Assessing the depletion of soil P following sequential extractions with Mehlich-3 and Olsen solutions

We analyzed in soils with contrasting cultivation histories the depletion of P following sequential extractions with soil testing solutions. Soil samples were collected in three experiments in eastern Canada (L’Acadie, Lévis, and Normandin) and P was sequentially extracted 16 times, once daily, using Mehlich-3 (M3) or Olsen (Ol) solution. The cumulative amount of P extracted was 252 mg P_M3 kg^?1 and 77 mg kg^?1 P_Ol for L’Acadie, 212 mg P_M3 kg^?1 and 66 mg P_Ol kg^?1 for Lévis, and 424 mg P_M3 kg^?1 and 83 mg P_Ol kg^?1 for Normandin. The depletion of P was described by a logarithmic function (Y = a ln (N) + b) for P_M3, and a power function (Y = αN^β) for P_Ol. The inorganic P pool decreased in the three soils. The organic P pool did not decrease possibly because soil testing solutions did not directly extract P from this pool. This study demonstrated that laboratory soil testing analysis using M3 or Ol solution principally target P from the inorganic pool, suggesting that P fertilizer recommendations to mineral soils relying on these methods do not account for the potential of the organic P pool to contribute to soil P availability.     

Evaluation of 3,4-dimethylpyrazole phosphate as a nitrification inhibitor in a <Emphasis Type="Italic">Citrus</Emphasis>-cultivated soil

 The objectives of this work were to evaluate the inhibitory action on nitrification of 3,4-dimethylpyrazole phosphate (DMPP) added to ammonium sulphate nitrate [(NH₄)₂SO₄ plus NH₄NO₃; ASN] in a Citrus-cultivated soil, and to study its effect on N uptake. In a greenhouse experiment, 2 g N as ASN either with or without 0.015 g DMPP (1% DMPP relative to NH₄ ⁺-N) was applied 6 times at 20-day intervals to plants grown in 14-l pots filled with soil. Addition of DMPP to ASN resulted in higher levels of NH₄ ⁺-N and lower levels of NO₃ ^–-N in the soil during the whole experimental period. The NO₃ ^–-N concentration in drainage water was lower in the ASN plus DMPP (ASN+DMPP)-treated pots. Also, DMPP supplementation resulted in greater uptake of the fertilizer-N by citrus plants. In another experiment, 100 g N as ASN, either with or without 0.75 g DMPP (1% DMPP relative to NH₄ ⁺-N) was applied to 6-year-old citrus plants grown individually outdoors in containers. Concentrations of NH₄ ⁺-N and NO₃ ^–-N at different soil depths and N distribution in the soil profile after consecutive flood irrigations were monitored. In the ASN-amended soil, nitrification was faster, whereas the addition of the inhibitor led to the maintenance of relatively high levels of NH₄ ⁺-N and NO₃ ^–-N in soil for longer than when ASN was added alone. At the end of the experiment (120 days) 68.5% and 53.1% of the applied N was leached below 0.60 m in the ASN and ASN+DMPP treatments, respectively. Also, leaf N levels were higher in plants fertilized with ASN+DMPP. Collectively, these results indicate that the DMPP nitrification inhibitor improved N fertilizer efficiency and reduced NO₃ ^– leaching losses by retaining the applied N in the ammoniacal form. Received: 31 May 1999     

西藏野生油菜种质资源千粒重分析

研究了西藏野生油菜,特别是野生白菜型油菜和野生芥菜型油菜种质资源的千粒重。通过对采集来的西藏野生白菜型油菜和野生芥菜型油莱种质资源千粒重的研究与鉴定发现：（1）野生芥菜型油菜千粒重要小于野生白菜型油菜;（2）从野生油菜种质资源千粒重的水平分布来看,千粒重较大的野生白菜型油菜种质资源明显集中分布于北纬27&#176;30′～31&#176;00′,东经89&#176;00′～92&#176;00′之间和北纬27&#176;30′～32&#176;00′．东经97&#176;00′－98&#176;00′;千粒重较大的野生芥菜型油菜种质资源明显集中分布于北纬29&#176;00′－30&#176;00′,东经87&#176;30′～94&#176;00′之间;（3）从野生油菜种质资源千粒重的垂直分布来看,在高海拔地区的野生油菜种质资源的千粒重有更大的趋势,野生芥菜型油菜与野生白菜型油菜千粒重随海拔升高而增加,具有垂直分布的生态适应性。     

Abortogenic viruses in horses

Viral causes of abortion include equine viral arteritis (EVA) and infection with equine herpesviruses‐1 and ‐4 (EHV‐1 and EHV‐4). Transmission of equine arteritis virus (EAV) occurs through respiratory, venereal or transplacental routes. Horizontal respiratory transmission of EAV results from exposure to infective nasopharyngeal secretions from acutely infected horses. For this transmission to occur, direct and close contact between horses is necessary. Venereal infection is an efficient method of transmission, with seroconversion of 85 to 100% of seronegative mares bred to virus shedding stallions. Asymptomatic carrier stallions are the essential natural reservoir of equine arteritis virus. Equine herpesviruses‐1 and ‐4 infect a susceptible host, replicate and establish a lifelong latent infection without any associated clinical signs. Reactivation of latent infections can result from factors such as stress and intercurrent disease. The control of these diseases is by implementation of appropriate management and hygiene measures, supplemented by vaccination and, in the case of EVA, by the identification of persistently infected stallions, which can be removed from breeding or continue to be bred to if managed under controlled conditions to prevent the risk of an outbreak of the disease.     

Effects of fasting and feeding on plasma amino acid levels in brown trout

Plasma amino acid (AA) levels were analysed at various intervals during fasting and after feeding in juvenile brown trout, Salmo trutta. After 3 days of food deprivation, total plasma AAs decreased significantly (–26% vs. control) due to a fall in the most abundant essential AAs (EAA): branched-chain amino acid (BCAA) and Thr, and there was also a decrease in non-essential AA (NEAA) levels, especially Ala and Asn. After 15 days of fasting, BCAA increased, possibly related to muscle protein mobilization. After 50 days of food deprivation, a significant increase in Gln levels (40% vs. 15 days of fasting) and a decrease in BCAA (–25% vs. 15 days of fasting) was noted. Feeding a commercial trout pellet caused a clear and progressive increase in plasma AA levels. Both EAA and NEAA concentrations peaked at 11 h post-feeding (4068 ± 160 and 4261 ± 239 µM NEAA, respectively) with a greater increase in EAA (+62%) than NEAA (40%) with respect to control values. These data show that changes in the plasma AA pool clearly reflect the nutritional state of fish and help us to understand the complex AA metabolism.     

Comparative pharmacokinetics of enrofloxacin and tissue concentrations of parent drug and ciprofloxacin after intramuscular administrations of free and liposome-encapsulated enrofloxacin in rabbits

Pharmacokinetic properties and tissue concentrations of enrofloxacin and ciprofloxacin were compared after intramuscular (i.m.) administrations of free and liposome-encapsulated enrofloxacin at the dose of 5 mg/kg body weight (bw). Twelve healthy adult New Zealand white rabbits were used in the experiment. Blood samples were obtained at 10, 20, 40, 60 and 90 min and 2, 4, 6, 8 and 12 h and tissue samples were collected 24 h after injection. Concentrations of drugs in serum were determined by high-performance liquid chromatography. Pharmacokinetics were best described by a two-compartment open model. Results indicated that absorption rate was slow, peak concentration was higher (P < 0.05), and the time to peak concentration (tmax congruent with 1.5 h) was significantly longer (P < 0.05) for liposome-encapsulated enrofloxacin (LEE) when compared with free enrofloxacin. Values of elimination half-life (t1/2beta = 12.9 h) and mean residence time (MRT = 17.6 h) of liposome-encapsulated enrofloxacin were longer (P < 0.05) and total clearance (Cl = 0.43 l/h/kg) was lower than those of free form. Moreover, the distribution volume at steady-state (Vd(ss) = 14.4 l/kg) of enrofloxacin administered encapsulated into liposomes was significantly higher (P < 0.05) than that of free enrofloxacin (FE). The tissue levels of enrofloxacin and ciprofloxacin after LEE injection were not different (P > 0.05) from FE. In conclusion, the result of present study suggest that LEE may be a beneficial and valuable formulation in the treatment of infectious diseases caused by sensitive pathogens in animals, providing sustained drug release from injection side and prolonged therapeutic serum concentrations after i.m. administration.     

Variations in chicken breast meat quality: implications of struggle and muscle glycogen content at death

1. Pectoralis major (P. major) muscle pH and meat quality traits were studied in relation to bird response to ante-mortem stress in three chicken lines: a fast-growing standard line (FGL), a slow-growing French 'Label Rouge' line (SGL) and a heavy line (HL). Ninety-nine birds of the three genetic types were slaughtered at their usual marketing age (6, 12 and 6 weeks for FGL, SGL and HL birds, respectively) on the same day. The birds of each line were divided into three different ante-mortem treatment groups: minimum stress (shackling for 10 s) (C), shackling for 2 min (SH) and acute heat plus shackling stress (exposure to 35 degrees C for 3.5 h and shackling for 2 min before stunning) (H + SH). 2. Regardless of chicken line, wing flapping duration (WFD) between hanging and stunning was strongly negatively related to P. major muscle pH at 15 min post-mortem. It was also moderately negatively related to P. major muscle glycolytic potential (GP), which represents glycogen level at death. Increasing WFD induced an increased ultimate pH (pHu) only in HL. The consequences of increased WFD for breast meat traits were dependent on the chicken line: it induced lower L* and b* and higher a* and drip loss in SGL while it only increased breast a* in HL birds. By contrast, WFD variations did not alter breast meat quality traits of FGL birds. Regardless of the chicken line, increased GP was associated with lower pHu and higher L* and drip loss. In SGL, it also increased b* and decreased curing-cooking yield of breast meat. 3. Struggling activity on the shackle line and muscle glycogen content at death could partly explain line and pre-slaughter variations in breast meat pH and quality traits. The water holding capacity of the raw and cooked meat was impaired by long shackling in the case of SGL birds while it was barely affected by ante-mortem conditions in the two standard lines. In conditions which minimised bird struggling (C), SGL and FGL birds had meat with a better water holding ability than that of broilers from the heavy line. However, when broilers were subjected to SH or H + SH conditions, the breast meat water holding capacity of SGL birds was lowered to the same level as that of the heavy line birds.     

业务员招聘识别、培训使用问题——饲料企业营销诊断之一

最近几年,饲料业都普遍存在一种现象,部分企业饲料销售量很难上升,有些品种甚至持续下降,虽然不断尝试新方式、新办法,但仍然没有明显好转。有必要对此进行一些诊断。     

浅谈木工机械最优化设计与MATLAB的应用

１最优化设计简介 随着生产和科学技术的迅速发展，木工机械产品与设备也逐步向高速、高效、精密、轻量化和机电一体化方向发展，产品的结构也日益趋向复杂，对其工作性能的要求也愈来愈高。传统的、静态的、经验的机械设计方法正在被动态的、优化的、计算机化的现代设计方法所取代。“最优化设计”是在现代计算机广泛应用的基础上发展起来的一项新技术，它是根据最优化原理和方法，综合各方面因素，以“人机配合”方式或“自动探索方式”，在计算机上进行半自动或自动设计，从而选出在现有工程条件下的最优化设计方案的一种现代设计方法。…