海水流速对网箱养殖卵形鲳鯵生长的影响

2000—2004年分别在马銮湾、火烧屿、鳄鱼屿和猴屿4个海区进行卵形鲳鯵网箱养殖,探讨在养殖模式和饲料投喂技术相同条件下,海水流速度对网箱养殖卵形鲳鯵生长的影响。结果显示,海水流速最慢的马銮湾海区养殖效果最好,海水流速最快的猴屿养殖效果最差。     

气力输送技术在农业机械中的应用

气力输送技术可在很大程度对农业机械进行结构简化,降低成本和提高作业效率,越来越多地被用于播种、施肥和捡拾收获等物料输送装置中。了解气力输送技术的特性以及在农业机械中的应用现状,对于提高农机作业效率、促进先进农业机械化技术研发具有重要意义。为此,在农业物料气力输送特性、气力输送技术在农机领域的应用情况等方面进行大量文献调研分析和归纳总结。根据正负压输送的不同特点,对气力播种、施肥、收获捡拾机械装备的主要结构、工作原理和特点进行分析和阐述。在此基础上,指出农业领域气力输送应用和研究中存在的问题,包括：气力输送方式存在易堵塞、精度稍低的问题,能耗较大的问题以及相关基础研究不足的问题。针对以上存在的问题,提出针对性的建议：优化结构、配套监测系统,提高工作可靠性;改用效率较高的智能风机,降低能耗;加强基础研究,充分利用仿真等研究手段,进一步促进气力输送技术的应用。     

秸秆成型燃料燃烧速度影响因素的研究

对影响秸秆成型燃料燃烧速度的因素进行了试验研究.结果表明,秸秆成型燃料燃烧初期的速度受温度的影响较大,温度越高,挥发分析出速度越快,燃烧平稳性越差;通风量增大导致炉膛内的温度降低,从而使挥发分析出速度相对平稳;成型密度的增大,一定程度上抑制了成型燃料挥发分的析出速度.而成型直径和成型质量的增加,使得燃烧初期的平均燃烧速度增大,即燃烧初期析出的挥发分增多;而在中后期挥发分的析出速度相对稳定.     

拖拉机发动机瞬时转速微机测量的研究

为定量分析拖拉机发动机动力性能,介绍了一种带微电脑瞬时转速测量仪,对其转速传感器的原理及测试数据进行了分析;给出单片计算机80C31及其扩展接口芯片实现瞬时转速测量的结构和设计全过程以及程序框图和部分软件。     

Enhancement of photosynthesis and growth of tomato seedlings by forced ventilation within the canopy

A forced ventilation system that directs airflow upward or downward within a canopy was developed for plant culture in order to enhance photosynthesis and growth of the plant canopy. Tomato seedling canopies including the seedlings, growing medium, and a plastic tray were used for the experiments. In the upward and downward ventilation systems, air flows upward and downward, respectively, within the plant canopy; this is achieved by blowing and drawing air from holes (Ø 6 mm) made in plastic pipes positioned on the surface of the growing medium. A horizontal airflow system was used as a conventional system to compare the performance of the experimental ventilation systems. Using the upward and downward ventilation systems, the effects of air directions and air velocities on the CO₂ exchange rate of the tomato seedling canopy and the growth of the seedlings were compared with those observed using the conventional horizontal airflow system. The forced ventilation within the plant canopy enhanced the CO₂ exchange rate of the canopy and the dry masses of the seedlings by 1.4–1.5 and 1.2–1.3 times, respectively, as compared to the conventional horizontal airflow. When the leaf area index (LAI) increased from 1.2 to 2.4, there was only a 5% decrease in the CO₂ exchange rate per unit leaf area in the downward ventilation system, whereas there was a 20% decrease in the CO₂ exchange rate per leaf area in the horizontal airflow system. The coefficient of variation for the dry mass of the seedlings was higher in the downward system than in the other systems. These results demonstrate that forced ventilation within the canopy is an effective technique to enhance the gas exchange of the plant canopy and the consequent plant growth.     

梨树干木质部液流速度径向分布特征

采用热脉冲法对梨树树干液流速度径向变化规律进行了系统研究。结果表明：①梨树树干木质部不同深度液流速度在生长旺盛的晴天、阴天和小雨天呈单峰或双峰曲线;而在中到暴雨天、9月底小雨天和即将休眠的10月底晴天,各深度液流速度日变化不规则。②树干同一深度液流速度日峰值、日均值、日变幅在晴天、阴天、小雨和中到暴雨天的比例相同,约为5:4:3:2;不同方向液流速度径向变幅在以上天气的比例为6:4:3:2,而同一深度液流速度最小值在不同天气时差异不大。③梨树树干不同深度白天液流速度和液流速度径向变幅分别在5—7月、8—9月相近,8—9月、10月同一深度液流速度分别是5—7月的50%～60%和33%～50%;5—7月、8—9月和10月液流速度径向变幅比约为5:2:1。液流速度峰值主要出现在形成层至髓0.12～0.29的位置。④晚上液流速度径向季节变化趋势与相应的白天相似,整个生长季晚上液流速度和径向变幅分别为白天的43%±1%和29%±7%。     

树干径向变化对茎液流以及气象因子的响应

应用改进的SF-L型热扩散式树液流测定装置和DC型植物生长测量仪,结合北京2007年6-10月的气象数据,探讨了北京山区油松、侧柏树干茎周长动态因素与液流速率和气象因子之间的相关关系,并运用树木径向变化周期分段法将树木径向生长量从径向变化过程中分离开,结果表明:(1)油松、侧柏茎周长变化与液流速率的关系显著(P<0.01),油松为正相关,侧柏为负相关.(2)空气水汽压亏缺、日温差、空气湿度和日照时数与油松、侧柏茎周长变化关系显著,但在回归拟合过程中侧柏的解释因子只有空气水汽压亏缺和日平均风速,且解释程度比较低(0.356).(3)油松、侧柏茎周长生长量的拟合水平较高,且影响气象因子相同,侧柏的液流速率也成为解释因子之一.水汽压亏缺、空气温湿度、日照时数、土壤水势和风速对树木的生长起到决定性的作用.     

酒泉地区高空风速分布特征及影响因素

利用酒泉国家气候观象台1980-2001年探空资料,分析其风速垂直分布和月、年际变化特征及其影响因子。结果表明:风速在对流层内随高度增加而增大,在200 hPa达到最大,对流层之上随高度增加而减小。酒泉站处在高空最大风带(副热带急流)最南和最北之间的位置,最大风带随季节南北移动,使酒泉站高空最大风呈现出规律性的季节变化。符合酒泉航天发射活动最佳气象条件的时间为每年10~11月。     

Fine-scale vegetation patches decline in size and cover with increasing rainfall in Australian savannas

Fine-scale vegetation patches (<5 m in width) are critically important in many landscapes because they function to obstruct surface flows of water and wind. These obstructions increase the infiltration of runoff and the capture of nutrients in runoff sediments and in wind-blown soil and litter. The importance of redistribution of runoff into runon patches from spaces between patches (fetches) is likely to be greater in drier than in wetter environments. In this paper we examine the hypothesis that the ratio of fetch to patch decreases as rainfall increases, and that this trend will be most evident on intermediate-textured soils because these soils are more prone to runoff. We measured fine-scale patches on 38 sites with sand, loam or clay soils. Sites were located along a 1000-mm rainfall gradient in the savannas of northern Australia. The width and intercept length of patches and the fetch between patches was measuring along line transects of 100–120 m oriented down slope. We found that the ratio of fetch to patch area did not decrease with decreasing rainfall, but increased on both sand and loam soils. This result was because with increasing rainfall mean spacing between patches disproportionally increased while mean patch size and cover declined. The cover of patches was negatively correlated with tree canopy cover, which significantly increased with rainfall. This negative correlation suggests that in higher rainfall savannas the size and spacing of ground-layer patches is controlled by the tree layer, and that as rainfall decreases this control decreases and runoff-runon processes increasingly structure the landscape. For savannas on clay soils these trends were not significant except that on the highest rainfall sites the cover of ground-layer patches was nearly 100% while trees were absent.     

旱地保护性耕作地表径流和土壤水分平衡模型

在田间试验和对现有径流模型及土壤水分平衡模型改进的基础上，建立了适用于保护性耕作的地表径流和土壤水分平衡模型。该模型以日为步长，根据气象数据、土壤水分状况、作物生长发育及耕作管理措施，模拟不同耕作管理体系下地表径流和田间水分平衡的变化。针对保护性耕作的特点，主要对径流曲线数字(USDA—Curve Number)法进行了改进，在PERFECT模型的基础上增加了坡度和降雨强度两因素的影响，从而使模型较全面地考虑了残茬覆盖、耕作、坡度及降雨强度等多种因素对径流的影响；采用简单实用的Priestley—Taylor公式计算潜在蒸散量，并考虑作物覆盖与残茬覆盖对土壤蒸发与作物蒸腾的影响。通过田间径流试验和根层有效贮水量测定数据的验证，证明了地表径流和土壤水分的模拟值与实测值比较接近。