When greenhouse atmospheres have been enriched with carbon dioxide (CO2) from the normal ambient air level of approximately 0.03 per cent to 0.1 per cent, increased yields, better quality and earlier crops have been produced.
CO2 produced by burning a suitable fuel, such as LPG or kerosine, is advantageous and economical; although pure CO2 can be introduced from cylinders or as dry ice.
The commercial advantages of introducing CO2 into greenhouse atmospheres was quickly realized by growers in Europe. It was accepted as commercial practice following very little research effort and in fact research has not kept pace with commercial development.
Whilst a great deal of data is available on photosynthesis covering many varieties of plants, the part played by CO2 is perhaps the least understood. The concentration required for maximum photosynthesis depends upon the levels of many other factors, such as light, temperature, humidity and water and nutrient supply. Some basic research to study the interaction of these factors has been carried out but the picture is far from complete.
Most research is now directed to field application to find the most economical levels of applying CO2 to obtain maximum yields under the different growing conditions. A great deal of practical knowledge is now becoming available.
Crops are sensitive to sulphur dioxide and incomplete combustion products, fuel quality and complete combustion is therefore important. There is now available a wide range of testing apparatus and these are examined.
For many years the importance of carbon dioxide as the basic material for photosynthesis, has been known. Early experiments, dating from the nineteenth by G. HEYS, Shell, Great Britain century, proved that when the natural CO2 level of air was increased, plants responded and greater weights and yields were obtained. It was thought possible to commercialize these results on a field scale. Various products were burnt, charcoal, special "fuels", coal, gas and paraffin. In some instances increased yields were obtained but too often the plants died due to toxic products produced during combustion. This was either due to inherent impurities in the fuel, or incomplete combustion products.
Work has continued sporadically over the last half century but it was not until the early 1960's in Holland that a real commercial interest was awakened.
In 1959 Gaastral at Wageningen, in Holland, studied the relationship of photosynthesis to carbon dioxide, light, temperature and stomatal diffusion resistance. He studied the way in which individual leaves of tomatoes and cucumbers, enclosed in special chambers but attached to the plant, responded to CO2 when the above mentioned factors were varied.
At about the same time, Klougart2 in Denmark was working on a semi-commercial scale to find the best conditions for growth, of various economic glasshouse crops.
Daunicht3 was working
