Effect of pruning intensities of three woody leguminous species grown in alley cropping with maize and cowpea on an alfisol

Field trials were carried out on an Oxic Paleustalf in the humid zone of southwestern Nigeria withLeucaena leucocephala (Lam.) de Wit,Gliricidia sepium (Jacq.) Steud. andSesbania grandiflora (L.) Pers. alley cropped with maize and cowpea. The three leguminous woody species were grown in hedgerows spaced at 2 m. Trials were carried out one year after establishment of the hedgerows using a split-plot design with four replications. TheLeucaena trial had twenty pruning combinations consisting of five pruning heights (25, 50, 75, 100 and 150 cm) and four pruning frequencies (monthly, bi-, tri- and six-monthly). TheGliricidia andSesbania hedgerows were subjected to nine pruning intensities consisting of three pruning heights (25, 50 and 100 cm) and three pruning intensities (monthly, tri- and six-monthly).For the three woody species, biomass, dry wood and nitrogen yield from the hedgerow prunings increased with decreasing pruning frequency and increasing pruning height. Biomass, dry wood and nitrogen yields were in the following orderLeucaena >Gliricidia >Sesbania.The various pruning intensities had no effect on survival ofLeucaena plants. Pruning frequency had a larger effect than pruning height on survival ofGliricidia andSesbania plants. With monthly pruning, about 25 percent of theGliricidia and all of theSesbania plants died within six months of repeated pruning. Even with lower pruning frequencySesbania plants showed lower survival rates thanGliricidia orLeucaena.The various pruning intensities of all the hedgerow species had more pronounced effects on the grain yield of the alley cropped cowpea than on maize grain yield. Higher maize and cowpea yields were obtained with increasing pruning frequency and decreasing pruning height.IITA Journal paper number 335     

SBELTS: A model of soybean production under tree shelter

Farmers in the North Central region of the United States often are reluctant to use shelterbelts because of inadequate information clearly showing their benefits. We developed a computer model, called SBELTS for ShelterBELT and Soybeans, that simulates the influence of a shelterbelt on soybean (Glycine max L.) production across an agricultural field in the midwestern United States. Objectives of this study were to 1) describe the structure of SBELTS, 2) present model simulations, and 3) discuss model limitations. SBELTS is composed of three submodels. The first submodel produces characteristics of a shelterbelt that are passed to the second submodel that estimates daily windrun at user-specified distances leeward (away from the prevailing wind) of the shelterbelt. Estimated daily windruns are merged with other microclimatic information to produce weather files for each specified distance. Finally, the third submodel uses a soybean growth/yield model to estimate soybean yield at specified distances, and the yields are averaged. Data collection was not a part of the present project, so SBELTS was evaluated by comparing predicted results with published information. SBELTS was used to predict soybean yield across a field leeward of a 7.6 m tall shelterbelt, and the predicted yield curve compared well with published yield curves. The sensitivity of SBELTS to variation in rainfall was evaluated by predicting yields for 3.8 m tall and 7.6 m tall shelterbelts in wet, normal, and dry years. Results showed no shelterbelt influence in wet years, some influence in normal years, and a sizable influence in dry years. Results showed that the 7.6 m shelterbelt had more influence than the 3.8 m shelterbelt. Although SBELTS has limited use, it is the first step in the development of more advanced models that will be able to simulate production of soybeans and other crops under the influence of shelterbelts on a variety of soil types.This revised version was published online in November 2005 with corrections to the Cover Date.     

Development and ecology of bottomland hardwood sites

A basic knowledge of the origin, development, and ecology of bottomland hardwood sites is important for assessing harvesting impacts on those sites. This paper presents an overview of the geologic origin and development of hardwood sites, species-site relationships and the natural patterns of ecological succession on those sites, and the implications of that information for forest management. Bottomland hardwoods occur on floodplain sites primarily in the Atlantic and Gulf Coastal Plains. Past geologic events led to the formation of broad stream valleys in those areas because of the erodible, sedimentary geologic materials. Natural patterns of ecological succession on floodplain sites are influenced by autogenic and allogenic processes in that the sites may undergo constant change because of deposition. Three natural patterns of succession are recognized for floodplain sites of major river bottoms—those occurring on permanently flooded sites, those on low elevation wet sites, and those on higher elevation, better drained sites. Floristic composition and successional patterns are strongly influenced by the hydrologic events on the sites and particularly by rates and types of deposition.     

油菜素内酯提高蔬菜作物抗逆性的研究进展

油菜素内酯化合物(Brassinosteroids,BRs)是国际上公认的一类高效、广谱、无毒的新型植物甾醇类生长激素。近年来研究发现,BRs的使用可显著提高植物对生物和非生物逆境的抗性,从而促进植物生长发育,大幅度提高作物产量。本文综述了BRs的类型、应用方式以及在提高蔬菜抵抗干旱、低氧、温度、盐离子、病害、重金属等环境胁迫方面的研究成果,并对未来的研究方向进行了展望。     

THE CHARACTERISTICS OF THE NUTRIENT CYCLING IN BIRCH STANDS WITH DIFFERENT AGE STAGES

SuccessionisthedynanucdeveloPInentofecosystemswhichcanbecharactetindbyenergyandndneralcyclings.Eachsuccessionstagehasitscharaceristicsofelementcycling.SomeschOlarshaveStatedbutbrieflawsofnutrienCyclinginsuccessionstagesI"3I.InthespaPer,thenutrientcyclingcharacterishcsofbirchsuccessionseriesinXiaokinganlingwerediscussed.SwrYAasAroarernoDSThestUdyareaislocatedinLiangshniNatUralReservesinthendddieofXiaox-ing'anlilg(l28"53,2o'rE,47olo'5O"N).Theclimat6belongstocontinentalmonsoonclimate,W…     

三种不同类型灌丛的结构特点及演替利用前景

在贵州省黔东南地区雷山、施秉、镇远三县调查了三种不同类型的灌丛，对样地内灌木树种和草本植物的种类、密度、覆盖度、水平及垂直分布等结构特点进行了分析．并对其演替及利用前景进行了评价。     

Comparison between old-growth stands and secondary stands regenerating after clear-felling in warm-temperate forests of Yakushima, southern Japan

In order to infer successional changes in structure, species composition and diversity of warm-temperate forest, we compared secondary stands regenerating after clear-felling (41–64-years old) with old-growth stands at altitudes between 300 and 800 m on Yakushima Island, southern Japan. Stem density and maximum stem diameter differed between secondary and old-growth stands, but basal area and aboveground biomass did not. At lower altitudes, the dominant species in old-growth stands with a strong sprouting capacity (Castanopsis cuspidata) also dominated secondary stands, and species composition of secondary and old-growth stands was similar. At higher altitudes, by contrast, the dominant species in old-growth stands (Distylium racemosum) had little sprouting capacity and was poorly represented in diverse secondary stands, which were dominated by Castanopsis or other less abundant species. Secondary stands had greater species diversity (Shannon–Wiener index) than old-growth stands, particularly at higher altitudes. This was due to greater species richness resulting from higher stem density per area, but not to greater evenness. We grouped the component species that share ecologically similar traits into four guilds (fagaceous, primary evergreen, secondary evergreen and deciduous species). Secondary stands were characterized by greater numbers of deciduous and secondary evergreen species. We concluded that different sprouting capacities of dominant species and different regeneration traits among guilds are responsible for the change in species composition and diversity during succession.     

Populus tremuloides Michx. postfire stand dynamics in the northern boreal-cordilleran ecoclimatic region of central Yukon Territory, Canada

Postfire vegetation development among 8–185-year-old stand was assessed based on 100 relevés from the northern boreal-cordilleran ecoclimatic region (61–63°N) in the central Yukon Territory, Canada. Vegetation sampling included only stands thought to have originated from postfire Populus tremuloides Michx. regeneration that occurred on well drained and low gradient sites. Seven vegetation types were recognized based on cluster analysis and Kruskal–Wallis testing. Relevé ordination using Detrended Correspondence Analysis (70% explained variance) indicated six of the vegetation types represented a secondary successional chronosequence, based on their juxtaposition and a strong correlation of the primary axis with stand age (r = 0.89, P < 0.001). No correlation (P > 0.05) occurred between stand location and age. The youngest vegetation (8–11 years) had a moderate cover of P. tremuloides and Salix spp. up to 5 m tall, with a ground cover of Ceratodon purpureus (Hedw.) Brid. and Bryum caespiticium Hedw. This vegetation was expected to result in P. tremuloides, mixed P. tremuloides and Picea glauca (Moench) Voss, and P. glauca/Hylocomium splendens forest stands with increasing age, respectively. P. tremuloides//Calamagrostis purpurascens—Arctostaphylos uva-ursi stands formed the mid-seral vegetation. Along the chronosequence, total tree, P. tremuloides, shrub, and herb cover peaked 50–70 years after stand initiation; P. glauca cover, total and nonvascular species richness, and dominance concentration gradually increased (P < 0.001); vascular plant richness decreased; bryophytes had a U-shaped abundance pattern; and total plant cover was constant through time (125%). Richness totalled 113 species with averages of 13–18 per relevé. Coarse woody debris was most abundant (maxima 100–223 m³/ha) during the first 20 years of stand development then declined to <50 m³/ha. Successionally, a stem exclusion stage occurred (years 8–18), but with a delayed peak of 2–4 years and reduced densities (1.47 stems/m²) relative to southern boreal stands. No understory suppression, and therefore, no reinitiation stage occurred. Following stem exclusion, an accelerated canopy transition stage occurred relative to southern boreal forests due to early establishment rather than better height-growth rate of P. glauca relative to P. tremuloides. P. glauca tended to equal the cover of P. tremuloides 95–100 years after stand initiation. The oldest vegetation type in the chronosequence more closely resembled old-growth than a gap dynamic stage of development, possibly because of its youthful average age of 125 years. A modification was proposed for the canopy transition stage (Chen–Popadiouk stand development model) to account for the “forced” replacement of P. tremuloides by P. glauca. Differences in stand development were attributed to the cold northern climate.     

Tree crop based agroforestry in Nigeria: a checklist of crops intercropped with cocoa

A survey of cocoa farmers in Bendel, Ogun, Ondo and Oyo States of Nigeria, carried out in 1985, showed that almost all the farmers intercropped other crops with cocoa. The intercrops included food crops such as plantain (92.3), cocoyam (85.7%), cassava (51.3%), yam (41.3%), maize (38.9%), melon (31.4%), cowpea (28.6%) and pineapple (26.0%) and tree crops such as oil palm (71.5%), kola (67.3%), coffee (41.0%), coconut (7.9%) and citrus (7.2%). Other crops are ewe-iran (Sarcophrynium brachystachys) and ewe-gbodogi (Megaphrynium macrostachyum) (45.2%), african walnut (Tetracarpidium conophorum) (42.2%), aligator pepper (Aframomum melegueta) (31.6%), and iyere (Piper guinense) (20.2%). Guava, mango, pawpaw and vegetables such as celosia, okra and solanum occur in cocoa plots at rather low frequencies. As many as six or more other crops can be intercropped with cocoa at the same time.