Increasing concerns about pesticide use and a steadily increasing conversion to organic farming have been major factors driving research in physical and cultural weed control methods in Europe. This article reviews some of the major results achieved with nonchemical methods and strategies, especially adapted for row crops (e.g., corn, sugar beet, onion, leek, and carrot) and small-grain cereals (e.g., barley and wheat). In row crops, intrarow weeds constitute a major challenge, and research has mainly aimed at replacing laborious hand-weeding with mechanization. A number of investigations have focused on optimizing the use of thermal and mechanical weeding methods against intrarow weeds, such as flaming, harrowing, brush weeding, hoeing, torsion weeding, and finger weeding. And new methods are now under investigation such as robotic weeding for row crops with abundant spacing between individual plants and band-steaming for row crops developing dense crop stands. The strategic use of mechanical weed control methods in small-grain cereals has been another area of considerable interest. Weed harrowing and interrow hoeing provide promising results when they are part of a strategy that also involves cultural methods such as fertilizer placement, seed vigor, seed rate, and competitive varieties. Although research in preventive, cultural, and physical methods have improved weed control in row crops and small-grain cereals, effective long-term weed management in low external input and organic systems can only be achieved by tackling the problem in a wider context, i.e., at the cropping system level. Basic principles of this approach, examples of cover crop and intercropping use for weed suppression, and an application in a 2-yr rotation are presented and discussed.

Mathematical modelling is a commonly used tool for studying the long-term dynamics of weed populations in agriculture. This was reflected in our review by the large number of scientific papers (134 original publications) and the continuing need to gain an overview over this fast developing field (20 previous review papers were found). In this article, we provide a more comprehensive review than earlier seen, striving to include all relevant publications. Thus, we cover models of the population dynamics of 60 weed species in 40 crops. An online, accompanying database provides an indexed bibliography. Despite the large variation in crops, weeds and geography, the models were surprisingly similar in their approach: structured around the weed life cycle, excluding environmental factors and giving little attention to validation or even documentation of model construction. In addition, their application was similar, limited mostly to strategic decision making. We hope that the overview provided by this review will inspire weed modellers and that it will serve as a basis for discussion and as a frame of reference when we proceed to advance the modelling of weed populations to a new level, developing new approaches and tackling new application domains.

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Three field experiments were carried out in organically grown winter wheat in Denmark. The treatments were sowing time (normal or late sowing) and false seedbed, row width (12 and 24 cm) and weed control method [untreated; mechanical weed control (weed harrowing at 12 cm supplemented with inter-row hoeing at 24 cm); and herbicide weed control]. Weed biomass in midsummer was greatest on plots sown at the normal sowing time (compared with delayed sowing) and was reduced by mechanical or chemical weed control (compared with untreated plots). Row width alone had no influence on weed biomass, but in the experiment with high weed pressure, the more intensive mechanical weed control used at a row width of 24 cm reduced weed biomass. Normal sowing time tended to give higher yields, but this was only statistically significant in one of the three experiments. Wide rows gave a yield decrease in the experiment with low weed pressure. The effect of weed control on yield was dependent on the weed pressure. At low weed pressure, mechanical weed control caused a yield decrease compared with untreated or herbicide treated. At intermediate weed levels there were no differences, whereas at high weed pressure, mechanical weed control and herbicide treatment caused a yield increase compared with untreated. False seedbeds were shown to contribute to a decrease in the soil seed reserve.*% Reduction in back-transformed values. Due to missing values, SEDs are different for different comparisons. The largest value is shown. àSignificant interactions with other treatments.Weed management in organic winter wheat 17

A field experiment is conducted which focuses on crop rotations for cereal production in organic farming. The objective of the experiment is to explore the possibilities for both short-term and long-term increases in organic cereal production through manipulation of crop rotation design on different soil types. This paper describes the design of a rather complex experiment, and later papers will describe and discuss the results. Three factors are included in the experiment in a factorial design with two replicates: A) fraction of grass-clover and pulses in the rotation (crop rotation), B) catch crop (with or without catch crop or bi-cropped clover), and C) manure (with or without animal manure applied as slurry). All fields in all rotations are represented each year.The experimental factors are defined to allow management to be adjusted for optimisation of the individual treatment combinations. This makes the systems more realistic and the results more applicable in practical farming. The experiment is conducted at four locations representing major soil types and climate regions in Denmark. The main design criteria are related to requirements for a long-term experiment and the need of performing studies and experiments within the experiment itself.Key words: nitrogen, weed control, slurry, winter wheat (Triticum aestivum), spring barley (Hordeum vulgare), spring oat (Avena sativa), triticale (Triticosecale), grassclover, pea (Pisum sativum), lupin (Lupinus angustifolius), ryegrass (Lolium perenne), catch crop. Introduction 3The most common organic farming system in Denmark is based on a large fraction of grass-clover and fodder crops in the rotation in combination with a stock of ruminant animals, typically for dairy production (Tersbøl & Fog, 1995). This farm type (0.9-1.4 livestock units ha -1 ) has with proper management proved to sustain a stable crop production with neglible problems (Askegaard et al, 1999). There is, however, a need to increase cereal production in organic farming in order to provide grain for both human consumption and non-ruminant animal feed.The design and management of organic crop rotations involves many considerations.Contrary to conventional crop production where the management factors can be optimised individually (e.g. fertilisation or weed control), many factors and their interactions must be included in the design and management of organic crop rotations.The main reason is that crop management of organic crop rotations must focus on the prevention of problems like diseases, pests and weeds, rather than the curing of problems. This prevention is based on the construction of sound crop rotations, which are able to reduce the propagation of diseases, and on nitrogen self-supply through the use of N 2 -fixing crops and cover crops (Lampkin, 1990). Another very important prevention factor is crop establishment, where a uniform seedbed and the right time of sowing constitute the preconditions for good crop growth and development, which again will improve its competitive ability agains...