantly among treatments. Tree-crop competition wasoverwhelmingly for light.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
15.
Yields under alley cropping might be improved if the most limiting nutrients not adequately supplied or cycled by the leaves
could be added as an inorganic fertilizer supplement. Three historic leaf management strategies had been in effect for 3 years
ina Leucaena leucocephala alley cropping trial on the Lilongwe Plain of central Malawi : 1) leaves returned; 2) leaves removed; and 3) leaves removed,
with 100 kg inorganic N ha−1 added. An initial soil analysis showed P status to be suboptimal under all strategies. A confounded 34 factorial experiment was conducted with the following treatments: leaf management strategy (as above), N fertilizer rate
(0, 30, and 60 kg N ha−1), P fertilizer rate (0, 18, and 35 kg P ha−1), and maize population (14,800, 29,600, and 44,400 plants ha−1). Both N and P were yield limiting, and interacted positively to improve yields. The addition of 30 kg N and 18 kg P ha−1 improved yields similarly under all leaf management strategies by an average of 2440 kg ha−1. Increasing the rates to 60 kg N and 35 kg P ha−1 improved yields an additional 1990 kg ha−1 in the ‘leaves returned’ and leaves removed + N’ strategies, but did not improve yields under the ‘leaves removed’ strategy.
Lower yields were related to lack of P response at the highest P rate in this treatment, which may have induced Zn deficiency.
Plots receiving leaves had higher organic C, total N, pH, exchangeable Ca, Mg, K, and S, and lower C/N ratios in the 0–15
cm soil layer than did plots where leaves had been removed. Leaf removal with N addition was similar to leaf removal alone
for all soil factors measured except for organic C and total N, which were higher where N had been added. The results show
that N and P were the primary yield-limiting nutrients. Historic N application maintained the soil's ability to respond to
N and P on par with leaf additions. 相似文献
16.
J. V. N. S. Prasad G. R. Korwar K. V. Rao K. Srinivas Ch. Srinivasarao B. Pedababu B. Venkateswarlu S. N. Rao H. D. Kulkarni 《New Forests》2011,42(1):51-61
On-farm experiments were conducted in Khammam district of Andhra Pradesh from 2001 to 2006 to evaluate the biomass productivity,
intercrop yields and profitability of Eucalyptus tereticornis clonal and Leucaena leucocephala variety K-636 based systems. Trees were planted at a spacing of 3 × 2 m and evaluated at three locations. Height growth was
significantly higher in leucaena during the 4 year where as difference in diameter growth was not significant. Biomass partitioning to the bole was high in case of leucaena, ranged from 83% in 2.5–5 cm diameter at breast height (DBH)
trees to 89% in 12.5–15 cm DBH trees and in eucalyptus clones the corresponding values were 71% in 2.5–5 cm DBH trees and
83% in 12.5–15 cm DBH trees. Marketable biomass productivity was higher with leucaena (95 Mg ha−1) in comparison to eucalyptus (87 Mg ha−1). Competition effects of trees on intercrops were observed from the 2 year (2002 post-rainy season). Intercrop yields were
45% of the sole crop in eucalyptus system and 36% in leucaena system during the 2 year. Sole eucalyptus and leucaena plantations
and intercropping systems recorded higher gross and net returns over arable cropping. Therefore, it can be concluded that
leucaena variety K636 and eucalyptus clonal based agroforestry systems are profitable alternatives to arable cropping under
rainfed conditions. 相似文献
17.
The amounts of earthworm surface casts were monitored for 200 days after commencement of casting in three alley cropping experiments
of different ages and hedgerow species. Casts were collected twice per week in transects from under the hedgerow to the middle
of the interrow space. Average annual cumulative amounts of casts were higher in alley cropping systems with one to five years
of cropping than in the no-tree control. After five years of cropping, amounts of casts were similar in all treatments. Within
the alley cropping systems, casting activity was highest immediately under the hedgerows and decreased towards the middle
of the interrow space. In systems using Leucaena leucocephala as hedgerow species, the hedgerow to interrow space gradient
of casting activity became more pronounced with increasing length of cropping. Casting activity in the interrow space was
reduced by 12%, 55%, 80% and 86% in the first, fourth, sixth and seventh year of cropping, respectively, compared to the casting
activity under the hedgerows. Senna siamea, which produced a more recalcitrant mulch, did not show such a strong decline in
casting in the interrow space. In a Dactyladenia barteri system, the difference in casting between interrow space and hedgerows
was insignificant. With perpendicular distance from the hedge, largest gradients in casting activity occurred close to the
hedgerows with up to −4.00 Mg ha−1 cm−1 in L. leucocephala but only −1.23 and −0.76 Mg ha−1 cm−1 in S. siamea and D. barteri, respectively. The shading effect of trees and a relatively low level of soil disturbance is
apparently more beneficial for earthworms in a cropped system than a high supply of readily available food from fast decomposing
L. leucocephala prunings.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
This paper discusses a plantation management approach involving a combination of “short” and “long” rotations designed to
allow farmers to receive income from trees as soon as possible after establishment. We present results from two plots that
represent extreme conditions: (a) a seasonally waterlogged, non-saline site (Nahalal), and (b) a saline site (Ginnegar) located
in the Yizre’el Valley, Israel. Six improved seed sources, four of Eucalyptus camaldulensis and two of E. occidentalis, were examined. The local Israeli seed source of E. camaldulensis (HA) performed best at both sites. In Nahalal, the short rotation thinning of the slower growing (50%) plantation trees could
provide economic returns approximately five years after establishment. The calculated mean annual increment (MAI) of these
trees reached 12.2 t ha−1 year−1. The long rotation, or better performing half of the plantation trees, could be used as a source of sawn timber, providing
higher-value products. By nine years after establishment, the average DBH of the various seed sources reached 25.8 ± 1.9 cm.
The calculated MAI of the combined cutting rotations reached 48.3 t ha−1 year−1. Eucalyptus grown under the combined (short- and long-term) management approach at Nahalal was more profitable than many other non-irrigated
local crops. Eucalyptus production in Ginnegar would be less profitable than in Nahalal. However, an additional ecological benefit was provided by
the crop’s ability to lower the water table. When this contribution to regional drainage is taken into account, trees become
economically competitive with other non-irrigated field crops under saline conditions.
Jim Morris–Deceased. 相似文献
19.
Tree based land use systems make a valuable contribution to sequester carbon and improve productivity and nutrient cycling
within the systems. This study was conducted to determine biomass production, C-sequestration and nitrogen allocation in Gmelina arborea planted as sole and agrisilviculture system on abandoned agricultural land. At 5 years, total stand biomass in agrisilviculture
system was 14.1 Mg ha−1. Plantations had 35% higher biomass than agrisilviculture system. At 5 years, leaves, stem, branches and roots contributed
4.1, 65.2, 10.0 and 20.7%, respectively to total standing biomass (17.9 Mg ha−1). Over the 5 years of study, trees had 3.5 Mg ha−1 more C and 36 kg ha−1 more N in plantation than agrisilviculture system. Biomass and C storage followed differential allocation. Relatively more
C was allocated in above ground components in plantations compared to agrisilviculture system. C:N ratios for tree components
were higher in stem wood (135–142) followed by roots (134–139), branches (123–128) and leaves (20–21). In agrisilviculture
system crops recommended are: soybean and cowpea in rainy season; wheat and mustard in winter season. After 5 years, soil
organic C increased by 51.2 and 15.1% and N by 38.4 and 9.3% in plantation and agrisilviculture system, respectively. Total
C storage in abandoned agricultural land before planting was 26.3 Mg ha−1, which increased to 33.7 and 45.8 Mg ha−1 after 5 years in plantation and agrisilviculture system, respectively. Net C storage (soil + tree) was 7.4 Mg ha−1 in agrisilviculture system compared to 19.5 Mg ha−1 in G. arborea monoculture stands. The studies suggest that competitive interactions played a significant role in agrisilviculture system.
Plantations were more efficient in accreting C than agrisilviculture system on abandoned agricultural land. 相似文献
20.
Veiko Uri Krista Lõhmus Ivika Ostonen Hardi Tullus Renal Lastik Merit Vildo 《European Journal of Forest Research》2007,126(4):495-506
The above-ground biomass and production, below-ground biomass, nutrient (NPK) accumulation, fine roots and foliar characteristics
of a 8-year-old silver birch (Betula pendula) natural stand, growing on abandoned agricultural land in Estonia, were investigated. Total above-ground biomass and current
annual production after eight growing seasons was 31.2 and 11.9 t DM ha−1, respectively. The production of stems accounted for 62.4% and below-ground biomass accounted for 19.2% of the total biomass
of the stand. Carbon sequestration in tree biomass reaches roughly 17.5 t C ha−1 during the first 8 years. The biomass of the fine roots (d < 2 mm) was 1.7 ± 0.2 t DM ha−1 and 76.2% of it was located in the 20 cm topsoil layer. The leaf area index (LAI) of the birch stand was estimated as 3.7 m2 m−2 and specific leaf area (SLA) 15.0 ± 0.1 m2 kg−1. The impact of the crown layer on SLA was significant as the leaves are markedly thicker in the upper part of the crown compared
with the lower part. The short-root specific area (SRA) in the 30 cm topsoil was 182.9 ± 9.5 m2 kg−1, specific root length (SRL), root tissue density (RTD) and the number of short-root tips (>95% ectomycorrhizal) per dry mass
unit of short roots were 145.3 ± 8.6 m g−1, 58.6 ± 3.0 kg m−3 and 103.7 ± 5.5 tips mg−1, respectively. In August the amount of nitrogen, phosphorus and potassium, accumulated in above ground biomass, was 192.6,
25.0 and 56.6 kg ha−1, respectively. The annual flux of N and P retranslocation from the leaves to the other tree parts was 57.2 and 3.7 kg ha−1 yr−1 (55 and 27%), respectively, of which 29.1 kg ha−1 N and 2.8 kg ha−1 P were accumulated in the above-ground part of the stand. 相似文献