黄淮海与环渤海设施蔬菜产区重金属累积特征和环境质量评价

黄淮海与环渤海设施蔬菜产区是全国蔬菜发展的六大优势产区之一。通过收集2011～2019年黄淮海与环渤海设施菜田重金属研究的文献数据,对该区域重金属污染和环境质量进行了统计分析。结果表明,黄淮海与环渤海设施蔬菜产区土壤重金属Cu、Zn、Cr、Ni、Pb、Cd、As和Hg的平均含量均低于温室蔬菜产地环境质量评价标准限量值。与各个省市土壤背景值相比,土壤出现了明显的Cu、Zn、Cd和Hg累积,Cr和As均没有出现累积。8种重金属元素单项污染指数范围在0.30～0.80,排序依次为:CdPbHg=NiZnCuAsCr,仅Cd处于警戒等级,其余重金属元素均处于清洁等级。8种重金属综合污染指数平均值为0.75,表明该区域重金属污染处于警戒水平,需采取相应的污染防控措施。     

温室茄子氮、磷、钾素最大利润施用量研究

为了研究温室茄子氮、磷、钾素最大利润施用量,为茄子合理施肥和安全生产提供参考,在甘肃省张掖市甘州区党寨镇温室内,采用田间小区试验方法,进行了温室茄子氮、磷、钾素最大利润施用量研究。结果表明:随着氮、磷、钾素施用量梯度的增大,茄子产量逐渐增加,边际产量、边际产值和边际利润均呈递减趋势,其中边际利润最终出现负值。根据最大利润施用量计算公式求得茄子氮、磷、钾素最大利润施用量分别为0.62、0.41、0.29 t/hm~2,进而得出最大利润施用量的理论产量分别为95.58、96.04、95.35 t/hm~2。     

基于分子生态学网络分析松嫩退化草地土壤微生物群落对施氮的响应

【目的】 氮素输入影响着全球草地生态系统的可持续性,关注施氮对土壤微生物群落的影响及其分子生态网络,为草地退化修复提供理论依据。【方法】 以松嫩退化羊草草地为研究对象,通过施氮和未施氮处理,利用高通量测序和随机矩阵网络构建理论构建土壤微生物群落分子生态网络。探讨氮素管理对退化羊草草地土壤微生物群落结构及网络的影响,氮添加条件下微生物网络结构中的关键微生物变化规律,以及该过程中微生物之间的互作关系,解析外源氮素添加条件下土壤细菌动态变化的关键结点和规律。【结果】 在门分类水平上施氮处理草地有细菌门22个,未施氮处理23个。7个菌门是施氮和未施氮处理草地的优势菌门,其中变形菌门（Proteobacteria）是含有OTU数量最多的门类,约占总序列的30.46%,酸杆菌门（Acidobacteria）是含有OTU数量次之的门类,约占总序列的30.15%,芽单胞菌门（Gemmatimonadetes）是含有OTU数量第3的门类,约占总序列的8.14%,放线菌（Actinomycete）约占总序列的6.15%,绿弯菌门（Chloroflexi）、拟杆菌门（Bacteroidetes）和硝化螺旋菌门（Nitrospirae）三者约占总序列的17.16%。施氮处理草地土壤微生物中的变形菌门、放线菌门、拟杆菌门的相对丰度均显著高于未施氮处理草地土壤（P<0.01）;未施氮草地土壤中绿弯菌门、酸杆菌门、芽单胞菌门相对丰度显著高于施氮草地土壤（P<0.01）,其他各门细菌施氮与未施氮处理间未呈现出显著差异。表征网络的正向连接比、平均路径长度、平均聚类系数和模块性均为施氮处理显著低于未施氮处理（P<0.001）。在土壤的分子生态网络中,未施氮处理有16个模块枢纽（Zi>2.5,Pi≤0.62）,施氮处理有6个模块枢纽,均属于酸杆菌门、芽单胞菌门和放线菌门。施氮导致土壤微生物种间关系改变,进而改变土壤整体生态网络。【结论】 施氮降低了退化草地土壤网络结构的复杂程度和紧密性;降低了退化草地土壤中的酸杆菌门和绿弯菌门相对丰度,提高了变形菌门、放线菌门和芽单胞菌门相对丰度。土壤中微生物关键物种（OTU）由16个（未施氮）减少为6个,且二者土壤中均没有重叠OTU,这表明施氮调控微生物群落网络的关键物种,进而改变其分子生态网络结构。     

Morphological and physiological characteristics of rice leaves in response to PASP-urea and optimized nitrogen management

Polyaspartic acid (PASP)-urea is known to increase crop yield. Field experiments were conducted to compare the morphological and physiological characteristics of the leaves between plots treated with urea (conventional urea or PASP-urea) and subject to different nitrogen (N) management methods [farmers’ standard fertilization practice (FFP, two splits) or optimized N management (ONM, four splits)] in Sichuan, China, in 2014 and 2015. A no-added-N plot served as the control. Grain yield was significantly associated with increased number of green leaves, total leaf area, chlorophyll concentration of rice leaves after the heading stage, photosynthetic rate per leaf lamina and accumulated temperature of senescence rate acceleration and deceleration. PASP-urea significantly enhanced the photosynthetic capacity of leaves to improve dry matter accumulation rate of the panicle after the heading stage over conventional urea, mainly by increasing the number of green lamina, leaf lamina area, chlorophyll concentration and photosynthetic rate per leaf lamina, as well as delaying senescence of the flag leaf. Compared with FFP, the ONM substantially improved the photosynthetic capacity of leaves to enhance dry matter accumulation rate of the panicle. Therefore, the ONM is a rational approach to applying PASP-urea that can improve grain yield by improving photosynthetic capacity.     

Carbohydrate and crude protein fractions in perennial ryegrass as affected by defoliation frequency and nitrogen application rate

The objective of this study was to evaluate the effects of defoliation frequency (either at two‐ or three‐leaf stage) and nitrogen (N) application rate (0, 75, 150, 300, 450 kg N ha^?1 year^?1) on herbage carbohydrate and crude protein (CP) fractions, and the water‐soluble carbohydrate‐to‐protein ratio (WSC:CP) in perennial ryegrass swards. Crude protein fractions were analysed according to the Cornell carbohydrate and protein system. Carbohydrate fractions were analysed by ultra‐high‐performance liquid chromatography. Sward defoliation at two‐leaf stage increased the total CP, reduced the buffer‐soluble CP fractions and decreased carbohydrate fractions of herbage (P < 0·001). The effect of defoliation frequency was less marked during early spring and autumn (P < 0·001) than for the rest of the seasons. An increase in N application rate was negatively associated with WSC, fructans and neutral detergent fibre (P < 0·001), and positively associated with CP and nitrate (N‐NO₃) contents of herbage. Nitrogen application rate did not affect CP fractions of herbage (P > 0·05). The fluctuations in CP and WSC contents of herbage resulted in lower WSC:CP ratios during early spring and autumn (0·45:1 and 0·75:1 respectively) than in late spring (1·11:1). The herbage WSC:CP ratio was greater (P < 0·001) at the three‐leaf than the two‐leaf defoliation stage and declined as the N application increased in all seasons (P < 0·001). The results of this study indicate that CP and carbohydrate fractions of herbage can be manipulated by sward defoliation frequency and N application rate. The magnitude of these effects, however, may vary with the season.     

便携式XRF仪现场快速测定土壤中Pb的可行性研究

便携式XRF分析仪具有轻便、快速和可测对象较多与测量元素较广等特点而广泛应用于矿石、土壤等方面快速检测,但土壤的现场快速测定结果的准确性有待进一步研究与探讨。以安宁河谷平原土壤中Pb为研究对象,通过对便携式XRF仪现场快速检测结果与实验室分析结果的对比和影响因素的分析,建立基于安宁河谷平原表层土壤快速测定结果的线性函数为y=1.170 9x-17.326 0(R~2=0.992 9,x为现场检测结果),探讨其影响因素,为该区域表层土壤中Pb快速检测结果提供依据。     

Effects of biodegradable mulch on soil quality

Biodegradable plastic films are desirable alternatives to traditional black polyethylene plastic for use as mulches in agroecosystems. Efforts are ongoing to engineer biodegradable plastic mulches that could be incorporated into the soil at the end of the crop season, and decomposed by microorganisms, ultimately to CO₂, H₂O, and biomass. Whether changes in soil quality occur during or following biodegradation is unknown. An 18-month study evaluated the effects on soil quality following burial of four potentially biodegradable mulches and a no mulch control in high tunnel and open field tomato production systems across three geographically distinct locations (Knoxville, TN; Lubbock, TX; Mount Vernon, WA). The mulch treatments included: two starch-based mulches (BioAgri^® Ag-Film and BioTelo Agri); one experimental 100% polylactic acid mulch (Spunbond-PLA-10); one cellulose-based mulch (WeedGuardPlus; positive control); and a negative control (no mulch). The soil management assessment framework (SMAF) was used to calculate a soil quality index (SQI) according to five dynamic soil properties: microbial biomass carbon, β-glucosidase, electrical conductivity, total organic carbon (TOC), and pH. Within the 18-month evaluation period, the effects of the biodegradable mulches on the SQI were minor, and dependent upon production system and time of incubation at all locations. In general, the SQI was higher in the high tunnel systems for some of the mulch treatments at Knoxville and Lubbock but the opposite was true at Mount Vernon. By the final sampling at 18 months, the SQI was lowest for WeedGuardPlus at Lubbock and Mount Vernon but at Knoxville, the WeedGuardPlus SQI was not significantly different from the no mulch control. Of the five SMAF indicators evaluated, soil microbial biomass and β-glucosidase activity were the most responsive to mulch and production systems, supporting the use of these variables as soil quality indicators for short-term changes due to this agricultural management practice.     

Soil sterilization effects on root growth and formation of rhizosheaths in wheat seedlings

Sterilized soils are frequently used in experiments related to soil biology. Soil sterilization is known to alter physicochemical characteristics of soil, plant growth and community structure of the newly developed bacterial population. However, little information exists regarding soil sterilization effects on belowground processes mediated through root–microbe–soil interactions, e.g., development of rhizosheaths which significantly promote the plant growth under stress environments. The present study was conducted to elucidate effects of soil sterilization on wheat root growth and formation of rhizosheaths in relation to chemical changes caused by soil sterilization and the proportion of expolysaccharide (EPS)-producers in bacterial population recolonizing the sterilized soils. Wheat plants were grown for two weeks under greenhouse conditions either in the unsterilized soil or in soils sterilized by autoclaving (121 °C, 1 h) or by gamma (γ)-irradiation (50 kGy). While soil sterilization had no effect on the release of macronutrients, both sterilization procedures significantly increased the electrical conductivity, water-soluble carbon and DTPA-extractable Mn. Seedlings grown in sterilized soils produced higher root biomass and the rhizosheath soil (RS) mass as compared to those grown in the unsterilized soil. Soil sterilization also increased the root length, surface area, volume and number of tips. In bulk soil, RS and on roots, the proportion of EPS-producers in the total bacterial population was higher in sterilized treatments than in the unsterilized. Amending the unsterilized soil with glucose-C increased the root biomass, whereas adding Mn II increased the RS mass. The results showed that soil sterilization by autoclaving or γ-irradiation increases the root growth and RS mass of wheat seedlings. The water-soluble C and DTPA-extractable Mn released upon sterilization, and the increased proportion of EPS-producers in the bacterial population recolonizing the sterilized soils were involved in the observed effects. The results may have implications in studies using autoclaved or γ-irradiated soils to investigate soil–plant–microbe interactions and signify the need to account for intrinsic stimulatory effects of soil sterilization.     

Effect of herbicide application on weed flora under conservation agriculture in Zimbabwe

Increased challenges of weed control in the smallholder farming sector of southern Africa have often resulted in small yields. The objective of this study was to evaluate the effects of different weed control strategies on weed flora and composition under conservation agriculture (CA) systems in Zimbabwe. This study was conducted at three on-station trial sites namely Domboshawa Training Centre (DTC), University of Zimbabwe farm (UZ farm) and Henderson Research Station (HRS) in a maize–soybean rotation for four seasons from 2009–2010 to 2012–2013 seasons. Hand weeding was done whenever weeds were 10 cm tall or 10 cm in circumference for weeds with a stoloniferous growth habit. Weed identification was done up to the weed species level, and the Shannon–Weiner diversity and evenness index was used to determine the response of weed flora to herbicides. Results showed that there were more weeds in the early years which decreased gradually until the final season. Weed species diversity was not affected by herbicide application and the results indicated that weed species diversity was small in CA systems. Annual weed species constituted a greater proportion of species, and species richness decreased with the duration of the study. Richardia scabra L. and Galinsoga parviflora Cav. were the most common dominant weed species at all sites and in all seasons. Moreover, herbicide application had no effect on the evenness of weeds in the plots but site characteristics had a significant effect on the distribution of weed species (weed species evenness). The results presented in this study suggest that herbicide application facilitates a depletion of weed seed bank/number of weeds over time. Thus, herbicide application in CA has potential to reduce weed density, species richness and species diversity in the long term which may lead to more labour savings and larger yields.     

发酵豆粕及其在水产动物生产中的应用

在日粮中使用发酵豆粕能够提高消化酶活性,增强免疫力,提高生产性能。文章就发酵豆粕的营养特性及其在水产动物生产中的应用作以简述。