The biology of African feather grass (Pennisetum macrourum Trin.) in Tasmania, I. Seedling establishment

Seedling establishment of Pennisetum macrourum was studied in a series of glasshouse and field experiments. Maximum germination of 88% occurred at a constant temperature of 30C. In the glasshouse, highest seedling establishment was obtained from seeds buried 1 cm deep; it was less than 25% from seeds sown on the soil surface. Dormancy was induced in seeds buried 8 cm deep but only 6.4% remained viable after 6 months. Few viable seeds of P. macrourum were found in the soil and only one seedling was observed to establish in the field over a 20 month period. Up to 98% of seedlings transplanted into the field established successfully. The results suggest that reproduction by seed would not be a major problem in the control of P. macrourum.     

Regeneration of yarrow (Achillea millefolium L.) rhizome fragments of different length from various depths in the soil

The regenerative response of the rhizomes of Achillea millefolium L. to fragmentation and burial was studied in field experiments on three different soils. The percentage of buds producing shoots (estimated from surviving rhizome fragments) from 4 cm (1·6 nodes), 8 cm (3·8 nodes) and 16 cm (6·7 nodes) rhizome fragments was 63, 44 and 32 respectively averaged over all soils and depths of 5, 10 and 15 cm. The depth at which 50% of the fragments failed to produce an emerged shoot (LD₅₀ depth) was 9·3, 12·4 and 17·9 cm for 4-, 8- and 16-cm fragments respectively averaged over all soils. No fragments survived on the soil surface. The time of emergence of the first shoots was delayed and the rate of emergence and ultimate shoot population reduced with increasing depth of burial. Dry-matter production by aerial shoots and new rhizomes decreased linearly with depth of burial of the rhizome fragments. Soil type had no effect on the regeneration of the fragments. The significance of the results for the control of A. millefolium is discussed.     

DEVELOPMENT OF CYNODON DACTYLON (L.) PERS.*

Summary. Early development of Cynodon dactylon (L.) Pers, was studied on one-node rhizome fragments planted at successive dates over a year. Aerial growth followed the changes in external temperature; in the cool season tops grew very slowly but remained alive. New rhizomes were formed only at temperatures exceeding 15–20°C. Flowering occurred in the warm season from May onwards. No relationship was found between flowering and rhizome formation. The age of plants forming new rhizomes decreased from 5 months for the January planting to less than 2 months for the May-September plantings. Rhizome bud germination was maximal between 23 and 35°C, slow below 20°C and inhibited at 10°C. The weight ratio of tops to subterranean parts of established plants was near 1 in winter, declined in March-April and remained at 0·5–0·6 from May onwards. An established sward of C. dactylon was sampled from September to November of the following year. Dry weight was lowest from January to mid-April, rose in spring and decreased in late summer. Almost no rhizomes were found deeper than 45 cm. Underground parts from the 0–15, 15–30 and 30–45 cm horizons constituted 62, 26 and 12% of the total weight, respectively; rhizomes formed more than 90% of the total underground dry weight. In the warm season the dry weight of the subterranean organs amounted to 2, 0·7 and 0·4 kg/m³ of soil in the three horizons, respectively. Percent dry matter in tops and subterranean parts was about 35–45% in the winter and 50–65% in the warm season. Up to 2% reducing sugars was found in various parts of the plants. The water-soluble sugar content of rhizomes was high in November-December, decreased in late winter, rose again in spring, and decreased in late summer. Percent germination of rhizome buds fluctuated greatly during the year, but complete dormancy was never recorded. Newly-formed rhizomes showed a high germinative capacity. Similar germination percentages were found on fragments with one node and those with several nodes. Développement du Cynodon dactylon (L.) Pers.     

Vegetative propagation of Solidago canadensis – do fragment size and burial depth matter?

Clonal species may benefit from human disturbance because their vegetative fragments may be distributed via soil. Solidago canadensis is an invasive rhizomatous perennial frequently found in ruderal environments. When creating new infrastructure, digging and cutting are two main factors that may influence the spread of S. canadensis into new areas. To have a better understanding of the invasive potential of S. canadensis, we investigated whether S. canadensis was able to survive and grow from stem cuttings as well as from rhizomes. Rhizomes and cuttings were collected from three populations in Eastern Norway. The rhizomes and cuttings were planted in a pot experiment to assess their vegetative ability to propagate. Rhizome fragments (5 and 10 cm long) were buried at 0.5, 10 and 30 cm depths. The cuttings were planted as 15 cm stems, with the bottom 5 cm pushed into the soil. The results showed that rhizome length did not have an effect on survival. Although some sprouting occurred at all burial depths, increasing depth had a negative effect on rhizome survival. In general, development of the cuttings was good, but there were differences between population performance and survival. These results imply that care must be taken when (i) constructing new sites, because digging and transport of soil masses may spread S. canadensis into new areas by rhizomes or cuttings, and (ii) mowing road verges and other ruderal areas to prevent the spread of stem cuttings from one area to another.     

The effects of desiccation on broad‐leaved dock (Rumex obtusifolius) and curled dock (Rumex crispus) root fragment regeneration

Fresh root fragments of Rumex crispus and Rumex obtusifolius, which initially contain 65–70% moisture, progressively lose moisture when desiccated under conditions matching summer weather in southeast England. The likelihood of shoot emergence and the time it took in glasshouse conditions were both affected by desiccation, with R. crispus the most affected up to 48 hr and R. obtusifolius slower to emerge after 48 hr. These effects converged after longer desiccation periods, and R. crispus entirely failed to emerge after 120 hr. The dry weight of emerged shoots was not significantly different between the species until they were desiccated for 96 hr, after which R. obtusifolius dry weight was significantly reduced. In outdoor trials, desiccation for 24 or 48 hr had a lesser effect on emergence in either species when fragments were planted at the soil surface or at up to a depth of 10 cm, compared to deeper plantings, but emergence was significantly lower in plantings at 15 or 20 cm. Emergence delays were not significantly different between the species until they were planted at 15 or 20 cm, when R. obtusifolius was slower to emerge than R. crispus, an effect exacerbated by increasing desiccation. Similar interactions of increasing soil depth and desiccation were found in reductions in dry weight, number of tillers and leaf area, with R. obtusifolius generally, but not exclusively, better able to withstand more extreme trial conditions. Our findings suggest that control of these highly troublesome weeds can be assisted by appropriate agricultural practices, notably exposing cut fragments to drying conditions followed by deep burial.     

Recruitment potential from asexual and sexual reproduction in Polymeria longifolia

Sexual and asexual reproduction in the perennial Australian weed Polymeria longifolia (polymeria take-all), was assessed using glasshouse and field studies. These studies aimed at elucidating the contribution that each reproductive mechanism makes to the success of the species as a weed in cotton in Australia. Asexual reproduction, including vegetative fragment movement because of cultivation and regeneration from in situ rhizome material, was the predominant means of dispersal and recruitment of the species. Sexual reproduction had a relatively minor but significant role in the reproductive biology of P. longifolia. Seedling establishment was <5% from buried seed in both the glasshouse and field. In the field, seedlings comprised <1% of the total number of new shoots recruited at the start of two consecutive seasons, with <3% of these reaching reproductive maturity. Vegetative fragments were more likely to survive and lead to subsequent shoot production when they were large and intact. Intensive cultivation, where plants of P. longifolia are cut into small fragments, may reduce the survival of fragments moved by cultivation and reduce recruitment from existing populations. Long-term management strategies should focus on reducing the large vegetative flushes of this weed, as well as controlling the small number of seedlings recruited.     

基于MTVDI与DDI二元回归模型对毛乌素沙地腹部土壤表层水分的研究

采用温度植被干旱指数法(MTVDI)与荒漠化指数法(DDI),利用2016年4月、9月的Landsat数据对毛乌素沙地腹部的土壤水分进行反演,并与实测的土壤水分进行对比检验,将所反演的土壤含水量图划分为4个等级,基于此分析了2个时期毛乌素沙地腹部的旱情土壤水分分布变化。结果显示：(1)4月份MTVDI指数与0~10 cm、10~20 cm、20~30 cm土层土壤含水量的R²值分别为0.656、0.646、0.637,整体高于9月份R²值0.457、0.436、0.431,MTVDI能够较好地反映毛乌素沙地腹部土壤表层水分,且精度较高;(2)荒漠化指数DDI与MTVDI结合建立二元线性回归模型监测区域土层0~10 cm深度含水量,平均相对误差为10.95 %;(3)4月份,研究区0~10 cm表层土壤含水量5%~10%区域占总面积的53.72%以上,达到了6 256 km²,含水量偏低,需要加强当地水资源管理。     

微孔渗灌环形布设对灵武长枣土壤水分分布及产量的影响

以6 a生灵武长枣为研究对象,设置微孔渗灌不同埋设深度D10(10 cm)、D20(20 cm)、D30(30 cm)和铺设半径R30(30 cm)、R40(40 cm)、R50(50 cm)的2因素3水平试验,分析了微孔渗灌不同环形布设方式对灵武长枣土壤水分分布、产量及水分利用效率的影响。结果表明:随着微孔渗灌埋深的增加,土壤含水率最大分布范围和湿润锋均向下移动,土壤含水率垂直方向最大分布范围可达到10～55 cm。随着微孔渗灌铺设半径的增大,土壤含水率最大分布范围和湿润锋均向外移动,并且各处理的最大湿润区域土壤含水率值均在20%以上。R40D20处理下枣树的枣吊长度、每吊开花数、每吊坐果数、坐果率、单果重、单株结果数、产量、水分利用效率均最大,分别为31.24 cm、66朵、39个、59.70%、19.20 g、444个、7 666.82 kg·hm~(-2)、2.83 kg·m~(-3),并且均与其他处理存在显著差异(p0.05)。因此,微孔渗灌埋深为20 cm、铺设半径为40 cm是灵武长枣最佳的铺设方式。     

An Introduction to the Use and Preparation of Artificial Diets with Special Emphasis on Diets for Phytophagous Lepidoptera

Abstract

In an experiment conducted in an almost pure stand of Imperata cylindrica to compare manual and chemical methods of control, forking out of rhizomes up to a depth of 45 cm gave long-lasting control. Slashing the grass to ground level at intervals of 4–6 weeks resulted in a low degree of control in terms of visual assessment of top growth and a high degree of control in terms of suppression of rhizome development, which was comparable to the most effective chemical methods; dalapon (22.2 kg a.i./ha) and dalapon–paraquat sequential spray. The results suggest that the effectiveness of control measures can be improved by timing the dalapon spray to coincide with adequate soil moisture reserve and by regulating frequency of slashing with regard to soil moisture status and the number of previous slashings imposed. The chemical treatment and the slashings suppressed development of rhizomes but did not cause increased rhizome mortality. The stage of growth at which dalapon was sprayed in dalapon–paraquat sequential spray treatment, did not influence the degree of control achieved as assessed visually.     

Factors affecting the distribution of pesticide drenches in soil using the fungicide metazoxolon as a model

The distribution resulting from the drenching of soil with a suspension concentrate of [¹⁴C]metazoxolon was studied in the laboratory and the field. Penetration of soil columns was increased by (a) increasing the drench volume from 1 to 7.8 litres m^?2, (b) changing the original soil moisture content from air-dry to field-capacity, and (c) including 1 % of ‘Renex 30’ surfactant in the drench. Penetration was greatest in soils containing large pores and was reduced when aggregates were broken down by sieving. Leaching the column with 1.56 cm of ‘rain’, 15 h after treatment, did not increase the penetration by metazoxolon. In all experiments, the maximum concentration of metazoxolon occurred in the top 2 cm of soil. Equivalent effects were found when metazoxolon was applied to a poorly-structured sandy clay loam in the field.     

SPATIAL GROWTH OF SORGHUM HALEPENSE (L.) PERS.*

Summary. Small plants of Sorghum halepense (L.) Pers. were planted in the field and grown without competition from weeds and crops for 2½ years. The plant spread by means of subterranean rhizomes from which aerial shoots developed at increasing distances from the plant centre, and by tillering around these aerial shoots to form clumps. No preferential direction of expansion was detected and established patches developed an approximately circular shape. Aerial growth stopped completely in the cold season. During the warm season the mean area increment amounted to 1·3 m²/month and was similar in both years of observations. After 2½ years of growth, patches had extended up to 3·4 m from the initial sprig and had a mean area of 17 m². In the second summer of growth, shoot density reached 190/m² and mean seed production was 84 g, or 28 000 seeds per plant. About 80% of rhizome dry weight was present in the upper 20 cm of soil and rhizomes did not penetrate deeper than 40 cm. About 80% of rhizome dry weight was present within 1 m radius from the plant centre. Croissance dans l'espace de Sorghum halepense (L.) Pers.     

Johnsongrass (Sorghum halepense) growth characteristics as related to rhizome length

Growth characteristics of johnsongrass [Sorghum halepence(L) Pers] grown in the field from rhizomes 2.5, 5, 10, 15, 20, or 25 cm long were studied in a sandy loam soil for 2 years. Plant height, number of leaves per plant, number of tillers per plant, and fresh weight of new rhizomes and shoots were significantly dependent on the length of the planted rhizome 20, 40, 60, or 80 days after planting. All growth characteristics increased significantly as the length of planted rhizome increased from 2.5 cm to 10 cm to 25 cm Growth characteristics of Johnsongrass plants grown on rhizomes of adjacent lengths (differing by 5 cm) generally were not significantly different. Longer rhizomes (15, 20, or 25 cm) initiated new rhizome growth much earlier (about 20–30 days) than shorter rhizomes (2.5, 5, or 10 cm) Although all rhizome lengths showed a parallel growth potential, the lunger rhizomes were capable of more and faster growth, especially early after planting. It is suggested that Johnsongrass plants associated with longer rhizomes in the field as a result of limited tillage, coupled with their faster growth rate, are expected to interfere with crop production earlier than plants on shorter rhizomes unless controlled.     

基于高光谱与电磁感应技术的干旱区绿洲土壤含水量反演研究

为实现干旱区绿洲土壤含水量的快速、准确监测,利用采集自渭干河-库车河绿洲的84个表层(0~10cm)土壤样本,通过利用电磁感应仪(EM38)将所测解译后数据代替实测土壤含水量数据,将高光谱反射率重采样为Landsat8卫星遥感波段反射率,在选取光谱特征参数、提取敏感波段的基础上,利用偏最小二乘回归(PLSR)方法建立土壤含水量模型,将最优估算模型应用于遥感影像,实现研究区土壤含水量遥感反演。研究结果表明:(1)利用EM38所测水平模式土壤表观电导率与土壤含水量拟合效果最优,能够代替实测土壤含水量进行后续建模分析。(2)相比3种单一的光谱特征指数,利用多种光谱特征指数所建土壤含水量估算模型的建模效果更优,其干、湿各季建模集决定系数R~2大于0.7,均方根误差(RMSE)均小于0.5%,RPD均大于2,能够作为有效手段估算干旱区绿洲土壤含水量。(3)不同季节土壤含水量遥感反演值与实测值决定系数R~2均大于0.6,均方根误差(RMSE)均小于0.6%,显示了较高的预测精度,证明利用电磁感应技术与高光谱相结合能够实现对干旱区绿洲土壤含水量的精准、高效监测。     

应用岩棉材料提高丘陵区经济林土壤水分保蓄能力

为缓解无灌溉丘陵区土壤季节性干旱问题,以岩棉为供试材料,通过室内模拟结合野外林地试验,研究了岩棉对不同质地土壤的增水潜力、岩棉水分扩散能力、岩棉材料对不同坡位土壤水分保蓄能力以及对山核桃林地土壤水分保蓄和油菜生长的影响,以期探索出一种新型实用的土壤水分保蓄技术。室内模拟试验结果表明,供试岩棉最大容积持水量为64.64%;分析了岩棉应用于松砂土、砂壤土、中壤土和轻粘土等4种不同质地土壤的保水潜力,土壤最大容积有效含水量分别增加54.02%、50.67%、41.41%和50.31%。将吸水饱和岩棉埋入风干土壤中,水分在垂直和水平方向均有扩散作用,并在一定时间内达到相对稳定状态。距岩棉垂直方向和水平方向5 cm处最高土壤含水量分别为27.89%和20.67%,10 cm处土壤最高含水量分别为13.13%和13.00%,由此建议,岩棉埋设位置距离根系不宜太远。林地试验表明,岩棉对红豆杉林地不同坡位土壤均能充分发挥水分保蓄作用,持续晴天无雨时,红豆杉林地上、下坡位土壤含水量顺序为岩棉附近岩棉地植物根附近无岩棉地(对照)。久旱和雨后山核桃林地岩棉附近土壤含水量比无岩棉地分别提高29.19%和23.39%(P0.05);油菜生长宽度范围为80 cm,岩棉保水影响范围是岩棉自身宽度的5倍之多;与无岩棉对照相比,埋设岩棉处油菜植株(开花期)的地茎、株高、叶面积和单株鲜重等指标分别提高了58.63%、62.85%、65.66%和44.51%(P0.05)。在土壤中合理使用岩棉材料是解决无灌溉丘陵区土壤季节性干旱问题的有效措施之一。     

藏蓟的生物学特性、危害损失与防治

在青海海南州共和县对藏蓟生物学特性和危害损失进行调查研究明确,藏蓟株高100-150 cm,多分枝,每株藏蓟开花9-30朵,平均每朵结种籽79粒。种子于室内存放225 d,仅7％-15.0％发芽。气温达0-12℃时藏蓟根茎萌发出苗,高峰期为5月上旬,全生育期约142 d。1 m²内有藏蓟8-10株时,青稞产量损失达30.3％-32.8％。     

Clonal growth and fragment regeneration of Rumex obtusifolius L.

Clonal growth and fragment regeneration of Rumex obtusifolius L. were analysed in two dif ferent studies. Clonal growth system was des cribed by a morphological study of underground structure of different-aged individuals, using maximal branching order in the stem system as an age estimator. Glasshouse experiments were conducted, testing the regenerative capacity of different below-ground parts and the estab lishment of above root-collar fragments planted at different depths under contrasting water regimes. Results showed the presence of a ‘phalanx’ type clonal growth system in grassland populations of Rumex. The main structure in volved in clonal growth proved to be the stem system; the region above the root collar was also the only part able to regrow after damage. Stem fragment regeneration occurred to depths of 15 cm, but was prevented in soils maintained at waterlogging and field capacity. The significance of these results in relation to nonchemical con trol of Rumex populations in grasslands is discussed.     

Effects of soil moisture and sowing depth on the development of bean plants grown in sterile soil infested by <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> and <Emphasis Type="Italic">Trichoderma harzianum</Emphasis>

The effects of soil moisture (varying from 15% to 42% (v/v)) and sowing depth (1.5–6.0 cm) on the development of bean plants grown in sterile soil infested by the pathogen Rhizoctonia solani and its antagonist Trichoderma harzianum were studied under greenhouse conditions. The four possible combinations of soil infestation with both fungi were tested. Disease severity, percentage of plants emerged, plant height and dry weight were evaluated 3 weeks after sowing. Emergence rate and growth of plants inoculated only with R. solani were not affected by soil moisture, but in the presence of both fungi, plant emergence, plant height and dry weight significantly decreased when soil moisture diminished. Deep sowing significantly reduced the emergence rate and growth of those plants that were inoculated with R. solani only. However, when the soil was infested with both fungi, the effect of sowing depth was not significant. At a sowing depth of 6.0 cm, the percentage of plants emerged was 50% in the presence of T. harzianum, but only 6.7% when the pathogen was inoculated alone. The antagonist protected bean seedlings from pre-emergence damping-off, reduced disease severity and increased plant growth in the presence of R. solani, especially in moist soil.     

基于微地形和土地覆被的土壤水分空间变异性——以玛纳斯河流域绿洲为例

采用经典统计学和地统计学方法,对玛纳斯河流域绿洲0～70 cm土层土壤水分的空间异质性及其影响因子进行研究.结果表明:各层土壤水分均符合正态分布.从变异系数看,均属于中等变异,变异系数介于0.293～0.371,其中表层水分变异程度最高,达到0.371;0～10 cm,10～20cm,20～30 cm和30～50 cm...     

Effect of rhizome fragment length and burial depth on emergence of Tussilago farfara

Mechanical control of Tussilago farfara is carried out mainly by soil cultivation. The aim is to deplete the energy stored in the rhizomes. The treatment includes cutting the rhizomes, to stimulate increased shooting, followed by renewed soil cultivation to destroy the shoots and incorporate them into the soil. Factors generally regarded as important in the control of perennial weeds are extent of fragmentation and burial depth. In this study, the importance of these two factors on T. farfara emergence was studied in detail in two pot experiments. Rhizomes were cut into different lengths (5–25 cm) and buried at various depths (1–42 cm) in pots filled with peat soil or clay loam. Shoot germination, emergence and early plant performance were studied. Intensive fragmentation and deep burial (possible to achieve using conventional tillage) are not enough to completely hinder emergence of T. farfara; 6‐cm fragments emerged and developed normal leaves from 42 cm depth, regardless of soil type. However, there were higher total emergence and emergence rates in peat soil than in clay soil. Burial depth was correlated with time to emergence; burying rhizome fragments, not longer than 25 cm, to at least 20 cm depth gave a time to emergence of at least 20 days. The delay of weed emergence should allow good establishment of a crop and ensure a significant competitive effect against T. farfara.     

生物炭施用对冬麦田土壤水热环境及土壤呼吸的影响

探究施用生物炭对冬麦田土壤水热因子及土壤呼吸的影响,对生物炭在麦田应用及农田固碳减排有重要的实践意义。2018年10月至2021年6月在关中灌区连续3 a进行了麦田生物炭施用试验,试验设置生物炭施用量水平分别为：0 t·hm^-2·a^-1（C0）、10 t·hm^-2·a^-1（C10）、20 t·hm^-2·a^-1（C20）,通过测定小麦生长季的土壤温度、土壤水分、土壤呼吸速率及产量,明确不同施炭量对冬小麦田土壤水热因子及土壤呼吸的影响。各处理生育期内土壤呼吸速率及全生育期CO₂排放量存在显著性差异（P<0.05）,均表现为C0>C20>C10。生物炭施入增加了生育期内的平均土壤温度,同时显著提高了0～20 cm土壤含水量（P<0.05）,并减弱了土壤水分在生育期内的变化幅度。C10、C20处理3 a平均土壤含水量较C0分别增加了17.0%、29.0%。5 cm及10 cm土壤温度能分别解释土壤呼吸变化的54.7%～...