Correction of TDR-based soil water content measurements in conductive soils

Time Domain Reflectometry (TDR) is a widespread technique for measurement of soil water content (SWC). The main assumption behind the use of Time Domain Reflectometry (TDR) is of negligible losses, therefore assuming that only the real part determines the value of the TDR-measured apparent dielectric permittivity. This assumption does not hold for soils where surfaces are conductive (clay soils) or where high concentrations of electrolyte are present in the soil solution (saline soils) because under these conditions the contribution of the imaginary part becomes important. One of the main effects of dielectric losses on the TDR measurement is overestimation of SWC. In this study we present a methodology for separating the real and the imaginary part from the measurement of the apparent dielectric permittivity. This approach allows correction of the SWC overestimation, by using the TDR-measured electrical conductivity as indicator of dielectric losses. Oven-dry gravimetric soil water content was used as an independent method for soil water content assessment. The original SWC overestimation (in respect to the oven-dry gravimetric based measurement) reached values of up to 20% of total soil saturation, after the correction the differences were reduced to a 3–5%. The methodology can be applied based on knowledge of measured permittivity and electrical conductivity only, making it readily applicable to field experiments.     

Cold temperatures and boron deficiency caused grain set failure in spring wheat (Triticum aestivum L.)

Boron (B) deficiency and cold temperatures during the reproductive development of wheat (Triticum aestivum L.) cause failure of grain to set. A pot experiment at the Plant Environment Laboratory, The University of Reading, UK, in 1996 examined whether wheat cultivars differ in response to these stresses, if any stage during reproductive development was more sensitive than another, and whether the effects of B deficiency and cold temperature were reversible. The experiment comprised a full four-factor combination of two cultivars of spring wheat with different field responses to B and cold temperature (Annapurna-3 and NL-683), three B treatments (no B added, 20 μM B L⁻¹ from sowing to maturity and 20 μM B L⁻¹ from flag leaf first visible (GS 37) to maturity), two temperature regimes (ambient UK temperatures and 8°/2°C day/night temperatures in growth cabinets), and three stages for different temperature regimes to be applied [flag leaf ligule visible (GS 39) to awn first visible (GS 49), from GS 49 to full ear emergence (GS 59) or from GS 59 to the completion of anthesis (GS 69)]. Control plants remained outdoors throughout. An additional B treatment was also applied in which 20 μM B L⁻¹ was supplied only until GS 37 without any cold treatments. NL-683 was more sensitive to cold temperature, producing >80% sterility, than Annapurna-3 (40% sterility). In contrast, Annapurna-3 was more susceptible to B deficiency (22% sterility compared to only 14% in NL-683). The principal effect of cold was to impair pollen viability: anthers were poorly developed, small, shrivelled and rarely dehisced. More than 75% of pollen grains were dead in NL-683 compared to about 25% in Annapurna-3. All periods from GS 39 to GS 69 were vulnerable to cold damage although the first stage (GS 39–49) was relatively more sensitive. The adverse effect of cold was irreversible even if ear emergence and anthesis of the stressed plants was in ambient temperatures. Cold temperature significantly reduced the response of plants to B and when cold stressed the cold susceptible cultivar (NL-683) accumulated less B. The effect of added B in terms of improved fertility was smaller in the main shoot ear but the fertility of tillers was greatly enhanced. Plants were more responsive to added B after the emergence of the penultimate leaf: the interruption of B supply during this stage led to a similar degree of sterility, as in plants grown without B throughout. However, resupply of B at this stage in the plants initially grown without B led to similar B concentrations and grain set as in plants grown with adequate B throughout. Boron concentrations in the flag leaf and ear also increased considerably from GS 39 to GS 60 indicating that these are the most sensitive stages for B nutrition and wheat plants can recover all of their B requirements if supply is not restricted from GS 37 onwards.     

秋覆膜对辽西春玉米水肥利用效率和产量的影响

为了探明旱地秋覆膜对春玉米水分和氮肥利用效率的影响,2013—2015年在国家农业环境阜新观测实验站设置了秋覆膜(秋季收获后开始覆膜,AM)、春覆膜(传统生育期覆膜,SM)和不覆膜(NM)3个处理,利用田间观测结合15N同位素示踪的方法,分析秋覆膜栽培春玉米的水分与氮肥利用特征。结果表明,在连续2个较干旱的年份,AM促进了玉米干物质积累,2a的玉米籽粒产量分别较SM提高了19%和11%,较NM提高了14%和75%,但玉米生物产量与SM无显著差异(P0.05);AM在休闲期减少了水分消耗,在播种期土体蓄水量较SM和NM平均多35 mm,并在玉米生育期耗水量较SM和NM多,主要体现在玉米的抽雄期和灌浆期作物耗水量的显著增加(P0.05);在2014年,3个处理的玉米籽粒产量和生物产量水分利用效率无显著差异(P0.05);在2015年,AM与SM的玉米籽粒产量和生物产量水分利用效率无显著差异(P0.05),但均显著高于NM(P0.05),较NM平均提高了60%和65%;AM减少了氮肥损失,同时也较SM减少了土壤中氮肥的残留,显著提高了当季和翌年氮肥利用效率(P0.05),2a累计氮肥利用效率达到了50.5%,高于SM和NM,但AM在当季0～100 cm土层中残留的肥料氮显著高于NM(P0.05)。综合分析认为,在较干旱的年型下,旱地秋覆膜是辽宁西部半干旱区提高春玉米产量和水肥利用效率的一项有效技术措施,如进行氮肥优化施用,可进一步提升该技术在区域农业发展的应用价值。     

Long-term warming of a subarctic heath decreases soil bacterial community growth but has no effects on its temperature adaptation

We tested whether bacterial communities of subarctic heath soil are adapted to elevated temperature after experimental warming by open-top greenhouses for 7 or 17 years. The long-term warming by 1–2 °C significantly decreased bacterial community growth, by 28% and 73% after 7 and 17 years, respectively. The decrease was most likely due to decreased availability of labile substrate under warming. However, we found no evidence for temperature adaptation of soil bacterial communities. The optimum temperature for bacterial growth was on average 25 °C, and the apparent minimum temperature for growth between −7.3 and −6.1 °C, and both were unaffected by warming.     

风沙半干旱区不同时期覆膜对玉米田固碳及碳平衡的影响

通过对比秋季覆膜(AM)、春季覆膜(SM)和不覆膜(NM)3种模式栽培玉米对短期土壤有机碳储量和碳平衡影响的异同,旨在明确风沙半干旱区覆膜的固碳减排效应,为构建低碳地膜覆盖模式提供理论依据。结果显示,AM显著增加玉米籽粒产量、地上生物量和0~60 cm土层根系生物量(P<0.05);在0~100 cm土层,AM、SM、NM和初始的有机碳储量分别为83.7、84.2、89.2、90.53 Mg/hm²,各处理相同土层间差异不显著(P>0.05);NM、SM和AM土壤呼吸CO₂-C释放量平均值分别为2.10、2.09、2.37 Mg/(hm²·a),碳平衡分别为-522、-498、-474 kg CO₂-C/(hm²·a)。以上表明,AM增加系统碳输入的同时,增加了土壤呼吸碳排放,但在短期内不会引起土壤有机碳库的衰退,并能更大程度上减少单位面积产量的碳排放,是一种气候友好型的低碳农业技术。     

基于3S技术的区域蒸散研究进展

 从蒸散测量方法,区域蒸散研究理论基础,模型方法及参数获取,GIS、GPS时空扩展等多个方面对区域蒸散研究进行分析,探讨目前存在的蒸散计算模型、遥感反演模型参数精度及时间空间尺度转换等若干问题。指出以良好的物理基础为背景、以模拟SPAC中能量、物质交换过程并利用遥感技术确定地表关键参数来建立的区域蒸散数值模型是今后的发展趋势。方法上与3S技术紧密结合、多源数据(不同分辨率、不同时序卫星资料及数字高程模型等)结合可以减少模型中的非遥感参数,提高参数的反演精度和时空尺度转换精度,也将对区域蒸散的空间不均匀性问题解决带来希望。     

青藏高原冷季积雪对后期暖季植被的影响

研究青藏高原冷季积雪对后期暖季植被的影响和机制,有助于生态系统保护和应对全球变化适应性对策的制定。使用回归、相关和合成分析法以及1996?2013年积雪、归一化植被指数、国家环境预报中心大气再分析资料降水量融合分析降水量资料,研究了青藏高原冷季(1月?3月)积雪对后期暖季(4月?9月)植被的影响。结果表明,当高原冷季积雪异常偏多,后期暖季植被也异常偏多,这种正相关关系是通过大气环流将积雪和植被联系到一起的。当高原冷季积雪偏多,暖季东亚夏季风减弱,太平洋副热带高压加强西移并影响高原东部地区,该地暖季地面温度升高,积雪融化,土壤湿度增大,日照增加,降水量减少,前4个要素均对植被生长起促进作用。特别是积雪消融可以有效补给到土壤中,增加土壤水份,有利于植被返青及其前期生长,而降水量更是土壤水份的主要补给来源,但由于在植被生长的旺盛期,降水量往往较为充沛且能够满足植被生长的需求,同期归一化植被指数也恰好是一年中最高的,此时降水量过多可能导致植被生长受到抑制,降水量略减少反而可能会促进植被的生长。     

Airborne spread of foot-and-mouth disease – Model intercomparison

Foot-and-mouth disease virus (FMDV) spreads by direct contact between animals, by animal products (milk, meat and semen), by mechanical transfer on people or fomites and by the airborne route, with the relative importance of each mechanism depending on the particular outbreak characteristics. Atmospheric dispersion models have been developed to assess airborne spread of FMDV in a number of countries, including the UK, Denmark, Australia, New Zealand, USA and Canada. These models were compared at a Workshop hosted by the Institute for Animal Health/Met Office in 2008. Each modeller was provided with data relating to the 1967 outbreak of FMD in Hampshire, UK, and asked to predict the spread of FMDV by the airborne route.A number of key issues emerged from the Workshop and subsequent modelling work: (1) in general all models predicted similar directions for livestock at risk, with much of the remaining differences strongly related to differences in the meteorological data used; (2) determination of an accurate sequence of events on the infected premises is highly important, especially if the meteorological conditions vary substantially during the virus emission period; (3) differences in assumptions made about virus release, environmental fate and susceptibility to airborne infection can substantially modify the size and location of the downwind risk area. All of the atmospheric dispersion models compared at the Workshop can be used to assess windborne spread of FMDV and provide scientific advice to those responsible for making control and eradication decisions in the event of an outbreak of disease.     

巴西大豆产量预报方法研究

利用1961～2007年巴西大豆平均单产资料、西太平洋月平均海温、北半球500 hPa平均高度场环流资料以及巴西大豆种植区域代表气象站的逐日气温资料,建立了基于海温、环流资料和基于地面气象要素的巴西大豆产量预报模型.利用3种模型分别对1996～2005年巴西大豆平均单产进行预报检验;综合3种模型的模拟效果,利用加权方法建立了巴西大豆产量预报集合模型.1996～2005年预报检验和2006～2007年预报试验的准确率基本都在90%以上,能够满足业务服务的需要.     

湖北省棉花洪涝灾害风险分析

为准确和定量的评估洪涝灾害对棉花造成的风险,减少洪涝灾害对湖北省棉花造成严重影响和重大损失,以湖北省3个农业气象观测站近30年的气象资料和生育期资料,对湖北省洪涝风险进行了研究。结果表明:洪涝指数与降水距平百分率和降水标准化序列相关性显著。洪涝指数的计算过程涉及多个参数,运算过程复杂,而降水距平百分率和降水标准化计算相对容易,且数据容易获得,所以定义降水距平百分率或降水标准化作为划分洪涝致灾的指标。以此指标将洪涝导致减产的风险数值化,得到因洪涝导致减产的风险值分别为:襄樊10.5%,麻城16.1%,荆州4.2%。麻城棉花风险值最大,需要做好洪涝的防范措施。