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...
