Root and shoot competition between established grass species and newly sown seedlings during spring growth

Competition between established Dactylis glomerata or Festuca pratensis / Taraxacum officinale swards and seedlings of Trifolium pratense was studied under field conditions in Norway. Root competition from the Festuca pratensis / Taraxacum officinale sward was significantly greater than that from a Dactylis glomerata sward. The balance in root and shoot competition varied between experimental years because of variation in environmental conditions. In the first experimental year, root competition had a greater effect on seedling dry weight than shoot competition, whereas the opposite was found in the second year. However, both root and shoot competition (full competition) in comparison with no competition gave proportionally the same effects in both years, indicating that an alleviation in root competition will be followed by intensified shoot competition. An increasing effect of shoot competition with time on plant dry weight was found. In a second experiment, seedlings of Lolium perenne and Trifolium pratense produced the highest plant dry weights in competition with an established Phleum pratense sward, followed by seedlings of Poa pratensis , Phleum pratense and Trifolium repens in decreasing order. However, no interactions between seedling species and competition treatments were found, indicating no differences in sensitivity between seedling species to competition from the established grass sward. The results are discussed in the context of renovating grassland by direct drilling.     

水稻机械化直播优势、问题与发展对策

随着现代农业与农业机械化技术不断发展,传统水稻种植方式与技术越来越呈现出一定的不足,难以满足水稻高质量生产发展的需求,也与从事农业生产的农民利用农业机械减轻劳动强度、利用机械化生产节本增效的出发点不一致.从水稻机械化技术的相关问题着手,阐述了水稻机械化直播的现实性与必要性.     

玉溪玉米茬免耕直播油菜杂草的防除

在对当地油菜苗期杂草种类调查的基础上,选择触杀型复合除草剂2K草甘膦和土壤封闭型除草剂禾耐斯(乙草胺)组合处理玉米收获后免耕直播油菜田。45 d后调查,对照区有16科27种杂草发生,处理区8种杂草少量发生,平均株防效为97%,平均鲜重防效为95%。     

Root system response of selected lowland Thai rice varieties as affected by cultivation method and potassium rate under alternate wetting and drying irrigation

ABSTRACT

Root system is an important factor for crop productivity under water- and nutrient-limited environments. A pot study was conducted to evaluate root system response of three Thai rice varieties (Pathumthani 1, RD57, RD41) under three cultivation methods (dry direct seeding [DDS], wet direct seeding [WDS], transplanting [TP]) and three levels of alternate wetting and drying irrigation (–5, –15, –30 kPa). A second pot experiment examined the effect of potassium (K) rates (0, 80, 120, 160 kg ha^–1) on root system response of the same varieties under DDS and TP subjected to alternate wetting and drying at –5 kPa. Pathumthani 1 was more tolerant to moisture stress; RD57 and RD41 showed an inconsistent response to moisture-deficit conditions. Rice plant under TP was more sensitive to moisture stress; rice plant performed better under DDS even at the highest soil moisture stress of –30 kPa. K application at the rate of 120 kg ha^–1 as basal under DDS was optimum for root system development of Pathumthani 1, while RD57 and RD41 had higher actual root length at the same K rate regardless of cultivation methods. Alternate wetting and drying up to –30 kPa could be safely applied for the three tested varieties. The performance of root system of Pathumthani 1 was better under DDS method of cultivation. K fertilization at 120 kg ha^–1 can be recommended as optimum rate under water-saving cultivation techniques for the three tested varieties.     

Crop uptake of 15N labelled fertilizer in spring wheat affected by application time

Time of nitrogen fertilizer application on crop recovery was studied in a field experiment at Foulumgaard, Denmark, in 2001. A solution of ¹⁵N-ammonium-¹⁵N-nitrate was applied in bands parallel to a single row of spring wheat grown in frames of 30 cm×40 cm. The labelled fertilizer was applied on 16 dates with intervals of 4–5 days from tillering to the start of grain-filling. Crop ¹⁵N recovery increased by 0.47%-point day^?1 when the time of fertilizer application was postponed from tillering until the second node stage (GS32). On the other hand, a decrease in crop ¹⁵N recovery of –0.19%-point day^?1 was recorded from GS47 to maturity (GS85–87). The effect of the 16 application times on ¹⁵N recovery was described by two straight lines having intersection at the time of full expanded flag leaf and ear emergence halfway (GS55). It was concluded that leaf area expansion is important for crop N demand and ¹⁵N recovery.     

Ammonium nitrogen in soil solution and seed nitrogen affect the percentage of establishment of rice plants in submerged soil

The effect of ammonium nitrogen concentration in soil solution on the establishment of rice plants was examined. The increase of the concentration decreased the percentage of establishment of seeds sown in submerged soil, although most of seeds sown on submerged soil became established. Therefore, the increase of ammonium nitrogen concentration in soil solution may impair the establishment of seeds sown in submerged soil, which would occur presumably because the increase delays the spear growth and emergence without the decline of soil redox potential. Several seed lots with various nitrogen contents were obtained from rice plants grown under various conditions. The percentage of establishment of low-nitrogen seeds sown in submerged soil was much lower than that of high-nitrogen seeds, especially in soils whose solution contained a large amount of ammonium nitrogen. However, the difference in the percentage of establishment between high- and low-nitrogen seeds sown on submerged soil was much smaller. Therefore, the increase of seed nitrogen content may improve the percentage of establishment of seeds sown in submerged soil, presumably because the increase accelerates the spear growth and emergence. Consequently, for direct sowing in submerged soil, ammonium nitrogen concentration in soil solution should remain low because ammonium nitrogen exerts an adverse effect on seedling establishment, and vigorous seeds with a high nitrogen content should be sown because seed nitrogen exerts a beneficial effect on seedling establishment.     

我国目前供热形式优劣浅谈

本文就我国目前存在的几种供暖形式的优点及其存在的局限性和弊病分别进行了阐述，提出了如何克服缺陷，以取得更好的供暖发展空间。     

论信用权及其制度构建

信用是现代市场经济的基石,市场经济就是信用经济的理念获得广泛认同.当前我国社会的信用危机已成为制约我国市场经济深入发展的重要因素.信用权是一种独立的人格权,通过民法典构建完整的信用权制度,有助于完善社会信用体系并促进我国市场经济的健康发展.我国应在未来民法典上确立信用权的独立人格权地位并给予直接保护,不断完善信用权制度.     

鸡痘病毒282E4株2.2kbTK基因序列分析

将鸡痘病毒２８２Ｅ４弱毒株基因组中的３．７ｋｂＨｉｎｄⅢ片段克隆到ＫＳ（－）质粒中，亚克隆后，获得含ＴＫ基因正反方向插入的２．２ｋｂＨｉｎｄⅢ－ＣｌａＩ片段的质粒ｐＫＦＡ和ｐＫＦＢ，进而构建出正反方向的系列嵌套缺失质粒。用Ｔ７、Ｔ３引物所做的核苷酸序列分析表明，２．２ｋｂＨｉｎｄⅢ－ＣｌａＩ ＴＫ基因序列长为２１５９ｂｐ，含有两个完整的读码框架（ＯＲＥ）Ｘ和ＴＫ，并确证了ＴＫ基因内存在单一酶切点Ｎ     

水电厂高频直流电源充电装置

介绍用于小型发电厂或变电站的一种微机型直流电源充电装置的设计方法。主回路使用半桥式功率变换电路，输出整流采用全桥式电路，降低了快恢复二极管反向耐压要求。控制回路为微机型高频脉宽调制电路，设计有IGBT驱动保护电路。控制软件根据电力工业局要求的充电控制流程对蓄电池组进行冲电过程的控制，采用PID控制算法。给出了主回路、控制回路及部分软件的具体实现方法。