An evaluation of Colwell‐P as a measure of plant‐available phosphorus in soils of volcanic and non‐volcanic origins in the highlands of Papua New Guinea

Various soil test methods including Olsen, Colwell, Bray and Truog have been used to assess the levels of plant‐available P (PAP) in soils situated in the highlands of Papua New Guinea (PNG). Up until now, though, there has been no guarantee that these tests provide valid assessments of PAP in these somewhat atypical organic matter‐rich tropical soils. Furthermore, the critical soil‐P concentrations associated with the tests have been based on studies conducted elsewhere in sub‐tropical and temperate latitudes and as such may or may not be valid for soils or cropping situations in PNG. Soil (Colwell)‐P and leaf‐P data collected during a recent survey of sweet potato gardens in the highlands of PNG were therefore used to determine if useful relationships existed between these variables for different groups of soils, and if they do, to use these relationships to evaluate critical soil Colwell‐P concentrations corresponding to a known critical concentration of P in sweet potato index leaf tissue. Separate, highly significant linear relationships were obtained between leaf‐P and Colwell‐P for soils of volcanic and non‐volcanic origins. Based on these relationships, the critical Colwell‐P concentration for volcanic soils was found to be four times greater than that for non‐volcanic soils, presumably because much of the P extracted from the former soils with alkaline sodium bicarbonate had been chemically ‘fixed’ via sorption and precipitation reactions with sesquioxides and rendered unavailable to plants at ambient soil pH. These critical Colwell‐P concentrations if adopted as benchmark values for the soil groups in question should ensure that the results of future soil fertility surveys involving Colwell‐P assessments are correctly interpreted.     

动态载荷下基于声发射技术的杨木破坏过程检测

利用声发射检测和力学试验相结合的方法,研究山杨木材在动态载荷下的声发射演变过程;结合木材粘弹性特点,通过声发射参数分析研究在不同受力阶段木材的声发射特点.结果表明:1)声发射信号幅值不连续,是跃迁的;材料断裂前声发射信号的幅值和能量比断裂后小,在断裂点对应声发射信号幅值和能量的局部极大值.2)随时间和载荷的变化,声发射累计撞击数和累计能量增加快慢可以体现杨木在受力条件下的完全弹性、弹性为主的弹塑性共存、塑性为主的弹塑性共存3种状态.3)声发射率和幅值参数可以预测材料纤维开始断裂进入危险期的第一"临界点"和材料大量纤维断裂进入严重危险期的第二"临界点",如果继续加载材料将会破坏断裂.     

复杂荷载作用下单轴对称开口薄壁梁柱的弯扭屈曲

采用Rayleigh-Ritz法求解两端等弯矩、横向集中荷载和均布荷载作用下单轴对称开口薄壁截面梁柱弯扭屈曲临界荷载。分析中考虑了3种常见边界条件以及屈曲前变形的影响。将本文弯扭屈曲临界荷载理论值与试验值比较，吻合较好。     

阿拉善查汗套海滩生态建设区最佳水文地质环境评价研究

干旱沙漠区环境治理，水文地质环境是制约其它因素的关键。地下水位过高引起土壤盐渍化，地下水位过低则引起沙漠化。而正确确定地下水临界深度将成为查汗套海滩生态环境建设的瓶颈。本文提出地下水资源的允许开采量作为解决生态环境建设的重要途径之一，具有很好的资源效益和环境效益。     

Critical Phase Transition of the Two-dimensional Microcanonical Ising Model by Cellular Automata Q2R Method

The authors construct a microcanonical ensemble system and analyzes the phase change of the two-dimensional Ising model Cellular Automata Q2R/WQ2R method. The result indicates that the numerical value simulation can show the spontaneous magnetization of two-dimensional crystal lattice in isolated system. The authors have observed the critical phase transition phenomenon and gotten the critical energy. The simulation of three-dimensional Ising model can be grounded on the method that this article establishes.     

棉籽和蓖麻籽的冷榨试验与数值模拟

探讨棉籽和蓖麻籽植物油料的冷榨应力-应变关系、应力-压缩比关系以及加载速率对应力-应变关系和应力-压缩比关系的影响，探讨临界压榨压力选取问题。进行了棉籽和蓖麻籽冷榨试验，采用川北方程建立双曲线型应力-应变模型和压缩比的理论计算模型。研究表明，加载速率对油料破碎应力、应变以及应力-应变关系有影响，速率越大，破碎应力和应变越大；棉籽和蓖麻籽的模拟结果与实测值比较吻合。根据压缩比变化率及其斜率曲线近似确定出棉籽和蓖麻籽工程临界压榨压力分别为70 MPa和100 MPa。     

Diagnosis of sugar beet (Beta vulgaris L.) nutrient imbalance by DRIS and CND-clr methods at two stages during early growth

High yield of sugar beet require adequate mineral nutrition. To be diagnosed across interacting nutrients using appropriate interpretation models, the plant must be sampled at a critical physiological stage. This study aimed to develop and validate norms at the 7-leaf and well-developed rosette stages, for diagnostic purposes using the Diagnosis and Recommended Integrated System (DRIS) and Compositional Nutrient Diagnosis based on centered log ratios (CND-clr). Data on nutrient concentrations and plant performance were obtained from 409 plots in West-Central Poland. With respect to the growth stages, for physiological and practical reasons, the 7-leaf stage is preferable for diagnostic purposes. At this growth stage, the high-yield subpopulation characterized by higher concentration of potassium and sodium compared to other nutrients. CND-clr indices were closely related to DRIS indices (R² > 0.93). The CND-clr indices, however, better explained the differences in the white sugar yield within the validated dataset than the DRIS indices.     

Effects of acid deposition on Dutch forest ecosystems

Effects of elevated S and N deposition on the solution chemistry of Dutch forest soils are mainly manifested by increased concentrations of Al associated with increased concentrations of SO₄ and NO₄. Presumed critical Al/base cation ratios are often exceeded below 20 cm soil depth. There is also evidence that elevated N deposion during the last decades affected the forest nutrient status and caused large changes in forest vegetation. About half of the Dutch forests have absolute shortage of P and relative Mg deficiencies compared to foliar N contents. Evidence from field studies of a relationship between soil acidification and nutrient imbalances in the soil and the foliage on one hand and the vitality of forests on the other hand is, however, lacking.