施氮方式对强筋小麦济南17产量和品质的影响

以优质强筋小麦济南17为材料，研究氮肥不同施用量、基追比和追氮时期对小麦籽粒产量和品质的影响，分析了产量与品质的关系。结果表明：适当地增加施氮量和拔节期追氮比例可显著地提高产量，籽粒蛋白质含量和干、湿面筋含量与产量同步增加；施氮量和拔节期追氮比例超过一定值时再增加施氮量和拔节期追氮比例，籽粒蛋白质含量和干、湿面筋含量继续增加，而产量则显著下降；延迟追氮时期可使籽粒蛋白质含量和干、湿面筋含量有较大幅度地提高，但对产量形成不利。以施氮量为262．5～328．1kg／hm^2且基追比为4：6或5：5，拔节和始花两次追肥的施氮方式，强筋小麦济南17能较好地实现优质与高产的统一。     

主要栽培措施对中筋小麦皖麦44产量和品质的影响

为了给中筋小麦——皖麦44优化栽培提供参考，以此品种为试验材料，研究了播期、密度以及氮肥应用对其产量和品质的调节效应。结果表明．施氮量在0～300kg／hm^2范围内，氮素与籽粒产量呈二次曲线关系，与蛋白质含量、湿面筋含量、沉淀值、面粉吸水率、面团形成时间、稳定时间和粉质质量数等呈极显著正相关，与弱化度呈极显著负相关。增施氮素能显著提高蛋白质含量、湿面筋含量、沉淀值和粉质评价值，降低弱化度，延长面团的形成时间和稳定时间。氮肥全部基施和返青追肥产量和品质指标都较低；在拔节期施肥可有效地提高产量，并促进品质改善；在抽穗期施肥能改善粉质性状。皖麦44在淮北地区中等肥力地块的适宜施氮量为150～225kg／hm^2，在施足基肥的基础上，追施拔节肥效果更佳。播期和密度对皖麦44的产量有显著影响，对品质作用不明显。     

氮素运筹对弱筋小麦扬麦9号产量、品质和旗叶衰老特性的影响

为了解弱筋小麦植株衰老特性与籽粒产量及品质形成的关系,选用弱筋小麦扬麦9号,设置不同的氮肥处理,测定和分析了植株生育后期旗叶光合特性和衰老特性及品质指标.结果表明,低氮(180 kg/ha)和高氮(240 kg/ha)在氮肥比例[基肥∶壮蘖肥(5叶期施)∶拔节肥(倒3叶施)∶孕穗肥(倒1.5叶施)]为7∶1∶2∶0时的两处理生产的籽粒品质均符合国标(GB/T 17893-1999).施氮量180 kg/ha、氮肥比例5∶1∶2∶2处理植株生育后期净光合速率、Rubisco含量、SPAD值、POD和SOD酶活性在品质符合国标的处理中最高,旗叶蔗糖含量高,籽粒转化蔗糖能力强,产量最高;施氮量240 kg/ha、氮肥运筹5∶1∶2∶2处理,虽然有效延缓了植株衰老,产量最高,但籽粒品质不符合国标.说明弱筋小麦扬麦9号后期衰老速率快虽有利于降低籽粒蛋白质和湿面筋含量,但不利于产量提高;延缓衰老虽有利于产量提高,但易致品质下降.本试验条件下,弱筋小麦扬麦9号采用施氮量180 kg/ha、氮肥运筹5∶1∶2∶2的栽培方式,后期衰老速率适度,有利于品质改善,产量亦较高.     

氮肥运筹对不同茬口强筋小麦籽粒产量和品质的影响

为了探讨不同茬口下施氮对强筋小麦籽粒产量和品质的最佳效应,以强筋小麦品种烟农19号为材料,研究了施氮量和追氮时期对不同茬口小麦籽粒产量及品质的影响。结果表明,施氮量和追氮时期对不同茬口下强筋小麦的籽粒产量和品质均有显著的影响。在0～240kg／ha施氮量范围内烟农19号单位面积穗数、每穗粒数和产量随施氮量的增加而显著提高,且旱茬麦产量极显著高于稻茬麦,主要是提高了每穗粒数和千粒重。小麦籽粒蛋白质和面筋含量、沉淀值均随施氮量的增加而显著增加,旱茬麦的品质显著优于稻茬麦。在两种茬口下,烟农19号籽粒产量、蛋白质产量与施氮量均成二次曲线关系,稻茬麦在施氮量为251．26～280．24kg／ha、旱茬麦在施氮量为281．03～303．02kg／ha范围内籽粒产量和蛋白质产量可达到同步提高。拔节期和孕穗期追施氮肥可有效提高单位面积穗数、每穗粒数和产量,且籽粒蛋白质、湿面筋含量和沉淀值显著提高。本试验条件下,旱茬麦在拔节期至孕穗期、稻茬麦在孕穗期追施氮肥可同步提高强筋小麦籽粒产量和品质.     

稻田套播和施氮对弱筋小麦产量和品质的调节效应

为研究稻田套播及不同施氮量对小麦产量和品质的效应,采用稻田套播与传统条播两种栽培方式比较的方法,研究稻田套播和氮肥对优质弱筋小麦宁麦9号籽粒产量和品质的调节效应.结果表明,与传统条播方式相比,在相同的氮肥运筹下稻田套播弱筋小麦除籽粒总淀粉及其组分含量高于条播处理外,籽粒产量、蛋白质含量、磨粉品质、面粉品质以及淀粉糊化特性的主要指标均低于传统条播,且差异显著.在江淮地区采用稻田套播方式较利于弱筋小麦优质的形成.增加施氮量则宁麦9号的产量、蛋白质含量、面粉品质和磨粉品质的主要指标提高,但不利于弱筋专用品质的优化.稻田套播弱筋小麦宁麦9号在总施氮(纯氮)量为225 kg/ha、基蘖肥与拔节追肥比例为5:5:0的条件下可实现高产与优质相协调.     

施氮量对强筋春小麦氮素代谢、产量和品质的影响

为给春小麦合理施肥提供依据，在肥力中等的土壤上设置了不同施氮水平的春小麦肥料试验，对东北地区春小麦氮素代谢特性、氮素与春小麦产量和品质的关系进行了研究。结果表明，施氮量对产量的影响呈二次曲线关系，y=2024．2＋24．095X-0．0958X^2（R^2=0．9856，P=0．0039）。获得春小麦最高产量的施氮量为125．8kg／ha，产量达3539．3kg／ha;最佳经济施氮量为107．5kg／ha，产量这3507．3kg／ha。在一定氮肥用量范围内，随着施氮量的增加，小麦叶绿素含量和硝酸还原酶活性（NRA）均呈增加趋势，小麦品质特性也得到了明显改善。处理间相比，以施氮量120kg／ha处理的小麦籽粒品质及面团流变学特性表现较好，小麦籽粒蛋白质、淀粉、湿面筋含量及沉淀值分别为17．3％、64．7％、42．5％和65．2mL。因此，在肥力中等的土壤上，为获得春小麦的最佳产量与品质，氮肥施用量应控制在120kg／ha左右。     

施氮时期对弱筋小麦产量和品质的调节效应

在大田条件下,以饼干专用小麦宁麦9号为材料,研究了不同时期施氮对淮南地区弱筋小麦产量和品质的影响。结果表明,在总施氮量相等、基肥和追肥各占50%的情况下,小麦产量随追肥时期的推迟而提高,于拔节期达到最大值,拔节期以后追肥产量下降;蛋白质含量和沉淀值有随追肥时期的推迟而提高的趋势,返青期及返青期以前追肥蛋白质含量和沉淀值达到弱筋小麦的理想指标;在拔节期前追肥湿面筋含量符合弱筋小麦的要求,拔节期及拔节后追肥变化不大;峰值粘度、低谷粘度、最终粘度表现为随追肥时期的推迟而下降的趋势。返青期是弱筋小麦实现高产和优质相协调的适宜追氮时期。     

群体调控与氮肥运筹对强筋小麦济南17号产量和品质的影响

以强筋小麦济南 17号为试验材料 ,选择不同气候、生态条件和地力水平的菏泽市牡丹区和陵县研究播种期、播种量以及氮肥应用对小麦产量和品质的影响。结果表明 ,氮肥的施用时期和施用水平对多项品质性状都有影响。在追肥期的对比研究中 ,起身期追肥产量和有关品质指标都较低 ,综合品质差 ;拔节期以后施肥可有效地提高产量 ,并对改善品质有重要的促进作用。拔节期和孕穗期两次追肥对提高蛋白质含量、湿面筋含量、沉淀值以及面团稳定时间等具有明显的效果。在氮肥用量上 ,各项品质性状均以 75kg/hm2 的纯N处理最差 ,而在 15 0～ 30 0kg/hm2 范围内有利于提高综合品质。通过群体的调控 ,不仅对群体LAI、单位面积穗数、产量有重要影响 ,而且对品质指标如籽粒容重、蛋白质含量、湿面筋含量和面团稳定时间均有显著的作用。济南 17号小麦优质栽培的适宜播种期范围为 9月 2 8日～ 10月 14日 ,最佳基本苗范围为 15 0× 10 4/hm2 ～ 2 2 5× 10 4/hm2 。具有耐大群体的特点 ,但不宜晚播 ,适宜在高肥地力条件下种植     

不同品质类型冬小麦籽粒产量和品质性状对氮肥的响应

为了研究不同品质类型冬小麦籽粒产量和品质性状对氮肥水平和追氮时期的响应,以两个强筋品种济南17和PH82-2-2以及两个筋力弱的品种PH97-4和PH97-5为材料进行了品种、施氮量、施氮时期三因素试验。结果表明,增施氮肥能显著提高小麦产量和氮收获量。起身期追肥比抽稳期追肥产量和氮收获量显著提高;不同品质类型的小麦蛋白质含量对施氮量和追氮时期反应不尽一致,蛋白质含量相对较低的两个品种济南17和PH97-4施氮处理间差异不显著,而蛋白质含量相对较高的品种PH82-2-2和PH97-5在高施氮量下抽穗期追肥蛋白质含量比起身期追肥提高0．6个百分点,差异达显著水平。不同品种的湿面筋含量、籽粒容重和硬度在不同施氮量下差异不显著。沉淀值、降落值对施氮处理不敏感;吸水率和面团稳定时间不同施氮量间差异不显著,抽穗期追肥吸水率提高0．7个百分点,但面团形成时间和稳定时间分别降低1．39min和0．61min;不同品种的粉质特性差异显著。运筹氮肥能改善小麦加工品质,但效果不明显。     

播期、密度和氮肥运筹对瑞华麦520产量和品质的影响

为确立抗病小麦品种瑞华麦520高产优质高效栽培管理措施,在大田研究了播期、密度、施氮量及氮肥基追比对瑞华麦520籽粒产量和品质的影响。结果表明,播期和密度对籽粒产量和品质均有明显影响,不同施肥量间差异显著,且播期效应大于密度和施肥效应。播期与密度试验中,10月10日播种、基本苗225万株·hm~(-2)时产量最高,10月10日后随着播期的推迟籽粒产量下降;籽粒蛋白质含量、湿面筋含量和面团稳定时间均随播期的推迟而增加;籽粒蛋白质含量随密度增加而降低,湿面筋含量和面团稳定时间受密度影响不大。氮肥运筹试验中,施氮量180～270kg·hm~(-2)范围内,籽粒产量随施氮量的增加而快速增加,施氮量超过270kg·hm~(-2)后产量增长缓慢;氮肥基追比7∶3时产量最高;籽粒蛋白质含量、湿面筋含量和面团稳定时间随着施氮量的增加而上升。综合分析,在本试验条件下,10月10日播种、基本苗225万·hm~(-2)、施氮量270kg·hm~(-2)、基追比7∶3时瑞华麦520可以获得更高的产量和品质。     

In vitro reproduction in the annual pasture legumes subterranean clover (Trifolium subterraneum L.) and French serradella (Ornithopus sativus Brot.)

Pasture legumes are important components of both mixed farming rotations and permanent pastures in temperate climates. Breeding of two widely sown pasture legumes, subterranean clover (Trifolium subterraneum L.) and French serradella (Ornithopus sativus Brot.), is constrained by the long generation cycle, typically enabling only one generation per year. We hypothesized manipulation of culture medium and conditions would enable the development of a laboratory‐based protocol for in vitro reproduction in subterranean clover and French serradella. In vitro flowering and viable seed set was induced from both species. For subterranean clover, the most effective treatment was culturing on modified MS medium with 1 μm kinetin and 0·1 m sucrose under a 100 μmol m^?2 s^?1 light intensity and continuous photoperiod. For French serradella, culture on a hormone‐free B5 medium with 5 mm NH₄Cl and 0·1 m sucrose under a 100 μmol m^?2 s^?1 light intensity and 20 h photoperiod was optimum. It is expected this technique will have application in accelerating generation turnover within breeding programs, for the study of factors influencing flowering in pasture legumes, and for the propagation of valuable yet enfeebled plants such as embryo‐rescued hybrids.     

Pharmacokinetics of Marine-Derived Drugs

Marine organisms represent an excellent source of innovative compounds that have the potential for the development of new drugs. The pharmacokinetics of marine drugs has attracted increasing interest in recent decades due to its effective and potential contribution to the selection of rational dosage recommendations and the optimal use of the therapeutic arsenal. In general, pharmacokinetics studies how drugs change after administration via the processes of absorption, distribution, metabolism, and excretion (ADME). This review provides a summary of the pharmacokinetics studies of marine-derived active compounds, with a particular focus on their ADME. The pharmacokinetics of compounds derived from algae, crustaceans, sea cucumber, fungus, sea urchins, sponges, mollusks, tunicate, and bryozoan is discussed, and the pharmacokinetics data in human experiments are analyzed. In-depth characterization using pharmacokinetics is useful for obtaining information for understanding the molecular basis of pharmacological activity, for correct doses and treatment schemes selection, and for more effective drug application. Thus, an increase in pharmacokinetic research on marine-derived compounds is expected in the near future.     

Estimation of lucerne yield stability for enabling effective cultivar selection under rainfed conditions

Evaluation of crop and forage yield stability is of increasing relevance in the context of current and recent environmental changes but, in contrast to other field crops, there are no published systematic analyses among forage crops in Europe. A study of stability performance was conducted with 13 Czech cultivars of lucerne at four locations over a 2‐year period with the following aims: (a) to evaluate yield stability of varieties across different environments and (b) to calculate measurable benefits of variety selection in relation to the specific environment. The cultivar Vlasta was identified as the highest yielding cultivar (annual yield 16.0 t DM/ha), whereas the lowest yielding cv. Magda, Tereza and Oslava averaged around 14.9 t DM/ha. Effect of genotype × environment interaction (G × E) was two times higher than for genotype alone. Additive main effects and the multiplicative interaction (AMMI) model showed that the highest yielding cultivars may not be stable across environments. This study demonstrated further that significant yield improvement could be detected, even among a relatively homogenous group of domestic cultivars, and this was driven mainly by site productivity: the improvement was +10% in low‐yielding sites, compared with +3% in high‐yielding sites. Results highlight that advanced agronomy should also consider stability parameters such as AMMI stability value or superiority measures for forage crops in response to the challenges associated with climate change.     

La pourriture fongique des tubercules de pomme de terre en atmosphère contrôlée

Résumé Fusarium culmorum et, dans une moindre mesure,F. avenaceum, F. sambucinum, Colletotrichum coccodes etCylindrocarpon sp. ont été isolés de tubercules entreposés en atmosphère contr?lée (AC) et atteints de pourriture grave. Des expériences d'inoculation de tubercules avec 10 espèces ou variétés fongiques et conservation en AC à 8 et 10°C ont montré que: 1) les champignons non pathogènes en atmosphère normale (ex.:Cylindrocarpon sp.) le devenaient en AC, 2) ceux qui étaient faiblement pathogènes en atmosphère normale étaient nettement plus virulents en AC (ex.:F. culmorum), 3) les espèces ou variétés virulentes en conditions d'air normales (Fusarium sulphureum etPhoma exigua var.foveata) ne provoquaient pas de pourriture plus grave en AC et leur activité pouvait même être légérement freinée.

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Summary The extensive rotting of tubers which occurred during storage trials in controlled atmospheres has led to a mycological and pathological study of the rots. The most frequently isolated species wasFusarium culmorum althoughF. avenaceum, F. Sambucinum, Coletotrichum coccodes and aCylindrocarpon sp. were also present. Tubers of cvs Bintje and Ulla were inoculated with 19 isolates of 10 fungal species or varieties associated with rotting of stored tubers (Table 1). The tubers were incubated at 8 or 10°C in normal or controlled (2% O₂:1% CO₂, 2% O₂:6% CO₂, 2% O₂:12% CO₂, 6% O₂:6% CO₂) atmospheres and the extent of rotting was determined a month later (Tables 2 and 3 and Fig. 2). Species which were weakly virulent in a normal atmosphere (variousFusarium spp. andPhoma exigua var.exigua) were clearly more aggressive in the controlled atmosphere and this was especially evident in the case ofF. culmorum. Species ot pathogenic in a normal atmosphere under experimental conditions (Colletotrichum coccodes, Cylindrocarpon sp.,Phoma eupyrena) caused rotting in the controlled atmosphere. The two species which were virulent in a normal atmosphere (F. sulphureum andP. exigua var.foveata) were also virulent in the controlled atmosphere and in some cases the extent of rotting was even less. As a general rule, rotting caused by weakly virulent fungi was greater in both cultivars in the controlled than in a normal atmosphere.

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Zusammenfassung Eine starke F?ulnis von in Kontrotrollierter Atmosph?re gelagerten Kartoffelknollen veranlasste eine mykologische und pathologische Untersuchung. Der am h?ufigsten isolierte Pilz warFusarium culmorum. F. avenaceum, F. sambucinum, Colletotrichum coccodes undCylindrocarpon sp. wurden ebenfalls bestimmt. Neunzehn St?mme von 10 Pilzsorten oder-Arten welche bei Lagerf?ulnis vorkommen (Tab. 1) wurden auf Knollen der Sorten Bintje und Ulla inokuliert. Die Lagerung wurde bei 8 oder 10°C under Normalbedingungen oder kontrollierter Atmosph?re durchgeführt (2% O₂:1% CO₂, 2% O₂:6% CO₂, 2% O₂:12% CO₂, 6% O₂:6% CO₂). Der F?ulnisgrad (Abb. 1) wurde nach einem Monat bonitiert. Die Ergebnisse sind in den Tabellen 2 und 3 dargestellt und in der Abb. 2 illustriert. Unter in Normalbedingungen nur schwach virulente Arten (verschiedeneFusarien undPhoma exigua var. exigua) waren deutlich aktiver in kontrollierter Atmosph?re. Dies was besonders der Fall fürF. culmorum. Pilze, die im Versuch unter Normalbedingungen nicht pathogen waren (Colletotrichum coccodes, Cylindrocarpon sp., Phoma eupyrena), haben unter kontrollierter Atmosph?re Sch?den verursacht. Hingegen werden die beiden unter Normalbedingungen sehr pathogenen Arten (F. sulphureum undP., exigua var.foveata), durch kontrollierte Atmosph?re wenig beeinflusst. Es wurde sogar in einigen F?llen eine gewisse Verringerung des F?ulnisbefalls beobachtet. Ganz allgemein haben die getesteten kontrollierten Bedingungen die Entwicklung der Pilzf?ulnis an beiden Kartoffelsorten gef?rdert, speziell durch Pilzarten, welche unter Normal-bedingungen wenig Sch?den verursachen.

     

Marine Pharmacology in 2016–2017: Marine Compounds with Antibacterial,Antidiabetic, Antifungal,Anti-Inflammatory,Antiprotozoal, Antituberculosis and Antiviral Activities; Affecting the Immune and Nervous Systems,and Other Miscellaneous Mechanisms of Action

The review of the 2016–2017 marine pharmacology literature was prepared in a manner similar as the 10 prior reviews of this series. Preclinical marine pharmacology research during 2016–2017 assessed 313 marine compounds with novel pharmacology reported by a growing number of investigators from 54 countries. The peer-reviewed literature reported antibacterial, antifungal, antiprotozoal, antituberculosis, and antiviral activities for 123 marine natural products, 111 marine compounds with antidiabetic and anti-inflammatory activities as well as affecting the immune and nervous system, while in contrast 79 marine compounds displayed miscellaneous mechanisms of action which upon further investigation may contribute to several pharmacological classes. Therefore, in 2016–2017, the preclinical marine natural product pharmacology pipeline generated both novel pharmacology as well as potentially new lead compounds for the growing clinical marine pharmaceutical pipeline, and thus sustained with its contributions the global research for novel and effective therapeutic strategies for multiple disease categories.     

Effects of Micronutrient Deficiencies on Human Health: Its Status in South Asia

SUMMARY

Vitamin A, iodine, and iron deficiencies affect large numbers of people worldwide. A deficiency of one or more of these micronutrients adversely affects the physical and mental abilities of humans. South Asia contains a high percentage of these individuals, not just because of its large population, but also the prevalence of deficiency is higher there than in many other parts of the world. The reasons for the high rates of deficiency in South Asia are many, but they include inadequate availability of micronutrient-rich foods, sub-optimal dietary habits, and high rates of infection. Across the region, national plans vary from (a) increasing availability of appropriate foods, (b) introducing new dietary behaviors, (c) improving health status, and (d) directly addressing deficiency through intervention programs. The extent to which each of the countries is making progress toward the goals of these plans can help in understanding the priorities for future efforts to address micronutrient malnutrition. This article discusses the adverse effects of micronutrient deficiencies in humans with special reference to South Asia.     

稻文化的再思考3:稻与社稷——印度、泰国等东南亚、南亚主要国家

东南亚、南亚地区是世界上重要的稻米产区,稻米在民众饮食生活和国家社会政治中占有重要地位,民众生活中也保存了非常悠久和丰富的稻作文化习俗及稻谷起源神话传说。本文分析了水稻在东南亚、南亚主要国家印度、印度尼西亚、泰国、越南、菲律宾、孟加拉国、缅甸的作用、地位、生产、消费、文化等情况,并指出了印度、印度尼西亚稻文化的主要标志。     

Irrigation but not N fertilization enhances seedhead density in plains rough fescue ( F estuca hallii)

Plains rough fescue ( F estuca hallii) is an important forage grass species in western Canada. Seed for use in pastures and ecological restoration is in high demand but supply is limited because F. hallii is an erratic seed producer. Seed producers require an understanding of the factors that influence flowering and seed set in this species. The aim of this study was to assess the effect of irrigation and nitrogen fertilization on the flowering and growth of F. hallii in a native rough fescue prairie in Alberta, Canada. Irrigation had a strong positive effect on seedhead density, whereas fertilization had limited effects on growth and reproduction of F. hallii. These results demonstrate that under field conditions, available moisture is likely to be a key factor driving flowering and seed production in F. hallii.     

Management of Soil Micronutrient Deficiencies in the Rice-Wheat Cropping System

Summary

Within the last three decades, the rice-wheat cropping system has triggered, and with time, aggravated soil micronutrient deficiencies in the Indo-Gangetic Plains (IGP). This has largely been due to the shift from an earlier rice and wheat monoculture with low yielding, long duration indigenous varieties, to an intensive rice-wheat rotation cropping system with short duration modern high yielding varieties on the same piece of land. The problems related to micronutrient deficiency in the IGP are more due to the size of its available pools in the soil rather than its total contents and are greatly influenced by crop management, or rather its mismanagement. Deficiency of zinc is widespread in the IGP, but with the extensive use of zinc sulfate, zinc deficiency has reduced in some areas of the region. Meanwhile, the deficiency of Fe, Mn and B has increased in the IGP. Deficiency of Cu and Mo is location specific and can limit rice and wheat yields. The adoption and spread of the rice-wheat system in permeable coarse textured soils, particularly in the western IGP, not only caused iron deficiency in rice but also resulted in the emergence of manganese deficiency in wheat. In highly calcareous and acidic soils, boron is the next limiting micronutrient in crop production after zinc. Bumper rice and wheat harvests in the past decade, the declining use of organic manures in the region and except for the widespread use of zinc sulfate, a general lack of awareness amongst farmers on micronutrient deficiency problems has contributed to micronutrients limiting rice and wheat yields in the IGP. Approaches to alleviating micronutrient deficiencies include matching the crop removals of the micronutrients with its replenishments through their respective external carriers, supplementation through organic sources and mobilization/utilization through cultivation of micronutrient efficient crop cultivars. Identification of efficient micronutrient carriers and finding the optimum rate, mode and time of its application is important in ameliorating the micronutrient deficiencies. This article reviews the extent of micronutrient deficiency and discusses various management options available to reduce micronutrient deficiency induced crop yield reduction for rice and wheat in the Indo-Gangetic Plains.     

Model of wheat yield response to application of diclofop-methyl to control ryegrass (Lolium rigidum)

A general model of crop yield response to herbicide application is proposed. The model includes three components: the effect of herbicide dosage on weed density, the effect of surviving weed density on crop yield and the effect of herbicide directly on the crop. The model is used to estimate the response of wheat yield to application of diclofop-methyl to control ryegrass (Lolium rigidum) in Australia. It is found that the competitiveness of ryegrass plants surviving treatment is reduced by the treatment and that the proportion of yield loss at a given ryegrass density is not independent of the absolute weed-free yield. The response function is used to calculate economic thresholds and optimal herbicide dosages.