ISHS Acta Horticulturae 98: Symposium on Research on Recirculating Water Culture
AERATION IN THE NUTRIENT FILM TECHNIQUE OF GLASSHOUSE CROP PRODUCTION AND THE IMPORTANCE OF OXYGEN, ETHYLENE AND CARBON DIOXIDE |
| Author: | M. B. Jackson |
| Abstract:
To grow and function properly, roots require sufficient oxygen for aerobic respiration and a minimal accumulation of gases such as ethylene and carbon dioxide. In N.F.T., slow rates of gas diffusion through water can prevent these requirements being met by direct diffusive exchange with the aerial environment. Instead roots are aerated by a mass flow of gases dissolved in water. This contrasts with the diffusion through a gaseous phase, that occurs in well structured soil. Factors are discussed that influence aeration in N.F.T., particularly temperature and the metabolic activities of roots and micro-organisms. Measurements of oxygen dissolved in N.F.T. solutions show some depletion even in a healthy tomato crop. The largest depletion (up to 95%) and considerable microbial breakdown of nitrate (denitrification) have been found in 'whale-hide' pots where the flowing solution that transports gases to and from roots cannot penetrate. The concentrations to which oxygen in the nutrient solution must decline before roots are killed or their growth retarded are assessed together with the effects of accumulated carbon dioxide and ethylene. The possibility of toxin production by anaerobic micro-organisms is also discussed. Repercussions for the shoots of an anaerobic root system include slow growth rates, senescence and abscission of leaves, petiole epinasty and adventitious rooting. Interference in hormonal, nutritional, and water relationships between roots and shoots are thought to be responsible. | |
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