Carbon sequestration and global warming potential of irrigated and rainfed wheat fields in semi-arid regions (Case study: Shirvan)

Carbon sequestration in biomass and soils is one of the simplest and least expensive ecological strategies for removing carbon dioxide (Uri, 2000). According to researchers, carbon sequestration is an important factor in reducing global warming (Wiesmeier et al., 2014). It was demonstrated that returning fifty percent of plant residues increased the soil's capacity to sequester carbon (Yan et al., 2007). Another study revealed that the wheat-rice cultivation system sequestered 55% more carbon in fields with animal manure and 70% more carbon in fields with chemical fertilizer than the wheat-corn system (Kukal and Benbi, 2009). Given the low levels of soil organic matter in Iran's arid and semi-arid regions, particularly in the agricultural ecosystems of North Khorasan, it is crucial to employ strategies that increase the carbon content of soil organic matter. Therefore, the purpose of this study was to assess the carbon sequestration capacity of the aerial and subterranean portions of wheat and the global warming potential of the wheat production ecosystems in the province of North Khorasan.

In order to assess the carbon sequestration and global warming potentials of irrigated and rainfed wheat cultivars, an experiment was conducted in Shirvan, North Khorasan province, during the 2020-2021 growing season. For this purpose, systematic random sampling was conducted in 30 farms with 0-30 cm of soil depth, and a face-to-face questionnaire was used to assess greenhouse gas emissions and global warming potential. The studied irrigated varieties included Mihan, Pishgam, and Heydari, while the studied rainfed varieties include Azar 2 and Baran.  In order to carry out the research, systematic random sampling (Chambers, 1983) was done from six points in 30 farms from a soil depth of 0-30 cm (Mahdavi et al., 2009). In the spring, vegetative and reproductive organs such as seed + spike, stem, leaf, and root were harvested at three distinct phenological stages (shooting, flowering and physiological ripening). To study the soil, six 30-cm-deep profiles were dug under each plant and soil samples were collected. The combustion method (Abdi et al., 2008; Foroozeh and Mirzaali, 2006) was utilized to determine the organ conversion coefficients.

The results indicated that irrigated cultivars had a higher shoot conversion efficiency than rainfed cultivars, with the Pishgam cultivar having the highest average conversion efficiency at 49.68%. Among the irrigated cultivars studied, the Mihan cultivar had the highest total carbon sequestration capacity, averaging 3,398.70 kg/ha. Among rainfed cultivars, the Baran cultivar had a higher total carbon sequestration than the Azar 2 cultivar, which had an average of 512.60 kg/ha. The amount of greenhouse gases (CO2, N2O, and CH4) produced in irrigated and rainfed wheat fields in Shirvan was estimated to be 1626.932 kg/ha and 651.33 kg/ha, respectively, and the global warming potential of one hectare of wheat was equal to 3404.890 kg of carbon dioxide and one hectare of rainfed wheat was equal to 919.263 kg of carbon dioxide. The cultivation of Mihan (irrigated) and Baran (rainfed) cultivars in the agroecosystem of North Khorasan will increase carbon sequestration capacity and decrease CO2 emissions, according to the findings of this study.

Based on the results of this study, the aerial carbon sequestration capacity of irrigated wheat cultivars was greater than that of rainfed cultivars. Moreover, among plant organs, the wheat leaves had a greater capacity for carbon sequestration than the wheat roots. Mihan was the cultivar with the highest aerial carbon sequestration capacity among irrigated cultivars, while Baran was the cultivar with the highest aerial carbon sequestration capacity among rainfed cultivars.