Effect of burial depth and soil water regime on the fate of Lithospermum arvense seeds in relation to burial time

Lithospermum arvense is an increasing annual weed in winter crops of the semiarid region of southern Argentina under low impact tillage systems, an agricultural practice that has become popular in recent years. Seed distribution in the soil profile under conventional tillage will change when reduced tillage is implemented, thus affecting the germination microenvironment. The effect of seed burial depth and soil water regime on field germination, enforced dormancy, innate dormancy and seed decay was studied in relation to burial time in a field experiment. In addition, the effect of burial depth on seed germination and seedling emergence was examined under laboratory controlled conditions. Field germination of buried seed ranged from 55% to 65% for shallow (2 cm) and from 5% to 30% for greater depths (20 cm). Enforced dormancy levels were significantly higher among deeper seeds. The amount of innate dormant seeds was reduced to <10% after a year of burial. Lithospermum arvense seedbanks can be classified as short-term persistent. Germination in the laboratory was unaffected by burial depth, while seedling emergence reduction was adequately described by a sigmoidal model. Results indicate that agricultural practices that accumulate L. arvense seeds near the soil surface enhance seedling recruitment.     

Phalaris minor seedbank studies: longevity, seedling emergence and seed production as affected by tillage regime

Studies were conducted to investigate seed longevity, seedling emergence and seed production of the weed Phalaris minor in wheat in northern India. The longevity of P. minor seeds buried in bags in the field was often limited to less than 1 year, although many seeds buried at 30 cm depth in a rice–wheat rotation remained viable for longer. The application of direct seeding in wheat reduced the seedling emergence rate of P. minor , when compared with conventional ploughing and sowing. However, a larger P. minor seedbank in the upper soil layer in plots under direct seeding partly reversed this positive effect in one of the two studies. Besides differences in relative distribution of weed seeds through the soil profile, it was likely that other factors such as reduced soil disturbance and soil characteristics associated with the application of direct seeding were also involved in regulating the emergence rate. Mature P. minor plants in wheat were found to invest a stable part (27%) of their aboveground biomass in seed, so that total seed weight was strongly linearly correlated with the aboveground biomass of the mother plant. Individual seed weight, however, was little affected by the weight of the mother plant.     

Germination, persistence, and emergence of flaxleaf fleabane (Conyza bonariensis [L.] Cronquist)

Flaxleaf fleabane ( Conyza bonariensis [L.] Cronquist) is a difficult-to-control weed in dryland minimum tillage farming systems in the northern grains region of Australia. Experiments under field and controlled environments were conducted to study the seed germination, emergence, and persistence of C. bonariensis . The base, optimum, and maximum temperatures for seedling germination were estimated at 4.2, 20, and 35°C, respectively, with light stimulating germination. The soil types and burial depths had significant effects on seed persistence and emergence. The persistence pattern showed an initial rapid drop, followed by a slow but steady decline over time. After 3 years of burial, there were ≈ 7.5%, 9.7%, and 1.3% viable seeds at 10, 5, and 0–2 cm soil depths, respectively. Conyza bonariensis predominantly emerged from the soil surface or from the burial depth of 0.5 cm. Very few seeds emerged from a depth of 1 cm and none emerged from ≥ 2 cm. The emergence was greater in lighter soils. On-farm monitoring of the field emergence over time in a light sandy loam soil showed that 99% emergence occurred in late autumn, early and late winter, and a small fraction of 1% emerged in mid-spring. The predominant emergence from the soil surface suggests that the fleabane problem is a result of weed species shift toward the minimum tillage systems that provide moist conditions for better emergence compared to conventional tillage systems. The seed longevity of at least 3 years in the soil and the prolonged emergence patterns between autumn and spring have posed great difficulties for the long-term management of C. bonariensis .     

Influence of after-ripening environments on the germination characteristics and seed fate of Italian ryegrass (Lolium multiflorum)

Italian ryegrass ( Lolium multiflorum Lam.) is an exotic winter annual weed that recently has seriously infested wheat fields in central Japan. To understand the influence of tillage systems on the germination ecology and seedbank dynamics of naturalized Italian ryegrass, we compared the fate of the seeds that were after-ripened in the soil with that of the seeds on the soil surface, and then examined the germination characteristics of the seeds retrieved from both treatments by germination tests in both a light/dark (12 h photoperiod) condition and in constant darkness. The seedling emergence was greater initially for the seeds after-ripened on the soil surface than for the seeds in the soil. The component of emergent seeds after-ripened on the soil surface increased as time passed during the summer, whereas that of emergent seeds in the soil scarcely increased. This contrasting emergence was, in part, attributable to the ability of the seeds to germinate at higher temperatures in the light/dark condition than in constant darkness. These results suggest that untilled systems, which leave many seeds on the soil surface, might promote the rapid depletion of Italian ryegrass seeds through germination before wheat sowing in early winter. In contrast, seed burial by tillage might inhibit the germination of the seeds and form a large transient seed bank available to germinate during the wheat-growing season.     

Dormancy and viability of Phalaris minor seed in a rice–wheat cropping system

Seed placement, soil temperature and soil moisture content influenced the process of after-ripening in Phalaris minor seeds. Seeds of P. minor collected from the soil just after wheat harvesting exhibited higher germination than seeds from P. minor threshed directly. There was a pronounced impact of periodic inhabitation of seed into the soil on germination after its dispersal. Germination was strongly inhibited when the seed was kept in soil at more than field capacity (FC) or in water. Maximum germination of seed incubated in soil at FC occurred at 30°C while a temperature of 40°C favoured after-ripening of seed when mixed with dry soil or kept dry without any medium. Release from conditional dormancy was quicker in the seed retrieved from the soil kept at 20°C than at 10°C. Seed release from conditional dormancy and germination increased with a rise in temperature from 30 to 40°C when the seed was retrieved from incubation in soil at FC for 70 days. The seed kept immersed in water was least responsive to a rise in temperature. Seed recovered from dry soil, or kept without any medium, responded quickly at both temperatures. Light enhanced the germination of Phalaris minor seed. The seedbank subjected to rice (Oryza sativa) field management conditions lost vigour in comparison with the seed stored in laboratory. There was significant variability in seed viability when exposed to differential water management conditions in rice.     

Influence of environmental factors on seed germination and emergence of Iresine diffusa

Iresine diffusa has become more abundant under no‐till soyabean in Argentina. The influence of temperature, light, cold‐wet storage, osmotic potential, dry storage and depth of seed burial on germination and emergence of I. diffusa was examined in a growth chamber experiment. Iresine diffusa seeds germinated at the highest proportion (>0.80) in all fluctuating day/night temperatures tested. Conversely, under a constant temperature regime, maximum germination rates occurred at 15 (0.78) and 20°C (0.82), and minimum germination rates occurred at 10 (0.19) and 30°C (0.36). Seed germination was not influenced by light exposure. However, germination decreased after 12 (0.76) and 16 (0.65) weeks in cold‐wet storage. To reduce germination significantly, ?0.4 MPa of osmotic potential (induced by PEG‐6000) or 120 mmol L^?1 of salt (NaCl) concentration was required. Seeds of I. diffusa showed high viability (0.85) after 720 days of dry storage. Low emergence was recorded for seeds buried at 2 cm, and seedling emergence was completely inhibited when seeds were buried at 5 and 10 cm. Iresine diffusa seeds had high viability and were capable of emerging in a broad range of environmental conditions. The thermal germination conditions, shallow soil depths and high moisture conditions in germination phase for I. diffusa are congruent with the conditions in Argentina no‐tillage soyabean. Thus, no‐tillage could provide better conditions for germination than conventional tillage systems. However, due to the fact that I. diffusa can reproduce by rhizomes, further research should be conducted to understand the relative importance of the vegetative reproductive strategy in relation to the presence and persistence of this weed in fields.     

耕作模式和播种方式对旱地小麦产量形成的影响

于2015—2017年在山西省闻喜旱地小麦试验示范基地开展大田试验,以耕作模式为主区,设休闲期深翻和免耕两种模式,以播种方式为副区,设探墒沟播、膜际条播和常规条播3种方式,研究旱地小麦土壤水分、产量形成和经济效益的差异。结果表明：休闲期深翻显著提高旱地小麦播前0～300 cm土壤蓄水效益,达46.97%～240.44%;提高旱地小麦生育时期土壤耗水量,达6.48%～13.07%;提高穗数、穗粒数、千粒重和产量,分别达3.32%～7.22%、3.67%～6.53%、1.11%～3.61%、10.23%～13.16%。探墒沟播和膜际条播较常规条播显著提高了旱地小麦茎蘖成穗率,达5.99%～16.87%,显著提高穗长0.8～1.7 cm,提高可孕小穗数1～3个;提高了穗数、穗粒数,分别达5.28%～15.75%和1.51%～11.25%,此外,休闲期深翻后采用探墒沟播较膜际条播减少投入1 200元·hm^-2,主要是旋耕机械投入、地膜和回收地膜人工投入,增加经济效益622～754元·hm^-2。休闲期深翻后采用探墒沟播较常规条播减少投入300元·hm<...     

Factors affecting the seed germination and seedling emergence of redflower ragleaf (Crassocephalum crepidioides)

Redflower ragleaf (Crassocephalum crepidioides) is a weed, as well as a minor vegetable, in tropical and subtropical regions of the world. The influence of environmental factors and seed conditions on the germination and emergence of redflower ragleaf have been evaluated in order to help understand its distribution and to develop effective management strategies. The seeds germinated at a constant temperature in the range of 10–30°C and reached a maximum at 15–20°C. The highest germination rate was recorded at an alternating temperature of 20/15°C (day/night). The seeds germinated over a wide pH range (2–12), with the highest germination rate at between 4 and 10. Germination under saturated and flooded conditions was also high. The germination of seeds from opened (mature) capitula was significantly higher than from partially opened or unopened capitula. The germination of seeds without a pappus was significantly higher than for seeds with a pappus. The germination rate of 1 year old seeds decreased drastically when compared to that of freshly harvested seeds. The seedling emergence rate was ～63% for those seeds placed on the soil surface, but no seedling emerged from a depth of ≥1 cm. These results indicate that redflower ragleaf seeds can germinate in various environmental conditions, but that the percentage that germinates will be different in different environments. Regeneration could be effectively prevented by at least a 1 cm soil covering or by destroying the plant before the capitula open. In contrast, freshly harvested seeds from opened capitula should be sown on the soil surface when redflower ragleaf is to be cultivated as a vegetable.     

不同贮藏条件对大赖草种子萌发的影响

将野外观测与室内实验相结合,研究不同贮藏条件对大赖草种子萌发的影响。结果表明：室内干藏与野外埋藏于地表的种子随贮藏时间的延长,种子萌发率呈现缓慢升高后逐渐降低的趋势,说明大赖草种子存在着后熟现象;埋藏5 cm深度的种子,埋藏2、7、8个月时,种子自然萌发率分别为5.15%、7.52%和94%,剩余种子在室内条件下萌发率大于95%。而埋藏于原生境的种子埋藏2个月无萌发现象,埋藏8个月自然萌发率为90%;说明大赖草的种子在土壤中属于瞬间种子库;黑暗有利于大赖草种子的萌发。不同贮藏条件下大赖草种子的含水量表现为：埋藏5 cm深度>埋藏于地表>室内干藏,大赖草种子萌发的最低含水量为19.5%。在自然生境中,野外埋藏的种子被动物搬运的占12%～90%,平均达44.5%,致使土壤中种子数量锐减。因此,大赖草种子在土壤种子库中数量匮乏;自然生境中干旱少雨、水分缺少,导致种子萌发后易“闪苗”。这些因素是大赖草有性繁殖更新率低的主要原因。     

Burial effects on seed germination and seedling establishment of Prosopis juliflora (SW.) DC

Seed germination and seedling establishment are critical stages in plant life history, and both processes may be affected when buried under soil. Our aim was to investigate the effects of soil burial on the germination and seedling establishment of invasive Prosopis juliflora (Fabaceae). We studied the effects of burial, from soil surface to 4?cm deep, under greenhouse conditions and the effects of seed-storing in burial conditions at two depths (5 and 20?cm) and two storing periods (during 6 and 12?months) in field conditions. Soil burial limited the germination and the establishment of P. juliflora, which did not germinate at soil depths deeper than 3?cm. Some seedlings coming from seeds germinated at 2?cm, and every seedling at the soil surface and at 3?cm deep died. In contrast, survivorship of emerged seedlings was close to 90% between 0.5 and 2?cm depth. Seedlings developed the longest shoots at 1?cm deep, indicating that P. juliflora was able to get advantage at a moderate soil depth. Un-embedded seeds survived buried in the soil for months; however, their germination and the emerged seedling survivorship decreased after burial for 12?months.     

Longevity,dormancy and germination of Cyanus segetum

Cyanus segetum is an iconic, colourful weed in arable fields that provides ecological and societal services. To understand better both the infestation dynamics of C. segetum as an abundant, harmful weed and maintain sustainable populations where it provides beneficial services, we compared information on seed dormancy, seed longevity and germination conditions in two populations. Persistence of seeds buried in the soil was low, with <10% viable after 3 years. Periodic dormancy cycling was observed over the 4 years in the soil, with a maximum of dormant seeds in the spring and a minimum in the autumn; however, 20% of the seeds were non‐dormant all the time. Seeds of C. segetum were positive photosensitive, but light requirement varied among populations. Base water potential for germination was ?1 MPa. Base temperature ranged from 1 to 2°C. Optimum temperature for germination was about 10 to 15°C, but the mean thermal time varied greatly between populations, from 80 to 134 day °C. Photoperiod and temperature combinations had no effect on germination percentage, but both reduced the germination rate. Burial deeper than 2 cm greatly reduced germination and seedling emergence strongly decreased at depths >0.5 cm. No seeds buried deeper than 8 cm emerged. Low seed longevity and a wide range of germination conditions could partly explain the rapid disappearance of C. segetum populations after herbicide application began in western Europe. However, yearly sowing in restoration areas does not seem to be essential.     

Effects of the seed weight and burial depth on the seed behavior of common ragweed (Ambrosia artemisiifolia)

Common ragweed (Ambrosia artemisiifolia L.) is one of the annual plants that were described recently as invasive weeds in Europe. This species is described as an invasive plant that produces seeds that are highly variable. Its production of variably sized seeds is regarded as promoting its spread in different environments. Experiments were carried out to determine the influence of the seed weight and temperature on germination and the influence of the seed weight and burial depth on seedling emergence. The seeds were divided into a number of classes of weight and the seed weight effect on germination was evaluated by Petri dish assays. In another experiment, the seeds were buried at different depths in a clay soil/sand mix to estimate the burial effect on germination and seedling emergence. The germination level of A. artemisiifolia was high overall, between 76.8% and 94.2%. The seed germination was modified by temperature but it was not influenced by the seed weight. The amounts of germination and seedling emergence were greater for the seeds on the soil surface and decreased with an increasing burial depth, from 2 to 8 cm. No germination or emergence was observed for the seeds that were buried at 10 and 12 cm. The lightest seeds were more sensitive to burial. A greater level of seedling emergence for those seeds that were placed near the soil surface could explain the success of this species in open habitats, where the probability of deeper burial is low. After high seed production, the management of A. artemisiifolia in fields could be partly achieved through soil tillage, burying seeds below 10 cm, and not carrying out deep soil tillage the following year.     

Seedling emergence and seed longevity of the tree weeds Celtis sinensis and Cinnamomum camphora

Factors influencing germination and seed survival of Celtis sinensis Pers. and Cinnamomum camphora (L.) Presl. were investigated in a series of experiments conducted under natural rainfall regimes in the field and under irrigation in a growth tunnel. Germination from surface-sown seeds of C. camphora was virtually nil under natural rainfall, in contrast to almost 100% germination under irrigation. This suggests that surface-lying seeds of this species will germinate only in highly protected microsites in the field. For C. sinensis , however, in one of the two field experiments germination from surface-sown seeds was similar (≈40%) to that achieved under irrigation. Germination from intact fruits of both species was generally considerably less than from seeds. Seeds of both species were relatively short-lived under field conditions. A maximum of 1% of seeds of C. camphora remained viable at 12 months post-sowing under field conditions, whereas a maximum of 8% viable seeds of C. sinensis was detected at 24 months post-sowing in one of the field experiments.     

Assessment of the differential response of weeds to soil solarization by two methods

The efficacy of solarization in weed control under field conditions of the United Arab Emirates was evaluated by two methods: on-farm weed assessment and a seed germination test. In the on-farm weed assessment method, the weed frequency, density, and dry weight were compared in the solarized and non-solarized plots that were cultivated with cabbage. Prior to solarization, the soil was artificially infested with the seeds of 10 weeds. Generally, the densities of seven species and dry weights of five species were significantly lower in the solarized plots as compared to the control. Launea mucronata , Capsella bursa-pastoris , and Echinochloa colona were very sensitive to solarization, as they did not appear in the solarized plots. However, Portulaca oleracea and Melilotus indica were not significantly affected by soil solarization. In the second method, the germination was assessed for the seeds of four weedy species buried at three depths for different durations of solarization. The results confirmed the great sensitivity of L. mucronata and C. bursa-pastoris seeds to solarization, as all had not germinated after 15 days of solarization, even at the 15 cm depth. The seeds of E. colona , however, were less sensitive after 15 days of solarization, especially at 7.5 cm and 15 cm, respectively. The seed germination method confirmed the resistance of the P. oleracea seeds to solarization. The results emphasized the importance of the germination test to provide accurate predictions about the spatial and temporal changes of the soil seed bank in solarized farms. This would help to determine the optimal duration of solarization in each farm, depending on the kind of weeds infesting the farm.     

不同环境因素对节节麦萌发的影响

节节麦Aegilops tauschii Coss.是麦田难治杂草,研究环境条件对节节麦发芽的影响对预测其适生区域及综合治理有重要意义。以采自陕西、山东和河南的3个节节麦种群为对象,通过室内和室外萌发试验研究了水势、pH、盐分和播种深度与节节麦萌发的关系。结果表明,3个节节麦种群在不同的环境条件下表现出相似的萌发及出苗特性,其萌发对水势敏感,发芽率随水势的下降而降低,当渗透势小于-1.0 MPa时,种子不萌发;节节麦萌发对pH要求不高,在pH 3～10条件下发芽率均超过70%;其萌发具有一定的耐盐性,盐浓度为0 mmol/L时,发芽率最高,盐浓度大于420 mmol/L时,节节麦不能萌发;节节麦出苗率随播种深度的增加而降低,播种在土壤表面时,出苗率最高,播种深度大于10 cm时,未发现节节麦出苗。3个节节麦种群发芽对上述不同环境因子的反应差异不显著。     

渭北旱地小麦留茬深松膜侧沟播耕作技术体系研究

试验结果表明,留茬、深松、膜侧沟播是融“深松储水效应”、“残茬覆盖保水增肥效应”和“起垄覆膜沟播聚水、保水、增温、透光效应”于一体的旱地小麦机械化保护性耕作技术体系,具有极好的生态效益、社会效益和经济效益;夏闲期留茬覆盖、深松耕可把占小麦全生产年度50％的夏闲期降水最大限度地蓄积并保存于土壤之中,较传统翻耕法多蓄水76.2mm,蓄水率达50％以上;在夏闲期多蓄水的基础上,种麦时再应用起垄覆膜沟播技术,既可以把夏闲期蓄积到土壤中的水分最大限度地保住,又可把小麦生育期的降水量最大限度地蓄住,加之地膜覆盖的增温效应,从而使旱地小麦的水、热条件明显改善,达到既增产增收,又保水保土的效果。     

不同秸秆还田模式冬麦田土壤水分特征比较

在陕西杨凌区布设田间试验,在冬小麦发育期间观测5种不同玉米秸秆覆盖与耕作方式相结合模式的土壤水分特征。结果表明5种覆盖耕作模式的土壤水分垂直变异系数大小排列为传统翻耕(0.1376)>浅旋覆盖(0.1360)>传统覆盖(0.1309)>深翻覆盖(0.1265)>免耕留茬(0.1167);免耕覆盖土壤水分贮存量(342 mm)最高,以浅旋覆盖(289 mm)、传统翻耕(287 mm)土壤水分贮存量相对为低,深翻覆盖(307 mm)、传统覆盖(300 mm)土壤水分贮存量相对居中。     

Factors affecting seed germination and emergence of Gomphrena perennis

Controlled growth chamber experiments were conducted to determine factors affecting seed germination and emergence of the troublesome weed Gomphrena perennis. The objective of this research was to examine the effects of temperature, light, moist chilling, osmotic potential, dry storage and depth of seed burial on G. perennis germination and emergence. The optimum temperature for germination was around 15–20°C. Seeds showed germination rates above 90% under 20/10 and 25/15°C temperature regimes. The minimum exposure to light needed to stimulate germination was 1 min. However, the light requirement was reduced after a long storage period. Furthermore, germination was high (>90%) in all moist‐chilling treatments tested. Germination was highly sensitive to increasing osmotic stress. The highest germination percentage (94%) was achieved at 0 MPa, and decreasing osmotic potential from 0 to ?0.3 MPa reduced germination to 11%. The highest seedling emergence occurred for seeds placed from 0 to 1 cm deep, and no seedlings emerged from a 5‐cm burial depth. Gomphrena perennis has a suitable environment in a no‐till soybean field, where seeds remaining on the surface have the required temperature, light and depth needed for germination.     

水分和温度对冬小麦和玉米免耕作产量影响的研究

本文对宁夏彭阳县旱地冬小麦、玉米的免耕作中水分和温度对产量的影响进行了探索。试验结果表明:播种前、后,旱地免耕作膜侧种植冬小麦处理比无地膜覆盖常规耕作处理的土壤含水量高,膜侧种植冬小麦生育后期土壤水分明显高于无地膜覆盖常规耕作处理。膜侧的土壤含水量高于膜内的土壤含水量,有利于膜侧冬小麦的生长。旱地免耕作膜侧冬小麦产量达3540kg/hm2,比对照增产78.8%,纯收益比对照提高79.7%。旱地玉米免耕作秸秆覆盖处理的土壤含水量明显高于常规耕作玉米处理的土壤含水量。覆盖1/2玉米秸秆、全部玉米秸秆处理的土壤平均含水量分别比常规耕作增加11.1%和9.8%。但是常规耕作有地膜覆盖,对耕层土壤的增温效果最好,而玉米秸秆覆盖对土壤增温的效果较差。覆盖1/2玉米秸秆、全部玉米秸秆处理产量分别比常规耕作减产25.4%和11.2%。     

Effects of soil temperature, moisture, and burial depths on carpogenic germination of Sclerotinia sclerotiorum and S. minor

Extensive studies have been conducted on the carpogenic germination of Sclerotinia sclerotiorum, but carpogenic germination in S. minor has not been studied adequately. It remains unclear why apothecia of this pathogen have seldom been observed in nature. In this study, a new method was developed to produce apothecia in the absence of soil or sand, and carpogenic germination without preconditioning was recorded for 95 of the 96 S. sclerotiorum isolates tested. Carpogenic germination of the two species was compared under a variety of temperature, soil moisture, burial depths, and short periods of high temperature and low soil moisture. The optimal temperatures for rapid germination and for maximum germination rates were both lower for S. minor than for S. sclerotiorum. The temperature range for carpogenic germination was also narrower for S. minor than for S. sclerotiorum. A 5-day period at 30 degrees C, either starting on the 10th or 20th day of incubation, did not significantly affect carpogenic germination of S. sclerotiorum. For both S. minor and S. sclerotiorum, the percentage of carpogenically germinated sclerotia increased as soil water potential increased from -0.3 to -0.01 MPa. In the greenhouse, a 10- or 20-day dry period completely arrested carpogenic germination of S. sclerotiorum, and new apothecia appeared after an interval of 35 days following rewetting, similar to the initial carpogenic germination regardless of when the dry period was imposed. In naturally infested fields, the number of sclerotia in 100 cc of soil decreased as depth increased from 0 to 10 cm before tillage, but became uniform between 0 and 10 cm after conventional tillage for both species. Most apothecia of S. minor were, however, produced from sclerotia located at a depth shallower than 0.5 cm while some apothecia of S. sclerotiorum were produced from sclerotia located as deep as 4 to 5 cm. These results provide the much needed information to assess the epidemiological roles of inoculum from sexual reproduction in diseases caused by the two Sclerotinia species in different geographical regions. However, more studies on effects of shorter and incompletely dry periods are still needed to predict production of apothecia of S. sclerotiorum in commercial fields under fluctuating soil temperature and moisture.