陆川县湿地松工程林经济效益分析

通过建立观测样地，研究广西陆川县湿地松工程林的生长过程和经济效益，基本情况是林分生长正常，投资项目可行，但经济效益不够理想．其主要原因是：（１）过林密度小，每公顷仅１６６７株，（２）投入偏低；导致林分单位面积蓄积量少，按林价计算的单位面积产值较低．     

Release and activity of allelochemicals from allelopathic rice seedlings

3-Isopropyl-5-acetoxycyclohexene-2-one-1 (1), momilactone B (2), and 5,7,4'-trihydroxy-3',5'-dimethoxyflavone (3) were isolated and identified from an allelopathic rice accession PI312777. These three compounds at low concentrations could inhibit the growth of weeds Echinochloa crusgalli and Cyperus difformis associated with rice, especially mixtures of the compounds had stronger inhibitory activity than did individual compounds. Studies with hydroponic culture, continuous root exudates trapping system (CRETS), and direct resin adsorption methods showed that a total of 7.6 n moles 1, 2, and 3 were exuded from living roots of each seedling into the environment at 10 days after seedlings were transplanted. Furthermore, 1, 2, and 3 were found in the soil growing PI312777 seedlings at day 15 after seedlings emergence and reached a total of 39.5 microg/g soil at day 30. The results indicated that PI 312777 seedlings could release sufficient quantities of 1, 2, and 3 into the environment to act as allelochemicals inhibiting the growth of associated weeds. Investigations on the distribution of 1, 2, and 3 in PI 312777 plant, and its root exudates showed that the levels of 1, 2, and 3 were significantly higher in the shoots and root exudates than in the roots, and only trace 1 was observed in the roots. The results suggest that the roots of rice seedlings are not major site of synthesis or accumulation 1, 2, and 3, but a pathway for their release into the environment. The levels of 1, 2, and 3 in the root exudates were over 2-folds higher under direct resin adsorption than under hydroponic culture and CRETS, and hence, it is the preferred method to collect and identify active allelochemicals in rice exudates in future studies on rice allelopathy.     

留营养枝棉花根系生长发育与分布规律的研究

棉花根系建成是棉花高产、优质、高效的前提。本文针对留营养枝和整枝棉花在不同的种植方式、不同密度条件下进行了根系生长发育和分布规律研究,结果表明,（１）留营养枝棉花根系生长发育早,一般比整枝棉花早１０～３０ｄ达到根系生长高峰期;（２）留营养枝棉花根系生长量大,峰值高,比整枝棉花最大根长密度高１．８～３．４ｍｍ·ｃｍ－２,即高１４．４％～１６．６％;（３）留营养枝棉花根系的生长速率大于整枝棉,一熟条件下可为整枝棉的３．２倍,达到０．９９ｍｍ·ｃｍ－２·ｄ－１;（４）留营养枝棉根系中后期易早衰。本文还研究讨论了留营养枝与整枝棉花根系在土壤中的分布规律。并针对留营养枝棉花根系的生长发育和分布特点,提出留营养枝棉花高产栽培中应注意早施肥、早浇水,而且肥、水量要比常规管理大,中后期应注重及时追施花铃肥和根外补肥,防止棉花早衰。这项研究对于制定棉花简化栽培规范化技术有一定的理论指导意义。     

浅圆仓充氮气调技术实仓应用探究

通过对浅圆仓采用不同方法进行充氮试验,探索最佳的浅圆仓充氮气调储粮工艺。试验结果表明,采用上充下排方式,先以设备允许的最大流量(流量165m~3/h,浓度95%)充入氮气,当仓内氮气浓度接近95%时,再逐步提高设备氮气浓度至99%(流量90m~3/h),此工艺相较其他方法充氮速率略高,能耗相对略低,仓内氮气分布均匀。     

保护性耕作条件下浅松作业的试验

浅松作业是保护性耕作中推广使用的一种表土作业方式，适用于旱作保护性耕作的播前作业，能够达到松土、除草、整地等目的，也可以用于中耕除草作业。试验结果表明，该作业有良好的除草作用。能显著地提高地表平整度，降低表土容积密度，对根荏榭盖和土壤水分影响不显著，基本上满足了保护性耕作对土壤的要求。     

CO2气调防治储粮害虫试验仓的研制与应用

通过CO2气调防治储粮害虫试验仓的研制及应用试验,提出了试验仓在试验中应考虑的因素及解决的方法,例如,试验仓的密封问题、充气与补气的问题、测试装置的布置与参数的采集、虫笼的放取与虫情的检查等。试验仓的试验结果为,杀虫的最佳温度是(25±3)℃,CO2达到25%~35%,杀虫的持续时间为10d以上,从而为实际应用CO2防治储粮害虫提供了可靠的依据。分析了在农村建造小型钢板仓的可行性,为全面推广CO2气调防治储粮害虫技术奠定了基础。     

基于流场数值模拟的高速磁力泵汽蚀性能研

为了改善高速磁力泵的抗汽蚀性能,在泵吸入口处设置导流栅.建立了吸入口设置导流栅和未设置导流栅的两种模型,采用Fluent软件对高速磁力泵内流场进行数值模拟,给出了各自内部压力分布以及粒子流动迹线图.通过两组数据的比较,得到了内部流场的主要特征,模拟表明高速磁力泵吸入口设置轴向可变位导流栅可以有效提高抗汽蚀性能.数值模拟与高速磁力泵真机的试验对比表明,两者几乎一致,为高速磁力泵的改进设计提供了一定的理论依据.     

北京典型边缘区25年来土壤有机质的时空变异特征

采用地统计学和GIS相结合的方法,研究了北京典型边缘区25 a来两个阶段(1981～2000年,2000～2006年)土壤有机质含量(SOM)的时空变异特征.研究结果表明:土地利用类型及土地利用方式的转换对土壤有机质含量产生重要影响.1981～2000年,荒草地向耕地的转换以及因灌溉设施的完善而引起水浇地面积的增加使得整个研究区域土壤有机质含量普遍增加,有机质含量平均值从9.64 g/kg增加到12.35 g/kg,增加了28%;在利益的驱使下,农户改变了土地利用方式,不再向种植粮食作物的土地追加投入,研究区域土壤有机质含量平均值由12.35 g/kg降低到11.46 g/kg(2000～2006年).空间上,1981年土壤有机质含量自北向南逐渐降低;与1981年相比,2000年的土壤有机质含量普遍增加一个级别,增加最多的区域分布在研究区域的中部,这些区域也是土地利用类型变化明显的地方,主要是荒草地向其他农用地的转换;与2000年相比,2006年研究区域内土壤有机质含量增加的只有3个地区,并且大部分增加不显著,增幅不到1g/kg.     

Transitioning from standard to minimum tillage: Trade-offs between soil organic matter stabilization, nitrous oxide emissions, and N availability in irrigated cropping systems

Few studies address nutrient cycling during the transition period (e.g., 1–4 years following conversion) from standard to some form of conservation tillage. This study compares the influence of minimum versus standard tillage on changes in soil nitrogen (N) stabilization, nitrous oxide (N₂O) emissions, short-term N cycling, and crop N use efficiency 1 year after tillage conversion in conventional (i.e., synthetic fertilizer-N only), low-input (i.e., alternating annual synthetic fertilizer- and cover crop-N), and organic (i.e., manure- and cover crop-N) irrigated, maize–tomato systems in California. To understand the mechanisms governing N cycling in these systems, we traced ¹⁵N-labeled fertilizer/cover crop into the maize grain, whole soil, and three soil fractions: macroaggregates (>250 μm), microaggregates (53–250 μm) and silt-and-clay (<53 μm). We found a cropping system effect on soil N_new (i.e., N derived from ¹⁵N-fertilizer or -¹⁵N-cover crop), with 173 kg N_new ha⁻¹ in the conventional system compared to 71.6 and 69.2 kg N_new ha⁻¹ in the low-input and organic systems, respectively. In the conventional system, more N_new was found in the microaggregate and silt-and-clay fractions, whereas, the N_new of the organic and low-input systems resided mainly in the macroaggregates. Even though no effect of tillage was found on soil aggregation, the minimum tillage systems showed greater soil fraction-N_new than the standard tillage systems, suggesting greater potential for N stabilization under minimum tillage. Grain-N_new was also higher in the minimum versus standard tillage systems. Nevertheless, minimum tillage led to the greatest N₂O emissions (39.5 g N₂O–N ha⁻¹ day⁻¹) from the conventional cropping system, where N turnover was already the fastest among the cropping systems. In contrast, minimum tillage combined with the low-input system (which received the least N ha⁻¹) produced intermediate N₂O emissions, soil N stabilization, and crop N use efficiency. Although total soil N did not change after 1 year of conversion from standard to minimum tillage, our use of stable isotopes permitted the early detection of interactive effects between tillage regimes and cropping systems that determine the trade-offs among N stabilization, N₂O emissions, and N availability.     

来自海南等地的17个Bt分离株质粒多样性分析

本研究采用琼脂糖凝胶电泳对分离白海南岛的12个反菌株与分离自广西、黑龙江的5株＆菌株及2株胁模式菌株进行质粒数量、大小等特征分析。19个供试菌株可区分为16种独特的质粒电泳图谱,充分显示出不同来源肪菌株的质粒多样性。进一步选择了其中的10个菌株,利用包埋法制备琼脂块进行脉冲场凝胶电泳（PFGE）,结果表明苏云金芽孢杆菌大质粒组成特征也具有丰富多样性。但是供试菌株的质粒电泳图谱并未体现与地理和生态特征相关联的特征差异。研究结果初步证实海南分离株S3078—1是一株无内生质粒的助菌株,而S3031-1和S3073—1两个分离株仅有一个大质粒存在,这三个分离株将为进一步研究质粒功能提供初始菌株。本研究进一步暗示将琼脂糖凝胶电泳和脉冲场凝胶电泳结合起来研究质粒特征提高了结果的可靠性。