Studies on the occurrence of ethylene in soil and its effect on root growth.

Soil samples were collectd from different depths of several selected soil types under both arable and grassland situations. The production of ethylene in the laboratory under anaerobic conditions by these soils, in fresh, air dried and oven dried states were compared. Drying was found to stimulate ethylene production, oven drying having most effect on initial ethylene production.Ethylene formation was related to organic matter content, ethylene concentrations increasing with increased organic matter levels. Ethylene concentrations in arable soils were also related to the acidity, low pH favouring ethylene production. Grassland soils did not show this relationship.High levels of added nitrate were found to reduce ethylene formation but even at 2000 ppm production was not inhibited completely. Low levels had a transient inhibitory effect but the maximum level of ethylene produced was unaffected.Ethylene formation was stimulated in air dried soil by the addition of wheat and barley straw and by the addition of caesin, pepsin, ethanol, lactic acid and pyruvic acid. The exact nature of this stimulation is not known. Ethylene production in undried soil depleted of microbial substrates was promoted by all the three organic substrates supplied: ethanol, glucose and butyric acid.Pea plants treated with 1.1 vpm ethylene showed a 50% reduction in root extension, 4.2 and 10 vpm treatments inhibited root extension completely.Exposure of pea and clover plants to air containing 10 vpm. ethylene resulted in a reduction in nodulation and in the nitrogen fixing capacity of those nodules present. Fresh and dry weight yields of pea pods and clover stems were reduced