旱地土壤中残留肥料氮的动向及作物有效性

氮素是作物生长最重要的必需元素之一。合理施用氮肥能促进作物生长并提高产量,但是,过多施用氮肥则抑制作物生长并导致大量的肥料氮残留在土壤中,这部分氮素不但会引起土壤养分不平衡,而且为生态环境带来潜在威胁,因此,研究残留氮的动向及作物有效性可为合理施用化肥氮、高效利用土壤残留氮素和减少残留氮素的损失提供依据。应用~(15)N示踪技术,通过4年定位试验,研究了黄土高原南部旱地冬小麦/夏玉米轮作过程中土壤残留肥料氮的变化及作物吸收利用。在冬小麦和夏玉米轮作的第一个周期,为了制造高肥料氮残留背景,于冬小麦播种前向微区施入240 kg hm~(-2)的~(15)N标记氮素;在夏玉米拔节期,为了研究氮肥施入对残留肥料氮的影响,设置0和120 kg hm~(-2)两个氮水平,以普通尿素施入微区。在第2至第4个轮作周期内,为了分析残留肥料氮的动向及其对作物的有效性,微区内不施任何肥料。结果发现,冬小麦播种前施用的~(15)N标记氮肥于收获期在0~200 cm土壤剖面中均有残留,但大部分累积在0~40 cm土层中,累积总量达到200.9 kg hm~(-2),占当季施入量的83.7%。在随后的夏玉米生长季残留的肥料氮迅速减少,之后随生长季的后移缓慢减少,然后保持相对稳定。经过4年的冬小麦/夏玉米轮作,0~300 cm土壤剖面仍残留大量的~(15)N肥料,后季不追施氮肥和追施氮肥处理的残留量分别为47.1 kg hm~(-2)和54.0 kg hm~(-2)。可见,有一部分肥料氮被固定在土壤有机质中。作物对残留氮的回收量逐年减少,且因后季追施氮肥与否而异,4年中作物对肥料氮的总利用率不追施氮肥和追施氮肥处理的分别为46.9%和50.4%,其中在第1个轮作周期中,小麦和玉米的总利用率分别41.6%和42.0%,后3年利用率分别仅有5.3%和8.4%;4年中残留~(15)N的损失率分别达38.1%和29.7%,其损失主要发生在第1个轮作周期的夏玉米生长季节。说明,在旱地土壤上,氮肥的残留是不可避免的,残留肥料氮的有效性较低,只有少量被作物逐年吸收,一部分以有机形态残留在土壤剖面中,另一部分发生了无效损失。后季追施氮肥可促进作物对土壤残留肥料氮的吸收且增加肥料氮在土壤中的保留,减少残留肥料氮的无效损失,但是以自身的大量损失为代价的。     

Attributes affecting residual benefits of N<Subscript>2</Subscript>-fixing mungbean and groundnut cultivars

Legumes grown for grain may or may not contribute net N benefits to soil and succeeding crops. An experiment was conducted to assess N₂ fixation attributes of six mungbean cultivars and two groundnut cultivars (Tainan 9 and Non-nod), which determine their residual benefit to the subsequent maize. Nodule number and dry weight of mungbeans peaked early (at 45 days) and declined thereafter strongly. In groundnut nodulation peaked later and declined only by 50% towards the final harvest. The N₂-fixing groundnut produced higher total dry matter yield than mungbeans; however, mungbeans produced higher seed yields. Dry matter harvest index and nitrogen harvest index (NHI) were higher in mungbeans (average 0.44 and 0.69) than groundnut (0.23 and 0.47, respectively, in Tainan 9). The percentage of nitrogen derived from air (%Ndfa, ¹⁵N isotope dilution) ranged from 54% to 62% in mungbeans, similar to that of groundnut (64%). However, Tainan 9 fixed more N₂ (82 kg N ha^–1) than mungbeans (35–50 kg N ha^–1) and resulted in a positive soil net N balance (+22 kg N ha^–1) while negative values were found for Non-nod groundnut and mungbeans (–3 to –12 kg N ha^–1). Maize grown after groundnut Tainan 9 had the highest total dry weight and total N uptake. This was equivalent to maize grown in fallow plots, which received 60–90 kg N ha^–1, while the respective benefits after mungbeans were 30–60 kg N ha^–1. Maize yield was directly related to the amount of residue N returned. Thus, the combination of high N yield, residue quality, %Ndfa and low NHI proved most beneficial to soil fertility and the succeeding crop.     

施用农药福美胂对苹果果园砷污染的研究

 重金属元素砷是果品质量安全的重要控制对象之一。为了解苹果生产过程中砷元素的残留污染情况，为其污染控制提供依据，对连续使用福美胂农药5年的苹果园的果实、叶片、枝干、根系及土壤中的砷含量进行了调查。结果表明，果树喷施或主干涂抹福美胂均不同程度提高了树体各部位和果园土壤中的砷元素含量，其中叶片、主枝皮部、主干皮部和浅层主根（0～40 cm）中的砷含量较高，果实中砷含量也有所增加。喷施处理显著提高了叶片和主枝中的砷含量，使表层土壤（0～20 cm）砷含量也明显提高；涂抹处理显著提高了主干和主枝皮部的砷含量，果实中的砷含量也明显高于对照。涂抹处理的树体砷总累积量高于喷施处理，且地上部分砷总累积量均高于地下部分；各器官中，浅层主根是砷残留累积的主要部位。使用福美胂对苹果园的砷污染表现出持效期长、范围广的特点。     

吡蚜酮在水稻中的残留动态研究

[目的]了解吡蚜酮在水稻植株中的残留动态以及在收获期水稻中的最终残留量。[方法]通过田间试验和高效液相色谱分析技术,研究了25%吡蚜酮可湿性粉剂在水稻植株中的消解动态以及在收获期水稻中的最终残留量。[结果]吡蚜酮在水稻植株中的降解半衰期为0.51～0.53 d,符合一级化学反应动力学方程。在水稻生长期喷施1次,按推荐剂量300 g/hm2和2倍剂量600 g/hm2施用25%吡蚜酮可湿性粉剂,在收获期植株、糙米和稻壳中均未检出。[结论]吡蚜酮属于易降解农药（T1/2〈30 d）。在水稻田使用25%吡蚜酮可湿性粉剂时,按推荐剂量300 g/hm2施药1次,建议水稻上最大残留限量值暂定为0.02 mg/kg。     

市售三七中五氯硝基苯的残留情况调查

目的：建立三七药材中分析五氯硝基苯（CBPN）残留量的毛细管气相色谱法,考察文山三七药材中的五氯硝基苯残留量情况。方法：样品用正已烷提取,用硅镁吸附剂预处理小柱净化,采用OV-17毛细管柱（30m×0．53mm,1um）及电子捕获检测器（ECD）,外标法计算含量。结果：平均加样回收率为93．6％,部分样品检出的五氯硝基苯残留量超过日本肯定列表限量。结论：建立的方法适用于三七中五氯硝基苯残留量的测定,有必要对三七药材中有机氯农药残留量制定相应的限量标准,并强令禁止销售和使用。     

敌敌畏、溴氰菊酯、三氟氯氰菊酯在香蕉上的残留动态

采用气相色谱法及田间试验方法,研究敌敌畏、溴氰菊酯、三氟氯氰菊酯在香蕉上的残留动态。结果表明,在香蕉上的原始沉积量,敌敌畏>溴氰菊酯>三氟氯氰菊酯,同一农药的原始沉积量与施用量密切相关。敌敌畏在香蕉上消解迅速,在施药1 d后消解率均在80%以上,施药后3 d的残留量≤0.005 mg/kg。溴氰菊酯、三氟氯氰菊酯在香蕉上的残留消解动态符合一级动力学方程,溴氰菊酯推荐剂量为C=0.129 8×e-0.1201t,加倍剂量为C=0.248 9×e-0.114 5t,半衰期(T1/2)为5.8～6.1 d,消解99%所需要时间(T0.99)为38.4～40.3 d;三氟氯氰菊酯推荐剂量为C=0.033 9×e-0.070 0t,加倍剂量为C=0.070 7×e-0.069 5t,T1/2为9.9～10.0 d,T0.99为65.8～66.3 d。敌敌畏、溴氰菊酯、三氟氯氰菊酯在距第2次(末次)施药后60～70 d,香蕉产品的最终残留量均分别<0.005 mg/kg、<0.01 mg/kg、<0.008 mg/kg。     

Relaxation mechanism of residual stress inside logs by heat treatment: choosing the heating time and temperature

 Some methods to reduce residual stress inside logs have been reported, although the conditions for stress relaxation are not yet clarified. Our study using precise experiments revealed that residual stress relaxation occurs only when both heat and moisture exist inside the logs. We then determined the heating time and temperature required to relax the residual stress inside the logs. Short air-drying treatments did not relax residual stress even though free water in the logs was greatly reduced. The residual stress of the 33-h 80°C-heated bolts was relaxed, whereas that of the 48-h 70°C-heated bolts was not. As for the influence of treatment time, bolts heated at 100°C were relaxed after 18 h of treatment. The 13-h heated bolts did not show any relaxation. Therefore, residual stress relaxation occurred rapidly owing to the thermomechanical change of the individual wood components comprising the cell wall. The moisture content inside all the bolts was much higher than the fiber saturation point. This is because relaxation occurs only when the heating temperature is maintained above 80°C for a particular duration of treatment. Received: December 12, 2001 / Accepted: February 18, 2002 Present address: Institute for Structural and Engineering Materials, National Institute of Advanced Industrial Sciences and Technology, Independent Administrative Institution, Nagoya 463-8560, Japan Tel. +81-52-736-7320; Fax +81-52-736-7419 e-mail: m.nogi@aist.go.jp Part of this report was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000 Correspondence to:M. Nogi     

河南省林业企业全要素生产率的测定

河南省林业企业主要分布于第一产业、第二产业,利用生产函数和索洛增长速度方程法来测算科技对林业企业贡献大小。经测算,河南省林业企业2000-2004年平均全要素生产率为11.74%。科技对河南省林业企业发展贡献较低。     

常用除草剂对家蚕的毒性试验

８种常用除草剂对家蚕的毒性试验,结果表明：家蚕对其中４种除草剂有一定的毒性反应,表现轻微的中毒症状。除草剂对家蚕的角杀毒力和残毒期因除草剂品种不同而有明显的差异。家蚕对除草剂的抗性因龄期大小不同而异。     

Nutrient surpluses on integrated arable farms

From 1990 to 1993 nutrient fluxes were monitored on 38 private arable farms that had adopted farming strategies aiming at reduced nutrient inputs and substitution of mineral fertilizers by organic fertilizers. The nutrient surplus was defined as the difference between inputs (including inputs through deposition, seeds and biological fixation) and outputs in crop products, and amounted to 117 kg nitrogen (N), 14 kg phosphorus (P) and 21 kg potash (K) ha⁻¹ year⁻¹ on average. Potato and sugar beet had relatively high nutrient surpluses resulting both from crop characteristics and the use of organic manure. The surplus varied markedly among farms due to differences in cropping frequency, fertilizer inputs and crop outputs. Averaged over the years, ca. 70% of the participants achieved surpluses below 150 kg N, 20 kg P and 50 kg K ha⁻¹ year⁻¹.

The amounts of residual soil mineral N (RSMN) exceeded those normally found in field experiments except for data collected after the wet summer of 1993. Distinct differences between crops were observed. Only in the case of potato a significant relationship was observed between the effective N input and RSMN. On a whole-farm level, RSMN amounted to more than 70 kg ha⁻¹ N on 77, 74, 87 and 18% of the farms in the consecutive years.