番鸭新病——花肝病的研究：Ⅰ．分离毒的致病必及感染途径试验

番鸭花肝的是近年流行的一种新的番鸭疫病，其特征性病变是死亡番鸭的肝、脾、小肠等部位出现灰白色的坏死点，本文自广东省主要疫区分离到几株病毒，这些病毒在番鸭胚上可继代繁殖，其胚液可使番鸭妇病。不同途径感染试验表明该病毒通过肌肉注射、爪垫部注射、口服，同居感染均可使番鸭发病和死亡，并具有典型病变，分离毒不能使半番鸭，本地鸭，鸡发病。     

Transfer of Grain Legume Nitrogen within a Crop Rotation Containing Winter Wheat and Winter Barley

In a crop rotation trial, conducted from 1985 to 1988 at TU-Munich's research station in Roggenstein, the transfer of grain legume nitrogen was evaluated in crop rotations containing fababeans and dry peas as well as oats (reference crop) and winter wheat and winter barley as following crops. The results obtained can be summarized as follows: Dinitrogen fixation by fababeans ranged from 165 to 240 kg N ha¹, whereas N₂-fixation by peas amounted from 215 to 246 kg N ha^?1. In all seasons the calculated N-balance where only grain was removed was positive, with a net gain being on average 106 (peas) and 84 (fababeans) kg N ha^?1. After the harvest of peas 202 kg N ha^?1 remained on the field on average over seasons (158 kg N ha^?1 in the above ground biomass and 44 kg N ha^?1 as NO₃-N in 0–90 cm depth). As compared to peas, fababeans left 41 kg N ha^?1 less due to smaller amounts of nitrogen in the straw. After oats very small amounts of residual nitrogen (33 kg N ha^?1) were detected. After the harvest of grain legumes always a very high nitrogen mineralization was observed during autumn especially after peas due to a close C/N-relationship and higher amounts of nitrogen in the straw as compared to fababeans. In comparison with fababeans, N-mineralization after the cultivation of oats remained lower by more than 50%. During winter, seepage water regularly led to a considerable decrease of soil NO₃-N content. The N-leaching losses were especially high after cultivation of peas (80 kg N ha ^?1) and considerably lower after fababeans (50 kg N ha^?1) and oats (20 kg N ha^?1). As compared to oats, a higher NO₃-N content in soil was determined at the beginning of the growing period after preceding grain legumes. Therefore, winter wheat yielded highest after preceding peas (68 dt ha^?1) and fababeans (60 dt ha^?1) and lowest after preceding oats (42 dt ha^?1). The cultivation of grain legumes had no measurable effect on yield formation of the third crop winter barley in either of the growing seasons.     

Effects of the Adaptable Distribution for Lateral Forces Considering modes Coupling on Structural Pushover Analysis

Two high and flexible RC frame structures are analyzed;the paper explains the rise in the structural damping ratio and the base mode's drifting,and the modes coupling is caused by the greatly rising damping ratio.The paper also proposes that the modes coupling need be considered in the pushover analysis of the high and flexible RC frame structures.A CQC adaptive distribution for lateral forces in considering the modes coupling at every load step is given,and is compared with the traditional SRSS one.Meanwhile,some practical engineering suggestions are given.     

Effects of tillage on productivity of a winter wheat-vetch rotation under dryland Mediterranean conditions

An experiment was conducted to determine the effects of three tillage systems on crop yield in a winter wheat-vetch (Vicia sativa L.) rotation during 3-year growing seasons on a clay-loam soil in the northwest region of Turkey. The three tillage treatments were: (1) conventional tillage (CT); (2) shallow tillage (ST); (3) double disk tillage (DD).The wheat grain yield was significantly affected by tillage when averaged across years. The highest wheat grain yield was obtained with shallow tillage treatment. The year affected wheat grain yield significantly, mainly due to the distribution of rainfall through the growing season and probably due to the wheat-vetch rotation. Heads density and head length increased significantly with shallow tillage when compared with conventional tillage. Tillage practices had no significant influence on thousand kernel weight. Results from this study indicated that for a dryland wheat-vetch rotation cropping system, shallow tillage had higher wheat grain yields than that obtained from conventional tillage. Furthermore, mouldboard ploughing tillage in this crop rotation could be replaced by shallow tillage that would increase yield and would be likely to improve soil properties in the long-term. On the other hand, double disk tillage proved to be a promising soil management practice to improve vetch grain yield when compared with conventional tillage.     

氮肥用量及施用时间对土体中硝态氮移动的影响

土连续两年小麦—玉米轮作条件下 ,播前一次施氮量 130～ 5 2 0kghm-2 a-1时 ,氮肥用量对硝态氮在土体中的移动深度没有影响 ,但土壤剖面中残留的硝态氮量随施氮量增加显著增加。播前一次施用氮肥 ,差减法计算的肥料氮表观回收率 (作物携出量和土壤硝态氮的残留量 )为 6 2 %～ 82 7% ;就作物而言小麦的携出率高于玉米 ,在玉米生长季节有更多的硝态氮可能被淋移至土壤剖面的下层。小麦—玉米轮作一年 ,不同的施氮时间对肥料氮的表观回收率以及硝态氮在土壤剖面中的分布、累计没有明显影响。土区合适的氮肥用量是控制硝态氮向深层移动的主要措施     

烟蒜轮作与套作对土壤农化性状及烤烟产量的影响

为了探讨烟蒜轮作与套作对土壤农化性状及烤烟产量的影响,本试验在烤烟不同生育时期,采取单作烤烟、烟蒜轮作与套作种植方式下的土壤样品分析农化指标和统计烟叶产量,并对其结果进行对比分析.结果表明随生育期的推进,不同种植方式下根际土壤pH值呈增加趋势,烟蒜轮作与套作根际与非根际土壤的pH值均高于单作烤烟.上部叶成熟期,烟蒜轮作与套作根际与非根际土壤有机质含量均高于单作烤烟.下部叶与上部叶成熟期,烟蒜轮作与套作非根际土壤速效氮含量显著高于单作烤烟.而上部叶成熟期,烟蒜轮作与套作处理根际土壤速效磷、速效钾含量高于单作烤烟.烟蒜轮作与套作烟叶产量、上中等烟率较单作烤烟提高了35.04％和17.55％、5.88％和3.88％.烟蒜轮作与烟蒜套作种植方式均有利于缓解烟草连作障碍,改善土壤微生态环境,提高烤烟产量,但烟蒜轮作对其效果更加突出.本研究探讨烟蒜轮作与烟蒜套作种植方式对土壤农化性状及烤烟产量的影响,可为改良植烟土壤、减轻连作障碍及栽培制度的创新提供理论基础和技术支撑.     

Rainfall and tillage effects on soil structure after alfalfa conversion to maize on a clay loam soil in New York

Soil degradation is accelerated when perennial crops are converted to annual row crops, primarily due to increased soil disturbance from tillage. Subsequent heavy rainfall may induce soil settling, reduce macroporosity and increase hardsetting upon drying. An experiment involving plow and no-tillage and two simulated rainfall treatments (‘wet’ and ‘dry’) was conducted on Kingsbury clay loam soil in northern New York in 1992 and 1993 to study their effects on soil structure under maize (Zea mays L.) after conversion from alfalfa (Medicago sativa L.), and to evaluate the use of spectral analysis of micropenetrometer observations for studying soil aggregation. Undisturbed soil cores were collected from the row and trafficked and non-trafficked interrow positions at the 0.05 and 0.15 m depths and used for laboratory measurement of soil strength and pore system properties. These well-structured soils show a high contribution (up to 0.15 m³ m⁻³) of macropores to the total porosity of the soil. Soil strength was generally slightly higher for no-till (NT) than plow till (PT), although only significant in 1992. Soil strength in the surface layer did not change significantly with drying. Spectral density patterns did not show strong treatment effects, although distinct peaks reflect 3.0–3.5 mm stable structural units within macroaggregates. Simulated rainfall treatments and tillage treatments generally did not strongly affect measured soil properties, presumably due to stable soil structure. Structurally stable clay loam soils show little effect of tillage or settling on soil physical properties in the first years after alfalfa to maize conversion, and have good potential for long-term annual crop production if properly managed.     

Crop management effects on soil carbon sequestration on selected farmers’ fields in northeastern Ohio

Soil organic carbon (SOC) pool is the largest among terrestrial pools. The restoration of SOC pool in arable lands represents a potential sink for atmospheric CO₂. Restorative management of SOC includes using organic manures, adopting legume-based crop rotations, and converting plow till to a conservation till system. A field study was conducted to analyze soil properties on two farms located in Geauga and Stark Counties in northeastern Ohio, USA. Soil bulk density decreased with increase in SOC pool for a wide range of management systems. In comparison with wooded control, agricultural fields had a lower SOC pool in the 0–30 cm depth. In Geauga County, the SOC pool decreased by 34% in alfalfa (Medicago sativa L.) grown in a complex rotation with manuring and 51% in unmanured continuous corn (Zea mays L.). In Stark County, the SOC pool decreased by 32% in a field systematically amended with poultry manure and 40% in the field receiving only chemical fertilizers. In comparison with continuous corn, the rate of SOC sequestration in Geauga County was 379 kg C ha⁻¹ year⁻¹ in no-till corn (2 years) previously in hay (12 years), 760 kg C ha⁻¹ year⁻¹ in a complex crop rotation receiving manure and chemical fertilizers, and 355 kg C ha⁻¹ year⁻¹ without manuring. The rate of SOC sequestration was 392 kg C ha⁻¹ year⁻¹ on manured field in Stark County.     

不同施肥措施对小麦－玉米轮作中作物产量和土壤肥力的影响

A 15-year field experiment was carried out in Henan Province, China, to study the effects of different fertilization practices on yield of a wheat-maize rotation. Fertilizers tested contained N alone (N), N plus P (NP) or plus P and K (NPK), all with or without manure (M). Different long-term fertilization practices affected the yields under the rotation system of wheat and maize differently and the effects on yields was in a general trend of MNPK＞MNP＞MN＞NPK＞NP＞M＞N＞the control. The average contribution rate of soil fertility to the highest yield was 37.9%, and the rest 62.1% came from fertilizer applications. The yield effects of the chemical fertilizers were in the order of N＞P＞K and were increased by application of manure.Balanced fertilization with multielement chemical fertilizers and manure can be effective in maintaining growth in agricultural production. Combined application of chemical fertilizer and organic manure also increased the content of soil organic matter.     

连栽马尾松人工林土壤肥力比较研究

采用配对样地法,以不同栽植代数(1、2 代)、不同发育阶段(8、15、18、20 a)的马尾松人工林为对象,研究了连栽幼龄林、中龄林土壤肥力的变化情况。结果表明:连栽后,无论是幼龄林还是中龄林,林地土壤密度趋于下降,土壤总孔隙度和含水率则呈上升趋势,林地土壤物理性质得到改善,且中龄林20~40 cm层土壤密度和总孔隙度在1、2代间的差异达显著水平;连栽后,林地土壤全K、全Mg及pH值趋于下降,而有机质、全N、全P、全Ca及速效N、P、K养分均呈上升趋势,且幼龄林0~20 cm层土壤有效P含量以及土壤pH值、中龄林0~20 cm层土壤水解N含量以及土壤全N、有效P、速效K、全K含量在1、2代间的差异达显著或极显著水平。连栽后,幼龄林和中龄林土壤全Fe、Al、Cu、Zn、Mn含量均呈下降趋势,且Mn含量在1、2代幼龄林和中龄林间的差异达显著水平。