Subsurface Drip Irrigation Reduced Nitrous Oxide Emissions in a Pomegranate Orchard

Abstract

Soil fertilization is one of the major sources for nitrous oxide (N 2 O) emissions and soil moisture is among the most important factors affecting its production. Thus, one of the important mitigation strategies in semiarid or arid regions is through irrigation and/or fertigation management. The objective of this research was to evaluate the effects of different drip irrigation methods and N application levels on N 2 O emissions. Nitrous oxide emission flux and N 2 O concentration in soil profile were measured in a pomegranate field for two growing seasons under two irrigation systems [subsurface drip irrigation (SDI) at ~0.5 m depth and traditional surface drip irrigation (DI)], and three N application rates (50%, 100%, and 150% of current practice rate). Both years' data showed that N 2 O emissions has a high and positive correlation with N fertilization events and application levels. Nitrous oxide emissions from DI at 100% and 150% N levels were over an order of magnitude higher compared to those from SDI based on the data of the first year. Data from the second year confirmed the first year's findings of high emissions from DI. A positive linear correlation between the N 2 O emission flux and N 2 O concentration in soil-gas phase was identified that supported emission data. This research demonstrated that although N fertilization is a major cause for N 2 O emissions, subsurface drip irrigation/fertigation can lead to a significant emission reduction in addition to other benefits, such as increased water and nutrient use efficiencies, and reduced weed pressure.Index Terms-Chemical nitrogen fertilizer, greenhouse gas emission, high-frequency drip irrigation.

Carbon Dioxide Emissions and Spatial Variability Affected by Drip Irrigation Methods in a Pomegranate Orchard

“…The DI showed much higher moisture than SDI in surface soils. Gao et al (2019) [25] reported that soil water content increased as soil depth increased in SDI, but was relatively uniform under DI because the high frequency irrigation resulted in surface soil (5 cm depth) near field capacity most of the time. Under SDI, much drier surface soil was monitored with higher water content at deeper depth.…”

“…Tirado-Corbalá et al [24] examined C and N dynamics from this field research. We also measured greenhouse gas nitrous oxide (N 2 O) emissions for two years and the results were reported in Gao et al [25]. The previous studies have concluded that SDI led to water savings and much lower weed pressure in comparison with DI and there was significantly higher N uptake in fruits from SDI at least in two out of the last three years of measurements [22].…”

“…The no significant difference in DOC (Table 3) from the various N level may suggest that microbial activities were not limited by nutrients and possibly energy source, but more by moisture condition affected by irrigation methods. However, N 2 O emissions were much higher at higher N application levels (25).…”

“…The soil has 17% water content at 33 kPa that can translate to a field capacity of ~ 26% (v/v) with an average bulk density of 1.55 g cm -3 [26]. Details on the project, soil property, and orchard operation can be found in Ayars et al [22] and in Gao et al [25]. All trees received the same amount of N fertilizers during the first two years to ensure uniform growth prior to different irrigation and fertilization treatments starting in 2012.…”

“…Although soil N concentration was higher in subsurface soil under SDI from fertigation, using high irrigation frequency can reduce leaching potential [24]. The SDI resulted in significantly lower N 2 O emissions than DI [25]. The objective of this paper was to evaluate the effects of drip irrigation method and N fertilization level on CO 2 emissions during growing season and evaluate spatial variations.…”