Carbon dioxide emissions and spatial variability affected by drip irrigation methods in a pomegranate orchard

Authors: Gao, Suduan; Hendratna, Aileen; CAI, ZEJIANG - Chinese Academy Of Agricultural Sciences; PFLAUM, TOM - Retired ARS Employee; QIN, RUIJUN - Oregon State University; PHENE, CLAUDE - Collaborator

Submitted to: International Journal of Environmental Science and Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2020
Publication Date: 5/1/2020
Citation: Gao, S., Hendratna, A., Cai, Z., Pflaum, T., Qin, R., Phene, C. 2020. Carbon dioxide emissions and spatial variability affected by drip irrigation methods in a pomegranate orchard. International Journal of Environmental Science and Development. 11(5):217-224. https://doi.org/10.18178/ijesd.2020.11.5.1254.
DOI: https://doi.org/10.18178/ijesd.2020.11.5.1254

Interpretive Summary: Subsurface drip irrigation (SDI) provides the benefits for water savings, nutrient use efficiency, reduced weed pressure, and reduced nitrous oxide emissions, but it is not clear if SDI reduced carbon dioxide (CO2) emissions. This research measured CO2 emission flux from irrigation line in a pomegranate orchard during a growing season and also spatial variability and diurnal changes to estimate total CO2 emissions from the orchard. Conventional surface drip irrigation (DI) led to much higher CO2 emissions flux at the irrigation line compared to that from SDI with drip tubing installed at 0.5 m soil depth. The differences were mainly attributed to differences in soil water content that affect biological activities in surface soil. Due to relatively small wetting areas affected by surface irrigation, estimated cumulative emissions from the whole orchard were not significantly different. Integrating with previous findings, SDI is still a promising efficient strategy for water and nutrient management, and improvement on sustainability of crop production systems.

Technical Abstract: Mitigation of greenhouse gas emissions is not only essential to combat climate change, but also for sustainable agriculture. California, the most productive state in United States of America (USA), faces a growing number of challenges including water shortage and environmental degradation that threaten crop production. In this research, field monitoring was carried out to evaluate the effects of drip irrigation methods and nitrogen (N) fertilization level on carbon dioxide (CO2) emissions in a pomegranate field with surface drip irrigation (DI) and subsurface drip irrigation (SDI) systems as main treatments. Under each irrigation method, three N application rates (50%, 100%, and 150% in reference to current practices) were applied as sub-treatments. CO2 emission data were collected during the growing season when the orchard entered its fifth year. Data show that CO2 flux near the irrigation line was strongly affected by irrigation with significantly higher flux from DI (ave. 2.67 µmol m-2 s-1) than SDI (ave. 1.74 µmol m-2 s-1). There were significant spatial variations surrounding a tree from DI but much less from SDI. Although much higher flux was measured from the DI irrigation line than from SDI, which occupied only small areas in the field, cumulative CO2 emissions estimated from the orchard were not significantly different between DI (7.5–9.5 Mg ha-1) and SDI (7.7–9.0 Mg ha-1). These values are subject to error due to the limited number of times in measuring spatial variations. Dissolved organic carbon (DOC) concentration in surface soil was found higher from DI than SDI. All data suggest that higher DOC and water content from DI largely contributed to the higher CO2 emissions. Improvement on estimates of total emission in field with high spatial variation is needed, especially in orchard settings with irrigation systems that create nonuniform distribution of water in soil. In summary, SDI provides great benefits in water savings, improved nutrient use efficiency, and reduced greenhouse gas emissions.