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1.
The paper describes a tree/crop interface (TCI) experiment designed to investigate the effects of row orientation using Leucaena leucocephala Lam. Each TCI plot consisted of a regularly pruned Leucaena hedge in the middle and 12 crop rows on either side. Eight such plots were arranged at 45° around a sole Leucaena plot with rows oriented in four compass directions viz., North-South, East-West, Northeast-Southwest and Northwest-Southeast.Results of four years from 1984 to 1987 did not show any effect of row orientation, and similarly, no effect was seen on crop rows due to their location on the windward or leeward side of the hedge. The TCI effect was positive on the first crop row in the first year because Leucaena grew slowly, but depressed the yield of the first 4 to 6 crop rows(1.8 to 2.7 m from hedge) in subsequent years. The negative effect of Leucaena was noted more on sunflower in a relatively dry year than on sorghum in other years.Results from the TCI plots were used to estimate the yield of five hedgerow intercropping (HI) systems with varying alley widths (2.7 to 9.9 m). Comparison with sole stands of Leucaena and crops indicated that HI was more productive particularly at close alley widths. For example, hedges spaced at 2.7 m and 3.6 m averaged 37% and 25% higher productivity than the respective sole stands; but this advantage may be an overestimation of the real potential.The relevance of TCI experiments for studying agroforestry systems, their merits and limitations, especially of the design employed in this study are discussed. 相似文献
2.
When combining pine and cattle production on improved pastures, grazing may have to be delayed for several years until trees
are large enough to resist injury. During this period forage would be lost unless harvested for hay. This study in south Georgia,
USA, examined hay production during the first 3 years, cattle production during the next 3 years, and effects of this management
system on survival and growth of slash pine(Pinus elliottii) planted in widely-spaced rows within the pastures.
Pines were planted at 225 trees/ha in configurations of 3.0 x 14.6 or 4.9 x 9.1 m in pastures recently sprigged or seeded
with Coastal bermudagrass (Cynodon dactylon) or Pensacola bahiagrass(Paspalum notatum). Pastures were fertilized annually and cut for hay four or five times each year.
Wide-row spacings permitted haying operations, but tree rows and turning areas removed 5 to 8 percent of the area from production.
However, hay yields and liveweight gains by yearling cattle were near normal for this locale.
Slash pine planted in these fertilized pastures survived well, grew rapidly, and only a few trees were killed during haying
operations. After 6 years, 83 percent of the trees survived and averaged 6.5 m in height and 13.2 cm in diameter. Cattle killed
a few trees by rubbing during the 4th year.
Wide-row spacing of pines permits harvesting forage for hay while waiting for the trees to become large enough to permit grazing.
This approach to agroforestry produces annual returns to the landowner while awaiting maturity of the pines. 相似文献
3.
Robin Duponnois Marija Kisa Yves Prin Marc Ducousso Christian Plenchette Michel Lepage Antoine Galiana 《New Forests》2008,35(2):105-117
Australian acacias like Acacia holosericea are excellent candidates for the revegetation of arid zones in Africa. Their high ability to develop multiple symbioses with
soil microorganisms is crucial to their rapid development in adverse climatic and edaphic conditions. These symbioses include
nitrogen fixation with rhizobia, vesicular arbuscular mycorrhization and ectomycorrhization. We set up an experiment to test
the growth response of A. holosericea to ectomycorrhizal inoculation in 13 different soils from Senegal. After autoclaving the soil, the experiment was conducted
in a greenhouse for four weeks. Plants were inoculated with Pisolithus albus strain IR100. The following parameters were measured: plant biomass, N, P, K and Ca foliar composition, spontaneous nodulation
rate, and ectomycorrhizal colonization. Data were analyzed in light of the physical, chemical and total microbial characteristics
of the soil. The results demonstrated a global promoting effect of P. albus inoculation on plant (shoot and root) growth and on foliar P and K, together with a depressive effect on N, while Ca rates
were barely affected. Interestingly, spontaneous nodulation with putative water- or airborne rhizobia was stimulated after
P. albus inoculation. However, these nodules seemed poorly effective, as they failed to cause any change in plant growth or in foliar
N composition within the nodulated and nonnodulated control plants. These results show that plant growth response to ectomycorrhizal
inoculation is greatly dependent on soil characteristics, and that root ectomycorrhizal colonization is influenced by biotic
factors such as soil microbiota. From a practical point of view, data from the present study demonstrate that it is possible
to optimize the effect of fungi on plant growth by screening soils under nursery conditions. 相似文献
4.
When combining pines and cattle on tame pasture, grazing is often delayed for several years until trees are large enough to
resist injury. As an alternative approach to delayed or deferred grazing during the early years, this study in central Louisiana,
USA, examined the effects of cattle grazing in subterranean clover (Trifolium subterraneum L.) pastures on slash (Pinus elliottii Engelm.) and loblolly pine (P. taeda L.) seeding survival and growth during the first 3 years of tree establishment. Pines were planted at about 1200 trees/ha
in 3 rows on 0.4-ha subclover units with 1.3 m spacing within rows. Three grazing treatments included: (1) ungrazed pines,
(2) limited grazing with a single-wire electric fence above the planted pines, and (3) grazed pines. Thirty Brahman crossbred
cows with calves and a bull grazed the tame pasture on a controlled grazing, rotational basis from December through May each
year, during the subterranean clover growing season. Pine trampling injury during the year was 8% on the grazed seedlings
while essentially none occured under limited grazing. During the first 2 growing seasons, survival and height of the pines
were significantly less on the grazed seedlings than on either the limited grazing or ungrazed seedlings. Pine heights from
the limited grazing and ungrazed treatments were not different during the 3-year study; loblolly pine heights from the limited
grazing treatment continued to be taller than the grazed treatment through the third year while the slash pine heights were
similar for all treatments by the third year. Seedling mortality became more acute as severity of grazing injury increased;
the greatest mortality occured when the terminal bud and needles were both browsed off. 相似文献
5.
D. J. Makus S. C. Tiwari H. A. Pearson J. D. Haywood A. E. Tiarks 《Agroforestry Systems》1994,27(2):121-127
Conventional planted okra in Booneville, Arkansas and Lorman, Mississippi were mulched with loblolly pine straw (Pinus taeda L.) and longleaf pine straw (P. palustris Mill.), respectively, at a rate of 11 t/ha or left bare. At Booneville, plant stand, season yields (18.6 t/ha), pod weight (16.3 g), plant dry weight (2.3 kg), or stem diameter (3.5 cm) were not affected by the loblolly pine mulch. However, mulch application increased pod number (1.22 vs. 1.06×106/ha) and plant height (1.5 vs. 1.6 m), while reducing weed competition (0.05 vs. 0.40 t/ha) and visible plant stress, during periods of soil moisture deficits. Soil temperatures at 5 and 15 cm depth were reduced by mulch until mid-August when plant canopies covered the rows. Seasonal moisture at 30 and 45 cm depths was similar between mulched and bare soils, based upon unreplicated neutron probe measurements. At Lorman, season okra yield (29.8 vs. 24.6 t/ha), number of pods per ha (1.24 vs. 1.07×106) and weed competition were reduced and soil pH lowered 0.56 units by longleaf pine straw mulch. Mulch reduced early season yield at both locations. 相似文献
6.
The choice of an appropriate hedgerow species is one of the most critical decisions in exploiting the value of a contour hedgerow system. The implications of hedgerow species with nitrogen (N)-fixation capacity on hedgerow-crop competition and crop productivity have been widely debated. We examined the agronomic significance of N-fixation by comparing the performance of species representing three classes of hedgerow vegetation: A nitrogen-fixing tree legumeGliricidia sepium), a non-nitrogen fixing tree (Senna spectabilis syn.Cassia spectabilis), and a forage grass (Pennisetum purpureum). The 4-year study investigated the hedgerow biomass and nutrient yields, and their relative effects on the performance of two annual crops commonly grown in alley farming systems, with emphasis on hedgerow-crop interference. The work was done on an Ultic Haplorthox (pH 4.8, organic C 1.9%, total N 0.18%).Senna produced 46% more pruning biomass on an annual basis than didGliricidia; N supplied to the alley crops was similar toGliricidia in the first year of observation, but 20–30% higher in the succeeding years. Upland rice and maize grain yields and total dry matter were unaffected by tree species, but the nitrogen-fixing tree exerted less competitive effects on the annual crops growing in adjacent rows. Grass hedgerows reduced maize yields 86% by the second year, indicating an unsustainable drawdown of nutrients and water. We conclude that hedgerow systems composed of a nitrogen-fixing tree did not exert significant advantages compared to a non-fixing tree species, and that factors other than N-fixation were more important determinants for the choice of hedgerow species. 相似文献
7.
Toxicity and repellent activities of aqueous extracts of nine medicinal plants were evaluated on different life stages of
the sweet potato whitefly, Bemisia tabaci. Tomato plants infested with whiteflies were dipped in 10% (wt/wt) of each plant extract for toxicity evaluation. Repellency
was evaluated in a choice experiment with detached tomato leaves. All extracts evaluated were relatively ineffective against
the adult stage. Extracts of Ruta
chalepensis, Peganum harmala and Alkanna strigosa were effective in reducing the numbers of B. tabaci immatures similar to the reduction observed in the imidacloprid treatment. These three extracts were not detrimental B. tabaci parasitoid, Eretmocerus mundus. In addition, the plant extracts Urtica pilulifera and T. capita were repellent to B. tabaci adults. These results indicate that the extracts from the plants R. chalepensis, P. harmala and A. strigosa could act as a potential source for natural product developed for B. tabaci management. 相似文献
8.
The psyllid insect (Heteropsylla cubana) is known to reduce biomass production in Leucaena species, but little information is available on the level of reduction, or whether a commonly used plant damage rating scale
can be related to production losses. Biomass production losses due to predation by the psyllid were determined for 12accessions
of Leucaena in a randomised split-plot field experiment conducted at Brisbane, Australia. Regrowthfrom well-established Leucaena trees, cut back to bare stems 50 cm high, was measured over a 9–week period from plants subjected to psyllid damage and from
plants with psyllids controlled by spraying with chlorpyrifos (1 mg ai/l water). Psyllid damage was scored using a ratings
scale developed by the University of Hawaii. Lossof potential DM production due to psyllids ranged from 10% for L. trichandra OFI53/88 to 76% for L. collinsii ssp. zacapana OFI56/88. Production losses were significantly correlated with psyllid damage ratings for 10 of the 12 accessions, and also
for a combined data set comprising these 10 accessions. From correlations for the combined data set, a 50% loss of potential
DM production occurred at a psyllid damage rating of approximately3.2. Results indicated that a “0” rating should be added
to the scale to indicate the absence of psyllids.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
9.
Yield, maturation, and forage quality of alfalfa in a black walnut alley-cropping practice 总被引：2，自引：1，他引：1
Robert L. McGraw W. Terrell Stamps James H. Houx Marc J. Linit 《Agroforestry Systems》2008,74(2):155-161
There is interest in producing alfalfa as an alley crop because alfalfa (Medicago sativa L.) is the most profitable hay crop in the USA. Field experiments were conducted near Stockton, MO in 2003 and 2004. Treatments
consisted of alfalfa grown in open plots and in plots that were alley cropped between 20-year-old black walnut trees (Juglans nigra L.) planted in rows 24.4- and 12.2-m apart. Alfalfa was sampled for three harvest cycles each year. In the alley-cropping
plots, samples were taken beneath the canopy (2.5 m from the tree row) and in the center of the alleys. Data were taken on
dry-matter yield, maturity, and forage quality. At all harvest dates over both years, yields from beneath the canopy of both
alleys and the narrow alley centers were less than yields from the wide alley centers and open plots. Yield from the wide
alley centers was similar to that in open plots in every harvest but the final harvest of 2004. Transects across the plots
indicated that yields increased linearly from the tree row to the center of both alleys. Alfalfa tended to mature faster in
the open and wide alley centers compared to beneath the canopy of both alleys and the narrow alley centers. Forage quality
differences were inconsistent across treatments. Alfalfa yield was significantly reduced and maturity was delayed by the narrow
12.2 m tree spacing, but yield was not reduced in the centers of the wider 24.4 m alleyways. 相似文献
10.
The sequence of events leading to necrophylactic periderm formation was studied throughout the year following the abiotic wounding of the non‐infected roots of 10‐ and 27‐year‐old western larch (Larix occidentalis) and 11‐ and 25‐year‐old Douglas‐fir (Pseudotsuga menziesii) trees that were infected with Armillaria ostoyae. The sequence was the same for both ages and species of trees. Wound repair was more rapid in the summer compared with the spring and autumn. Following cell hypertrophy, a zone of lignified impervious tissue was in the initial stages of formation within 10 days of wounding in the summer and 14 days in the spring or autumn. The new phellogen produced a layer of phellem three to four rows of cells thick after 20 days in the summer or 40 days in the spring. Modified cells abutting the inner boundary of the impervious zone frequently developed thick lignified abaxial walls and thin suberized adaxial walls. A typical exophylactic periderm in healthy root bark tissue of both western larch and Douglas‐fir consisted of stone phellem one to four rows of cells thick and a layer of thin‐walled phellem three to six rows of cells thick in western larch and two to three rows thick in Douglas‐fir, a single row of phellogen cells and one to three rows of phelloderm cells. Mature thin‐walled phellem cells had pigmented contents, red in western larch and light brown in Douglas‐fir. In response to wounding, 27‐year‐old western larch and 25‐year‐old Douglas‐fir developed necrophylactic periderms with annual bands of phellem. The bands included a layer of phellem that was six to 12 and nine to 15 rows of cells thicker than the layer of phellem observed in the respective naturally developed exophylactic periderms. Fifty days following wounding in the summer, stone phellem, one to three rows of cells thick, was observed in the necrophylactic periderm of 10‐year‐old trees. When fully developed, the necrophylactic periderm in 27‐year‐old western larch also had a layer of stone phellem three to five rows of cells thick in each band. Stone phellem development was only sporadic in 25‐year‐old Douglas‐fir. Wounds in the winter showed no signs of activity associated with repair until dormancy broke in the spring. 相似文献
11.
Data from a Brazilian Inga/maize/bean alleycrop experiment are used to illustrate patterns of variation between and within
crop rows and their possible effects in the determination of a sampling strategy. Three methods for the determination of sample
sizes in agroforestry experiments are compared: the combined plant technique, the formula of Snedecor and Cochran and variance
component estimation. Results show that variability in the edge rows was generally greater than variability in the inner rows
and suggest three sampling strata – one for each of the two edge rows and the third for the inner rows. For all three sampling
methods a sample size greater than ten plants per stratum per block gave little extra precision. Increasing the number of
blocks improves precision and may permit a smaller sample size per row to achieve the same precision. The comparison of different
methods of sample size determination shows that variance component estimation is the most flexible and efficient approach.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
Although only Leucaena leucocephala is widely used, most members of the Leucaena genus have potential as multipurpose species for tropical agroforestry systems. To investigate the wood and biomass production
potential of the Leucaena genus, 116 accessions covering the 22 species were evaluated over a two-year period at Brisbane, southeast Queensland, Australia.
Trees were planted into replicated line plots 5 m long, with rows spaced 3 m apart. Trees were initially planted at 0.5 m
spacings within the plots, but were thinned to 1 m spacings prior to the evaluation period. The hybrid accessions, KX2 (L. pallida × L. leucocephala) and KX3 (L. diversifolia × L. leucocephala), were the most productive, yielding over 50 kg dry matter (DM)/tree. L. trichandra OFI53/88 and L. diversifolia CPI33820 were the most productive non-hybrid accessions producing total yields of 41 and 37 kg DM/tree, respectively. Cultivar
Tarramba (26 kg DM/tree) was the most productive of the 26 L. leucocephala accessions assessed in the trial but all these accessions suffered from psyllid (Heteropsylla cubana) attack at this site. A series of non-destructive growth measurements was recorded every three months over the two-year evaluation
period. Root collar diameter (RCD), stem number and plant height were found to be the most useful of the measurements for
non-destructive assessment of accession agronomic characteristics. A relationship between yield and a growth index (calculated
as RCD2 × Height/1000), was derived from data from all accessions and could be used as a reliable predictor of yield (r
2 = 0.94). The widespread use of the F1 hybrid leucaenas is currently limited by a lack of seed. Technologies to economically
produce F1 hybrid seed on a commercial scale are required before the potential of these accessions in agroforestry systems
can be fully realized.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
13.
Robert I. McDonald Glenn Motzkin David R. Foster 《Forest Ecology and Management》2008,255(12):4021-4031
Forest harvesting is one of the most significant disturbances affecting forest plant composition and structure in eastern North American forests, yet few studies have quantified the landscape-scale effects of widespread, low-intensity harvests by non-industrial private forest owners. Using spatially explicit data on all harvests over the last 20 years, we sampled the vegetation at 126 sites throughout central and western Massachusetts, one-third of which had not been harvested, and two-thirds of which had been harvested once since 1984. Seedling and sapling densities increased with increasing harvest intensity, but decreased to levels similar to unharvested sites by year 20 for all but the most intensive harvests. The composition of understory trees appears to be only slightly changed by harvesting, and was strongly correlated with adult tree composition. Regeneration was dominated by Betula lenta followed by Pinus strobus; Quercus spp. exhibited little sapling recruitment, even in Quercus-dominated stands. Total vascular plant species richness increased substantially with harvesting on low C:N sites (i.e., rich soils), but was only slightly increased on high C:N sites. While harvesting was associated with a statistically significant change in vascular plant composition, non-metric multidimensional scaling revealed that climate (temperature, precipitation) and C:N ratios were the major correlates of composition. Overall, the compositional impacts of harvesting were minor, perhaps because of the low-intensity of harvesting. However, our results support observations from elsewhere in the northeastern U.S. of limited oak regeneration on both harvested and unharvested sites. In addition, our results suggest that increased harvest intensity may be expected to alter forest composition, particularly on rich sites where invasive species may increase as a result of harvesting. 相似文献
14.
[目的]了解环境因子对毛红椿适生区分布的影响,为其资源保护、引种及其人工林的发展提供参考。[方法]基于MaxEnt模型能利用现存不完整、小样本、离散型分布数据构建物种适生区预测模型,用受试者工作曲线线下面积(AUC)检验预测模型的精度,面积越大精度越高等优点,本研究应用毛红椿在云南的分布数据及1个地型因子和6个气候因子,来构建其适生区分布模型。[结果]毛红椿适生区分布MaxEnt模型平均训练AUC和平均测试AUC分别为0.891、0.885,说明对毛红椿适生区的预测是可靠的;降水量变异系数和最干季度降水量是决定毛红椿适生区分布的主要因子,年均气温变化范围、最冷季度平均气温、最湿季度降水量、最冷季度降水量是次要因子。在当代和未来(2050S、2070S)气候变暖条件下(RCP2.6情景),云南省和全国适生区面积计算结果直观、定量的反应了全球变暖对毛红椿适生区变迁的影响。[结论]预测云南省及全国的毛红椿适生区随全球变暖而小幅萎缩。 相似文献
15.
The potential of hedgerow intecrropping with Leucaena leucocephala was explored on vertic Inceptisols over 4 years at ICRISAT Center, Patancheru, India. The study was conducted using a systematic layout involving different alley widths ranging from 1.35 to 4.95 m and with varying distances between hedge and crops. The alleys were cropped with alternate rows of sorghum and pigeonpea. Hedges composed double Leucaena hedgerows 60 cm apart were periodically harvested for fodder. Sole crops of all components and a sorghum/pigeonpea intercrop were included in all four replications of the study.Starting in the second year, Leucaena was progressively more competitive to annual crops, causing substantial yield reduction. Competition (primarily for moisture) was most severe in narrow alleys and was greatest on pigeonpea.The growth of Leucaena was not sufficient to compensate for reduced crop yields. Land equivalent ratios (LERs) calculated on the basis of grain yield of crops and Leucaena fodder yields showed that hedgerow intercropping (HI) was advantageous over sole crops only during the first two years using wide alleys, but disadvantegeous in the last two years. LERs calculated on the basis of total dry matter indicated only a small advantage for HI (13–17 percent) over sole crops in wider (>4 m) alleys. Average returns per year from HI exceeded those of the most productive annual crop system (sorghum/pigeonpea intercropping) by 8 percent in 4.05 m alleys, and by 16 percent in 4.95 m alleys. Fodder production during the dry season was 40 percent of the annual total in these alley widths. Thus hedgerow intercropping at 4–5 m alley width is not very attractive for farmers in semi-arid India, which has 600–700 mm of annual rainfall. There is a need to examine the potential of HI in wider alleys. The merits and limitations of the systematic design are discussed. 相似文献
16.
The entomophagous Serangium parcesetosum Sicard (Col., Coccinellidae) is an effective predator of some whitefly species. However, information on the influence of the preys host plant species on its biological and ecological characteristics is still lacking in the literature. Therefore, the current study focuses on the possible influence of three greenhouse and two field host plant species of Bemisia tabaci (Genn.) (Hom., Aleyrodidae) on the number of eggs laid by S. parcesetosum. In addition, because of the economic importance and widespread planting of cucumber in greenhouses and cotton in the field, these plants were selected for further investigation into the development, mortality, longevity and reproduction of S. parcesetosum at a high temperature in the laboratory. Results showed that S. parcesetosum was able to lay eggs on all five host plant species of B. tabaci, whether greenhouse or field plants. However, among the three greenhouse plant species studied, S. parcesetosum females laid the highest number of eggs on cucumber followed by tomato and then sweet pepper. Of the two field plant species, significantly higher numbers of eggs were laid on tobacco than on cotton. S. parcesetosum could develop either on cucumber or on cotton as preferable host plant species for B. tabaci. There were significant differences in mean developmental duration of larval instars of the same sex between both host plant species; the duration was significantly shorter on cucumber than on cotton. There were no significant differences for mean total developmental duration from egg to adult emergence between both host plant species within the same sex; females showed a mean of 15.9 days and males of 15.1 days on cucumber, while on cotton the means were 17.2 days for females and 16.2 days for males. Total mortality percentage of S. parcesetosum during development from egg to adult stage was lower on cucumber than on cotton, 20.6 and 23.8%, respectively. Longevity of S. parcesetosum varied according to host plant species and sex with a mean of 63.4 days for females and 50.3 days for males on cucumber, and 92.4 days for females and 52.5 days for males on cotton. On cucumber, mean period of oviposition of S. parcesetosum was significantly longer than on cotton. Mean total fecundity was significantly higher on cucumber than on cotton, with means of 97.7 and 31.0 eggs/female, respectively. 相似文献
17.
The aim of the study is to compare selected theoretical distributions (normal, lognormal, Weibull, gamma, logistic, and exponential)
in describing the tree diameter (DBH) distributions of mixed near-natural forests consisting of fir Abies alba Mill. and beech Fagus sylvatica L. growing in various vertical structures. Tree DBH data were collected between 1997 and 2008 from 51 sample plots established
in the Świętokrzyski National Park in Poland. The empirical data represent differentiated DBH distributions, ranging from
almost symmetric to extremely asymmetric ones. The chi-square test and the modified Kolmogorov–Smirnov test were chosen for
the goodness-of-fit testing. In addition to the test statistics, the bias (B), the root mean square error (RMSE) and the graphical method (quantile–quantile plots) were used. In one-storied stands,
the most suitable distributions were the normal and logistic distributions; in two-storied and multilayered stands, the Weibull
and gamma distribution were the most suitable; and in selection stands, the exponential distribution was the most appropriate
to describe the DBH distribution. The order of precision of the tested distributions (from the highest to the lowest) was
Weibull, gamma, logistic, normal, exponential, and lognormal. The normal and exponential distribution should be applied only
to one-storied and selection forests, respectively. The least suitable distribution for DBH distribution modelling was the
lognormal one. 相似文献
18.
The use of pollarded Erythrina poeppigiana as shade tree in coffee plantations is apparently an old practice in Costa Rica. The tree is not native to this country but was introduced between late 19th and 20th century and was rapidly dispersed in the coffee and cacao areas. Currently, the Erythrina tree is widespread in the Turrialba Valley (elevation 600—1300m) and in the Central Valley (elevation 1200m) where the species is always associated with present or past coffee crops. Pollarding carried out by Costa Rican farmers constitutes a long dated and functional practice, hence the objective of this study was to evaluate the amount of biomass produced by pollarding of Erythrina poeppigiana used as shade in coffee crop planted at a density of 280 trees/hectare under different pollarding frequencies. Results showed that by pollarding once a year, 18,470 kg of dry matter per hectare are produced; with two pollardings per year 11,800 kg/ha are produced and with three pollarding per year 7,850 kg/ha are produced. The total amount of nitrogen removed is very similar for pollarding once and twice a year, but is lower for three times a year. The amount of nitrogen removed was approximately 230 kg/ha/year in the first two cases and 170 kg/ha/year in the last one.The above observations suggest that a considerable supply of nutrients exist in the systems with shade trees, when they are periodically pollarded.Finally some conclusions and follow up activities related to research on the species are suggested, such as higher biomass production techniques, appropriate planting practices, selection of genetic material, nutrient depletion when biomass is harvested, conversion of leaves to marketable feed sources (flour, pellets), alley cropping and green manure production and restoration of degraded areas and improductive savannas by planting large cuttings that would improve the soil by adding biomass and shade out undesirable grasses.This work is part of a Ph.D. Dissertation submitted to the Southeastern University, New Orleans, Lousiana by R.O. Russo. 相似文献
19.
Shi-xiang Zong You-qing Luo Ya-qin Cui Jian-wei Wang Wei Yan Ai-jie Liu Heliövaara Kari 《中国林学(英文版)》2009,11(1):24-27
The population density and distribution of the three major boring pests, Holcocerus artemisiae, Sphenoptera sp. and Adosopius sp. were studied in their host plant Artemisia ordosica. Results show that the larvae of H. artemisiae mainly bore the rhizome of A. ordosica, but also the larvae of Sphenoptera sp. and Adosopius sp. bore the rhizome of A. tordosica. The adults of Sphenoptera sp. and Adosopius sp. feed on the leaves of A. ordosica as a nutritional supplement. The distribution of the larvae of three pests in their host plant is completely different. H. artemisiae and Sphenoptera sp. are distributed in the whole A. ordosica plant. The newly hatched larvae first feed on the phloem and xylem of stem and then burrow to the roots before the winter
of the same year. However, Adosopius sp. is distributed mainly in the roots. The newly hatched larvae move from the phloem to the xylem, and gradually damage
the lower part of the trunk. The larvae of the three pests sometimes coexist in a single A. ordosica plant. However, the probability of the coexistence of the three pests is very small. The highest probability of coexistence
of two pests was observed in Sphenoptera sp. and H. artemisiae, while the probability of coexistence of Sphenoptera sp. and Adosopius sp. as well as H. artemisiae and Adosopius sp. was smaller. The reasons for coexistence or its avoidance are not only related to the amount of food provided nor the
volume of larval living space in a single A. ordosica plant, but also related to the development characteristics of different kinds of larvae and interspecific competition. 相似文献
20.
Herbaceous plant control with mulchor hexazinone herbicide influenced planted longleafpine (Pinus palustris Mill.) seedling totalheight on a silt loam site in central Louisiana. Thesite had been sheared and windrowed in 1991 and rotarymowed before three treatments were established in arandomized complete block design: (1) Untreatedcheck: no herbaceous plant control after planting;(2) Five mulches: on each plot, five randomlyassigned mulches were placed around seedlings; themulches were either a mat of cotton, hemlock andpolyester, pine straw, woven polypropylene, orperforated polyethylene; and (3) Hexazinone: theherbicide hexazinone at 1.12 kg active ingredient/hawas annually sprayed in the first two growing seasonsover the rows of unshielded seedlings. The longleafseedlings were planted in February 1993.After three growing seasons, seedlings on the mulchand hexazinone treatments were taller than those onthe check plots. About 59% of the mulched andhexazinone treated seedlings had grown out of thegrass stage (at least 12 cm tall) compared to 17% ofthe check seedlings. After five growing seasons, thepercentage of longleaf pine seedlings out of the grassstage was similar on all treatments and averaged 87%. However, these better growing pines were taller on themulch and hexazinone treatments (a 142-cm average)than on the checks (78 cm). Pine straw was anineffective mulch probably because the straw smotheredthe seedlings. The longleaf saplings were tallestwhen the perforated polyethylene mat was used. 相似文献