In field trials in 1987\88 near Pangbourne, England, wheat (Triticum aestivum) and field beans (Vicia faba) were grown in an organic farming system as sole crops and additive intercrops. The sole crops were grown at 25, 50, 75, 100 and 150 % of the recommended density (RD) for conventionally grown crops. The intercrops consisted of all density combinations of wheat and beans from 25 to 100 % RD in a factorial experiment. The grain yield of sole cropped wheat and beans increased significantly as their density was increased. The highest yield of both was achieved at 100 % RD, indicating that the conventional recommendation was the optimum when applied to organically grown crops. Land equivalent ratio (LER) values for the intercrops were significantly greater than 1n0 when the wheat was sown at 5 % RD and beans at 50 % RD. The highest LER of 1n29 was achieved when wheat and beans were both sown at 75 % RD. There was resource complementarity, expressed as relative yield total (RYT) 1n0, in all of the density combinations. There was a significant decrease in resource complementarity with increasing wheat and bean density. The nitrogen content of the wheat grain and whole plant biomass was significantly increased when the density of beans in the intercrops was increased ; this was reflected in a significant increase in grain protein at harvest. The total amount of N accumulated by the wheat, however, decreased with increasing bean density due to a reduction in the biomass of wheat. Beans also showed a significant increase in %N as the density of the other component increased and a decrease in total N accumulation due to reduced biomass. All of the intercrops accumulated more N than the sole cropped wheat, but did not exceed that accumulated by sole-cropped beans. The biomass of weeds was greater under beans than under wheat. Weed biomass in intercrops was significantly reduced when the density of wheat and beans was increased, resulting in a lower weed biomass in the intercrops than was achieved in either the sole cropped wheat or beans. The N content of weeds was significantly reduced with increasing wheat density but was significantly increased with increasing bean density. The total amount of N accumulated by weeds per unit area was reduced significantly by increasing the density of both components. The levels of disease on the wheat were low, but mildew (Erysiphe graminis) increased significantly as bean density increased. The incidence of chocolate spot (Botrytis fabae) increased significantly with increased bean density. The experiment demonstrated that it was possible to harvest the crop with a combine harvester and the wheat and beans can be planted separately mechanically, therefore this system is suited to mechanized agricultural systems.

Abstract. This paper compares nitrate leaching losses from organic farms, which depended on legumes for their nitrogen inputs (66 site years) with those from conventional farms using fertilizers under similar cropping and climatic conditions (188 site years). The conventional farms were within Nitrate Sensitive Areas in England, but sites following special practices associated with that scheme were excluded. Nitrate losses during the organic ley phase (including the winter of ploughing out) were similar (45 kg N ha–1) to those from conventional long‐term grass receiving fertilizer N inputs of less than 200 kg N ha–1 (44 kg N ha–1) and from the grass phase of conventional ley‐arable rotations (50 kg N ha–1). Losses from conventional grass receiving higher N inputs were greater than from organic or less intensive grass. Nitrate losses following arable crops averaged 47 and 58 kg N ha–1 for the organic and conventional systems respectively, with part of the difference being due to the greater proportion of non‐cereal break crops in the latter. Thus under similar cropping, losses from organic systems are similar to or slightly smaller than those from conventional farms following best practice.

No abstract

No abstract

SummaryTwo experiments were conducted in central southern England between September 1994 and August 1996 to identify the critical weed‐free period in organically grown winter wheat (Triticum aestivum, cv. Mercia). In competition with a mixed weed infestation of predominately Alopecurus myosuroides and Tripleurospermum inodorum it was found that wheat yield decreased as the duration of the weed‐infested period increased and that the crop needed to be kept free of weeds from sowing in order to completely avoid any yield loss. Also, weeds emerging in the wheat crop (predominately T. inodorum) during the growing season had a significant and detrimental effect on yield. The existence of the critical period, therefore, depends on the imposition of an acceptable yield loss. If a 5% yield loss gives a marginal benefit compared with the cost of weed control, the critical period will begin at 506°C days after sowing (November) and end at 1023°C days after sowing (February). This information could be used by farmers to target mechanical weeding operations to control weeds at a time that will have maximum benefit to the crop.

Organic agriculture has grown rapidly throughout the world in recent years as a result of increasing consumer interest in healthy food and environmental concerns. The use of land in this operation helps to conserve the environment and promotes the sustainable use of natural resources. The demand for organic products has increased, especially in Europe, North America and Oceania, and hence has created export potential for developing countries. Turkey is a typical case among developing countries of the establishment of organic agriculture based on export potential. About 85% of its current organic production is exported to EU countries, and this is predicted to expand further. The main objectives of the study were to define the concept of organic agriculture and to describe the state of organic agriculture both worldwide and specifically in Turkey. The paper also describes major issues affecting Turkish organic agriculture and presents recommendations for developing this and related sectors in the hope that they will help to solve common problems faced by developing countries and improve policy programmes along with extension and research activities.

BACKGROUND: There is a need for information on the performance and carcass quality of pigs under different organic management systems. This study compared Duroc-sired progeny from three maternal breed types when kept either at pasture or in housing with an outdoor run and offered ad libitum concentrate either alone or with fodder beet or grass/clover silage as additional forage.

This paper briefly reviews the source and extent of ingested nitrates in the human diet. In response to the possible health risk, several countries in Europe have set maximum and/ or recommended concentrations of tissue nitrate in vegetables and salad crops. The consequence of adopting such limits in Great Britain is considered.In order to assess the range of nitrate concentrations in vegetables and salad crops, a market survey was conducted over two winters (1985 and 1986) with samples being taken from commercial outlets. Food offered as conventionally and organically produced was sampled. Samples of both organically and conventionally produced leafy winter vegetables contained high nitrate levels, some exceeding recommended and maximum levels in certain European countries. Various approaches to the minimisation of the dietary intake of nitrate are discussed.