Cumulative Emergence Research Articles

Relationship between laboratory indices of soybean seed vigor with field emergence and yield

This study was conducted for evaluation the correlation of laboratory seed quality indices with field emergence in 2013. First the standard germination test and seed vigor tests were conducted for of two cultivars (Williams and L17) which were produced in last year and also recent year and germination percent and seedling vigor index were measured. Then vigor tests including cold and accelerated aging tests were conducted. The laboratory experiments were done as a factorial experiment with two factors based on completely randomized design in 4 replications and field experiment was as a factorial experiment with two factors based on randomized complete block design in 4 replications. According to results germination percent and seedling vigor index had a high correlation with final seedling emergence percent and cumulative emergence rate. The seedling vigor index in cold test specified the highest correlation with final seedling emergence percent (r= 0.941) and cumulative emergence rate (r=0.756). The correlation of laboratory traits and yield related traits defined that standard germination percent (r=0.756) and seedling vigor index (r=0.711) in cold test showed a high correlation with final yield and the related traits to accelerated aging test had a lesser correlation.

Efficacy of Pre-Emergence and Post-Emergence Soybean Herbicides for Control of Glufosinate-, Glyphosate-, and Imidazolinone-Resistant Volunteer Corn

Glyphosate-resistant corn and soybean are grown in rotations in the Midwest, including Nebraska. Volunteer corn is a problematic weed in soybean fields because it causes harvest problems, reduces yield and seed quality, and potentially harbors insects, pests, and diseases. Several pre-packaged herbicides have been registered in soybean in recent years, but response of volunteer corn to these herbicides has not yet been documented. Greenhouse experiments were conducted to evaluate the response of glufosinate-, glyphosate-, and imidazolinone-resistant volunteer corn to 20 pre-emergence (PRE) and 17 post-emergence (POST) soybean herbicides. Cumulative emergence of volunteer corn was not affected by PRE soybean herbicides compared with the nontreated control regardless of herbicide-resistant trait at 21 days after treatment (DAT). Although comparable with several other treatments, clomazone provided ≥ 90% control of glufosinate- and imidazolinone-resistant volunteer corn at 21 DAT. The POST soybean herbicides were applied when volunteer corn plants were at the 2 to 3 or 5 to 6 leaf stage. The ACCase-inhibiting herbicides, including clethodim, fenoxaprop plus fluazifop, fluazifop, quizalofop, and sethoxydim, provided ≥ 96 and ≥ 85% control of the 2 to 3 or 5 to 6 leaf stage volunteer corn, respectively, regardless of the herbicide-resistance trait at 28 DAT. Glyphosate tank mixed with acifluorfen, chlorimuron-ethyl, or imidazolinones usually provided > 83% control of glufosinate-and imidazolinone-resistant volunteer corn when sprayed at the 2 to 3 leaf stage at 28 DAT, but control was ≤ 71% for the 5 to 6 leaf stage volunteer corn. Similar results were usually reflected in volunteer corn biomass. It is concluded that PRE soybean herbicides partially controlled volunteer corn; therefore, ACCase inhibiting herbicides are the only highly effective option for soybean growers.

Synthetic Auxin Herbicides Control Germinating Scotch Broom (Cytisus scoparius)

Scotch broom is a large, nonnative shrub that has invaded forests and grasslands in 27 U.S. states. Without treatment, Scotch broom's persistent seedbank ensures a continuing source of regeneration after soil disturbance. In growth chamber studies, five rates of three synthetic auxin herbicides, aminocyclopyrachlor (AC), aminopyralid (AP), and clopyralid (CP), were compared for PRE control of Scotch broom. Cumulative 90-d emergence, mortality, and biomass of seedlings did not vary among herbicides, averaging 42% of seeds sown, 75% of emerged seedlings, and 9 mg seedling−1 for treated containers, respectively, versus 46%, 17%, and 26 mg seedling−1 for nontreated containers. Low rates of each herbicide (< 50% of the maximum labeled rate [MLR]) provided 60 to 80% control, whereas 100% MLR provided 69 to 89% control. Although the herbicides differed in cost per unit seedling mortality (AP < CP < AC), each demonstrated strong potential as a viable treatment for PRE control of Scotch broom.

Do Common Waterhemp (Amaranthus rudis) Seedling Emergence Patterns Meet Criteria for Herbicide Resistance Simulation Modeling?

A study was conducted to quantify the magnitude and sources of variation in common waterhemp temporal patterns of emergence over 1 yr. In 2008 and 2010, emergence patterns in the absence of soil disturbance were determined for replicated samples of maternal families (progeny from one individual) separately harvested during the previous year from four plants within each of four agricultural fields (16 maternal families yr−1) at a university research farm near Urbana, IL. Combining data across years, variance partitioning indicated that seed sample within maternal family explained 48% of total variation in the percentage of viable, buried seeds that produced seedlings. Differences within, rather than among, maternal families also accounted for large fractions (60 to 99%) of total variation in cumulative percentage emergence at specific points during the growing season. Within years, seed samples characterized by delayed or accelerated emergence patterns did not originate from specific maternal plants. These results indicate that common waterhemp seed populations are without strong maternal plant effects that limit emergence to narrow intervals within the overall emergence period. Thus, results of this study support the use of contemporary approaches for modeling herbicide resistance evolution in common waterhemp, which assume seedling cohorts contain offspring from all individuals occurring within the maternal population.

Predicting Emergence of 23 Summer Annual Weed Species

First- and second-year seedbank emergence of 23 summer annual weed species common to U.S. corn production systems was studied. Field experiments were conducted between 1996 and 1999 at the Iowa State University Johnson Farm in Story County, Iowa. In the fall of 1996 and again in 1997, 1,000 seeds for most species were planted in plastic crates. Seedling emergence was counted weekly for a 2-yr period following seed burial (starting in early spring). Soil temperature at 2 cm depth was estimated using soil temperature and moisture model software (STM2). The Weibull function was fit to cumulative emergence (%) on cumulative thermal time (TT), hydrothermal time (HTT), and day of year (DOY). To identify optimum base temperature (Tbase) and base matric potential (ψbase) for calculating TT or HTT, Tbaseand ψbasevalues ranging from 2 to 17 C and −33 to −1,500 kPa, respectively, were evaluated for each species. The search for the optimal model for each species was based on the Akaike's Information Criterion (AIC), whereas an extra penalty cost was added to HTT models. In general, fewer seedlings emerged during the first year of the first experimental run (approximately 18% across all species) than during the second experimental run (approximately 30%). However, second-year seedbank emergence was similar for both experimental runs (approximately 6%). Environmental effects may be the cause of differences in total seedling emergence among years. Based on the AIC criterion, for 17 species, the best fit of the model occurred using Tbaseranging from 2 to 15 C with four species also responding to ψbase= −750 kPa. For six species, a simple model using DOY resulted in the best fit. Adding penalty costs to AIC calculation allowed us to compare TT and HTT when both models behaved similarly. Using a constant Tbase, species were plotted and classified as early-, middle-, and late-emerging species, resulting in a practical tool for forecasting time of emergence. The results of this research provide robust information on the prediction of the time of summer annual weed emergence, which can be used to schedule weed and crop management.

Integrated management of Bromus diandrus in dryland cereal fields under no‐till

SummaryAs herbicides have limited effect in controlling Bromus diandrus in no‐till dryland cereal fields, the integration of chemical and cultural methods needs to be investigated. A field study was carried out in Lleida (Spain) during 2008–09, 2009–10 and 2010–11 seasons, in a no‐till winter cereal field integrating delayed crop sowing with herbicides in a barley–wheat–wheat rotation. Three crop sowing dates were considered: D1, mid‐October; D2, mid‐November; and D3, early December, and the herbicides mesosulfuron‐methyl plus iodosulfuron‐methyl‐sodium were applied in wheat. Weed density, cumulative emergence and fecundity were estimated for each sowing date. In all three seasons, a significant reduction in the cumulative emergence of B. diandrus as compared to D1 was observed in D2 (82.0, 97.5 and 98.1%) and D3 (80.8, 98.7 and 97.2%). In addition, a significant decrease in weed density and seed rain was observed across all sowing dates and seasons. The herbicide used in wheat was more effective under delayed sowing, due to lower weed density and presence of less developed weed seedlings. After three seasons, the populations of B. diandrus were completely depleted in D2 and D3. This study demonstrates the possibility of eliminating brome infestations in dryland cereal fields in no‐till systems through the integration of cultural and chemical strategies.

Environmental Triggers of Winter Annual Weed Emergence in the Midwestern United States

Winter annual weeds are becoming prolific in agricultural fields in the midwestern United States. The objectives of this research were to understand the roles of soil temperature (daily average and fluctuation) and moisture on the emergence of nine winter annual weed species and dandelion and to develop predictive models for weed emergence based on the accumulation of modified thermal/hydrothermal time (mHTT). Experiments were established at Lincoln, NE; Mead, NE; and at two sites (irrigated and rainfed) near Clay Center, NE, in 2010 and 2011. In July of each year, 1,000 seeds of each species were planted in 15 by 20 by 6-cm mesh baskets installed between soybean rows. Soil temperature and water content were recorded at the 2-cm depth. Emerged seedlings were counted and removed from the baskets on a weekly basis until no additional emergence was observed in the fall, resumed in late winter, and continued until emergence ceased in late spring. Weather data were used to accumulatemHTT beginning on August 1. A Weibull function was selected to fit cumulative emergence (%) on cumulativemHTT (seven base temperature [Tbase] by six base water potential [Ψbase] by three base temperature fluctuation [Fbase] candidate threshold values = 126 models); it was also fit to days after August 1 (DAA1), for a total of 127 candidate models per species. The search for optimal base thresholds was based on the theoretic-model comparison approach (Akaike information criterion [AIC]). All three components (Tbase, Ψbase, andFbase) were only important for Virginia pepperweed. For downy brome and purslane speedwell, includingTbaseand Ψbaseresulted in the best fit, whereas for dandelion includingTbaseandFbaseresulted in the best fit. A model including onlyTbaseresulted in the best fit for most species included in this study (Carolina foxtail, shepherd's-purse, pinnate tansymustard, henbit, and field pansy). For field pennycress, the model based on DAA1 resulted in the best fit. Threshold values were species specific. Soil temperature was the major environmental factor influencing winter annual weed emergence. Even though soil moisture and often temperature fluctuation are essential for seed germination, ΨbaseandFbasewere not as critical in the predictive models as initially expected. Most seedlings (> 90%) of downy brome, pinnate tansymustard, Carolina foxtail, henbit, and field pansy emerged during the fall. Virginia pepperweed, purslane speedwell, dandelion, shepherd's-purse, and field pennycress seedlings emerged during both fall and spring. The results of this research provide robust information on the prediction of the time of winter annual weed emergence, which can help growers make better management decisions.

Prediction of annual weed seed emergence in garlic (Allium sativum L.) using soil thermal time

Avena fatua L. and Polygonum aviculare L. are two competitive weeds in garlic (Allium sativum L.) fields. Knowledge of the temporal pattern emergence will contribute to optimizing the timing of control measures, thus maximizing efficacy. The development of predictive models can contribute to control measures at early growth stages. The objective of this study was to develop and validate predictive empirical models of emergence for A. fatua and P. aviculare based on thermal time. Cumulative seedling emergence data were obtained during two years from a garlic field and used to develop and validate the models. The relationship between cumulative seedling emergences and cumulative thermal time (TT) under field conditions was analyzed using the Gompertz function. The models accounted for 98% and 96% of the variation observed in A. fatua and P. aviculare, respectively. Model validation performed well in predicting the seedling emergence of both species. According to this model, A. fatua emergence started at 381 TT after sowing and reached 50% and 90% of total emergence at 407 and 478 TT, respectively, with a soil base temperature of 1°C. P. aviculare started emergence at 410 TT after sowing and reached 50% and 90% of total emergence at 505 and 590 TT, respectively, with a base temperature of 0°C. Results indicate that these models could be useful as predictive tool contributing to a effective control of A. fatua and P. aviculare populations in garlic crops.

Fates of Setaria faberi and Abutilon theophrasti seeds in three crop rotation systems

SummaryWeed seeds in and on the soil are the primary cause of weed infestations in arable fields. Previous studies have documented reductions in weed seedbanks due to cropping system diversification through extended rotation sequences, but the impacts of different rotation systems on additions to and losses from weed seedbanks remain poorly understood. We conducted an experiment in Iowa, USA, to determine the fates of Setaria faberi and Abutilon theophrasti seeds in 2‐, 3‐ and 4‐year crop rotation systems when seed additions to the soil seedbank were restricted to a single pulse at the initiation of the study. Over the course of the experiment, seedlings were removed as they emerged and prevented from producing new seeds. After 41 months, seed population densities dropped >85% for S. faberi and >65% for A. theophrasti, but differences between rotation systems in the magnitude of seedbank reductions were not detected. Most of the reductions in seedbank densities took place from autumn through early spring in the first 5 months following seed deposition, before seedling emergence occurred, suggesting that seed predation and/or seed decay was important. For S. faberi, total cumulative seedling emergence and total seed mortality did not differ between rotation systems. In contrast, for A. theophrasti, seedling emergence was 71% lower and seed mortality was 83% greater in the 3‐ and 4‐year rotation systems than in the 2‐year system. Results of this study indicate that for certain weed species, such as A. theophrasti, crop rotation systems can strongly affect life‐history processes associated with soil seedbanks.

Effect of Insecticide Management History on Emergence Phenology and Neonicotinoid Resistance in <I>Leptinotarsa decemlineata</I> (Coleoptera: Chrysomelidae)

Emergence phenology and fitness attributes of several Colorado potato beetle, Leptinotarsa decemlineata (Say), populations were measured under field and greenhouse conditions. Anecdotal observations by producers and pest managers in many locations of the upper Midwest increasingly suggested that select populations of Colorado potato beetle were emerging over a longer period in the spring and were less sensitive to systemic neonicotinoids in cultivated potato. These changes in emergence phenology may be related to changes in systemic insecticide concentration over time. Specifically, a prolonged period of adult emergence in the spring increases the potential of low-dose chronic exposure to systemic neonicotinoid insecticides in potato. In 2010 and 2011, our objectives were twofold: 1) establish a common garden experiment to compare the emergence phenology of Colorado potato beetle populations uniquely managed with variable insecticide inputs, and 2) measure postdormancy fitness of emerged adult beetles from among these selected populations. Cumulative adult emergence was modeled with logistic regression. Results from this study found no clear evidence for direct relationships between phenology and management history or resistance. Differences in reproductive capacity, sex ratio, and body size were apparent in some instances. However, these results did not uniformly correspond to one specific form of potato pest management tested here. In this study, long-term reliance on systemic insecticides for Colorado potato beetle control did not serve as a strong predictor for variable life history for selected populations in Wisconsin.

Modeling seed dormancy release and germination for predicting Avena fatua L. field emergence: A genetic algorithm approach

Avena fatua is a cosmopolite weed species which produces severe yield losses in small-grain production systems in temperate and semiarid climates. In the semiarid region of Argentina, A. fatua field emergence patterns show great year-to-year variability mainly due to the effect of highly unpredictable precipitation regimes as well as a complex seedbank dormancy behavior regulated by both, genetic and environmental factors. Previously developed models for the same agroecological system based on Non-Linear Regression techniques (NLR) and Artificial Neural Networks (ANN) were either unable to accurately predict field emergence or lacked explanatory power. The main objective of the present work is to develop a simple (i.e. parsimonious) model for A. fatua field emergence prediction for the semiarid region of Argentina based on the disaggregation of the dormancy release phase from the germination/pre-emergence growth processes, using easy accessible soil microclimate derived indices as input variables and observed cumulative field emergence data as output variable. The parsimony and predictive capability of the newly developed model were compared with NLR and ANN approaches developed by the same authors for the same agroecological system. Specifically, dormancy release was modeled as a logistic function of an after-ripening thermal-time index while germination/pre-emergence growth was represented by a logistic distribution of hydrothermal-time accumulation. A total of 528 input/output data pairs corresponding to 11 years of data collection were used in this study. Due to its implementation simplicity and good convergence features, a Genetic Algorithm (GA) was adopted to solve the resulting optimization problem consisting on the minimization of the Mean Square Error (MSE) between training data and experimentally obtained field emergence data. The newly developed GA based approach resulted in a significantly more parsimonious model (BIC=−1.54) compared to ANN (BIC=−1.36) and NLR (BIC=−1.32) models. Model evaluation with independent data also showed a better predictive capacity of the GA approach (RMSE=0.07) compared to NLR (RMSE=0.19) and ANN (RMSE=0.11) alternatives. These outcomes suggest the potential applicability of the proposed predictive tool in weed management decision support systems design.

Variability in seedling emergence traits of Patagonian Cypress marginal steppe populations

Genetic information on adaptive traits is crucial for prediction of the evolution of natural populations in relation to global climate change. The seedling emergence process together with germination is a key adaptive stage in any seeding species. We aim to analyze variability in seedling emergence traits within and among marginal populations of Patagonian Cypress (Austrocedrus chilensis (D.Don) Pic. Ser. et Bizzarri), which have been suggested to be of conservation relevance. We performed an emergence trial in a greenhouse with seeds collected from 177 open-pollinated trees from 10 populations. A sigmoidal curve was fitted to the cumulative emergence data (in percentage of the sown seeds) for each replicate of each family. Variability was estimated using ANOVA for six variables: emergence capacity (EC), emergence energy (EE), energy period (EP), emergence initiation (t 10), emergence cessation (t 90) and emergence duration (Dur). The overall trial mean for EC was 76.2 %, while EE was only 27.6 %. Hence, most seedlings emerged after the energy period, which is interpreted as a bet-hedging strategy. Both “population” and “family” factors significantly affected all variables. The proportions of “family” variances were higher than “population” ones for EC, EE, Dur and t 90, but the opposite was found for EP and t 10, which is evidence of differentiation among populations. Variability among families may be due to both genetic and environmental causes, including maternal effects. However, the relatively high proportion of family variability in EC and EE suggests acceptable levels of additive genetic variance, which would not hinder the potential to evolve in these specific traits. Conversely, the chances to adapt in EP and t 10 are lower, and consequently local extinctions driven by global climate change seem possible.

A forecasting model for the adult emergence of overwintered Monochamus alternatus (Coleoptera: Cerambycidae) larvae based on degree-days in Korea

Emergence data from 1999 to 2011 were analyzed to develop a forecasting model of the adult emergence of overwintered Monochamus alternatus Hope (Coleoptera: Cerambycidae) larvae. The cumulative emergence curves of M. alternatus adults showed high variation year to year and were fitted by the Weibull function to obtain an all-combined preliminary model that was then used to separate fractional models. The emergence curves were grouped into three fractional modes—advance, regular, and delay—based on the number of discrepant days between actual and predicted date by the preliminary model at 50 % emergence date (predicted − observed), resulting in the mean number of discrepant days of 8.7, −0.2, and −8.0, respectively. Three assumptions were made to support the grouping: delay mode is selected when the third instars prevails in overwintering stages; advance mode is selected when the fourth instars prevail, since fourth instars immediately can go into pupal stage; regular mode is located between advance and delay mode. These three modes produced a 340, 420, and 500 degree-days (DDs) at 50 % emergence date, respectively, when each was fitted by the Weibull function, with DDs based on 11.9 °C from 1 January. The emergence models developed in this study considerably described the actual population phenology of M. alternatus, with the selection of advance, regular, and delay modes. Consequently, the models should be useful in establishing management strategies against M. alternatus in Korean forests.

Seed Burial Physical Environment Explains Departures from Regional Hydrothermal Model of Giant Ragweed (Ambrosia trifida) Seedling Emergence in U.S. Midwest

Robust predictions of weed seedling emergence from the soil seedbank are needed to aid weed management. A common seed accession (Illinois) of giant ragweed was buried in replicate experimental gardens over 18 site years in Illinois, Michigan, Kansas, Nebraska, Ohio, and South Dakota to examine the importance of site and climate variability by year on seedling emergence. In a nonlinear mixed-effects modeling approach, we used a flexible sigmoidal function (Weibull) to model giant ragweed cumulative seedling emergence in relation to hydrothermal time accumulated in each site-year. An iterative search method across a range of base temperature (Tb) and base and ceiling soil matric potentials (ψband ψc) for accumulation of hydrothermal time identified optima (Tb= 4.4 C, ψb= −2,500 kPa, ψc= 0 kPa) that resulted in a parsimonious regional model. Deviations between the fits for individual site-years and the fixed effects regional model were characterized by a negative relationship between random effects for the shape parameterlrc(natural log of the rate constant, indicating the speed at which emergence progressed) and thermal time (base 10 C) during the seed burial period October through March (r= −0.51, P = 0.03). One possible implication of this result is that cold winter temperatures are required to break dormancy in giant ragweed seeds. By taking advantage of advances in statistical computing approaches, development of robust regional models now is possible for explaining arable weed seedling emergence progress across wide regions.

Estimation and Comparison of Base Temperatures for Germination of European Populations of Velvetleaf (Abutilon theophrasti) and Jimsonweed (Datura stramonium)

Weed emergence models require biological parameters such as base temperature for germination, determination of which is costly and time-consuming. Transferability of these parameters across different populations may therefore represent one of the main constraints for the development and practical use of emergence models at a large scale. A collaborative project was undertaken to assess the interpopulation variability of base temperature for germination in different European populations of velvetleaf and jimsonweed and evaluate possible applicative consequences in terms of weed control. Seeds were collected in Italy, Portugal, and Spain, and each population was then sown in every country, obtaining nine seed batches named as experimental lots. Base temperature for germination was estimated for each experimental lot to calculate lot-specific accumulation of growing degree days (GDD) under three dissimilar climatic scenarios. Threshold date (TD50) was calculated as the date when GDD accumulation of a given experimental lot surpassed the values corresponding to 50% of cumulative field emergence of seedlings. GDD accumulation and TD50were then used as indicators to identify differences among experimental lots within each climatic scenario. No significant differences were detected among base temperatures estimated for velvetleaf experimental lots or among their patterns of accumulation of GDD and TD50values within climatic scenarios. Each value of base temperature determined for a single experimental lot could therefore be adopted to model germination for all the lots regardless of the population of origin or cultivation site. In contrast, the population of origin affected the base temperature for jimsonweed, with significantly higher values for experimental lots of the Portuguese population. From an applicative perspective, differences among patterns of accumulation of GDD and TD50of several experimental lots within each climatic scenario suggest the need to use population-specific values as base temperature for germination and emergence modeling of jimsonweed.

English

Affiliation of seed size with germination rate and percentage, seedling emergence rate and percentage, 50% mean emergence time, cumulative emergence rate, through 4 Safflower cultivars (Isfahan, Goldasht, Padideh, and Sina), in three different sizes of seed, were investigated under two separate experimental conditions in the field and laboratory of Seed and Plant Certification and Registration Institute Karaj-Iran, during 2008 to 2010. Both experiments were conducted in a factorial arrangement based on randomized complete block design, with three replications. The field results showed that cultivars Goldasht and Padideh were superior compare to other cultivars and large seeds with the highest seedling emergence rate, 1000-SW, and seed yield were superior to control and small. In the laboratory, morphological traits consisted of germination percentage, fresh and dry weight of root and shoot were significantly different, so that cultivars Goldasht and padideh with large seeds displayed better reaction. Thus, due to display better performance by cultivars Goldasht and Padideh, also creating vigorous seedlings by large seeds, using cultivars with adequate food storage as well as selecting large seeds with more germination potential to obtain higher yield and good plant establishment should take into consideration.   Key words: Cultivar, Goldasht, mean germination time, morphological traits, vigorous seedling.

Development and evaluation of a model for predicting Lolium rigidum emergence in winter cereal crops in the Mediterranean area

SummaryLolium rigidum is an extremely competitive and prevalent grass weed in cereal fields of Mediterranean areas. The proper timing of control measures is a prerequisite to maximising herbicide efficacy, in terms of both improved control and reduced herbicide inputs. The development of models to predict emergence flushes will contribute to this goal. Pooled cumulative emergence data obtained during three seasons from a cereal field were used to develop a Gompertz model. This explained relative seedling emergence from crop sowing onwards as a function of: (i) standard soil thermal time accumulation (TT) with a base temperature of 1.8°C and (ii) soil thermal time accumulation corrected for soil moisture (cTT). For the latter, no thermal time accumulation was computed for days in which the soil water balance within the upper 10‐cm soil layer indicated no water available for plants, because evapotranspiration was greater than rainfall plus the stored water remaining from the previous day. The model was validated with six datasets from four different sites and seasons. Compared with TT, the model based on cTT showed better performance in predicting L. rigidum emergence, particularly in predicting the end of emergence. Complemented with in‐field observations to minimise deviations, the model may be used as a predictive tool to better control this weed in dryland cereal fields of Mediterranean climate areas.

A hydrothermal seedling emergence model for Conyza bonariensis

SummaryConyza bonariensis is a South American native annual Asteraceae that has been introduced to the Mediterranean, where it behaves as a ruderal plant and a weed that is difficult to control in several crops. The development of predictive models can contribute to control measures at early growth stages, but currently there are no studies to predict seedling emergence of Conyza species. Our objectives were to develop and evaluate a model for predicting emergence response of C. bonariensis to the soil hydrothermal environment. A hydrothermal seed germination model was fitted to time course germination data from germination tests carried out at different constant temperatures and water potentials with the aim of establishing the hydrothermal parameters characterising C. bonariensis seed germination. The relationship between cumulative seedling emergence and cumulative hydrothermal time under field conditions was analysed using the Gompertz function. Model development was based on 2 years' data from a field experiment. Base temperature and base water potential for seed germination were estimated at 10.6°C and −0.70 ± 0.151 MPa, respectively. The emergence model showed a very good fit to the experimental data. According to this model, seedling emergence starts at 15 accumulated hydrothermal time (HTT) after sowing, and 50 and 95% emergence is completed at 53 HTT and 105 HTT, respectively. For model evaluation, independent field experiments were carried out in two localities. Cumulative seedling emergence was accurately predicted by the model. Results indicate that this model can be useful as a predictive tool contributing to effective control of C. bonariensis populations.

Hydrothermal Emergence Model for Ripgut Brome (Bromus diandrus)

A model that describes the emergence of ripgut brome was developed using a two-season data set from a no-tilled field in northeastern Spain. The relationship between cumulative emergence and hydrothermal time (HTT) was described by a sigmoid growth function (Chapman). HTT was calculated with a set of water potentials and temperatures, iteratively used, to determine the base water potential and base temperature. Emergence of ripgut brome was well described with a Chapman function. The newly-developed function was validated with four sets of data, two of them belonging to a third season in the same field and the other two coming from independent data from Southern Spain. The model also successfully described the emergence in different field management and tillage systems. This model may be useful for predicting ripgut brome emergence in winter cereal fields of semiarid Mediterranean regions.

Establishment of rare flood meadow species by plant material transfer: Experimental tests of threshold amounts and the effect of sowing position

The transfer of freshly cut seed-containing plant material is a widely applied method to re-establish grassland of high biodiversity. Still, the amount of plant material applied varies greatly across restoration projects. Therefore, we set up a two-year common garden experiment where we assessed the effect of plant material amount (0, 400, 800, 1600, 3200gm−2) and relative seed position (on top and beneath a litter layer) on seedling establishment, seedling fate and seedling fitness of eight target species for restoration of alluvial meadows.Most seedlings (85.6%) emerged within the first year. Cumulative seedling emergence and final seedling establishment across all species were highest on control plots and low litter plots but were very low or failed completely, at 1600 and 3200gm−2, respectively. In general, large-seeded species were significantly more successful than smaller seeded species. Relative seed position had only a small impact on seedling emergence and establishment but was decisive for seedling survival at high litter quantities. Across all species, seedlings that died had a significantly lower relative height than surviving seedlings. Interestingly, co-occurring resident grassland vegetation had a neutral rather than negative impact on the response variables.Our results suggest an upper threshold of 1000gm−2 for the amount of plant material applied in grassland restoration, since higher amounts will inhibit seedling establishment. The prompt emergence of most seedlings during the first vegetation period highlights the importance of creating optimal conditions for seedling establishment already in the early phase of vegetation development on restoration sites.