Net Carbon Fluxes Over Burned and Unburned Native Tallgrass Prairie

Prescribed burning of aboveground biomass in tallgrass prairie is common and may influence dynamics and magnitudes of carbon (C) movement between the surface and atmosphere. Carbon dioxide (CO₂) fluxes were measured for 2 yr using conditional sampling systems on two adjacent watersheds in an ungrazed tallgrass prairie near Manhattan, Kansas. One watershed was burned annually (BA) and the other biennially (BB). Leaf and soil CO₂ fluxes were measured in the source area. Net ecosystem exchange (NEE) of CO₂ reached a maximum daily gain of 26.4 g CO₂·m^?2·d^?1 (flux toward surface is positive) in July 1998 (year when both sites were burned and precipitation was above normal); gains were similar between sites in 1998. The maximum daily NEE loss of CO₂ was ?21.8 g CO₂·m^?2·d^?1 from BA in September 1997 (year when only BA was burned and precipitation was below normal). When data were integrated over the two years, both sites were net sources of atmospheric CO₂; NEE was ?389 g C·m^?2·2 yr^?1 on BA and ?195 g C·m^?2·2 yr^?1 on BB. Burning increased canopy size and photosynthesis, but the greater photosynthesis was offset by corresponding increases in respiration (from canopy and soil). Carbon losses from fire represented 6–10% of annual CO₂ emissions (bulk came from soil and canopy respiration). Data suggest that annual burning promotes C loss compared to less-frequently burned tallgrass prairie where prairie is not grazed by ungulates. Greater precipitation in 1998 caused large increases in biomass and a more positive growing season NEE, indicating that C sequestration appears more likely when precipitation is high. Because C inputs (photosynthesis) and losses (canopy and soil respiration) were large, small measurement or modeling errors could confound attempts to determine if the ecosystems are long-term CO₂ sources or sinks.     

Restoring Tallgrass Prairie and Grassland Bird Populations in Tall Fescue Pastures With Winter Grazing

Restoration of grasslands dominated by tall fescue (Schedonorus phoenix [Scop.] Holub) to native tallgrass prairie usually requires burning, herbicides, or reseeding. We tested seasonal grazing by livestock in winter, combined with cessation of fertilization, as a restoration tool for modifying the competitive dynamics among herbaceous plants to restore tallgrass prairie communities in southeastern Kansas. In 2004–2005, we compared responses of grassland plants and birds across a chronosequence of pastures that were winter-grazed from 1 yr to 5 yr. We compared winter-grazed pastures to pastures grazed year-round and to local native prairie remnants as starting and endpoints for restoration, respectively. Abundance of native warm-season grasses increased from 2% to 3% mean relative frequency in pastures grazed year-round to 18% to 30% in winter-grazed pastures, and increased with duration of winter-grazing. Native warm-season grasses accounted for 1–6% of total live aboveground biomass in pastures grazed year-round, 1–34% in winter-grazed pastures, and 31–34% in native prairie remnants. Tall fescue abundance and biomass were similar among grazing treatments, with a trend for tall fescue to be less dominant in winter-grazed pastures. Tall fescue made up 9–40% of total aboveground biomass in year-round grazed pastures and 10–25% in winter-grazed pastures. Grassland birds showed variable responses to winter-grazing. Dickcissels (Spiza americana) and Henslow’s sparrows (Ammodramus henslowii) were more abundant in winter-grazed pastures, whereas eastern meadowlarks (Sturnella magna) and grasshopper sparrows (A. savannarum) had similar abundance in pastures grazed year-round and during winter. Winter-grazing of pastures dominated by tall fescue combined with suspension of nitrogen fertilization could be an effective restoration technique that allows use of prairie rangeland while improving habitat for sensitive grassland birds.     

Spring Clipping,Fire, and Simulated Increased Atmospheric Nitrogen Deposition Effects on Tallgrass Prairie Vegetation

Defoliation aimed at introduced cool-season grasses, which uses similar resources of native grasses, could substantially reduce their competitiveness and improve the quality of the northern tallgrass prairie. The objective was to evaluate the use of early season clipping and fire in conjunction with simulated increased levels of atmospheric nitrogen deposition on foliar canopy cover of tallgrass prairie vegetation. This study was conducted from 2009 to 2012 at two locations in eastern South Dakota. Small plots arranged in a split-plot treatment design were randomized in four complete blocks on a warm-season grass interseeded and a native prairie site in east-central South Dakota. The whole plot consisted of seven treatments: annual clip, biennial clip, triennial clip, annual fire, biennial fire, triennial fire, and undefoliated control. The clip plots consisted of weekly clipping in May to simulate heavy grazing. Fire was applied in late April or early May. The subplot consisted of nitrogen applied at 0 or 15 kg N · ha^?1 in early June. All treatments were initially applied in 2009. Biennial and triennial treatments were reapplied in 2011 and 2012, respectively. Canopy cover of species/major plant functional groups was estimated in late August/early September. Annual clipping was just as effective as annual fire in increasing native warm-season grass and decreasing introduced cool-season grass cover. Annual defoliation resulted in greater native warm-season grass cover, less introduced cool-season grass cover, and less native cool-season grass cover than biennial or triennial defoliation applications. Low levels of nitrogen did not affect native warm-season grass or introduced cool-season cover for any of the defoliation treatments, but it increased introduced cool-season grass cover in the undefoliated control at the native prairie site. This study supports the hypothesis that appropriately applied management results in consistent desired outcomes regardless of increased simulated atmospheric nitrogen depositions.     

Influence of Abrams M1A1 Main Battle Tank Disturbance on Tallgrass Prairie Plant Community Structure

The Department of Defense's Range and Training Land Assessment program provides information and recommendations to range managers regarding the condition of training lands. This information is used to assist in scheduling training areas and in monitoring the effectiveness of rehabilitation projects. Fort Riley Military Installation is a major training reservation located in the Flint Hills of northeastern Kansas, within the tallgrass prairie ecosystem. A randomized complete block design composed of three treatments (M1A1 Abrams tank traffic during wet and dry soil conditions, and a nontrafficked control) with three replications was established in each of two soil types, a silty clay loam and a silt loam soil, on Fort Riley in 2003. Disturbance was created by driving the tank for five circuits in a figure-eight pattern during either during wet or dry soil conditions. Two additional experimental treatments were added during the study: five additional tank passes on one-half of each figure eight in 2004 and burning in 2006. Two areas, a curve and straightaway, within each traffic intensity (and later, burn treatment) subplot were designated for sampling. Aboveground biomass, species composition, and ground cover were measured during each growing season. Recovery of grass and total aboveground biomass in silty clay loam soil was delayed for curve areas and following disturbance in wet soil conditions, respectively. Species composition and ground cover continued to exhibit significant disturbance effects in 2007, with greatest damage observed for repeated traffic under wet soil conditions. Fire effects on vegetation were variable and generally greater for undisturbed control plots than for disturbed areas. The tallgrass prairie typically is considered to be among the most resilient of military training lands, but our research suggests that resiliency is dependent upon soil type and training conditions, and may require longer periods of recovery than previously thought.     

Tallgrass Prairie Plant Community Dynamics Along a Canopy Cover Gradient of Eastern Redcedar (Juniperus virginiana L.)

North American grasslands make up less than 75% of their historic pre-European settlement area, and they continue to be converted to woodlands by woody plant encroachment. Conversion of grassland to woodland alters nutrient cycling, water use, and light penetration, which drives herbaceous plant community dynamics. Because studies examining this relationship among Juniperus species are limited largely to individual trees, we designed a study to examine the relationship between stand-level canopy cover of eastern redcedar (Juniperus virginiana L.) and the herbaceous plant community. We documented herbaceous plant species composition, abundance, and biomass within a North American tallgrass prairie invaded by eastern redcedar in which canopy cover of eastern redcedar ranged from 0% to 80%. Herbaceous species richness declined as a function of increased canopy cover of eastern redcedar and subsequent loss of open space, but this decrease in species richness closely followed a species–area model. Moreover, composition of C₃ and C₄ grasses and forbs did not change with increasing canopy cover. Herbaceous biomass, which declined with increasing canopy cover, varied most within those plots with intermediate canopy cover. While we found that species richness and biomass declined as canopy cover increased, the decline followed a species–area relationship and was without abrupt change typical of ecological thresholds. We recommend additional research with removal of eastern redcedar trees over a range of canopy cover to assess restoration potential along the encroachment gradient.     

谈我国草原绒山羊发展问题

通过对我国绒山羊饲养现状和羊绒产品市场销售状况的调查与分析,就该产业一直未引起国家和政府的重视,行业内部缺乏有效的组织、计划与监控,生产成本上升,市场不健全,等其生存与发展所面临的诸多困难展开讨论。建议国家和地方首先要通过规划绒山羊饲养量、立法、制定合理的羊绒生产补贴政策等措施解决宏观发展问题;农民应建立起自己的利益共同体,解决羊原料绒生产和环境保护问题;技术人员积极参与解决绒山羊养殖低效益问题;企业改变经营战略,提升产品质量,解决产品市场问题。     

兽药残留危害及监控对策

论述了动物源食品中兽药残留及其他有害物质污染的来源、危害和残留监控的现状，提出了建立符合我国国情的可溯源的兽药残留监控体系的对策。     

Spring Precipitation as a Predictor for Peak Standing Crop of Mixed-Grass Prairie

Ranchers and range managers need a decision support tool that provides a reasonably accurate prediction of forage growth potential early in the season to help users make destocking decisions. Erroneous stocking rate decisions can have dire economic and environmental consequences, particularly when forage production is low. Predictions must be based on information that is easily obtained and relevant to the particular range. Our goal was to evaluate monthly precipitation in spring months as a potential predictor of forage production compared to annual and growing-season precipitation. We analyzed the relationships between grazed and ungrazed peak standing crop (PSC) and precipitation using nonlinear regression and a plateau model, Akaike’s information criterion for model selection, and data from three locations: Streeter, North Dakota; Miles City, Montana; and Cheyenne, Wyoming. The plateau model included a linear segment, representing precipitation limiting production, and a plateau, an estimate of average production when precipitation is no longer the limiting factor. Both the response and predictor variables were rescaled so variability in production from average production was related to variability in precipitation from the long-term average. We found that grazing did not affect the relationship between PSC and precipitation, nor were annual or growing-season precipitation good predictor variables. The best predictor variable was total precipitation in April and May for Montana, May and June for North Dakota, and April, May, and June for Wyoming, with r² ranging from 0.74 to 0.79 for precipitation less than long-term average. These results indicate that spring precipitation provides useful information for destocking decisions and can potentially be used to develop a decision support tool, and the results will guide our choice of possible predictor models for the tool.     

Linking Phenology and Biomass Productivity in South Dakota Mixed-Grass Prairie

Assessing the health of rangeland ecosystems based solely on annual biomass production does not fully describe the condition of the plant community; the phenology of production can provide inferences about species composition, successional stage, and grazing impacts. We evaluated the productivity and phenology of western South Dakota mixed-grass prairie in the period from 2000 to 2008 using the normalized difference vegetation index (NDVI). The NDVI is based on 250-m spatial resolution Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery. Growing-season NDVI images were integrated weekly to produce time-integrated NDVI (TIN), a proxy of total annual biomass production, and integrated seasonally to represent annual production by cool- and warm-season species (C₃ and C_4, respectively). Additionally, a variety of phenological indicators including cool-season percentage of TIN were derived from the seasonal profiles of NDVI. Cool-season percentage and TIN were combined to generate vegetation classes, which served as proxies of the conditions of plant communities. TIN decreased with precipitation from east to west across the study area. However, the cool-season percentage increased from east to west, following patterns related to the reliability (interannual coefficient of variation [CV]) and quantity of midsummer precipitation. Cool-season TIN averaged 76.8% of the total TIN. Seasonal accumulation of TIN corresponded closely (R² > 0.90) to that of gross photosynthesis data from a carbon flux tower. Field-collected biomass and community composition data were strongly related to TIN and cool-season percentage. The patterns of vegetation classes were responsive to topographic, edaphic, and land management influences on plant communities. Accurate maps of biomass production, cool- and warm-season composition, and vegetation classes can improve the efficiency of land management by facilitating the adjustment of stocking rates and season of use to maximize rangeland productivity and achieve conservation objectives. Further, our results clarify the spatial and temporal dynamics of phenology and TIN in mixed-grass prairie.     

高山草原蝗虫种群空间格局研究

以１９９３－１９９６年在甘肃省夏河县甘加高山草原蝗虫种群调查资料为基础,了草原蝗虫混合种群的空间格局及其聚集与扩散优势,并用聚块性指标研究了其聚集强度的时序变化。研究结果表明;蝗蝻呈集各随机分布,成虫随随机型分布,近似Ｐｏｉｓｓｏｎ分布、蝗 孵化初期呈现扩散地趋势,孵化盛期聚集趋势,而成虫则主要表现出扩散趋势。     

正交设计法优选大蒜乳剂的制备工艺

目的：优选大蒜乳剂的制备工艺，制备大蒜新剂型。方法：根据影响乳剂稳定性因素，选用正交设计法L93^4优选大蒜乳剂的制备工艺。结果：工艺优选结果表明，乳化剂司盘-80的用量对乳剂形成及其稳定性影响显著（P〈0．05），乳剂制备的最佳工艺条件为D1B2C3A2．即可盘-80为1．0％。油、水相的比例为2：1．吐温-80为0．5％．乳化温度为60℃。结论：用该工艺制备的大蒜乳剂符合《中国典曲》2005年版乳剂要求。     

优化高效液相色谱法测定棉籽粕中游离棉酚的含量

本试验旨在建立一种测定棉籽粕中游离棉酚含量的高效液相色谱(hPLC)法的优化方法.试验采用丙酮提取棉籽粕样品,经超声、离心、抽滤、旋转蒸发处理,用乙腈-0.2％磷酸(体积比为85∶15)溶液溶解;色谱条件为:色谱柱Agilent TC-C18(250mm×4.6mm,5μm),流动相为乙腈-0.2％磷酸(体积比为85∶15)溶液,流速1.0mL/min,紫外检测波长235nm,进样量20μL,柱温25℃.结果得出,游离棉酚的回归标准曲线为y=189347x+24969(r=0.99999),在游离棉酚含量为0.1224～78.336 μg/mL范围内线性良好,最低定量限为0.52mg/kg;棉籽粕样品36h内4℃稳定性的相对标准偏差在1.51％～3.43％;平均回收率在94.72％～99.49％,相对标准偏差在1.72％～3.13％.可知,本方法稳定性好,准确度、灵敏度和回收率高.     

频控阵雷达频率合成器技术研究与设计

频控阵雷达作为近年来提出的一种新体制雷达,其对频率合成器的需求与传统的相控阵雷达对频率合成器的需求较为不同;频控阵雷达频率合成器除了阵列雷达所需求的相位相参性要求以外,还对各个通道输出信号频率及对应通道频率偏移也提出了新的要求。本文以频控阵雷达对频率合成器需求为前提,研究并设计了几种直接数字频率合成器与锁相环相结合的频率合成器方案,对其原理及性能指标等进行分析对比,并给出应对不同频率特性需求的设计建议。     

规模养鹅安全高效管理措施

一科学饲养管理1 适度的饲养规模决定饲养规模的大小要根据养殖户的劳力资金、草料资源等条件,以及市场销售情况来确定.如果条件尚不够完善,饲养技术跟不上,不必追求大规模,否则饲养管理不善,鹅群生产性能下降,患病死亡增多,反而得不偿失.一般农户饲养肉鹅500只左右,种鹅150只左右,专业大户可适当多养,肉鹅可为1 000～2 000只;种鹅可为500～1 000只.     

鸡群的夏季管理措施

高温高湿的夏季是一年之中鸡群最难过的季节。炎热的酷暑使鸡群处于长时间的喘息状态,饮水量大幅度增加而且导致食欲下降。如果这一阶段鸡群采食量也不足的话,就很容易造成产蛋率和体质的下降,不仅影响鸡的抗病能力,使鸡只更容易生病,直接造成产蛋时间和高峰期的缩短以及产蛋率的降低,严重减少养鸡的经济效益。因此鸡群的夏季管理非常重要,必须做好鸡群的防暑降温工作,创造条件让鸡群安全度夏。     

氧氟沙星掩味微囊的制备及优化筛选

为了屏蔽药物的不良味道,本试验以聚丙烯酸树脂IV为囊材,采用液中干燥法制备了氧氟沙星掩味微囊。试验以包封率及载药量为指标,通过考察溶剂、囊材、乳化剂、抗黏剂的用量对微囊的影响来筛选处方工艺。应用最佳工艺制备的氧氟沙星掩味微囊,载药量为57.4%,包封率为48.6%。该微囊在模拟口腔环境(pH值为7.0)介质中释放极其缓慢,60min仅释放总药量的2.1%;随着释放介质的酸度提高,药物的释放速率显著加快;除此之外,在胃酸酸度(pH值为1.0~3.0)范围内,氧氟沙星的释放还呈现缓释特征,可持续近10h。体外试验显示,采用液中干燥法制备得的氧氟沙星微囊,既可掩味又能实现持续释药,而且制备工艺简便,具有很好的应用前景。     

Long-Term Production and Profitability From Grazing Cattle in the Northern Mixed Grass Prairie

Conventional wisdom among rangeland professionals has been that for long-term sustainability of grazing livestock operations, rangeland should be kept in high good to low excellent range condition. Our objective was to analyze production parameters, costs, returns, and profit using data generated over a 34-yr period (1969–2002) from grazing a Clayey range site in the mixed-grass prairie of western South Dakota with variable stocking rates to maintain pastures in low–fair, good, and excellent range condition classes. Cattle weights were measured at turnout and at the end of the grazing season. Gross income · ha^?1 was the product of gain · ha^?1 and price. Prices were based on historical National Agricultural Statistics Services feeder cattle prices. Annual variable costs were estimated using a yearling cattle budget developed by South Dakota State University agricultural economists. All economic values were adjusted to a constant dollar using the Bureau of Labor Statistics' Consumer Price Index. Stocking rate, average daily gain, total gain, net profit, gross revenue, and annual costs · ha^?1 varied among range condition classes. Net income for low–fair range condition ($27.61 · ha^?1) and good range condition ($29.43 · ha^?1) were not different, but both were greater than excellent range condition ($23.01 · ha^?1). Over the life of the study, real profit (adjusted for inflation) steadily increased for the low–fair and good treatments, whereas it remained level for the excellent treatment. Neither drought nor wet springs impacted profit differently for the three treatments. These results support generally observed rancher behavior regarding range condition: to maintain their rangeland in lower range condition than would be recommended by rangeland professionals. Ecosystem goods and services of increasing interest to society and associated with high range condition, such as floristic diversity, hydrologic function, and some species of wildlife, come at an opportunity cost to the rancher.