Outlook on Agriculture

Replacement of wood by aluminium alloys as the main structural material for glasshouse construction posed new problems for designers and, in Britain, has resulted in a wide range of different types–-from the single wide span of over 20 m to the 3 m multi-span Venlo. Many environmental factors which influence plant growth in the glasshouse can now be controlled automatically, such as lighting, ventilation and air movement, heating, carbon dioxide enrichment and air humidity.

Many uses have been found for plastics in intensive horticulture throughout the world, but the present article is concerned more specifically with their use as coverings for greenhouses and walk-in tunnels, whether as thin flexible films or as flat or corrugated rigid sheets. The plastic may be supported on a metal or timber frame or, in the case of “bubble” houses, simply by air pressure.

Eastern Europe, extending from northern Russia to Czechoslovakia and Bulgaria, embraces a wide range of climates, all experiencing wider extremes of temperature and humidity than the maritime climates of the West. Noteworthy technological features of horticultural production include the development of walk-in plastic tunnels supported on tubular metal frames, the use of power station waste water for greenhouse heating, and the large-scale use of peat as a substrate in place of soil.

Growers in NW Europe face competition from imports, particularly of salad vegetables, from countries which enjoy higher solar radiation in winter, but it is in consumers’, producers’ and importers’ interest if NW European and Mediterranean growers can each concentrate on supplying the market in those periods of the year to which they are best suited, and to minimize overlap. The domestic producer's competitive position is expected to improve, despite rapidly rising costs.

There is a large and increasing export business in outdoor vegetables and cut flowers which are sent by air from Kenya to Europe, the main products being capsicums and chillies, French beans, brinjals (aubergines), courgettes, carnations, okra and a wide range of vegetables grown specifically for Asians, particularly in the United Kingdom. Tropical flowers, Asparagus plumosus and rooted chrysanthemum cuttings are also exported. Cultural methods are briefly described in this article.

Climatic conditions in California are so favourable that intensive outdoor horticultural production is economically feasible despite the inconvenience and expense of long-distance transport to high population centres in NE and N Central USA. Processing tomatoes typify the warm season, machine-harvested, outdoor crops, and crisp-headed lettuce the cool season, fresh market, hand-harvested crops. Cultural practices, including control of weeds, pests and diseases, are outlined.

Greenhouse production of fresh winter season tomatoes in North Central and North-eastern USA faces higher costs than outdoor production in Florida or Mexico, including freight charges for delivery to northern markets. The higher the fuel price, the greater will be the relative disadvantage of the producer relying on environmental controls. Success must therefore depend on effective exploitation of quality differences rather than competing on a price per pound basis.

The glasshouse environment differs both physically and biologically from crop production in the open, and its cost structure permits the use of more sophisticated products and techniques for pest and disease control. From the wide range of control methods that are available, including integrated programmes in which chemical and biological methods are combined, experience indicates those should be selected which limit the risk of developing resistant strains of insects or pathogens.

Control of foliar and soil-borne diseases is the most important aspect of crop protection in enclosed environments in Japan, particularly in the widely used “vinyl” houses where humidity can be high. The principal diseases of cucumbers, melons, tomatoes, eggplant, pepper, strawberries, other vegetables and flower crops are discussed, together with methods of control. Pests, in general, present a less serious problem than diseases, the most important being aphids and mites.

High quality at harvesting is of great importance in fruit and vegetables that are to be transported to distant markets. The aim in post-harvest handling is to eliminate or minimize potential causes of deterioration. “Pre-cooling”, good hygiene in the packing-house, use of specific chemicals where appropriate, “cold chain” handling from packing-house through to the retail distributor, and display of perishable products in cool cabinets at the retail level, all contribute to this end.

Plant growth in protected environments may be increased by improving light transmission or by providing supplementary artificial light, or perhaps eventually by improving the efficiency of the photosynthetic process. Much has yet to be learned, both of the inter-relations between crop growth and various environment factors, and of mechanisms and metabolic processes within the plant, but there is no doubt that plants have a physiological potential to yield more than they now do.