Synchronizing N Supply from Soil and Fertilizer and N Demand of Winter Wheat by an Improved Nmin Method

Excessive nitrogen (N) fertilizer application and poor timing of N fertilizer application to winter wheat are common problems on the North China Plain. To study the possibilities of optimizing the timing and rate of N application, a field experiment was conducted from 1999 to 2001 in a suburb of Beijing. A control (no nitrogen) and two N fertilization strategies (conventional N application and optimized N fertilization) were designed to compare their effects on wheat growth, N nutrient status, grain yield and N balance. The conventional N fertilization strategy was given a fixed N rate of 300 kg N ha⁻¹, which was split, half in autumn and half in spring as a top-dressing. The timing and rate of N and application of the optimized N fertilization strategy were determined by the target value of soil mineral nitrogen demand for three growth periods of wheat, which is related to the target yield, and soil mineral N (N_min) in the effective rooting depth at the beginning of these three periods. Based on the optimized N fertilization strategy, a total of 55 and 65 kg N ha⁻¹ had to be applied to winter wheat in the re-greening and shooting stages of the first and second experimental years, respectively. Compared with the high N rate before sowing in the conventional N fertilization treatment, the optimized N fertilization treatment did not require any N fertilizer before sowing of wheat. Despite a much lower N fertilization rate, no significant difference in N nutrient status, growth during the wheat growing period or grain yield was observed between optimized N and conventional N fertilization treatments. As a consequence of optimizing the rate and timing of the N fertilizer application to match wheat demand, a much lower residual N_min and calculated apparent N loss was found as compared to the conventional N treatment. N recovery for the optimized N fertilization treatment (67% in 1999/2000 and 66% in 2000/2001) was much higher than that of the conventional N fertilization treatment (19% in 1999/2000 and 18% in 2000/2001). In conclusion, the optimized N fertilization strategy can synchronize N demand of wheat and the N supply from soil and fertilizer, and therefore drastically reduce N application rates without any yield losses.     

Fall Composition of Storage Lipids is Associated with the Overwintering Strategy of <Emphasis Type="Italic">Daphnia</Emphasis>

Diapause, which occurs through the production of dormant eggs, is a strategy used by some zooplankton to avoid winter months of persistent low temperatures and low food availability. However, reports of active zooplankton under the ice indicate that other strategies also exist. This study was aimed at evaluating whether the composition of storage lipids in the fall differs between diapausing and active overwintering Daphnia. We assessed the quantity of storage lipids and fatty acid (FA) composition of Daphnia species, along with FA content of seston, in six boreal, alpine and subarctic lakes at the onset of winter, and evaluated the association between storage lipids and Daphnia overwintering strategy. We found that active overwintering Daphnia had >55% body fat and the highest FA concentrations. Polyunsaturated FA, especially stearidonic acid (18:4n-3; SDA) and high ratios of n-3:n-6, were preferentially retained to a greater extent in active overwintering Daphnia than in those that entered diapause. Daphnia FA composition was independent of that of the seston diet, indicating that Daphnia adjusted their storage lipids according to the physiological requirements of a given overwintering strategy. The occurrence of an active overwintering strategy has consequences for zooplankton community structure, and can have important implications for the transfer of high-quality energy at higher trophic levels.     

设计对冬施混凝土抗冻临界强度考虑

从结构设计对建筑施工保证条件角度，分析了结构设计对冬施砼抗冻临界强度的要求与做法，并提出了冬施砼达不到抗冻临界强度会使结构可靠性下降问题。     

环境·流线·空间——第三届亚洲冬季运动会综合体育馆设计特点分析

文章介绍了１９９６年２月在哈尔滨举行的第三届亚洲冬季运动会的综合体育馆。该馆是从环境分析，整体流线安排及室内外空间的处理等方面进行设计的。作者通过对环境，流线和空间的探索，总结出在设计中应着重注意的几个问题及有关的解决办法。并希望它将有益于未来体育馆的设计。     

彩色水磨石现制地面冷作施工

冬期施工现制水磨石地面,是一个施工难点。本文介绍了在候车大厅现制水磨石冬期施工中,采用冷作法施工,取得成功的经验。采用冷作法冬施水磨石地面。只要措施得当,工程质量是可以保证的。     

中国寒冷地区混凝土工程冬期施工发展状况

综述了中国目前寒冷地区混凝土工程冬期施工中所采用的基本方法，探讨了研究中出现的问题，提出了供讨论的冬施混凝土今后研究课题。     

混凝土抗冻临界强度取值研究与实践

分析了冬期施工中存在的几种不同抗冻临界强度的概念，指出了空白砼的抗冻临界强度与防冻剂砼抗冻临界强度之间的本质区别，并提出了广义抗冻临界强度的概念，为负温砼工程实践提供了理论基础。     

新型高效油菜田除草剂丙酯草醚的创制研究

较全面地介绍了新型高效油菜田除草剂丙酯草醚（开发代号ZJ0273）的整个创制研究流程,系统论述了先导化合物的发现、知识产权的保护、生物活性的评价过程、毒理学试验结果、残留试验结果、生态环境安全性评价、合成工艺研究、剂型研究、全分析研究、作用机理和代谢途径研究以及应用前景评价等,对新农药创制研究具有一定的借鉴和启迪作用。     

Contamination of edible double-low oilseed rape crops via pollen transfer from high erucic cultivars

Contamination of double-low oilseed crops with pollen from high erucic varieties grown primarily on set-aside land may result in erucic acid concentrations above 2% resulting in its rejection as a double-low edible oilseed. An analysis of cross contamination between high and low erucic acid crops was carried out in field trials at Cockle Park, and Purley Farm, Essex in the 1992–1993 and 1993–1994 seasons. Contamination was generally low and at random across the test areas. This random fluctuations in erucic acid concentrations appeared to be due to insect activity rather than wind mediated pollen transfer. Roto-rod traps used at Cockle Park to measure pollen flow downwind from isolated blocks of oilseed rape showed that in both seasons a rapid exponential decline in pollen concentration occurred with distance from the source. Results presented in this study would suggest that contamination between edible and high erucic crops does not present a major problem under field scale cultivation. © 1998 SCI.     

The tribological behaviour and mechanism of action of sulphur-containing borate esters in rape seed oil

Three sulphur-containing borate esters and one borate ester based on boric acid and n-octanol were synthesised. The antiwear and friction-reducing properties of these synthetic compounds as additives in rape seed oil were examined using a four-ball machine. The relationship between the additive structure and tribological properties was explored, and the lubrication mechanisms of the additives investigated. The worn surfaces of a steel ball lubricated with the additive-containing rape seed oil were analysed using X-ray photoelectron spectroscopy and scanning electron microscopy. The elemental compositions of, and distributions in, the worn steel surfaces were determined with an electron probe micro-analyser. It was found that sulphur-containing borate esters as additives in rape seed oil at appropriate concentrations can be effective in improving antiwear and friction-reducing behaviour. The rape seed oil base stock experiences competitive adsorption and tribochemical reactions with additives on the rubbing steel surface. The introduction of the active element sulphur into the borate ester additives functions to improve the tribological behaviour of the base stock by increasing the rate of formation of a protective layer on the rubbing steel surface. However, the tribological behaviour of the additives is not dependent on the number of sulphur atoms in the additive molecules, and further work is needed to investigate the possible dependence of this behaviour on the ratio of boron to sulphur in the additive molecules.