Population dynamics of volunteer oilseed rape (Brassica napus L.) affected by tillage

Volunteer plants of oilseed rape (Brassica napus L.) from persistent seeds in soil can affect subsequent crops. Apart from the agricultural disadvantages, the environment and the marketing of the seeds may also be affected, particularly if plants with special ingredients or genetically modified (gm) plants are grown. In order to investigate the influence of soil cultivation and genotype on seed persistence and gene flow via volunteers, a field experiment was set up testing four tillage treatments and two cultivars in a split-plot design. The cultivars tested were near-isogenic to two gm cultivars. To simulate harvesting losses, 10 000 seeds m⁻² were broadcast on a soil in July. The subsequent tillage treatments were combinations of immediate or delayed stubble tillage by a rotary tiller, primary tillage with plough or cultivator, or zero tillage. Over the following year, the fate of the seeds was determined. Immediate stubble tillage with following cultivator or plough resulted in 586 resp. 246 seeds m⁻² in the soil seed bank. After delayed stubble tillage with following plough, 76 seeds m⁻² were found, and no soil seed bank was built up in the zero tillage treatment. Nevertheless, in the zero tillage treatment, several robust volunteer plants survived the herbicide application before the direct drilling in autumn until following spring. In the zero tillage treatment and in the cultivator treatment, 0.19 volunteers m⁻² resp. 0.06 volunteers m⁻² flowered simultaneously to ordinarily sown oilseed rape in the following crop of winter wheat and produced 73 resp. 18 seeds m⁻². Delayed stubble tillage reduced the risk of gene escape via the soil seed bank, while zero tillage resulted in the highest risk of gene escape by pollen and by production of a new generation of seeds. In terms of a labelling threshold for gm food this number of seeds would be below the threshold of 0.9% of transgenic parts in conventially bred food or feed.     

Genetic variation for secondary seed dormancy and seed longevity in a set of black‐seeded European winter oilseed rape cultivars

Secondary seed dormancy in oilseed rape is a phenomenon that allows seeds to survive in the soil for many years without germination. Following soil cultivation, dormant seeds may germinate in subsequent years, and they are the main reason for the occurrence of volunteer oilseed rape plants in successive crops. Inheritance of secondary dormancy may be related to seed longevity (SL) in the soil. Genetic reduction in secondary dormancy and SL could provide a mean to reduce the frequency of volunteer plants and especially the dispersal of transgenic oilseed rape. The aim of the present study was to analyse secondary dormancy, germination rate and SL of 28 black‐seeded winter oilseed rape cultivars using in vitro laboratory tests. The material was tested in field experiments at six different locations in Germany in 2008/2009. Significant effects of the genotype and the location on all traits were found. Heritability was high for secondary dormancy (0.97) and moderate for germination rate (0.70) and SL (0.71). Results indicate that a selection for low secondary dormancy would be effective.     

Emergence and performance of volunteer oilseed rape (Brassica napus) in different crops

Volunteer oilseed rape (OSR, Brassica napus L.) causes various agronomic problems in crop rotations and can contribute to gene dispersal by pollen and by seed admixture. A 4-year field experiment (2008–2011) was set up in south-west Germany to investigate the performance of volunteers derived from two OSR cultivars with different levels of seed dormancy. Volunteers of a high-dormancy (HD) and a low-dormancy (LD) OSR cultivar were deliberately generated by spreading 10,000 seeds m⁻² on a field in August 2008 and 2009. Four different crops were grown on that area in the first year following the seed rain: winter wheat (Triticum aestivum L.), winter turnip rape (Brassica rapa L.), spring barley (Hordeum vulgare L.) and field pea (Pisum sativum L.). In the second year, maize (Zea mays L.) was sown uniformly across all plots. Numbers of OSR seedlings emerging in early autumn shortly after seed rain were not connected with the size of the soil seed bank in early spring of the following year. The seeds of the HD-cultivar formed a much greater soil seed bank (up to 14% of the initially spread seed number) compared with the LD-cultivar (up to 1.3%) in the soil layer of 0 to 30 cm in early spring 2009 and 2010). Across all crops, considerably more volunteers of the HD-cultivar than of the LD-cultivar were present at several survey dates in the first year following seed rain. The highest number of volunteers originated from the HD-cultivar with up to 11 volunteers m⁻² in winter turnip rape compared with a maximum of 0.48 plants m⁻² in the other crops. Cultivar-specific differences in volunteer density were observed as well in maize two years after OSR seed rain. Flowering and seed setting volunteers were only present in 2010 and the flowering time was crucially overlapping with that of sown winter OSR. The reproductive ability (seeds produced m⁻²) of the LD-volunteers was five times lower in winter turnip rape than of the HD-volunteer; a similar trend was observed for the OSR volunteers in the other host crops.Strategies to definitely reduce unwanted effects of OSR volunteers, such as gene flow, should include the use of LD-cultivars with a low potential to form a soil seed bank, particularly if selective herbicides are not available, for instance in broad-leaved crops, or if the volunteers are herbicide-tolerant.     

Photobiologische Unkrautregulierung annueller Ackerunkräuter

Photocontrol of weed germination of arable annual weeds Field studies were conducted to test the effect of light during soil tillage on the emergence of common weed species. Soil tillage was conducted at night or during daylight. In 20 out of a total of 23 field experiments, weed density after nighttime tillage was reduced compared to conventional daytime tillage. The average reduction of weed density attributable to photocontrol was 28.4 %. Results of field trials in the literature suggest that the emergence of Chenopodium album, Matricaria species and Stellaria media is especially reduced by nighttime tillage practices, but photocontrol had almost no effect on the emergence of Galium aparine and Polygonum convolvulus. The level of reduction of weed emergence after nighttime tillage was very variable. Important factors affecting this variation were: (1) the different light sensitivities of weed species, (2) the different light sensitivities of populations within one species, (3) the dormancy status of the seeds in a natural seed bank, and (4) the variation of light sensitivity of seeds.     

The effect of wheat straw residue on the emergence and early growth of sugar beet (Beta vulgaris) and oilseed rape (Brassica napus)

The management of straw residue can be a concern in non-inversion tillage systems where straw tends to be incorporated at shallow depths or left on the soil surface. This can lead to poor crop establishment because straw residue can impede or hinder crop emergence and growth. Small container-based experiments were undertaken using varying amounts of wheat straw residue either incorporated or placed on the soil surface. The effects on days to seedling emergence, percentage emergence, seedling dry-weight and soil temperature using sugar beet and oilseed rape were investigated because these crops often follow wheat in a cropping sequence.The position of the straw residue was found to be the primary factor in reducing crop emergence and growth. Increasing the amount of straw residue (from 3.3 t ha^?1 to 6.7 t ha^?1) did not show any consistent trends in reducing crop emergence or growth. However, in some instances, results indicated that an interaction between the position and the amount of straw residue occurred particularly when the straw and seed was placed on the soil surface. Straw placed on the soil surface significantly reduced mean day-time soil temperature by approximately 2.5 °C compared to no residue. When the seed and straw was placed on the soil surface a lack of seed-to-soil contact caused a reduction in emergence by approximately 30% because of the restriction in available moisture that limited the ability for seed imbibition. This trend was reversed when the seed was placed in the soil, but with straw residue still on the soil surface, because the surface straw was likely to reduce moisture evaporation and improved seed-to-soil contact that led to rapid emergence. In general, when straw was mixed in or placed on the soil surface along with the seed, sugar beet and oilseed rape emergence and early growth biomass was significantly restricted by approximately 50% compared to no residue.The consequences of placing seed with or near to straw residue have been shown to cause a restriction in crop establishment. In both oilseed rape and sugar beet, this could lead to a reduction in final crop densities, poor, uneven growth and potentially lower yields that could lower financial margins. Therefore, if farmers are planning to use non-inversion tillage methods for crop establishment, the management and removal of straw residue from near or above the seed is considered important for successful crop establishment.     

Induction of secondary dormancy in rape seeds (Brassica napus L.) by prolonged imbibition under conditions of water stress or oxygen deficiency in darkness

Prolonged imbibition under conditions of water stress or oxygen deficiency can lead to the induction of secondary dormancy in rape seeds. During imbibition in darkness seeds develop light sensitivity. The percentage of seeds not germinating in the dark depends on various factors prevailing during and after the stress treatment, as well as on the intrinsic susceptibility of the seeds to these factors.

In experiments on the effect of water stress it was found that the percentage of secondary dormant seeds could be increased in the range of 0–75%, by greater water suction and duration of imbibition of the seeds. Additionally, there were indications that increasing treatment temperature resulted in increasing percentages of dormant seeds. However, fewer secondary dormant seeds were produced when treatment temperature and test temperature differed greatly from each other.

Experiments on the effect of oxygen deficiency also revealed a positive effect of treatment duration. The general degree of dormancy induction, however, in this series of experiments was low. At 20 °C almost no dormancy induction was observed, whilst at 12 °C there were between 0 and 30% dormant seeds.

Genotypic differences previously assessed in model experiments with buried seeds were confirmed in both studies. Oilseed rape cultivars Bienvenu and Liglandor were shown to be able to build up high percentages of secondary dormant seeds, whereas cultivars Jet Neuf and Falcon had a rather low susceptibility towards the dormancy imposing factors tested. Cultivar Rubin was intermediate in response. There was often much variation between experiments with the same experimental design. The reasons for this are unclear.     

Plasticity of seed weight compensates reductions in seed number of oilseed rape in response to shading at flowering

Understanding the response of the number of seeds and seed weight to the availability of assimilates is crucial for designing breeding strategies aimed to increase seed and oil yield in oilseed rape. This study aims to answer the questions: i) do seed number and seed weight in oilseed rape differ in their plasticity in response to the availability of assimilates at flowering? and ii) how sensitive are oil and protein concentrations to the availability of assimilates during flowering?A spring oilseed rape hybrid was sown in two field experiments and the treatments were combinations of i) two plant densities and ii) shading or no shading between the beginning and end of flowering. Seed yield was not affected by plant density or by shading. Lower plant density was compensated by an increase in seed number per plant, without effects on single-seed weight. However, the negative effect of shading during flowering on seed number per area was fully compensated by an increase in single-seed weight by 47–61%. The plasticity of single-seed weight observed in the present study of oilseed rape has never been reported for annual seed crops. Shading at flowering increased both the seed filling rate and the duration of the seed filling period at all positions in the canopy. We also observed that the reduction of the source-sink ratio at flowering increasing seed weight does not necessarily modify oil or protein concentrations. Thus, single-seed weight could be targeted to increase seed yield in oilseed rape without compromising oil content.     

厚皮甜瓜‘翠雪5号’种子破休眠方法研究

厚皮甜瓜‘翠雪5号’新收获种子存在休眠现象,采用自动破休眠、高温、低温冷冻以及外源激素等处理进行种子萌发试验,以期找出破除‘翠雪5号’种子休眠、提高种子发芽率的方法。结果表明,‘翠雪5号’种子的休眠解除主要依赖于自动破休眠过程,高温处理可加速该过程。另外,低温冷冻以及外源NAA和GA₃处理不能破除‘翠雪5号’的种子休眠、提高萌发率,而外源6-BA可以在延长发芽时间的基础上显著促进种子萌发。     

Development and primary genetic analysis of a fertility temperature-sensitive polima cytoplasmic male sterility restorer in Brassica napus

Over the past decade, the polima cytoplasmic male sterility ( pol CMS) three-line and two-line systems have been developed for the production of hybrid seed in Brassica napus oilseed rape in China. The discovery of the novel pol CMS restorer line FL-204 is described here. It restores male fertility of hybrid plants in the pol CMS system, but hybrid seed production can only be carried out under autumn sowing in Wuhan in south China under moderate temperatures at flowering. The restorer cannot be used as a male for hybrid seed production in northwestern China (Gansu) under spring sowing conditions, because there it is more or less male sterile due to high temperatures at flowering. Because of this behaviour, it is referred to as a fertility temperature-sensitive restorer (FTSR) in this paper. F₂, BC₁ as well as double haploid populations were constructed to determine the inheritance of fertility restoration of FL-204 in the autumn at Wuhan and under spring sowing conditions at Gansu, respectively. Deviations from Mendelian genetics were observed. It was hypothesized that the change of fertility was the result of the interaction between nuclear genes [restoring gene ( Rf ) and temperature-sensitive genes ( ts )] and the cytoplasm. The Rf gene in FL-204 was incapable of restoring male fertility of pol CMS lines under spring sowing conditions at Gansu where it is inactivated by the recessive ts gene present in FL-204. However, the ts gene(s) could be non-functional under moderate temperature conditions at flowering at Wuhan which allows full expression of male fertility in FL-204. The recessive ts gene(s) can only be expressed in plants containing the pol sterile cytoplasm. A method for the utilization of the FTSR pol CMS restorer FL-204 for the production of hybrid seed in B. napus oilseed rape is proposed.     

不同耕作方式对旱区春谷根系发育、产量及水分利用效率的影响

不同耕作方式对旱区春播谷子根系的生长发育有极为重要的影响。以晋谷21号为材料,以传统旋耕为对照,研究了翻耕、秋季深松和春季深松3种耕作方式对谷子地下根系性状与垂直分布、产量和水分利用效率的影响。结果表明,3种耕作方式均能提高谷子根系的长度、表面积、体积、平均直径与干重,深松处理能使谷子根系向40~60cm土层有效生长。与传统旋耕相比,2个深松处理均能显著提高穗长和穗粒重,3种耕作方式的谷子产量较传统旋耕均显著提高,提高幅度排序为春季深松、秋季深松和翻耕,2个深松处理间产量差异未达显著水平。春季深松耕作方式替代传统旋耕能有效提高旱作春谷区的谷子生产水平。     

Effect of preceding crop combination and N fertilization on yield of six oil-seed rape cultivars (Brassica napus L.)

Information about the effect of the cropping history on the seed yield of oil-seed rape is extremely scarce. In 1992/93 and 1994/95, the effects of different preceding crop combinations (winter barley and winter wheat as preceding crops, oil-seed rape and wheat as pre-preceding crops) on the yield of six double low oil-seed rape cultivars were examined in a field trial at Hohenschulen Experimental Farm, north-west Germany. In addition, eight nitrogen treatments (different amounts and distribution patterns) were tested for their potential to reduce negative effects of the preceding crops. Following the cropping sequence of oil-seed rape then wheat, oil-seed rape yielded only 3.12 t ha⁻¹; after oil-seed rape then barley, the yield was 3.43 t ha⁻¹ compared with 3.77 t ha⁻¹ following wheat then barley and 3.71 t ha⁻¹ following wheat then wheat. The number of seeds per m² showed a similar pattern, whereas the thousand-seed weight partly compensated for the reduced seed number. It was highest if oil-seed rape was grown 2 years previously. The cultivars differed significantly in their yield potential. Express (3.79 t ha⁻¹) yielded 0.6 t ha⁻¹ more than Falcon (3.18 t ha⁻¹). Increasing amounts of fertilizer-N (80–200 kg N ha⁻¹) increased the seed yield from 3.21 t ha⁻¹ to 3.84 t ha⁻¹. Changes in the distribution pattern within one fertilizer amount had no effect on seed yield. In addition, no interactions between preceding crop combination and the different cultivars or N treatments occurred. It is concluded that crop management cannot totally eliminate the negative effects of an unfavourable cropping history on the seed yield of oil-seed rape.     

不同耕作方式对玉米田土壤微生物功能多样性的影响

为提高黑土土壤地力,对玉米秸秆还田和耕作方式进行筛选研究。以位于吉林省公主岭市的不同耕作方式试验为基础,设置3个秸秆还田耕作方式处理：秸秆粉碎深翻还田(CK),玉米高留茬宽窄行栽培+秸秆覆盖+快速腐解菌剂处理(KZF),秸秆粉碎深翻+快速腐解剂(SF)。利用Biolog生态板法,测定黑土玉米田土壤微生物功能多样性对不同耕作方式的响应。结果表明,随着培养时间的延长,不同耕作方式的AWCD值均显著增大。培养期内,AWCD的变化顺序为：KZF>SF>CK。培养144 h,KZF和SF处理的AWCD值显著高于对照CK。不同耕作方式之间多样性指数H、优势度指数D和均匀度指数E均未表现出显著差异。主成分分析表明,耕作方式显著影响了土壤微生物利用碳源的能力。碳水类、氨基酸类和羧酸类是研究区微生物利用的主要碳源。玉米高留茬宽窄行栽培+秸秆覆盖+快速腐解菌剂处理(KZF)和秸秆粉碎深翻+快速腐解剂(SF)有利于提高土壤微生物活性。     

Evolution of weed beet (Beta vulgaris L.) seed bank: Quantification of seed survival,dormancy, germination and pre-emergence growth

Weed beet is an important weed of sugar beet crops. Weed and cropped beets can cross easily and the management of weed beet is therefore crucial in the case of the advent of GM sugar beet, especially herbicide-tolerant cultivars, in order to ensure the co-existence of GM and non-GM crops and to avoid the appearance of herbicide-resistant weed beet. The inability of weed beet to compete in most other crops of the rotation makes the seed bank evolution a crucial stage of the life-cycle because in the rotation, sugar beet is at the most cultivated only every 3 years. The present study used seed burial experiments and laboratory analyses to characterise each step of the evolution of the weed beet seed bank and the external factors that could modify seed persistence in the soil. A monthly seed mortality of 10% was observed between October and December, while mortality was nil during the other seasons. Equations were then developed to describe the observed seasonal variations in seed survival. Seed dormancy also varied with season: the proportion of non-dormant seeds increased during winter (appearance of secondary dormancy) and decreased during the remaining seasons (loss of dormancy). In addition, the germinating seeds decreased with seed age and seed depth, while the presence of light stimulated germination. These observations were also translated into equations. Last, the pre-emergence hypocotyl growth and its variability were studied according to seed age, but no significant effect was observed. The results confirm the importance of the effects of cropping system on the evolution of the weed seed bank, especially the effect of soil tillage, which determines the date and conditions of seed burial, seed excavation and germination stimulation.     

Evaluation of environmental and management effects on Fusarium head blight infection and deoxynivalenol concentration in the grain of winter wheat

During the past decade European wheat (Triticum aestivum L.) crops were increasingly affected by Fusarium head blight (FHB) infection and high deoxynivalenol (DON) concentration in the grain. This is discussed to be primarily caused by the application of conservation tillage practices and, simultaneously, enhanced cultivation of host crops such as maize and wheat.

This study investigated the effect of several environmental and management factors on DON formation and, particularly, interactions between factors. Moreover, a methodology was developed to quantify the relative effect of single factors, and combinations of two or more management factors on the DON concentration in order to evaluate management strategies with regard to their potential effect on DON formation.

In 2001 and 2002, FHB infection of wheat and DON concentration in the grain was determined on eight sites of a long-term on-farm tillage experiment located in southern and eastern Germany. In addition, three-factorial plot trials varying tillage, cultivar, and fungicide application were conducted at Goettingen, Lower Saxony, in 2001 and 2002.

Based on these data, the severity of the effect of year, preceding crop, tillage, wheat cultivar and fungicide application was calculated as follows: mean DON value of the treatment with the highest DON concentration obtained in the study divided by the lowest treatment mean value. For each influencing factor the calculation was done on average of the other factors included. The following ranking order was obtained: annual variation of rainfall during wheat anthesis (4.4) = Fusarium infection/susceptibility of the preceding crop (wheat versus sugar beet, 4.3) = Fusarium susceptibility of the wheat cultivar grown (4.3–5.6) > soil tillage applied to cultivate wheat (1.3–3.4) ≥ fungicide application at anthesis of wheat (2.1). The relative effect of combinations of two or more management factors on the DON concentration can be calculated by multiplying severity factors. Limitations of this method are due to strong interactions between some of the factors (e.g. cultivar × fungicide application, cultivar × tillage). Within tillage treatments shallow mixing conservation tillage increased the DON concentration only slightly compared to conventional mouldboard ploughing, if previous wheat straw soil cover was reduced to about 30%. In this case, the severity of the effect of tillage was much smaller compared to year, preceding crop, and cultivar. Data also reveal that FHB infection values counted in the field do not give a reliable prediction of the DON concentration.

It is concluded, that choosing a resistant cultivar is a powerful tool to ensure a low DON concentration in wheat grain even under highly infectious conditions. This strategy enables farmers to make use of the benefits of conservation tillage and, simultaneously, produce high quality wheat grain.     

Seed yield, oil and phytate concentration in the seeds of two oilseed rape cultivars as affected by different phosphorus supply

A greenhouse pot experiment was conducted for studying seed and oil yield, P uptake and phytate concentration in the seed of two oilseed rape cultivars (Brassica napus L. var. Oleifera, cv. Bristol and cv. Lirajet), grown on a soil substrate at different levels of plant available phosphorus (6, 19, 31 and 106 mg P-CAL kg⁻¹ soil, resp.). All other nutrients were maintained at a high level. At maturity, seed yield and seed quality were investigated. An increase in the phosphorus soil supply resulted in a significant (P<0.05) increase in seed and oil yield, oil and P concentration of the seeds, and P transported to the seeds. The phytate-phosphorus concentration ranged from 0.5 to 6.9 g kg⁻¹ in the seeds and from 0.9 to 12.8 g kg⁻¹ in rapeseed meal. Insufficient P supply resulted in a reduced concentration of phosphorus and phytate in the seeds. Significant interactions between the factors cultivar and P supply were found for the traits seed yield, oil yield, and P-harvest index.     

增施磷素种肥对免耕直播油菜生长发育及产量的影响

为研究免耕直播条件下磷素种肥的用量和施用效果,给油菜免耕直播提供配套的施磷技术,在豫南油菜主产区设不施种肥和种肥施用量分别为15 kg/hm2、30 kg/hm2、45kg/hm2、60 kg/hm2的随机区组试验。结果显示,随着种肥用量的增加,油菜冬前苗势明显增强：苗高增加10.41%,根颈粗增加28.89%,单株叶面积增加22.29%;产量性状明显改善：一次分枝数由4.5个增加到6.8个,二次分枝数由2.4个增加到3.3个,单株角果数增加118.57%,角粒数增加18.29%;千粒重随种肥用量增加而降低,但在15 kg/hm2用量时显著高于对照。产量在一定范围内随种肥用量增加而提高。全生育期延长6d。试验证明,免耕直播油菜增施磷素种肥能够促进秋发冬壮,具有显著的增产效果。在土壤含磷量中等田块,磷素种肥用量以30kg/hm2为最优,产量增幅达51.78%。     

No-tillage and direct seeding for super hybrid rice production in rice–oilseed rape cropping system

No-tillage and direct seeding (NTDS) is an effective crop production method for reducing production costs and soil conservation. In order to understand performance of super hybrid rice under NTDS in rice–oilseed rape cropping system, a researcher-managed trail (2004–2010) and an on-farm research (2002–2005) were conducted to compare different tillage (conventional tillage or no-tillage) and rice establishment methods (transplanting or direct seeding) in super hybrid rice–oilseed rape cropping system. Under researcher-managed condition, grain yields of super hybrid rice under NTDS and conventional tillage and transplanting (CTTP) were equal. Compared with under CTTP, super hybrid rice under NTDS was characterized by more panicle number per m² but less spikelet number per panicle, and lower aboveground biomass production before heading but higher aboveground biomass accumulated during heading to maturity. Higher maximum tiller number per m² and lower spikelet production efficiency were responsible for the more panicle number per m² and less spikelet number per panicle under NTDS, respectively. Under farmer-managed condition, super hybrid rice under NTDS had more panicle number m² than under CTTP, which resulted in higher grain yield. Labor input under NTDS was lower than that under CTTP. Moreover, adoption of NTDS for super hybrid rice production had no significant impacts on seed yield and yield components of oilseed rape in rice–oilseed rape cropping system. Our study showed that CTTP could be replaced with NTDS to maintain yield and save labor for super hybrid rice production in rice–oilseed rape cropping system.     

AlomySys: Modelling black-grass (Alopecurus myosuroides Huds.) germination and emergence,in interaction with seed characteristics,tillage and soil climate: I. Construction

Models quantifying the effects of agricultural practices on weed emergence, in interaction with the soil, are necessary to evaluate and design cropping systems. In the present study, such a model was developed for black-grass (Alopecurus myosuroides Huds.), a harmful weed frequently found in rotations consisting mostly of winter crops. The model AlomySys was based on sub-models predicting (a) soil environment (climate, structure) resulting from the cropping system and weather, (b) vertical soil seed distribution after tillage, depending on the tool, the characteristics of the tillage implement and the soil structure; and (c) seed mortality, dormancy, germination and pre-emergent growth depending on soil environment, seed depth, characteristics and past history. Seed movements during tillage depend on the tool used, its characteristics, soil structure and on the initial position of the seed. Seed mortality increases with seed age; seed dormancy depends on seed age, seed depth, the conditions in which the seeds were produced and the past moisture and dryness conditions undergone by the seeds; germination is triggered by rain or tillage and driven by hydro-thermal time; pre-emergent shoot elongation depends on seed weight, on the conditions in which the seeds were produced and increases with thermal time; pre-emergent seedling mortality increases with soil dryness, clod size and seed depth. The sub-models were based either on existing models, or developed with literature data or additional experiments. Simulations were carried out to show how weed emergence can be reduced by adapting tillage mode and date to previous crop history.     

Seed germination in weedy Brassica campestris and its hybrids with B. napus: Implications for risk assessment of transgenic oilseed rape

We studied the germination behaviour of the following types of seeds: weedy Brassica campestris, oilseed rape (Brassica napus), B. campestris (♀) × B. napus (♂), B. napus (♀) × B. campestris (♂) and, finally, seeds harvested on B. napus (♀) × B. campestris (♂) hybrids in open pollination with B. campestris and B. napus. The seeds were germinated in Petri dishes, using three different consecutive treatments and assaying the viability of non-germinated seeds with tetrazolium staining. B. campestris seeds varied in the treatment they required in order to germinate and many seeds were dormant, in contrast to B. napus seeds, which lacked dormancy. B. campestris (♀) × B. napus (♂) and B. napus (♀) × B. campestris (♂) seeds both resembled B. napus being non-dormant whereas seeds harvested on B. napus (♀) × B. campestris (♂) hybrids were more B. campestris-like in germination behaviour. We discuss implications for risk of transgene spread from oilseed rape to weedy B. campestris. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of Fungicide on Grain Yield of Barley Grown in Different Cropping Systems

The effect of fungicides and their combination on yield of barley under different nitrogen, slurry and tillage treatments was investigated at Hohenschulen Experimental Station near Kiel, Germany in 1991–97. Various fungicide treatments (no fungicide, and treatment with stem, leaf and ear fungicides and combinations of these), two nitrogen levels (120 and 240 kg N ha⁻¹), two tillage systems (minimum and conventional tillage) and four slurry applications (no application, and autumn, spring and autumn plus spring applications) were used. On average, fungicide application increased barley yield by 1.1 t ha⁻¹. The fungicide treatments could be classified into four types: (1) fungicides against stem diseases, which slightly increased yield by 0.25 t ha⁻¹, very similar to the results for the untreated control; (2) leaf fungicides and ear fungicides applied separately, and fungicides against a combination of stem and leaf diseases, which increased yield by 1.0 t ha⁻¹ on average; (3) fungicides against a combination of ear and stem diseases, which increased the yield by 1.22 t ha⁻¹, and (4) fungicides against a combination of leaf and ear diseases and a combination of stem, leaf and ear diseases, which increased yield by 1.59 t ha⁻¹ on average. The effects of fungicide on the yield were modified by crop husbandry. It can be concluded that application of fungicides against a combination of leaf and ear diseases could increase barley yield and reduce yield variation.