Upscaling Point Measurements of N2O Emissions into the Orchard Scale under Drip and Microsprinkler Irrigation

Agricultural activity is one of the major sources of nitrous oxide (N2O) emission into the natural environment. Yet, due to the soil's spatial heterogeneities it is hard to accurately upscale point N2O emission measurements into the orchard scale. This study aims to introduce a simple, yet robust, way for upscaling point N2O emission measurements into the orchard scale, under drip and micro-sprinkler irrigation systems. Surface point measurements of N2O emissions were performed at five distances from drip and micro-sprinkler emitters in two almond orchards, following irrigation and fertigation events. Principal component analysis (PCA) and linear regression were used to study the correlations between the soil water filled pore-space (WFPS), and subsurface N2O, NO3- and NH4+ concentrations down to depth of 60 cm. The correlation tables indicated that most of the N2O emission resulted from microbial nitrification in the top soil (< 10 cm). However, in many cases the correlations did not provide meaningful explanations to the relations between the subsurface parameters and the surface N2O emission flux. It was suggested that the main limitation of the analysis results from the current soil sampling method, where soil samples are not taken from the profile inside the collar in-order to keep the soil profile undisturbed over long measuring periods. In the microsprinkler irrigation, relative water application depth of the emitter, showed strong positive linear correlation to the soil NH4+ concentration and surface N2O emission flux. These correlations could be used for upscaling the point measurements into the tree and orchard scale. In the drip irrigation, the N2O emission flux was found to follow the water and NH4+ distribution pattern, and could be upscaled to the tree and orchard level using a sinusoidal function using only measurement of the peak emission and the radius of the wetting pattern. These results improve current understanding on the dynamics of N2O production in orchards irrigated with micro-irrigation systems in arid and semi-arid ecosystems and might contribute to modeling of N2O emissions using less rigorous methods.