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1.
In this paper we analyzed the dry matter yields (DM) produced in an agroforestry trial consisting of pine trees grown over (1) Control (bare ground), (2) ryegrass/clovers (Lolium perene/Trifolium spp.), (3) ryegrass only, and (4) lucerne (Medicago sativa) during the third growing season between 1992 and 1993. In addition these pastures were grown alone in separate plots in the open. The results show that:
1.  Pasture yields during the one-year period in the agroforestry plots were little affected by the presence of trees although there were seasonal trends: yields were generally unaffected or increased in summer, but reduced in spring as a result of tree shade. Total pasture yield during the one-year period was in the following order: lucerne > ryegrass/clovers > ryegrass. This trend was the exact opposite of that shown by the above-ground tree weight which was reduced in the pasture ground covers by between 16 and 52%. The reduction in tree weights was associated with reduced soil moisture availability arising from competition with the pasture species. Thus the relationship between the yields of trees and pasture species in the agroforestry plots was reciprocal.
2.  The combined DM for both the trees and pastures in the agroforestry plots during the one-year period was in the following order: lucerne (20 t ha–1) > ryegrass/clovers (16 t) > ryegrass (11 t) > control (6 t) which was consistent with the total water used and photosynthetically active radiation (PAR) intercepted. The trees accounted for 55, 44, 34 and 24% of water used respectively in control, ryegrass, ryegras/cclovers and lucerne ground covers. The balance was largely accounted for by pasture transpiration, except in the control where soil evaporation was significant. The fraction of intercepted PAR accounted for by the trees followed a similar trend to that of the water used.
3.  The crop coefficient for water use efficiency (k) (Pa) was 2.3 for radiata pine, 3.6 for ryegrass/clovers, 2.8 for ryegrass and 4.8 for lucerne. The DM produced per unit of water used (kg mm–1 ha–1) during the one-year period was 24.5 for radiata pine, 41.1 for lucerne, 30.0 for ryegrass/clovers and 23.1 for ryegrass. Radiation use efficiency (g DM MJ–1 m–2) was 1.33 for pine, 1.83 for ryegrass/clovers, 1.49 for ryegrass and 2.34 for lucerne.
4.  The land equivalent ratio (LER), i.e. the sum of ratios of DM produced by the plant species in the agroforestry plots to those produced in the sole plots, was 1.95 for ryegrass, 1.71 for ryegrass/clovers and 1.45 for lucerne ground covers.
5.  These results indicate the susceptibility of pasture species to shading and interception of rainfall by the tree crowns (aboveground interactions), and the trees to competition for soil moisture (underground interaction).
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2.
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:
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.
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3.
In designing agroforestry systems, the combination of tree genotype (orspecies) and pasture species and the spatial arrangement of trees are importantconsiderations. The spatial variation of fine root length density (FRLD) ofthree radiata pine (Pinus radiata D. Don) genotypes,referred to here as clone 3, clone 4 and seedlings, was studied in athree-year-old temperate silvopastoral experiment. The genotypes were plantedwith three understorey types: ryegrass (Lolium perenne)mixed with clovers (Trifolium spp), lucerne(Medicago sativa), and control (bare ground). Also fineroot distribution of both tree and pasture species with soil depth and inrelation to tree row (0.9 m north or south of and within the rippedtree row) was studied. Greater FRLD was found in clonal than in seedling treesin the bare ground treatment but not in the two pasture treatments, and in the0–0.1 m but not in the 0.1–0.2 or 0.2–0.3m soil layers. Clonal trees had a greater ability to develop a moreextensive root system, especially in the 0–0.1 m soil layer,but that advantage disappeared when they were planted with pasture species sincecompetition from the pasture species was most severe in the 0–10cm layer. The FRLD of lucerne was greater than that ofryegrass/clovers, consistent with the greater aboveground biomass production oflucerne. Pasture species FRLD was greater on the south (wetter) than on thenorth side of the ripline or in the ripline. The interception of prevailingsoutherly rain-bearing wind by tree crowns resulted in the south side beingwetter than the north side. Results indicated that production and distributionof fine roots of both tree and pasture species responded to changes in themicroclimate. We suggest that to optimize pasture/tree biomass productionplanting trees in the north-south direction is better than in the east-westdirection at the studied site. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

4.
Acacia melanoxylon, a N2-fixing timber tree occurring naturally in eastern Australia, is now promoted as a component of silvopastoral systems; but the interaction of the tree with pasture and soils has not been adequately studied. This study investigated the effects of Acacia melanoxylon on soil nitrogen (N) levels, N availability, soil pH, bulk density, organic carbon, C:N ratios and soil moisture in three separate silvopastoral sites with contrasting soil types in the North Island of New Zealand. At each site four tree stocking rates were studied (0, 500, 800, and 1700 stems ha–1). The trees were nine years old at the time of the study. Soil samples from each study site were taken once at three depths (0 to 75 mm, 75 to 150 mm, and 150 to 300 mm), with three replicates per tree stocking rate. Soil analyses showed that although there were differences between soil types, few statistically significant differences occurred due to tree stocking rate. A greenhouse pot trial growing ryegrass (Lolium multiflorum L. cv. Concord) in soil from the A horizon of each soil type from under the trees and the open pasture found that ryegrass yield, N uptake and N supply increased with increasing tree stocking rate. Increased N supply under the trees, coupled with greater soil moisture compared to the open pasture may have accounted for the higher pasture yield under Acacia melanoxylon compared to non dinitrogen fixing tree species. This study suggested that Acacia melanoxylon in a silvopastoral system had the potential to increase soil N availability.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

5.
Soil moisture content from 0 to 2 m depth was monitored under 2–6 year old radiata pine (Pinus radiata) with three understoreys of bare ground, lucerne (Medicago sativa) and ryegrass/clover (Lolium perenne/Trifolium spp.) and under adjacent open-grown lucerne and ryegrass/clover pastures. By the fifth year soil moisture depletion/recharge pattern under the trees alone was similar to that under open pasture and under trees with pasture understoreys. Maximum plant available moisture storage was 207–223 mm in the top meter of this Templeton silt loam soil but only 69–104 mm at 1–2 m depth where coarse textures often predominated. Lucerne reduced soil moisture content (SMC) to lower levels during drier summers and extracted more water from 1 to 2 m depth than ryegrass/clover. Evapotranspiration (ET) during early summer when soil moisture was high was close to the Penman potential evapotranspiration (E p ), but the difference increased when SMC in the top meter dropped below 200 mm. The silvopasture treatments had higher ET in winter than pasture alone but this was still less than E p . Soil moisture deficits (SMD) at the end of each summer were sufficiently large to require slightly higher than normal winter rainfall and ET < E p to recharge the soil to field capacity before the next summer. The soil moisture results, taken together with root and growth data, suggest that trees and understorey pastures are complementary in the first three or four growing seasons but this balance subsequently declines in favor of the pine trees. Management options, to extend the period that understorey pastures are productive, include reducing tree stockings, more vigorous pruning, using competitive understoreys and changing from pines to deciduous trees. Research on new silvopastoral combinations is suggested.  相似文献   

6.
Quantitative field measurements of biological nitrogen fixation (BNF) and biomass production by four different understorey pastures in a Pinus radiata-pasture agroforestry system were determined over a period of one year. The trees were two years old at the beginning of this study and the understorey pastures were being cut and removed for silage. The BNF was determined using the 15N dilution technique. Pastures of ryegrass+clover, cocksfoot+clover, phalaris+clover and lucerne were used. Substantial amounts of BNF were found (71 to 230 kg N ha–1 year–1) with lucerne showing the highest N fixation. However, lucerne derived only 71 to 72% of its N from the atmosphere (%Ndfa) during the spring/summer period compared to 83–97% with clovers, thus the net N demand from the soil was substantially higher with lucerne. This caused increased N stress to the trees. Clover in ryegrass+clover pasture fixed more N than the other grass+clover pastures. Although pasture position in relation to trees did not affect annual pasture total DMY and %Ndfa, pastures north of tree row grew better than those in other positions. Trees significantly affected the BNF of legumes and the botanical composition of pastures with highest BNF and legume production occurring in pastures midway between two rows of trees. These results suggest that it would be advantageous to evaluate different legumes and grasses for tolerance of shade and moisture stress in future studies. As the trees studied were only 1.5 to 3 m in height, their effects on BNF, seasonal pasture biomass production and botanical composition are expected to increase with tree dominance in the ecosystem with time. Amounts of N fixed were related to the productivity (i.e. dry matter and N yield) and seasonal persistence of the legumes. The productivity was high in spring and summer and low in autumn and winter.  相似文献   

7.
The tree-shrub savanna ‘Forêt Classée de Nazinon’ (Burkina Faso) is submitted to a management of grazing and rotational cutting of Detarium microcarpum. This species resprouts after cutting. In order to investigate whether this silvopastoral land use system is sustainable, aboveground herbaceous biomass was measured on subplots under uncut trees (‘uncut’), next to the stubs of cut trees (‘cut’) and on subplots not influenced by the (former) crowns of trees (‘open grassland’) in four lots. These lots were cut one, three, six and seven years before the study. Vegetation composition of the lots and the composition of the diet of cattle were also determined. Comparisons were made between treatments and lots. Herbaceous biomass was lower in the open grassland subplots than in uncut or cut subplots. We speculate that soil enrichment and more efficient precipitation input in (former) tree crown zones could have resulted in this pattern. Cutting and subsequent resprouting of trees did not lead to significant differences in herbaceous biomass between cut and uncut subplots. The most simple explanation for this is that the trees could extend their roots beyond the location of their neighbouring trees. Biomass and coverage of perennial grasses, mainly Andropogon ascinodis and Andropogon gayanus, did not change in lots cut one, three or six years before the study, but decreased dramatically in lots that were cut seven years before the study. When foraging, cattle spent more than 90% of their time feeding on these species. This indicates that, as a consequence of tree cutting, forage availability may be reduced to the point where local herdsmen are forced to take their cattle to another region. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

8.
Twenty-five species and hybrids in Populus were used as parents, and 26 cross combinations, including more than 5 000 seedlings, were obtained by artificial cross breeding. The length of infructescence, number of seeds per infructescence, thousand-seed weight, germination rate of seeds among these cross combinations were tested. The results indicated that the cross combinational effects were significant for these traits, and demonstrated that the length of infructescence, thousand-seed weight were positively affected by female parent. In addition, seedling height, diameter above ground, diameter at breast height (DBH) of 17 cross combination progenies were investigated. The analysis of mean and standard deviation of these three traits showed that seedling height, diameter above ground, DBH had extensive variation among combinations and individuals within combination. Variance analysis and estimate of heritability indicated that the three traits had wide variation and were controlled by heredity. It was feasible to select superior cross combinations and seedlings. Further more, the result of multiple comparison showed that P. deltoides ‘Lux’ × P. deltoides ‘D324’, P. ussuriensis cl. ‘U4’ × P. deltoides ‘T66’, P. ussuriensis cl. ‘U4’ × P. deltoides ‘T26’, P. deltoides ‘Lux’ × P. ussuriensis cl. ‘U3’, (P. tomentosa × P. bolleana) × (P. alba × P. glandulosa), (P. alba × P. tomentosa) × (P. alba × P. glandulosa), and (P. alba × P. glandulosa ‘No. 2’) × P. tomentosa ‘Lumao 50’ were superior cross combinations with higher growth rate. Finally, 123 elite seedlings were selected for further test. [Supported by the Doctoral Foundation of Ministry of Education (Grant No. 200220022004) and the National “863” Project (Grant No. 2002AA241071)]  相似文献   

9.
Traditionally, poplar (Populus spp.) have been planted to control erosion on New Zealand’s hill-slopes because of their capacity to dry out and bind together the soil. Two systems: (1) widely spaced, planted poplar for soil conservation, and (2) non-eroded open pasture were compared to determine the relative effect of the poplar–pasture system on the production, nutritive value and species composition of the pasture, and on the water balance. Measurements were made at three sites with mature poplar (>29 years and 37–40 stems ha−1) and at a replicated experiment with young poplar (5 years, 50–100 stems ha−1). Soil water relations did not suggest strong competition for water between poplar and pasture. Pasture accumulation under mature poplar was 40% less than in the open pasture, but under young poplar was similar to that in the open pasture. Chemical composition of pasture suggested that feed quality of pasture in the open was better than under the poplar canopy, except during spring, when most chemical components were similar. At the most, in vitro digestibility of pasture dry matter was 8.9% lower and metabolisable energy of pasture dry matter was 1.5 MJ kg lower under the poplar canopy than in the open pasture. Shade tolerant species were not dominant in the plant community under the poplar canopy with grasses such as browntop (Agrostis capillaris, L.) and ryegrass (Lolium perenne, L.) being a high proportion of the plant community. Differences in chemical composition were related to differences in the botanical composition between the open pasture and the poplar understorey. It was concluded that the greatest effect of poplar was on pasture production due to shading, and that management of this silvopastoral system needs to focus on control of the tree canopy to lessen the decrease in pasture production.  相似文献   

10.
Silvopastoral systems in New Zealand that incorporate trees planted to control soil erosion on hills largely rely on the productivity of the pastoral system for financial returns. The effect on pasture productivity of increasing the tree canopy height by pruning Italian gray alder (Alnus cordata) was investigated by measuring the response of light, soil moisture, soil temperature, pasture production of major pasture species, and grazing behaviour of sheep. A split-plot design with four replicates was used. The main plot treatments were three levels of shade (81, 23, and 12% of available photosynthetic photon flux (PPF)), created by pruning 11 year old alder grown at the same density. The sub-plot treatments were four pasture mixes: perennial ryegrass (Lolium perenne), Yorkshire fog (Holcus lanatus), and cocksfoot (Dactylis glomerata), each sown with white clover (Trifolium repens), and cocksfoot sown with lotus (Lotus pedunculatus). Soil temperature was highest under light shade. Total herbage yield at 50 mm stubble height from October to May under heavy and medium shade was 60 and 80%, respectively, of the total herbage harvested under light shade. Cocksfoot had the greatest herbage yield, either with lotus or white clover. The tillering of perennial ryegrass was suppressed by shade more than for the other grass species making ryegrass unsuitable for use in this silvopastoral system. More sheep grazed in the light shade than in the heavy shade, but there was no difference in sheep preference for cocksfoot or Yorkshire fog. Lotus was grazed more frequently than white clover. Pruning of alder to increase canopy height has the potential to improve the productivity of the understorey pasture and its acceptability to sheep.  相似文献   

11.
Understanding the changes in soil properties in silvopastoral systems is important in regulating the interactions between tree and understorey pastures. In this study, the effects of understorey management on soil mineral N and moisture availability, soil temperature, soil C, and tree growth were investigated in a seven-year-old silvopastoral agroforestry experiment in Canterbury, New Zealand. The systems included understorey treatments of bare ground and ryegrass (Lolium perenne) pasture. Soil mineral N, moisture content, and temperature were monitored from July 1997 to July 1998 in two positions (0.9 and 3.5 m north of tree rows) and two soil depths (0–10 and 10–20 cm). Soil C and N in the 0–10 cm depth were higher in the ryegrass than in the bare ground plots, reflecting the organic C and N input in the ryegrass plots, as well as greater N loss from the bare ground plots in the form of nitrate leaching and/or denitrification. Soil C was higher in the position 0.9 m than 3.5 m away from the tree rows, possibly caused by the greater C input from decomposing fine tree roots and needle litterfall at the 0.9 m position. Soil moisture availability was greater in the bare ground than in the ryegrass plots in the summer. No effect of understorey management on soil temperature was found. Soil nitrate levels were lower in the ryegrass plots and may be limiting when soil moisture supply was adequate. Tree volume growth from winter 1997 to 1998 was significantly greater in the bare ground treatment, reflecting better soil moisture and N supply conditions. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

12.
Poplar is one of the dominant tree species for the establishment of fast growing plantations in Shandong Province.Eighteen poplar clones belonging to Populus aigeiros section were introduced from Italy, Turkey and domestic regions. Populus deltoides cv. ‘Lux‘ 1-69/55 (1-69), which was widely used in Shandong Province, China, was taken as control clone (1-69).Following a randomized complete block design, seedling test and controlled afforestation trials were carried out at Juxian County,Caoxian County and Laiyang City. The results showed that the poplar clone (Populus x euramericana cv. ‘102/74‘), namely 102/74, performed well both in terms of adaptability and growth rate. The mean height of 13.9 m (H), diameter at breast height of 18.0 cm (DBH) and volume growth of 0.1445 m3 (V) were 2.2 %, 21.6% and 52.9% higher than those of 1-69 (CK), respectively,at the age of 5 years at three experimental sites. Moreover, the clone can be propagated easily and showed high resistance to poplar disease, pest as well as salinity and had longer growing period. Furthermore, wood basic density and fiber length of new poplar clone (102/74) were as same as 1-69 (CK). It was concluded that the selected clone (102/74) was ideal for the estab-lishment of fast-growing poplar plantations, especially for the pulpwood plantations in Shandong Province.  相似文献   

13.
Tree-based land-use systems could sequester carbon in soil and vegetation and improve nutrient cycling within the systems. The present investigation was aimed at analyzing the role of tree and grass species on biomass productivity, carbon sequestration and nitrogen cycling in silvopastoral systems in a highly sodic soil. The silvopastoral systems (located at Saraswati Reserved Forest, Kurukshetra, 29°4prime; to 30°15prime; N and 75°15prime; to 77°16prime; E) consisted of about six-year-old-tree species of Acacia nilotica, Dalbergia sissoo and Prosopis juliflora in the mainplots of a split-plot experiment with two species of grasses, Desmostachya bipinnata and Sporobolus marginatus, in the subplots. The total carbon storage in the trees + grass systems was 1.18 to 18.55 Mg C ha−1 and carbon input in net primary production varied between 0.98 to 6.50 Mg C ha−1 yr−1. Carbon flux in net primary productivity increased significantly due to integration of Prosopis and Dalbergia with grasses. Compared to 'grass-only' systems, soil organic matter, biological productivity and carbon storage were greater in the silvopastoral systems. Of the total nitrogen uptake by the plants, 4 to 21 per cent was retained in the perennial tree components. Nitrogen cycling in the soil-plant system was found to be efficient. Thus, It is suggested that the silvopastoral systems, integrating trees and grasses hold promise as a strategy for improving highly sodic soils. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

14.
At present, our understanding of the dynamics of microbial biomass and soil N in silvopastoral systems is very limited. In this paper, the effects of understorey management on soil microbial C and N, net N mineralization, and net nitrification were studied in two seven-year-old radiata pine (Pinus radiata D. Don) – pasture systems, consisting of plots with and without ryegrass (Lolium perenne) as an understorey. Mini-plots (1 × 1 m) with animals excluded and herbage repeatedly clipped and removed were used for soil sampling. Three mini-plots formed a transect at each of two positions: 0.9 and 3.5 m north of the tree rows. Measurements were taken from July 1997 to June 1998 about once every 40 days. One composite sample was collected from each of two sampling depths (0–10 and 10–20 cm) at each transect position on each sampling date. Temporal and spatial variability of N mineralization rates and microbial biomass C and N was large. Net mineralization and nitrification rates were higher in the bare ground than in the ryegrass plots for a major part of the year, particularly from late spring to early fall. Net N mineralization and nitrification rates were higher in the 0–10 than in the 10–20 cm soil layers in both the ryegrass and bare ground treatments; however, the depth effect on microbial biomass C and N was only significant in the ryegrass treatment. In the surface soil layer, microbial biomass C and N were substantially greater in the ryegrass than in the bare ground plots. Soil microbial properties and activities were closely linked to pasture root activities, soil depth, and site biophysical conditions. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

15.
Under artificially-simulated complex salt-alkali stress, the levels of active oxygen metabolism in roots were studied using three-year-old cutting seedlings of Spiraea × bumalda ’Gold Mound’ and Spiraea × bumalda ’Gold Flame’. The present study aimed at exploring the antioxidant capacity in roots of spiraeas and revealing their adaptability to salt-alkali stress. Results indicate that the oxygen free radicals contents, electrolyte leakage rates and MDA contents in roots of Spiraea × bumalda ’Gold Mound’ and Spiraea × bumalda ’Gold Flame’ show an increasing tendency with the increases of the salinity and pH value, whereas the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) all increased firstly and then decreased. With the increase in intensity of salt-alkali stress, the CAT activity in roots of Spiraea × bumalda ’Gold Flame’ is higher and the increasing extents in the oxygen free radicals contents, electrolyte leakage rates as well as MDA contents are lower compared with Spiraea × bumalda ’Gold Mound’, indicating that Spiraea × bumalda ’Gold Flame’ has a stronger antioxidant capacity.  相似文献   

16.
Microsite influences on resource allocation related to silvopastoral swards undergoing repeated defoliation are unclear. Defoliating traditional pasture species according to canopy development criteria may not be appropriate when the plants grow as understory crops in woodlots. An experiment using container-grown plants was conducted under field conditions to determine how open (O), shaded woodland (W) and open-to-shaded woodland transition zones (E O, E W), representing the partial shade conditions found in silvopastoral settings, influenced productivity and dry matter allocation in Dactylis glomerata L. Plants established in spring (SP) and late summer (LS) were clipped each time mean sward height reached 20 cm. Dry matter production differed for SP and LS plantings, and was greater in O than W sites. Dry matter allocation to shoots of SP plants indicated some agronomic benefit associated with the E O and E W sites. Leaf mass did not vary with irradiance, but stembase mass did. The SP plants had numerous small tillers whereas LS plants were composed of comparatively fewer but more massive tillers. Plants growing at O, E O and E W were similar, whereas plants in the W site were smaller and had the fewest tillers regardless of planting time. Results suggest that defoliation management for shaded components of silvopastoral systems should be based on some index other than sward height, and that management criteria might change during the growing season. Less intensive removal (e.g., 10-cm rather that 5-cm residue) should be considered for defoliated, shade grown plants, since this could allow more stembase and nonstructural carbohydrate storage tissues to remain. The US Government’s right to retain a royalty-free, non-exclusive copyright is achnowledged.  相似文献   

17.
This study aimed at evaluating the influence of a silvopastoral system (SPS) composed of “Aroeira” trees (Myracrodruon urundeuva) on the nutritional value of Brachiaria brizantha cv. Marandu forage grass over the rainy season. The experiment was conducted in the SPS located in the “Cerrado” biome in Lagoa Santa County, Minas Gerais state, Brazil, in the agricultural year of 2004–2005. It was evaluated the influence of “Aroeira”, whose density in the area was 140 trees/ha, on the following parameters of the B. brizantha cv. Marandu forage grass: forage mass harvest above stubble height, morphogenic attributes, bromatological composition and nutritional value. The effects of “Aroeira” trees on the micro-climatic conditions were also evaluated. The experiment adopted a randomized block design with five blocks (cutting seasons), two treatments (a shaded pasture—B. brizantha cv. Marandu shaded by M. urundeuva—and a pasture in full sun—B. brizantha cv. Marandu in full sun), and three replicates. The tree component, composed of the tree species M. urundeuva in the experimental density adopted, increased dry matter and crude protein of the forage mass harvest above stubble height, without affecting the concentration of neutral detergent fibre or acid detergent fibre, thus causing dry matter and organic matter in vitro degradability as well as effective degradability of the forage grass to remain the same as those obtained in full sun. Therefore, the results of this study show the possibility of using trees and grass to increase both animal production and environmental services.  相似文献   

18.

Introduction  

Triploid breeding is one of the most powerful approaches for improvement of the genus Populus L. Pollination with artificial unreduced (2n) pollen was inefficiency, owing to weak competition of 2n pollen. To induce 2n megaspores and improve the efficiency of triploid production, female buds of Populus pseudo-simonii × Populus nigra ‘Zheyin3#’ were exposed to high temperature during megasporogenesis.  相似文献   

19.
Silvopastoral systems involving poplars are widespread in rural landscapes in a number of regions of New Zealand. The effect of widely spaced trees of Populus nigra × P. maximowiczii, aged 8–11 years, on the growth and botanical composition of understorey pasture mixes was determined over 3 years at a southern North Island hill country site. Pasture mixes comprised existing pasture, and two introduced test swards comprising new grass (Agrostis capillaris, Dactylis glomerata, Lolium perenne) and legume (Lotus uliginosus, Trifolium repens) cultivars. Pasture accumulation beneath trees (6.6 t DM ha−1 year−1) was 23% less than open (unshaded, no trees) pasture (8.6 t DM ha−1 year−1) and differences in accumulation occurred between tree aspects (North and South sides of trees) when trees were foliated. In early spring, North plots produced 11–14% more herbage than South plots whereas in late summer, South plots produced up to 44% more herbage than North plots. Yield of both test swards (6.4 and 8.0 t DM ha−1 year−1) was not significantly different from that of the existing sward (7.4 t DM ha−1 year−1) but productivity varied between swards in spring and summer. One test sward included Lotus uliginosus cv. Grasslands Maku, and the sward produced 30% more DM than the other swards in mid-summer. Dactylis glomerata cv. Grasslands Wana comprised 37% of the DM of swards in which it was sown and was the most successful cultivar, followed by Grasslands Maku. Both cultivars are recommended for silvopastoral systems where pasture is lightly grazed.  相似文献   

20.
Riverine silvopastoral practices with native pecan (Carya illinoinensis) are a suitable land use for areas subjected to seasonal flooding in southern and central regions of the United States. Nut, timber and forage production, and the economics of managed pecan silvopastures were examined in southeastern Kansas. During 1981–2000, annual hulled nut production varied between 50 and 1600 kg ha−1 in stands averaging 72 years of age, and ranging in density between 35 and 74 trees ha−1. The nut crop had a pattern of biennial bearing with some exceptions. Tree stem diameter and stand basal area increased linearly with time. Nut production was not related to stand age or tree density, however, suggesting that nut production had reached a steady state level. Merchantable timber yield ranged between 0.25 and 1.35 m3 ha−1 year−1. In pecan silvopastures with a mean tree age of 37 years, forage production varied between 1500 and 4600 kg DM ha−1 in 2001 and 2002. In 2001 only, grass production decreased with decreasing solar radiation within the range of 0.25–0.83 of fraction light transmitted. In both years, the grass understory had acceptable quality for cow-calf production with average crude protein content between 9 and 11.8%, and no evidence of excessive levels of ergoalkaloids from tall fescue. Twenty-seven vascular plants were identified in the understory of which nut sedge (Cyperus esculentus), tall fescue (Festuca arundinacea), wild oat (Avena fatua) and Canadian wild rye (Elymus canadensis) were the most abundant. Economic simulations obtained with the U.S. Agroforestry Estate Model indicated that pecan nut price is the main variable driving economic outputs under current production conditions. Annual cash flows from nut sales had smaller fluctuations than nut yields because of an inverse relation between nut price and yield. Improved timber production appears an option for increasing profitability of pecan silvopastures.  相似文献   

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