Association of growth dynamics, yield components and seed quality in long-term trials covering rapeseed cultivation history at high latitudes

Brassica oilseed yield trend has declined in Finland by over 20% during the last 15 years. Improved genetic yield potential of turnip rape (B. rapa L.) and oilseed rape (B. napus L.) can be better realised with increased understanding of yield determining processes under northernmost growing conditions. This study aimed at (1) determining the genetic improvements in seed yield, yield components, quality traits and duration of the main growth phases and (2) comparing all these traits in turnip rape and oilseed rape. This work is based on the dataset from long-term Official Variety Trials (1976–2006), covering the entire historically relevant period of rapeseed cultivation in Finland. The results indicated that number of seeds per square metre dominated production of high yields, while single seed weight was not correlated with yield. Over the years, seed yields were produced with very different combinations of seed numbers and weights, differing markedly between the two crops. While high seed numbers were required for production of superior seed yields, single seed weights were not particularly high. Environmental variation markedly affected seed yield, seed number per square metre and duration of flowering compared with its effect on single seed weight. Duration of flowering was, however, negatively associated with seed number. Even though seed weight was largely determined by genotype, no marked plant breeding improvements were identified, contrary to those in number of seeds per square metre, seed yield, oil content and oil yield. For oilseed rape the increase in seed yield (41%) was far higher than for turnip rape (19%) without being associated with a longer seed-filling phase and later ripening, but rather the contrary.     

选育高含油量双低油菜品种的理论与实践

含油量作为油菜生产最终目标性状产油量的组成因素,与油菜生产效益的提高息息相关。在目前我国 油菜产量水平已得到相当程度提高的前提下,培育高含油量油菜品种是进一步发展油菜产业的必由之路。根据油 菜含油量的遗传特点,结合培育高含油量杂交油菜品种中油杂8号和中油杂11的体会,提出了除了利用黄籽以 外,培育大粒和适宜植株形态性状的品种也是提高油菜含油量的重要途径。初步构建了高含油量油菜品种的形态 组成,并基于近年来参加和通过国家区域试验的冬油菜品种含油量变化情况,展望了我国高含油量油菜育种的发 展前景。     

受控环境下光周期对小麦生长发育、产量及营养品质的影响

为探讨受控生态生保系统(CELSS)中利用光周期调控提高植物能量利用效率的可能性,以红蓝LED(90%红+10%蓝)为光源,在开花前及开花后各设置12、16、20和24h四个光周期水平,形成16个处理,研究光周期对小麦生长发育、产量和营养品质的影响。结果表明,开花前光周期延长使小麦开花时间显著提前,特别是导致出苗到拔节和拔节到抽穗的天数显著减少。开花后光周期延长会缩短开花到成熟的时间,且开花前和开花后光周期对小麦生育期长度的影响相互独立。在开花前,短光周期有利于小麦营养器官的构建,增加株高、分蘖数、叶片数和营养器官干重,进而提高籽粒产量、收获指数和能效比。在开花后,长光周期提高了灌浆期叶片光合速率,促进籽粒中干物质积累,提高籽粒产量、收获指数和能效比。开花前短光周期的增产作用主要是因穗数和穗粒数增加,而开花后长光周期的增产作用主要是因粒重增加。在开花前后,延长光周期均导致籽粒淀粉含量增加和蛋白质含量减少。在开花前12h光照、开花后24h光照的处理下小麦产量和能量利用效率均最高,说明开花前短光周期结合开花后长光周期最有利于小麦高产和能量高效利用。     

Duration of vegetative and generative development phases in oat cultivars released since 1921

Genetic yield improvements in oat (Avena sativa L.) cultivars grown at high latitudes have resulted from marked changes in harvest index and yield components. This study was designed to investigate whether such changes have entailed alterations in duration of different developmental phases: vegetative, generative and grain filling phases and pre-anthesis generative sub-phases such as pre-fertile, pre-abortion, fertile pre-abortion, fertile and abortion sub-phases. We tested 14 oat cultivars released between 1921 and 1988 and 6 breeding lines. Ten randomly sampled plants of each oat entry were collected every 3–4 d (18 times) from seedling emergence until pollination, and apical developmental stages were determined on the most advanced spikelet. Cumulated degree-days (Cdd) for each critical developmental stage and component phases were determined (5 °C as a base temperature). At each measurement the number of leaves, green leaves and tillers on main shoot, apex length (mm) and height to the uppermost node, and stipule (cm) were recorded. Phyllochron (°C d leaf⁻¹) and relative elongation rates (RER) for height characterising traits were calculated. Grain filling was the only period altered by breeding, while no consistent effects on duration of vegetative and generative pre-anthesis phases and sub-phases were detected. Different developmental phases were interrelated: in some cases cultivars with similar duration of pre-anthesis phase, however, differed in duration of some pre-anthesis sub-phases. Their duration was not, however, consistently associated with measured growth and yield parameters. Likely long days that make the northern growing conditions exceptional and unique, substantially narrowed the differences among oat entries in duration of different developmental phases, thereby making their role also less critical in yield determination contrary to the situation in the main global temperate cereal production regions.     

Maximizing oilseed rape's yield by glyphosate under Mediterranean conditions

Adverse hot and dry environmental conditions prevailing during the period of oilseed rape ripening can be blamed for considerable yield losses during the crop's mechanized harvesting in the Mediterranean area. In this paper, the effect of chemical dessication of oilseed rape with glyphosate applied 35 days after anthesis for reducing seed yield loss was studied. The experiment was conducted in four fields at two locations in central Greece and for two growth periods following a completely randomized plot design with 8 treatments in three replications. Treatments include all possible combinations of two crop varieties and four levels of glyphosate (as dessicant) application. A significant positive effect of dessicant application level on crop yield for both studied varieties was found. The application dose of 200 g a.i. of glyphosate per hectare had the best results. The highest dry weight was found among the plants sprayed with 200 g. a.i. of glyphosate per hectare. The highest seed yield and oil yield were found among the plants sprayed with 200 g a.i. per hectare, which makes clear the positive effect of this spraying minimizing pod shattering and yield losses. The greatest 1000-seed weight was found among the plants sprayed with 200 g a.i. ha⁻¹, due to the greater size of seeds that remained on the plants until harvesting.     

Variability of duration of pre-anthesis phases as a strategy for increasing wheat grain yield

In wheat, stem elongation phase (SEP) duration is critical for grain number (GN) per unit of area determination, as it is the phase in which the spikes grow. Lengthening SEP, for instance by photoperiodic sensitivity, without altering the cycle to anthesis (AT) has been proposed as an alternative way to increase spike dry weight, and in turn GN. As most works supporting this idea have modified only SEP by artificial manipulation (e.g. photoperiod extensions), it is relevant to evaluate this hypothesis in populations segregating for this attribute in natural conditions. The aim of this work was to analyse the variability in SEP duration relative to AT in two F4 populations; in order to select contrasting phenotypes to evaluate the impact of this attribute on grain yield components and to analyse the selection response of this attribute. These segregating populations (Las Rosas INTA × Triguero 230 (A) and Klein Estrella × ProINTA B. Alazán (B)) were derived from parental lines with similar flowering time but different relative duration of their pre-anthesis phases. Two field experiments with previous vernalization treatment in cool chamber were carried out. In 2006, F4 populations were characterized and from one of them (population B, which presented higher variability) four groups were selected, which presented contrasting phenotypes in the attribute under study. Progenies of these groups (F5), together with remnant F4 full-sib of each one, were studied during 2007. Grain yield per plant was higher, due to GN increases, when duration of the SEP was lengthened. However, selection response to longer SEP with similar cycle to AT could not be found, possibly as the result of a high environmental influence on this attribute. The phenotypic variability evidenced in this attribute was not clearly associated with major adaptation genes evaluated (i.e. Ppd and/or Vrn), suggesting that other minor genes could be associated.     

苗期渍水对直播冬油菜产量和农学利用率的影响及油菜在不同氮肥施用下的响应

在轻简化施肥背景下，为减少渍害损失，解决长江流域冬油菜产区生产面临的重要问题，开展氮肥施用 对油菜渍害的缓解作用研究。设置三因素田间试验，分别为不同氮肥用量（0、60、120、180、240和300 kg N/hm2）、氮 肥类型（油菜专用控释尿素和普通尿素）和水分处理（苗期渍水和正常排水），测定各处理产量和氮肥农学利用率， 明确苗期渍水对不同氮素供应水平油菜的影响，并比较油菜专用控释尿素一次性施用和普通尿素分次施用下油菜 对苗期渍水的响应。结果表明，直播冬油菜产量随氮肥施用量增加而提高，至240 kg N/hm2时不再增加。油菜专用 控释尿素一次性施用，在氮肥用量为60～180 kg N/hm2时产量高于普通尿素分次施用；在氮肥用量为240～300 kg N/hm2时，两种氮肥类型产量基本相当。氮肥施用通过增加收获密度、单株角果数和每角粒数提高产量。苗期渍水 导致直播冬油菜产量损失1.1%～41.9%，随氮肥用量增加，渍水引起的产量损失率呈先增加后降低趋势。0～60 kg N/hm2处理时，渍水使收获密度显著降低（降幅达29.4%~45.0%），单株角果数增加；施氮量为120~180 kg N/hm2时， 渍水导致收获密度和单株角果数分别降低19.5%~33.7%和1.4%~17.7%；施氮高于180 kg N/hm2时，收获密度和单 株角果数降幅减小（降幅分别为5%~30.9%和3.6%~9.5%）。普通尿素分次施用和油菜专用控释尿素一次性施用， 分别在施氮量为120和180 kg N/hm2时产量损失率最高，分别达29.8%和41.9%。相同氮肥用量下油菜专用控释尿 素一次性施用的产量损失率大于普通尿素分次施用。渍水显著降低氮肥农学利用率，降幅为8.4%～51.9%，施氮充 足（240～300 kg N/hm2）时氮肥农学利用率降幅低于氮素用量较低处理（120～180 kg N/hm2），油菜专用控释尿素一 次施用处理的农学利用率平均降幅（36.5%）高于普通尿素分次施用（17.3%）。综上可知，苗期渍水时，油菜专用控 释尿素一次施用，会加重油菜受渍影响；土壤氮素供应能力较低时，渍害逆境解除后，适量追施速效氮肥可有效缓 解产量损失，实现油菜稳产。     

油菜用地养地的作物优势及其在冬闲田开发中的应用潜力

油菜是我国种植面积最大的油料作物,是国产食用植物油的重要来源。油菜生长过程可以优化土壤结构、增加土壤养分、培肥土壤地力,具有用地养地的特征优势。同时,因其具有较强的环境适应能力,可作为先锋作物改良障碍土壤。然而,近年来由于劳动力不足、种植效益低、农民种植积极性不高等因素,导致冬闲田面积逐年增加,冬季光温水土自然资源未能得到有效利用。而油菜作为冬季种植的油料作物,不与粮争地,是开发利用冬闲田最有潜力的作物。利用冬闲田发展油菜生产,不仅可以提升油料产量,还可以充分发挥其养地优势提高后茬作物产量品质、增加种植收益,对维护我国食用油供给安全、助力粮油兼丰及农业绿色可持续发展具有重要意义。本文结合我国油菜生产现状,针对南方稻区冬闲田油菜轮作的生产发展需要,综述了油菜用地养地（油用或肥用）的作物优势,旨在为因地制宜利用南方冬闲田发展油菜生产助力油料产能提升提供科学依据。     

我国三熟制早熟油菜品种产量构成特点及育种对策

为提高三熟制地区油菜育种效率,本文研究了三熟制地区不同熟性油菜农艺性状对产量的影响。以2016-2020国家冬油菜品种区试中衡阳和宜春地区试验结果为基础数据,利用相关分析及通径分析研究了两个区域的油菜品种产量构成特点。结果发现,中熟组和早熟组株高、有效分枝数、菌核病发病率、病情指数、单株有效角果数、每角粒数、千粒重、密度、全生育期、含油量及产量差异显著。中熟油菜每角粒数、密度、菌核病抗性与产量呈极显著正相关,菌核病发病率、病情指数、生育期与产量极显著负相关,密度对产量的直接影响最大。早熟油菜株高、有效分枝数、单株有效角果数、每角粒数、密度、含油量与产量极显著正相关,菌核病发病率与产量显著负相关;对产量直接影响最大的是有效分枝数。认为育种策略中,两种油菜都应选育抗菌核病和适合高密度种植的品种,中熟油菜应提高单株有效角果数,而早熟油菜要增加有效分枝数。     

Factors that determine grain weight in rice under high-yielding aerobic culture: The importance of husk size

In water-saving rice culture, yield is unstable because spikelet number per unit area and grain weight fluctuate according to water availability. In this study, we investigated the factors that determine grain weight in aerobic culture. We grew four rice varieties in non-puddled, unsaturated (aerobic) soils with a soil water potential at 20-cm depth kept above −60 kPa and in continuously flooded culture in two years. We found a significant variety × water interaction in grain weight in 2009: weights under aerobic culture were 6% and 13% larger than under flooded culture in Sasanishiki and IRAT109, respectively, versus 4% and 10% smaller in Habataki and Takanari. There was no significant variety × water interaction in grain weight in 2010. Sink activity (grain sucrose synthase activity) and source capacity (biomass production and nonstructural carbohydrate content in vegetative tissue) per plant during ripening were higher under aerobic culture than under flooded culture in both years. However, an excessive increase in spikelet number per unit area in Takanari under aerobic culture in 2009 reduced the source capacity per spikelet and single husk size, decreasing grain weight. In 2010, frequent soil drying under aerobic culture during the late reproductive period (around 20 days preceding heading) reduced single husk size, thereby decreasing grain weight. We found that sink activity and source capacity per plant could be both higher under aerobic culture during the ripening period, producing larger grain weight at a soil water potential above-40 kPa at a 20-cm depth relative to those under flooded culture. In contrast, greater drying under aerobic culture during the late reproductive period reduced single husk size, thereby reducing grain weight.     

Biomass allocation patterns and reproductive output of four Oenothera L. accessions native to Argentina

Evening primrose (Oenothera spp.) has the potential to become an alternative oilseed crop in Patagonia, Argentina. This paper describes and compares phenology and allocation patterns of four wild accessions of Oenothera grown in a common garden, under non-limiting conditions. Our objective was to identify useful traits to shorten the domestication process. Accessions differed in the duration of the vegetative growth phase, which was negatively correlated to seed production per plant (reproductive output). Fruit set ranged between 70% and 95%, and did not differ among accessions. Differences found in the rate of capsule production did not explain the observed disparity in the number of fruits per plant. Reproductive output was mainly affected by the number of fruits per plant, vegetative biomass, and the proportion between seeds and total biomass (reproductive effort). Individual seed mass did not affect total seed production per plant. Seed-oil content was similar to that of domesticated species of evening primrose, but the content of gamma-linolenic acid was far too low (<2%) in comparison to the minimum acceptable standard necessary for seed commercialization (9%). Oenothera wild accessions are prone to seed losses by shattering. We concluded that short vegetative growth phase and high vegetative biomass would be useful traits for selection in breeding programs. Fruit shattering and low gamma-linolenic acid content are the main drawbacks that should be overcome to facilitate the domestication of one of these wild accessions.     

New winter oilseed rape varieties – seed quality and morphological traits depending on sowing date and rate

Many studies have focused on research about impact of time and density of sowing on the agronomic characteristics of different crops. However, the number of studies investigating such a response on the qualitative composition of different types of winter oilseed rape varieties is still limited. The aim of the research was to determine the effect of sowing date and density on yield, protein and oil content and quality of winter oilseed rape varieties: open-pollinated, a typical hybrid of traditional type of growth and a new semi-dwarf hybrid, which biology and yielding have not been thoroughly established. This experiment was conducted applying four sowing dates (August 14, August 25, September 4, September 15), three winter oilseed rape cultivars (PR45D03 -semi-dwarf hybrid, PR46W31 – hybrid, Californium – open-pollinated) and four sowing rates (30, 40, 50, 60 seeds/m²). Among the compared sowing dates, August 25 proved to be optimal for yielding of the tested winter oilseed rape cultivars. Semi-dwarf variety contained less protein and glucosinolate in seeds, but more oil in comparison to other studied varieties (hybrid and open-pollinated). The yields did not differ significantly within a density of 40, 50, 60 seeds/m², so it is important result, especially for the agricultural practice.     

Agronomic traits contributing to nitrogen efficiency of winter oilseed rape cultivars

Reducing the high nitrogen (N) balance surpluses occurring in oilseed rape production through the cultivation of N-efficient cultivars is imperative for environmental reasons. In this study, seed yield and N efficiency parameters of oilseed rape cultivars grown under three N rates were investigated in field experiments performed during five years. Seed yields differed significantly among cultivars especially at limiting N supply, with significant shifts in cultivar ranking according to the N level. At high N supply, cultivar differences relied more on year effects. The importance of N efficiency parameters for yield varied owing to year and N rate effects. N uptake was an important parameter for yield at all N rates. While at low N, the duration of N uptake was most decisive, shoot N uptake capacity during vegetative growth was relatively more important under high N conditions. N utilization efficiency became more important with increasing N supply. At high N supply, cultivars with low seed N concentrations were superior in yield. Harvest index was also significantly correlated to yield across N rates; however, its importance depended much on environmental conditions. In conclusion, the specification of plant traits that might contribute to enhanced N efficiency in oilseed rape will depend very much on the N supply of the target environment and the target yield level.     

Contrasting Ppd alleles in wheat: effects on sensitivity to photoperiod in different phases

Photoperiod sensitivity is an important feature of flowering time regulation, which enables wheat plants to adapt to a wide range of environments. Although some work has been done on how time to heading or flowering respond to photoperiod in relation to particular Ppd alleles, there is little evidence on whether these alleles contribute to responses at different phases and to associated yield component generation. The aims of this paper were: (i) to analyse the effects of photoperiod on substitution lines with contrasting Ppd alleles, in terms of duration of particular phases, (ii) to determine if there is any relationship between these alleles and the parameters of photoperiod response (photoperiod sensitivity, optimum photoperiod and basic length of the phase), and (iii) to analyse the effects of different photoperiods applied before and after the onset of terminal spikelet on yield component generation. The effects of length and timing of photoperiod extensions on these traits were analysed under field conditions in Chinese Spring and two substitution lines differing in photoperiod sensitivity.Although time to anthesis was similar in the three genotypes in photoperiods longer than 14.5 h, they did differ in their response to photoperiod in particular phases. Sensitivity to photoperiod for daylengths shorter than 14.5 h was also markedly different. The number of leaves generated was affected by photoperiod, determining the duration of the phase from emergence to floral initiation (EM-FI). The length of the phase from floral initiation to terminal spikelet (FI-TS) was determined by the number of spikelets generated and their rate of initiation, which was also affected by photoperiod. The terminal spikelet to anthesis phase (TS-ANT) was only affected by photoperiod in the most sensitive genotype, in which direct photoperiod effects, other than the effects on leaf number and phyllochron, were evident. There was no apparent relation between photoperiod response parameters such as basic length of the phase (Lb) and optimum photoperiod (Po) and particular Ppd alleles.     

高密度直播油菜氮磷钾肥推荐用量及影响因素

针对我国目前油菜生产上施肥过量与不足并存,肥料利用率低的问题,运用“3414”试验方案进行一年多点田间试验,研究了高密度(375 000株/hm2)直播油菜氮磷钾肥的适宜用量。结果表明,氮磷钾肥不同用量显著影响油菜籽粒产量,通过建立施肥与产量间的效应函数方程,得出供试条件下油菜氮磷钾肥推荐施用量,桂林试验点油菜产量2 416.3kg/hm2,施用量为N 118.5 kg/hm2、P2O5 36.5kg/hm2、K2O 60.6 kg/hm2;枝江试验点油菜产量3 095.1kg/hm2,施用量为N 176.3 kg/hm2、P2O5 73.0kg/hm2、K2O 100.6 kg/hm2;玉龙试验点油菜产量4 474.3kg/hm2,施用量为N 256.7 kg/hm2、P2O5 88.1kg/hm2、K2O 137.7 kg/hm2。结论认为不同地理区域和不同油菜品种在该区域生长发育的生态学特征,以及肥料的边际利润率、肥料和产品价格是油菜推荐施肥的重要依据,不能简单依据供试土壤基础肥力进行油菜推荐施肥。 [     

Determinants of barley grain yield in a wide range of Mediterranean environments

Barley grain yield in rainfed Mediterranean regions can be largely influenced by terminal drought events. In this study the ecophysiological performance of the ‘Nure’ (winter) × ‘Tremois’ (spring) barley mapping population (118 Doubled Haploids, DHs) was evaluated in a multi-environment trial of eighteen site–year combinations across the Mediterranean Basin during two consecutive harvest years (2004 and 2005). Mean grain yield of sites ranged from 0.07 to 5.43 t ha⁻¹, clearly dependent upon both the total water input (rainfall plus irrigation) and the water stress index (WSI) accumulated during the growing season. All DHs were characterized for possessing molecular marker alleles tagging four genes that regulate barley cycle, i.e. Vrn-H1, Vrn-H2, Ppd-H2 and Eam6. Grain yield differences were initially interpreted in terms of mean differences between genotypes (G), environments (E), and for each combination of genotype and environment (GE) through a “full interaction” ANOVA model. Variance components estimates clearly showed the greater importance of GE over G, although both were much lower than E. Alternative linear and bilinear models of increasing complexity were used to describe GE. A linear model fitting allelic variation at the four genes explained genotype main effect and genotype × environment interaction much better than growth habit itself. Adaptation was primarily driven by the allelic constitution at three out of the four segregating major genes, i.e. Vrn-H1, Ppd-H2 and Eam6. In fact, the three genes together explained 47.2% of G and 26.3% of GE sum of squares. Grain yield performance was more determined by the number of grains per unit area than by the grain weight (phenotypic correlation across all genotypic values: r = 0.948 and 0.559, respectively). The inter-relationships among a series of characters defining grain yield and its components were also explored as a function of the length of the different barley developmental phases, i.e. vegetative, reproductive, and grain filling stages. In most environments, the best performing (adapted) genotypes were those with faster development until early occurrence of anthesis. This confirmed the crucial role of the period defining the number of grains per unit area in grain yield determination under Mediterranean environments.     

玉米P群自交系的生物学特征特性评价

与温带骨干系相比,P群自交系苗期叶色、叶鞘特征特性明显,株型缺乏紧凑类型,生育期偏晚,单株产量低,抗性强,子粒百粒重和容重较高。P群自交系的光敏感反应主要表现在与营养生长相关的几个性状上,如株高、穗位和雄穗分枝数等。在生殖生长性状上光敏感反应比较迟钝。在温带玉米区适应性较好。但是一些P群自交系如沈137、齐319、1127等各项指标光周期敏感仍反应强烈。     

Growth,PAR use efficiency,and yield components of field-grown Vicia faba L. under different temperature and photoperiod regimes

N-fixing legume crops may be a good component of a general plan to improve cropping system efficiency. For this purpose, crop suitability to specific environments must be established. To estimate the yield potential we examined the growth and yield response of faba bean (Vicia faba L.) crops to different thermal and photoperiod regimes. Irrigated field experiments were conducted in northwest Spain for 3 years (2004–2007) with cv. ‘Alameda’ sown on five different dates in each year from mid-autumn to mid-spring. Environmental conditions experienced by plants across sowing dates were largely different. Sowing date had a great influence on biomass, grain yield and its components. This effect was associated with changes in PAR captured, PAR use efficiency (PUE) and biomass allocation to the different organs. Critical leaf area index (LAI_cr) tended to increase and the extinction coefficient, k, to decrease as the sowing date was delayed. Earlier sowing dates intercepted more radiation over the whole season than the spring sowing dates. Greatest crop growth treatments (2nd and 3rd sowing dates) had the highest values of PAR use efficiency probably due to more adequate temperatures for photosynthesis and a large number of reproductive sinks. The highest grain yield (7733 kg ha⁻¹) was obtained with the mid-February sowing date, which produced the most pods and seeds per m², the largest harvest index (62.0%), and large maximum leaf area index (5.41). Low yields of mid-autumn (1st) and mid-spring (5th) sowing dates were associated with reduced pods and seeds per m². Temperature and photoperiod had a large impact on faba bean growth, development, and yield. Best yields were obtained when abundant assimilate supply and moderate temperatures were available during pod set.     

Effect of trifluralin,pronamide, haloxyfop-p methyl,propaquizafop, and isoxaben on weed control and oilseed rape yield in Iran

In order to investigate the effect of trifluralin, pronamide, haloxyfop-p methyl, propaquizafop and isoxaben on weed control and oilseed rape yield, a two year field experiment was conducted at Darab, Iran, during 2004–2005 and 2005–2006 growing seasons. Herbicides reduced weed biomass compared with the weedy check. In 2004–2005, at 16 WAP (weeks after planting), application of trifluralin plus propaquizafop plus isoxaben at 1200 + 200 + 250 g a.i./ha and trifluralin plus haloxyfop-p methyl plus isoxaben at 1200 + 100 + 500 g a.i./ha provided best control (80%) of wild mustard (Sinapis arvensis L.), compared to other treatments. At 8 and 16 WAP, wild mustard control decreased to 47 and 42%, respectively, when trifluralin was applied alone at 1400 g a.i./ha. In 2005–2006 at 16 WAP, maximum reduction in wild mustard biomass (82%) was achieved with trifluralin plus propaquizafop plus isoxaben at 1200 + 200 + 250 g a.i./ha. In both years, all herbicide treatments controlled fumitory (Fumaria officinalis L.) 64–96%. In 2004–2005, at 16 WAP, wild oat (Avena fatua L.) biomass reduction by trifluralin plus propaquizafop plus isoxaben at 1200 + 200 + 250 g a.i./ha was 95%. In 2005–2006, at 8 and 16 WAP, minimum biomass reduction of wild oat (37–53%) was observed with trifluralin at 1200 and 1400 g a.i./ha. In both years, at 8 and 16 WAP, the most effective herbicide treatments were trifluralin plus propaquizafop plus isoxaben and trifluralin plus haloxyfop-p methyl plus isoxaben regardless of the dose applied and provided maximum reduction in total weed biomass (77–89%) compared to other treatments. Results of both years showed that all herbicide treatments increased oilseed rape grain yield as compared with the weedy check but percentage of oil was not affected by various herbicide treatments. Maximum grain yield was obtained with trifluralin plus haloxyfop-p methyl plus isoxaben at 1200 + 100 + 500 g a.i./ha.     

Effect of winter cover crop species and planting methods on maize yield and N availability under irrigated Mediterranean conditions

Under semiarid Mediterranean conditions irrigated maize has been associated to diffuse nitrate pollution of surface and groundwater. Cover crops grown during winter combined with reduced N fertilization to maize could reduce N leaching risks while maintaining maize productivity. A field experiment was conducted testing two different cover crop planting methods (direct seeding versus seeding after conventional tillage operations) and four different cover crops species (barley, oilseed rape, winter rape, and common vetch), and a control (bare soil). The experiment started in November 2006 after a maize crop fertilized with 300 kg N ha⁻¹ and included two complete cover crop-maize rotations. Maize was fertilized with 300 kg N ha⁻¹ at the control treatment, and this amount was reduced to 250 kg N ha⁻¹ in maize after a cover crop. Direct seeding of the cover crops allowed earlier planting dates than seeding after conventional tillage, producing greater cover crop biomass and N uptake of all species in the first year. In the following year, direct seeding did not increase cover crop biomass due to a poorer plant establishment. Barley produced more biomass than the other species but its N concentration was much lower than in the other cover crops, resulting in higher C:N ratio (>26). Cover crops reduced the N leaching risks as soil N content in spring and at maize harvest was reduced compared to the control treatment. Maize yield was reduced by 4 Mg ha⁻¹ after barley in 2007 and by 1 Mg ha⁻¹ after barley and oilseed rape in 2008. The maize yield reduction was due to an N deficiency caused by insufficient N mineralization from the cover crops due to a high C:N ratio (barley) or low biomass N content (oilseed rape) and/or lack of synchronization with maize N uptake. Indirect chlorophyll measurements in maize leaves were useful to detect N deficiency in maize after cover crops. The use of vetch, winter rape and oilseed rape cover crops combined with a reduced N fertilization to maize was efficient for reducing N leaching risks while maintaining maize productivity. However, the reduction of maize yield after barley makes difficult its use as cover crop.