1980-2007年喜马拉雅东段洛扎地区冰川和冰湖变化研究

利用1980年地形图、1988/1990年Landsat TM、2000年Landsat ETM＋、2007年ALOS AVNIR-2遥感资料和近41年（1967-2007年）的气温、降水量资料对喜马拉雅东段洛扎地区的冰川、冰湖变化特征及变化原因进行了研究。结果表明：1）1980-2007年,本区冰川面积从491.64...     

小麦对行免耕播种机试验研究

为解决一年可熟区小麦免耕播种作业的技术难题，提出了小麦对行免耕播种的思想；设计了2BMD-12型小麦对行免耕播种机．在玉米行何播种小麦．避开玉米秸秆和根茬。采用了新型高效的带状粉碎防堵机构，防堵性能优良。田问性能试验表明：2BMD-12型小麦对行免耕播种机在玉米直立秸秆和大量秸秆覆盖下。如能实现对行，可以顺利进行播种作业，满足作业质量和作物高产对施肥量的要求．适合我国中小地块、中小功率的特点。     

松嫩平原不同土壤基质条件下羊草种群年龄结构的研究

通过对不同土壤基质条件下羊草Leymus chinensis种群年龄结构进行研究,结果表明:5月中旬在松嫩平原羊草种群营养生长期,分蘖株均由1龄、2龄、3龄3个龄级组成,呈增长型年龄结构,其中均以1龄和2龄级分蘖株占绝对优势,为89.4%～99.7%,3龄株仅占0.3%～10.6%;根茎均由2龄、3龄、4龄3个龄级组成,根茎长度及其质量均以2龄级最高,3龄次之,4龄最小;根茎物质的储量均随着龄级的升高而降低,羊草种群对低龄植株、根茎的大比例投资是羊草种群扩大其空间的一种十分有效的生态对策.     

Soil water characteristics in glacial till at two forest sites in Sweden

Soil water characteristics were determined in 6 soil profiles along a Norway spruce forested sandy‐loamy till hillslope in Southern and Northern Sweden, respectively. The soil moisture class was mesic at both sites, i.e. having well drained soil water conditions. Two different Podzols; Leptic and Orthic, were developed at each site respectively. The vertical distribution of soil water retention capacity (SWRC) was similar in the different profiles at each site respectively. The SWRC of the mineral soil was significantly higher in the spodic B horizon compared to the other horizons. In concordance with the vertical distribution of SWRC, the largest amount of organic matter in the mineral soil, measured as ignition loss, was also found in the spodic B horizon. The significantly higher SWRC in the spodic B horizon, i.e. the ¡lluvial horizon, was suggested to depend on the accumulated organic‐sesquioxide material in this horizon. As SWRC reached maximum values in the spodic B horizon at all tensions applied, it was further suggested that soil formation in the studied profiles enhanced the formation of both micro‐ and macropores in the spodic B horizon. The variation of SWRC, at a certain level in the soil, was often larger within a profile than between the profiles at each site respectively.     

免耕与常规耕作潮棕壤交换性阳离子的剖面分布特征

通过田间定位试验.研究了不同耕作方式对潮棕壤0-100 cm深度6个土层土壤交换性阳离子的影响.结果表明,与常规耕作相比,免耕使土壤表层pH显著增,.而电导率下降;同时,免耕增加了表层土壤可交换性K~+含量,降低了可交换性Na~+含量,但对可交换性Ca~(2+),Mg~(2+)和阳离子交换量没有产生显著影响.相关分析结果表明,可交换性K~+与土壤养分含量没有显著相关性,而可交换性Na~+,Ca~(2+),Mg~(2+)和阳离子交换量与有机质和全氮含量均呈负相关关系.     

基于GIS的雪崩对冰湖风险性评估——以喜马拉雅山科西河流域为例

雪崩是冰湖风险性评估的因子之一,借鉴欧美发展起来的雪崩模型,在冰湖溃决洪水频发的喜马拉雅山地区开展雪崩对冰湖风险性评估研究具有重要意义。基于ICIMOD IKONOS DEM和Landsat-TM数据,利用GIS方法提取了研究区雪崩形成的海拔、平面曲率、坡度和地表覆盖类型等估算因子,根据Av=(Al+Fy)×S×Rg模型估算了研究区潜在雪崩形成区域,并应用GIS方法和α-β模型估算了雪崩的传播路径。结果表明:潜在雪崩不易形成的"低"值多分布在谷底及地表覆盖类型为密林的山坡上,而"高"、"较高"值多分布在坡度为30°~50°、地表类型以裸岩或草地为主的山坡和冰川上,这些分布符合雪崩形成的客观实际;分析判断发现研究区内"高"值区域,也就是潜在雪崩形成区共有98处,其中有10处能够进入冰湖,对这些冰湖的稳定性造成风险,这意味着在分析研究区所有冰湖的溃决风险性时,只有受到潜在雪崩影响的9个冰湖需要考虑雪崩因素,其余冰湖在冰湖溃决诱因筛选中无需考虑雪崩因子。     

Circular Disc Blade Considerations in Soil Force Prediction Modelling

Previous soil-disc force prediction models have considered spherical and concave blades, as used on disc ploughs and harrows, with many simplifying assumptions. This study proposes an approach applying the fundamental equation of earth moving mechanics for calculating the soil passive reaction acting on a rotating fiat disc blade as used on a zero-till single disc seeder. The study considers the effects of disc variable depth of cut, sweep and tilt angles, free rotation and a scrubbing reaction at the beveled edge. This paper outlines the modeling approach and prediction results for a fixed circular blade operating at 90° sweep angle over a range of speeds and at two tilt angles. To account for the varying depth across the circular disc shape width, elemental wide blade force reactions acting on wide blade segments of elemental width were integrated across the disc working width. By including inertia forces due to speed as well as additional bulldozing forces due to the loose soil accumulation in front of the blade the draught and upward vertical forces acting on the vertical disc blade were predicted with a deviation of 6%-19% and 1.5%-14% from measured data, respectively. The model was able to predict the effect of increasing the tilt angle from 0° to 20° on reducing both draught and upward vertical forces. Further development and validation of the model will be described in subsequent papers, reflecting a step by step approach of increasing complexity to model a disc blade as used on a zero-till single disc seeding system.     

Pocono mesic till barrens in retreat: topography,fire and forest contagion effects

The Pocono mesic till barrens (PMTB) are a unique assemblage of fire-maintained shrub communities that support numerous rare species. Historically these barrens covered a large area in the vicinity of Long Pond, Pennsylvania, USA. However, due largely to regional fire suppression instituted in the early 1960s, over 70% of the area covered by barrens succeeded to fire-intolerant forest that does not support the rare species. We investigated the influence of forest proximity on barrens succession across three geomorphic types during periods of high fire frequency and fire suppression, testing the hypothesis that forest processes such as seed rain, shading, and detrital enrichment of soils enhances barrens succession through a contagion effect. Evidence of a forest contagion effect should be shown by increased rates of barrens succession with increasing proximity to the nearest forest edge. In order to detect a forest contagion effect, barrens persistence and barrens succession were modeled in proximity zones of 0-50 m, 50-100 m, 100-200 m, and greater than 200 m from the nearest forest edge. We used existing GIS data layers for fire, geomorphology, and vegetation distribution in 1938, 1963, and 1992. The layers were modified and overlain using ArcView software to determine persistence and succession rates for each unique combination of layers in each proximity zone from 1938 to 1963 (pre-fire suppression) and 1963 to 1992 (post-fire suppression). ANCOVA results indicate that proximity to the nearest forest edge significantly affected barrens persistence rates in both time periods, but succession rates were significantly affected in 1938 to 1963 only. Twenty-eight percent of the 1938 barrens succeeded to forest by 1963; 56% of the 1963 barrens became forest by 1992. Results support previous findings that barrens persistence is enhanced by increased fire frequency, and that barrens persist longer where they overlie flat glacial till than on other geomorphology types.     

Low disturbance seeding suppresses weeds in no‐tillage soyabean

Germination is a key process in the dynamics of weed populations. In no‐tillage systems, crop seeding is often found to induce seed germination in the seeding strip. In this research, experiments to investigate options for reducing weed seedling establishment were conducted in no‐till soyabean fields located in two sites in south Brazil. A first experiment revealed that a reduction in emergence of some important weed species can be achieved by lowering seeding speed. Further experiments showed the ability of a modified seeder to contribute to an additional reduction in weed establishment. On the modified seeder, coulter discs were equipped with lateral blades, to diminish soil disturbance and to maintain a uniform soil cover by properly cutting the mulch layer. In a field with a high level of residues, the modified seeder, in contrast to the standard seeder, prevented the increase of soil exposure when seeding at high speed. The predominant weeds were annual species. Averaged over all seeding rates, the new equipment led to a 56% reduction in within‐row weed density, compared with the standard seeder. Regardless of seeder type, overall weed density increased with seeding speed, but with the modified seeder, this increase was only half that of the standard seeder. The modified seeder reduced weed biomass by 30% and increased soyabean grain yield by 42%. The research demonstrated that relatively simple changes, like a minor modification to a seeder and a lower seeding speed, can contribute to more diverse and sustainable alternatives to predominantly chemical‐oriented weed management strategies.