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

Abstract

Mitigation of greenhouse gas emissions is essential to combat climate change, and also for sustainable agriculture. Agriculture is facing 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 5-year old pomegranate orchard. Surface drip irrigation (DI) and subsurface drip irrigation (SDI) were tested as main treatments. 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. The CO2 flux near the irrigation line was significantly higher 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. However, no significant differences in cumulative CO2 emissions were determined between DI (7.5-9.5 Mg ha-1) and SDI (7.7-9.0 Mg ha-1) due to small wetting areas under DI. These values may subject to error due to the limited number of sampling times in spatial variations. The higher DOC and water content in surface soil from DI contributed to the higher CO2 emissions in comparison to SDI. The spatial variation should be considered to accurately estimate CO2 emissions in orchard settings especially with irrigation systems. The SDI provides overall benefits of water savings, improvement on nutrient use efficiency, and reduction in total greenhouse gas emissions.