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1.
In this study we determined soil moisture storage, evapotranspiration (ET) and light interception in an agroforestry trial consisting of pine trees grown over (1) control (bare ground), (2) ryegrass/clovers (Lolium perene/Trifolium spp.), (3) lucerne (Medicago sativa), and (4) ryegrass only during the third growing season between 1992 and 1993. The results show that:
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1. | In the period when rainfall was frequent and exceeded the evaporative demand (Epot), ET and depletion of soil moisture were not affected by the ground cover treatments. During summer when rainfall was less frequent, but with moisture readily available in the soil profile, ET was associated with plant canopy, and was significantly higher for the pasture ground covers than for the control. Therefore, the more rapid growth by lucerne caused higher ET in this ground cover than in the ryegrass/clovers ground cover in which the pasture was slow growing. At the end of the study period, total ET was in the following order: lucerne (757 mm) > ryegrass/clovers (729 mm) > Control (618 mm). |
2. | ET was dominated by pasture transpiration (Ep) during most of the growing season, but by tree transpiration (Et) in winter when large parts of the pasture canopy was shaded. Ep was always at least 16% higher for lucerne than for ryegrass/clovers species as a result of a greater radiation intercepted by the former. |
3. | Fraction of incoming radiation intercepted by the tree crowns was in the following order: control > ryegrass > ryegrass/clovers > lucerne. At the end of the one-year period, fraction of intercepted radiation was 140% greater for control than for lucerne ground cover. |
4. | The control produced the largest tree crowns, which were almost twice the tree crowns in the lucerne ground cover which produced the smallest trees. Accordingly, the trees in the control intercepted more radiation and rainfall, with the former being lost to evaporation, than the trees in the pasture. |
5. | The fractions of radiation intercepted and ET accounted for by the trees and pastures were associated with the proportion of the plot area they occupied. |
2.
Microsite influences development and resource allocation of Dactylis glomerata L. (orchardgrass), a traditional pasture species with potential as an understory crop in silvopasture of humid temperate
regions. An experiment using container-grown orchardgrass was conducted under field conditions to determine how open (O),
shaded woodland (W) and open-to-shaded woodland transition zone (E
O, E
W) microsites influenced leaf DM production. Plants established in spring (SP) and late summer (LS) were clipped each time
mean canopy height reached 20 cm. Dry matter production and allocation among structures differed, as a function of light attenuation.
Specific leaf area (SLA) and photosynthetic nitrogen-use efficiency (PNUE) were associated with leaf DM production, whereas
leaf N, net assimilation rate and shoot total nonstructural carbohydrates (TNC), were not. Specific leaf area was related
to leaf DM of LS plants, whereas PNUE influenced leaf DM of SP plants. Stembase TNC was inversely related to relative regrowth
rate (RGRR) with RGRR greatest and TNC the least at W. The relationship for RGRR and TNC for SP plants growing at O and LS plants growing at W was similar. Regardless of how indices of growth are related,
SP and LS plantings responded as separate populations (representing young and established plants respectively) that have different
leaf DM production efficiencies. Orchardgrass was able to sustain leaf production when subjected to simultaneous stresses
of shade and repeated defoliation. The LS plants growing at W respond in a manner similar to SP plants and may require management
practices attuned to establishing or immature plants.
The US Government’s right to retain a royalty-free, non-exclusive copyright is achnowledged. 相似文献
3.
Xiaobang Peng Yuanying Zhang Jing Cai Zaimin Jiang Shuoxin Zhang 《Agroforestry Systems》2009,76(3):569-577
Agroforestry is the most effective way to restore the disturbed lands on the Loess Plateau and to develop the poor local economy.
In order to maximize the potential benefits of tree-based intercropping systems, photosynthesis, growth and yield of soybean
and corn were studied by measuring photosynthetic active radiation (PAR), plant water deficit and soil moisture in a 4-year-old
plantation of walnut (Juglans regia L.) and plum (Prunus salicina) grown at a spacing of 5 m × 3 m on the Loess Plateau. The effects of tree competition significantly reduced PAR, net assimilation
(NA), growth and yield of individual soybean or corn plants growing nearer (1 m near tree row) to tree rows. NA was highly
correlated with growth and yield of the both crops. These correlations were higher for corn than soybeans, with corn, rather
than soybeans being more adversely impacted by tree shading. Plum, rather than walnut had the greatest competitive effect
on PAR and NA. Daily plant water deficits were non-significantly and poorly correlated with NA and growth and yield of the
both crops. However, soil moisture (20 cm depth) was significantly correlated with biomass and yield of both crops. Possible
remediation strategies are discussed to reduce tree competitive interactions on agricultural crops. 相似文献
4.
The soil water balance technique was used to study evaporation from two fodder tree species, tenEucalyptus species and annual pasture over a three year period after planting in the Western Australian wheatbelt. Evaporation is the total water loss by the processes of transpiration, evaporation from the soil surface and evaporation of water intercepted by plant canopies.Evaporation from both fodder trees and from seven of theEucalyptus species was greater than from pasture for one or more of the study years. The maximum difference in evaporation between trees and pasture was 82, 84 and 70 mm in the first, second and third study years, respectively. Higher evaporation from trees was associated with greater depletions in soil water than occurred beneath pasture. Upward movement of water from wet soil beneath the root zone was found under trees, with a maximum flux of 30 mm observed over a one year period beneathE. camaldulensis.The water use efficiency of fodder trees was significantly higher than for mostEucalyptus species, due to greater yields from fodder trees. Biomass production was found to be a good indicator of the water use of eucalypts over the first two years of growth, but the relationship between productivity and water use was found to differ for species with tree and mallee forms. In the third year of study, obvious differences in the relation between water use and yield were observed for some species of eucalypts with high evaporation. 相似文献
5.
辽西地区引种野杏的光合生理生态特性研究 总被引:1,自引:0,他引:1
利用LI-6400光合仪测定引种野杏家系苗木在辽西地区6、7、9月的光合生理参数,研究各参数的日变化和季节变化规律,以了解引种野杏的适应能力,为辽西地区品种选育和栽培利用提供理论基础。结果表明:野杏家系净光合速率(Pn)在夏季具有明显的"光合午休"现象,夏、秋季的日均Pn达10.0μmol·m-2·s-1,春季6.9μmol·m-2·s-1;蒸腾速率夏季(6.39 mmol·m-2·s-1)秋季(4.84 mmol·m-2·s-1)春季(2.33 mmol·m-2·s-1);水分利用效率春、秋高,夏季低;光能利用效率春季高、夏秋季较低;不同季节的生态因子影响野杏苗木的光合生理特性。引种野杏优良品种的选育要注重其对当地环境的适应能力,在了解其光合生理特性的基础上做出最佳选种策略。 相似文献
6.
The process of iterative diagnosis and design with the active participation of farmers and extension agents was found effective
in identifying appropriate agroforestry systems for farmers in the Bugesera and Gisaka-Migongo (BGM) regions of Rwanda. Periodic
re-evaluation of research assumptions and technology designs was based on feedback from farmers and extentionists through
regular visits to station trials, early initiation of on-farm testing, and interaction with farmer cooperators through informal
discussions and formal surveys focused on specific agroforestry technologies. Statistical analysis is valuable for comparison
between regions or periods. However, valid conclusions can be drawn without statistics, by employing several farmer-participatory
approaches and pooling and properly interpreting the data obtained from them.
Farmers' preferred uses of tree biomass in the BGM regions and appropriate agroforestry systems are discussed. If researchers
and development agents do not consider the farmers' real needs, circumstances, available resources and management capacity
with regard to tree planting, they will fail in identifying and extending suitable agroforestry systems for any region.
This study was a part of the ISAR/IITA/World Bank FSR Project, implemented in the BGM regions of Rwanda during 1983–1988. 相似文献
7.
S. Jose A. R. Gillespie J. R. Seifert D. B. Mengel P. E. Pope 《Agroforestry Systems》2000,48(1):61-77
An experiment was conducted in an 11-year-old black walnut (Juglans nigra L.), red oak (Quercus rubra L.), maize (Zea mays L.) alley cropping system in the midwestern USA to examine the extent of tree-crop competition for nitrogen and decomposition dynamics of tree leaves and fine roots. A below-ground polyethylene root barrier (1.2 m deep) isolated black walnut roots from maize alleys in half the number of plots providing two treatments viz. barrier and no barrier. The percentage of N derived from fertilizer (%NDF) and fertilizer use efficiency (%UFN) were determined using 15N enriched fertilizer. Further, maize grain and stover biomass, tree leaf biomass, tissue N concentration, and N content were quantified in both treatments. The barrier treatment resulted in a significantly greater grain (67.3% more) and stover (37.2% more) biomass than the no barrier treatment. The %NDF in both grain and stover was higher in the no barrier treatment as a result of competition from tree roots for water and mineralized N in soil. Maize plants growing in the no barrier treatment had a lower %UFN than those in the barrier treatment due to their smaller size and inability to take up fertilizer. Analysis of tree leaf and fine root decomposition patterns revealed faster release of N (39% over 15 days for black walnut and 17.7% for red oak) and P (30% over 15 days for both species) from roots compared to the leaves of both species. Following an early release of P (11.3% over 45 days), red oak leaves exhibited significant immobilization for the rest of the incubation period. The data indicate that competition for N from fertilizer is minimal since nutrient acquisition is not simultaneous among black walnut and maize. However, competition for mineralized N in soil can exist between black walnut and maize depending on water availability and competition. Tree leaves and fine roots can enhance soil nutrient pools through the addition of soil carbon and nutrients. Tree fine roots seem to play a more significant role in nutrient cycling within the alley cropping system because of their faster release of both N and P as compared to leaves. Selection of tree species and their phenology will impact the magnitude and rate of nutrient cycling.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
8.
Robert H. Wanvestraut Shibu Jose P.K. Ramachandran Nair Barry J. Brecke 《Agroforestry Systems》2004,60(2):167-179
Understanding the belowground interactions between trees and crops is critical to successful management of agroforestry systems.
In a study of competition for water in an alley cropping system consisting of pecan (Carya illinoensis) and cotton (Gossypium hirsutum) in a sandy loam soil (Rhodic Paleudult) in Jay, Florida, root systems of the two species were separated by trenching to
120 cm depth. A polyethylene barrier was installed in half of the plots. Spatial and temporal variations in soil water content,
root distribution and water uptake by both species, and leaf area development and height of cotton were measured. Interspecific
competition for water was greater in the non-barrier treatment near tree rows than at the alley center. Competition became
evident 3 to 4 weeks after emergence of cotton and increased during the following 7 to 8 weeks. Compared with the non-barrier
treatment, the barrier treatment had higher soil water content and better growth of cotton (height, leaf area, and fine root
biomass). Cotton lint yield in the barrier treatment (677 kg ha–1) was similar to that in a sole-crop stand, but higher than in the non-barrier (502 kg ha–1) treatment. Lint production efficiency of plants was higher in the interior rows in the non-barrier treatment (0.197 kg lint
per square meter of leaf area, compared to 0.117 kg in the barrier treatment). The results suggest that trenching or even
deep disking parallel to the tree row may reduce competition for water, but the impact on tree growth cannot be established
from this study.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
9.
We tested the economic value of ecological knowledge in a midwestern USA alley-cropping system where row crops are planted in alleys between fine hardwood trees grown for veneer. Economic models were constructed to compare among agroforestry designs as well as to compare agroforestry with traditional forest plantation culture and row crop monoculture and rotational management. The general modeling approach was to quantify production inputs and outputs, estimate costs and revenues, simulate tree growth and crop productivity in agroforestry configurations, and estimate discounted cash flows. We incorporated scenarios that controlled both above- and below-ground competition through appropriate management as found in our previous research. This research showed the importance of below-ground competition in determining crop yields and the period of time that crop income could be expected from the agroforestry interplanting. Net present values and internal rates of return showed that agroforestry systems were generally more favorable investments than traditional agriculture and forestry. More importantly, the use of simple management techniques targeted at reducing below-ground competition allowed longer cultivation of row crops, greatly increasing returns to the landowner. Thus, the economic benefit of understanding the ecological interactions within agroforestry plantings dictates that accurate assessment of agroforestry alternatives will require the modeling of agroforestry as an integrated, interactive system.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献