Delivery of gases via drip irrigation tubing: An exploratory study

Agrochemicals are typically applied in the solid or the liquid phase. Soil fumigants, such as methyl bromide (MeBr), can suppress invertebrate pests and pathogens found deep in the soil profile because of the chemical's movement in the gas phase through the soil air space. Replacement compounds for MeBr, or other agro- chemicals, may be applied in the gas phase. Experiments were conducted to explore whether or not two types of standard commercial drip irrigation tubing could be used to deliver gases when placed either above ground or at 20-22 cm depth. Air was introduced into one end and the flow rate was measured at varying distances from the source, and air flow from individual emitters was also measured. To see whether a gas introduced into buried tubing could be found in soil, propane mixed with air was introduced into both types of buried drip tubing over several time intervals. Samples were collected from soil gas sampling tubes placed 15, 30, and 45 cm to the side of the buried tubing and at selected distances from the inlet, and propane concentrations were quantified by gas chromatography. Propane concentrations decreased unevenly with distance from the inlet and lateral distance from the buried tubing. To approximate conditions in small plots, propane concentrations were measured in gas sampling tubes at three lateral distances from short (9.1 m) lengths of buried tubing. Propane concentrations in sampling tubes adjacent to these short tubing lengths were more uniform than those found for greater tubing lengths.