Shahar Baram
Asher Bar-Tal
Alon Gal
Shmulik P. Friedman
David Russo
Static chambers are commonly used to provide in-situ quantification of N2O fluxes. Despite their benefits, when left in the field, the physicochemical conditions inside the chamber's base may differ from the ambient, especially in drip-irrigated systems. This research aimed to study the effects of static chambers' bases on water and N-forms distribution and the impact it has on N2O measurements in drip irrigation. N2O emissions were measured in a drip-irrigated avocado orchard for two years, using bases with a dripper at their center (In) and bases installed adjacent to the dripper (adjacent). During the irrigation/fertigation season, the measured N2OIn fluxes were greater than the N2OAdjecent fluxes (0.82 ± 0.15 vs. 0.36 ± 0.05 ng cm-2 sec-1). In contrast, during the winter, when the orchard is not irrigated or fertilized, insignificant differences were observed between the measured N2OAdjecent and N2OIn fluxes. Three dimentional simulations of water flow and N-forms transport and transformations showed two opposing phenomena (a) increased water contents, N concentrations, and downward flushing when the dripper is placed inside the base, and (b) hampering of the lateral distribution of water and solutes into the most bio-active part of the soil inside the base when the base is placed adjacent to the dripper. It also showed that both "In" and "adjacent" practices underestimate the "true" cumulative flux from a dripper with no base by ~25 % and ~50 %, respectively. A nomogram in a non-dimensional form corresponding to all soil textures, emitter spacings and discharge rates, was developed to determine the optimal diameter of an equivalent cylindrical base to be used along a single dripline.
