CARBON DIOXIDE DOSING IN COMMERCIAL GREENHOUSES -GAS SENSORS FOR OPTIMAL CONTROL OF GROWTH CONDITIONS AND SAFETY

摘要

Crops such as aubergines, cucumbers, tomatoes, capsicum peppers and lettuce are now regularly grown in modern greenhouses where light, water, temperature and nutrient supply are well controlled. It is also common to adjust the carbon dioxide (CO_2) levels in greenhouses to create an environment that is optimally conducive to growth. The micro-climate that is created must be monitored and controlled to ensure good growing conditions, avoid expensive over dosing and ensure the safety of the people looking after and harvesting the crops. It is all about finding the sweet-spot for growth, the optimal balance. For food producing and exporting countries, such as Australia and New Zealand, investment in high yield growing processes using a mix of environmental management technologies has been intense in recent decades. Elevated levels of carbon dioxide during the 'daylight' growing hours enhance plant growth. In greenhouses, the growth rate and development of all plants can be improved by controlling CO_2 concentrations at levels of around 800 ppm. This is approximately twice as much as the natural concentration of CO_2 in natural ambient air. Higher CO_2 concentrations up to 2000 ppm have been used in greenhouses and hydroponics, but each incremental increase in CO_2 levels above 700 ppm has diminishing benefit to the plants. Despite these diminishing returns, some operators control the CO_2 levels at 1000 or 1200 ppm to fully exploit the potential of CO_2 addition. Optimised CO_2 levels in greenhouses raise productivity and crop yields considerably, up to 40% during the darkest time of the year. In addition, they also improve the quality of the crop. When the CO_2 level in the greenhouse is optimised, the plants will produce uniform fruit, salads and vegetables of the best quality. So, CO_2 can maximise both the crop yield and the sales price for the harvest. This technique is applied to greenhouses using both hydroponic and conventional soil growing techniques.