The effect of static chamber base on N2O flux in drip irrigation

Abstract. Static chambers are commonly used to provide in situ quantification of nitrous oxide (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 chamber bases on water and N distribution and the subsequent impact on N2O fluxes. N2O emissions were measured in a drip-irrigated avocado orchard for 2 years, using bases with a dripper at their center (In) and bases installed adjacent to the dripper (adjacent). During the irrigation and fertigation season, the measured N2OIn fluxes were greater than the N2OAdjacent fluxes (0.015 ± 0.003 vs. 0.006 ± 0.001 g m−2 d−1). By contrast, during the winter, when the orchard is not irrigated or fertilized, insignificant differences were observed between the measured N2OAdjecent and N2OIn fluxes. Three-dimensional simulations of water flow, N transport, and N 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. Further studies under variable conditions (soil types, wetting patterns, nutrient availabilities), rather than a single study, are needed to test the constructiveness of the suggested methodologies.