PERLITE AS A GROWING MEDIUM IN HIGH DENSTIY TOMATO AND CUCUMBER CULTURE

The progressive commercial grower is now nearing the point of exhausting the possibilities of significantly increasing yields in the case of tomato and cucumber crops grown in the traditional manner. Improvements in base fertilisation and liquid feeding programmes and the substitution of peat or peat mixes for soil will only result in relatively marginal improvements. However, each year the growers' plight becomes more serious as production costs are rising steeply, there is an increasing shortage and demand for competent labour and competition for markets both at home and abroad has become more intense.

Researchers and growers must, therefore, seek and devise alternative methods of production, which offer scope for increasing yields and reducing the labour requirements of growing. In the longterm the most fruitful line of investigation will be that which is directed towards the provision of more "factory-like" production methods.

Cooper at the Glasshouse Crops Research Institute in England was one of the first to investigate this challenging area of research and his studies culminated in the development of the Pyramid Trough System of tomato culture (2). This high density system, with up to 120, 000 plants per acre, was based on a single-truss method of production. Up to three crops per season were possible and the total annual yield potential was estimated to be in the region of 130 tons per acre, but in practice the yields obtained were considerably lower. This system, however, has not as yet been adopted commercially, principally because the installation costs are too high. The system also posed too many problems in relation to the controlling of both vegetative and reproductive growth during the poor light period of winter-early spring.