田间烤烟叶片缺钾症状与钾积累及土壤供钾水平关系

基于田间正常施肥烟株生长中期中、上部叶通常出现缺钾症状的现象,以烤烟品种K326为材料在砂质壤土上进行了田间试验,定期观察无钾(即K0,仅按常规施用氮磷肥,K_2O用量为0 kg·hm~(–2))、常规施肥但中后期出现缺钾症状(即CF,按常规施用氮磷钾肥,K_2O用量为364 kg·hm~(–2)但中后期仍有缺钾症状)、常规施肥且正常生长(即CK,按常规施用氮磷钾肥,K_2O用量为364 kg·hm~(–2)但中后期无缺钾症状)3处理烟株移栽后生长情况(特别是叶片缺钾症状的出现情况),并及时采集和测定了相应烟株的干物质、钾含量及根区土壤速效钾含量,以阐明正常施肥烤烟中、上部叶出现缺钾症状的可能原因。结果表明:(1)CF和K0烟株在移栽后33 d前叶片均未出现缺钾症状;但根区土壤速效钾含量移栽后42 d低于99.86 mg·kg~(–1)时,K0烟株第8～第15叶陆续表现缺钾;CF烟株根区土壤速效钾含量移栽后57 d低于131.1mg·kg~(–1)时,第12～第16叶也相继缺钾,而其他叶位叶片正常。(2)从移栽至42 d,CK和K0烟株干物质和钾素累积量虽皆明显增加,但K0烟株总量偏低趋势愈发显著;至移栽后57 d期间,CK和K0烟株前述两个指标继续增加,但此期CF干物质累积有相似的增加趋势,而钾素累积与出现缺钾症状前相比(即移栽后42 d时CK)则略有减少;(3)移栽后42 d至57 d,CF烟株上、中部叶和K0烟株上部叶钾净输出明显,而茎中净输入显著,其他器官或部位总体持平或略有增加;CK烟株上部叶钾素输入、输出维持平衡,其他器官有净增加。(4)生长期间,CK烟叶钾含量皆表现出随叶位上升而呈总体下降,K0烟叶前期有相似规律,但移栽后42 d、57 d呈"上升-下降-上升",CF于移栽后57 d为"下降-上升"趋势。上述结果说明,K0烟株移栽后42 d中部叶开始缺钾是钾整体吸收不足所致,后期则兼有上部叶钾净输出原因;CF烟株出现中、上部叶缺钾而下部叶正常则有3个原因,一是后期体内干物质累积持续增加导致的稀释;二是此期整株钾累积不仅未增加,且有下降;三是CF烟株中、上部叶钾净输出增加。     

林分密度对杉木人工林下物种多样性和土壤养分的影响

为研究不同林分密度对杉木人工林下物种多样性和土壤养分的影响,以38 a生5种密度杉木人工林为研究对象,调查林下植被,测定土壤理化性质及酶活性,对物种多样性指数和土壤指标进行单因素方差、相关性及主成分分析。结果显示:杉木人工林下物种种类多达121种,灌木层以杜茎山(Maesa japonica)为主,草本层以双盖蕨(Diplazium)、黑足鳞毛蕨(Dryopteris fuscipes)等蕨类为主。灌木层和草本层物种多样性各指数大多在初植密度为5 000 hm~(–2)时最高。不同土层间各种土壤养分变化趋势基本一致,不同密度间土壤养分变化趋势不同,更多的土壤养分在高密度或低密度林)分下达到最大。除了p H、有机碳以及纤维素酶外,其他土壤养分受林分密度变化响应均显著(P0.05)。0～20 cm土层的土壤养分与草本层物种多样性关系更为密切,而20～40 cm土层的土壤养分与灌木层物种多样性关系更为密切。p H、全氮、碱解氮、有效磷与灌草层多样性指数的相关性最为密切。主成分分析综合得分显示,初植密度为6 667 hm~(–2)时最高(1.17),第二为3 333 hm~(–2)(0.93),其次为5 000 hm~(–2)(0.28)、1 667 hm~(–2)(0.12)和10 000 hm~(–2)(–2.49),得分前两名显著大于其他得分。以上结果表明,初植密度在5 000 hm~(–2)更有利于林下物种多样性的稳定,但不利于土壤养分的累积;密度过低或过高皆不利于土壤理化性质和植物多样性的发展,特别是密度过高时,对林地伤害巨大;基于土壤理化性质和植物多样性的主成分分析结果出现"驼峰模式",杉木人工林初植密度6 667 hm~(–2)和3 333 hm~(–2)更适合土壤理化性质和植物多样性的发展。     

基于GIS的不同种植模式下凉州区日光温室土壤养分分析

采用GPS定位取样测试、ACIGIS软件数据分析和地统计分析方法,对凉州区日光温室土壤养分状况进行了分析评价。结果表明,在0~20 cm表层土壤中,不同种植模式的氮、磷、钾养分分布趋势基本一致。种植番茄—架豆、番茄—辣椒电导率最大,为1.97 ms/cm;种植番茄—架豆盐分最高,为11.9 g/kg;种植人参果CEC最大,为16.87%。在20~40 cm土壤中,种植番茄—辣椒电导率最高,为2.59 ms/cm;种植小乳瓜盐分最大,其值为17.9 g/kg;种植人参果CEC最大,为19.94%。     

连作及轮作土壤微生物菌群对黄瓜幼苗生长及土壤酶活性的影响

通过植物-土壤反馈试验,研究连作及轮作土壤微生物菌群对黄瓜幼苗生长和土壤酶活性的影响。结果表明,轮作土壤微生物处理黄瓜植株鲜质量、叶绿素含量、土壤中性磷酸酶、蔗糖酶活性显著高于连作土壤微生物处理;连作及轮作土壤微生物处理增加了黄瓜幼苗干质量、鲜质量、叶绿素含量及总叶面积,显著提高了土壤中性磷酸酶、蔗糖酶、脲酶活性。综上,连作及轮作土壤微生物菌群对黄瓜幼苗生长均产生正反馈作用,并且轮作土壤微生物的正反馈作用大于连作土壤微生物。     

Comparative soil distribution and dissipation of phoxim and thiamethoxam and their efficacy in controlling Bradysia odoriphaga Yang and Zhang in Chinese chive ecosystems

Bradysia odoriphaga Yang and Zhang (the chive gnat) is the major insect pest affecting Chinese chives (Allium tuberosum Rottl. ex Spreng.) in Northern China. Only three insecticide products are registered for its control. In the present study, we compared the persistence and distribution of thiamethoxam and phoxim in soil and determined their long-acting control effects against B. odoriphaga and two other secondary pests, Thrips alliorum Priesner and the Asiatic onion leaf miner Acrolepia alliella Semenov and Kuznetsov (Lepidoptera: Acrolepiidae), after a single soil application using the directional spray-washing method during the early Chinese chive root-rearing period. Under the same applied dosage, the rhizosphere soil at a depth of 4.0–10.0 cm had concentrations of thiamethoxam and phoxim ranging from 2.21 to 7.44 mg/kg and 0.09–0.44 mg/kg, respectively, at the 7th day after application. The half-lives of thiamethoxam and phoxim in the soil were 27.5 and 6.7 days, respectively. Thiamethoxam persisted for 210 days, whereas phoxim only persisted for 45 days in the soil and plants. In addition, thiamethoxam applied at 6.0 kg a.i./ha maintained a low population density of B. odoriphaga, T. alliorum and A. alliella for nine months longer than phoxim. In conclusion, thiamethoxam may help farmers more effectively manage B. odoriphaga and other secondary pests on Chinese chive and reduce the costs of insecticide use while sustaining protection.     

烤烟套种甘薯对烟叶质量、烟薯产量及土壤温湿度的影响

为筛选出适宜与烤烟套种的甘薯品种,解决部分烟区烤烟种植调茬难度大与综合效益低等问题,通过田间大区试验,研究烤烟套种不同甘薯品种对烟叶质量、烟薯产量及土壤温湿度的影响。结果表明,烟薯套种能够明显提升土壤相对含水率和烟叶产量,其相对含水率提高幅度介于12.03%~91.88%,烤烟产量增幅为12.29%~31.26%。烤烟套种甘薯以紫薯产量最高,块根产量达29400 kg/hm ²,且单薯质量大于100 g占总薯重的比例在紫薯中最高。烤烟套种甘薯提升了烤烟中上部烟叶的总糖和还原糖含量,降低了烟碱和总氮含量,有利于改善烟叶内在品质。烤烟套种甘薯降低了上部烟叶含梗率,但增大了上部烟叶叶面密度,以烤烟套种紫薯表现突出。烤烟与紫薯套种,可作为一种烟田增产、烟叶增值和烟农增收的种植模式。     

Phosphorus availability and farm structural factors: examining scarcity and oversupply in north‐east Germany

Assessing factors influencing phosphorus (P) availability in soils is important in preventing its overexploitation and excessive application in agricultural systems. Despite high historical P applications in the federal state of Brandenburg (Germany), county data on soil test P (STP) reveal considerable disparities in soil available P. In addition, negative soil balances as a result of small mineral P and manure inputs have been observed, raising questions about the factors leading to this situation. Our work focused on identifying possible causes operating at the farm management level by conducting a letter survey in two administrative districts of Brandenburg, the counties Barnim and Uckermark, linking farm management factors (ownership type, farm size, land tenure, animal husbandry with or without grassland and its intensity, presence of a biogas plant and organic production) to farmers’ self‐indicated levels of STP. Small‐ to medium‐sized individual farms tended to have (very) high STP, while large partnership farms and companies/cooperatives were sensitive to factors resulting in low STP. Farms with low shares of land ownership, the presence of grassland, extensive cattle farming and stockless organic farming had lower STP. On the other hand, biogas plants, partly in combination with intensive livestock (cattle) farming, were associated with larger STP. It was concluded that more care should be devoted to the design of agricultural policies and that further (inter‐ and transdisciplinary) research on this topic is needed.     

Organic input quality is more important than its quantity: C turnover coefficients in different cropping systems

Annual C input to soil is a major factor affecting soil organic carbon (SOC) dynamics. However different types of C-sources can have different behaviour, in relation to their chemical characteristics and how they interact with soil. Root-derived C, in particular, should be more efficient than other organic materials as a result of the physicochemical and biological characteristics of the surrounding environment, leading to a reduction in the C decomposition rate.To test this hypothesis, we considered a long-term experiment underway in Northern Italy since 1962, comparing permanent meadow and 6 different crop rotations over a wide range of nutrient inputs, in both organic and inorganic forms. C inputs from amendments were measured and those from crops were calculated using allometric functions and crop and residues yields. The time evolution of SOC was studied through a single-pool, first-order kinetic model, allowing the estimation of humification coefficients for residues, roots, farmyard manure and cattle slurries.The highest value of the humification coefficient was estimated for farmyard manure, which confirmed its high efficiency in stabilising SOC content. Root C presented a humification coefficient 1.9 times higher than above-ground plant materials while slurries were intermediate, with a humification coefficient roughly half that of farmyard manure and even lower that of roots.The quality of C input thus seems of fundamental importance for evaluating the sustainability of different cropping systems in terms of SOC dynamics.     

Strong functional stability of soil microbial communities under semiarid Mediterranean conditions and subjected to long-term shifts in baseline precipitation

We investigated the effect of soil microclimate on the structure and functioning of soil microbial communities in a Mediterranean Holm-oak forest subjected to 10 years of partial rain exclusion manipulations, simulating average drought conditions expected in Mediterranean areas for the following decades. We applied a high throughput DNA pyrosequencing technique coupled to parallel measurements of microbial respiration (R_H) and temperature sensitivity of microbial respiration (Q₁₀). Some consistent changes in the structure of bacterial communities suggest a slow process of community shifts parallel to the trend towards oligotrophy in response to long-term droughts. However, the structure of bacterial communities was mainly determined by short-term environmental fluctuations associated with sampling date (winter, spring and summer) rather than long-term (10 years) shifts in baseline precipitation. Moreover, long-term drought did not exert any chronic effect on the functioning of soil microbial communities (R_H and Q₁₀), emphasizing the functional stability of these communities to this long-term but mild shifts in water availability. We hypothesize that the particular conditions of the Mediterranean climate with strong seasonal shifts in both temperature and soil water availability but also characterized by very extreme environmental conditions during summer, was acting as a strong force in community assembling, selecting phenotypes adapted to the semiarid conditions characterizing Mediterranean ecosystems. Relations of climate with the phylogenetic structure and overall diversity of the communities as well as the distribution of the individual responses of different lineages (genera) to climate confirmed our hypotheses, evidencing communities dominated by thermotolerant and drought-tolerant phenotypes.     

Soil conditions and land use intensification effects on soil microbial communities across a range of European field sites

Intensive land use practices necessary for providing food and raw materials are known to have a deleterious effect on soil. However, the effects that such practices have on soil microbes are less well understood. To investigate the effects of land use intensification on soil microbial communities we used a combined T-RFLP and pyrosequencing approach to study bacteria, archaea and fungi in spring and autumn at five long term observatories (LTOs) in Europe; each with a particular land use type and contrasting levels of intensification (low and high). Generally, due to large gradients in soil variables, both molecular methods revealed that soil microbial communities were structured according to differences in soil conditions between the LTOs, more so than land use intensity. Moreover, variance partitioning analysis also showed that soil properties better explained the differences in microbial communities than land use intensity effects. Predictable responses in dominant bacterial, archaeal and fungal taxa to edaphic conditions (e.g. soil pH and resource availability) were apparent between the LTOs. Some effects of land use intensification at individual field sites were observed. However, these effects were manifest when land use change affected soil conditions. Uniquely, this study details the responses of different microbial groups to soil type and land use intensification, and their relative importance across a range of European field sites. These findings reinforce our understanding of drivers impacting soil microbial community structure at both field and larger geographic scales.