Evaluation of Carbon Sequestration for Above-Ground and Below-Ground Tissues and Global Warming Potential of Wheat (Triticum aestivum L.)

CO2 is considered the most important greenhouse gas, due to the dependence of world economies on fossil fuels. CO2 concentration are enhancing in the last decades, mainly due to the increase of anthropogenic emissions. Carbon dioxide capture is a technology aimed at mitigating greenhouse gas emissions from burning fossil fuels during industrial processes. Conservation tillage, crop rotation, and crop residue management are agronomic practices that potentially decrease CO2 and other greenhouse gas emissions from agriculture. Crop residues also improve organic matter decomposition due to declined soil-residue contact. Soil is one of the significant “friends” in combating climate change and global warming, and a zero-soil consumption approach is the best way to stop adverse effects, although it is not the only one that should be applied. The soil has been considered as a possible carbon sink for sequestering atmospheric CO2.
Our purposes were to determine a set of coefficients for calculating conversion coefficients, dry weight, organic carbon, and carbon sequestration of above-ground and below-ground tissues and assess global warming potential (GWP) for wheat as an essential crop in Khorasan-e Razavi province.

A systematic random sampling method was employed to select five samples from 25 fields situated in Khorasan-Razavi Province, Iran, during 2016 and 2017. The experimental design was a completely randomized design with three replications. Below-ground tissues by using a cylinder were manually sampled and then separated from the soil. After sampling, the above-ground tissues (such as flower and leaf) were isolated from below-ground tissues (including tunic and corm) to measure the above-ground and below-ground biomasses, respectively. Above-ground and below-ground biomasses were separately dried to constant weight and expressed on a dry matter basis. Conversion coefficients of above- ground and below- ground tissues were determined with the combustion method separately. Then, sequestration carbon potential for above- ground and below- ground tissues of saffron and soil were computed. The ash method was used to determine the conversion coefficients in spikes, stems, leaves, and roots. Finally, greenhouse gases (such as CO2, N2O, and CH4) emission were also calculated using emission coefficients. Cronbach's alpha was used for assessing the reliability of the questionnaire.
For statistical analysis, analysis of variance and Duncan’s test were performed using SAS version 9.3.

The results showed that dry weight, organic carbon content, conversion coefficients, and carbon sequestration for above- ground and below- ground tissues of wheat were significantly different. The biomass of above-ground tissues was higher than below-ground tissues of wheat. The results revealed that the maximum (52.0%) and minimum (31.99%) conversion coefficients of wheat were related to spikes (seeds included) and roots, respectively. Besides, the total carbon sequestration of below-ground and above-ground of wheat was calculated 8.25 t.ha-1 so that the maximum (4.28 t.ha-1) and minimum (0.35 t.ha-1) values were found in stems and roots, respectively. GWP was recorded as 8884.86 kg CO2-equiv. per one ton of seed.

This study shows that while there is significant potential for sequestering carbon in wheat agroecosystems through root and straw incorporations. It is recommended that returning wheat crop residues to the soil affected the soil's physical, chemical, and biological properties. Furthermore, as nitrogenous fertilizer application plays a crucial role in increasing GWP, thus it is suggested that organic fertilizers and legumes might be suitable alternatives for chemical fertilizers. It is therefore concluded that the application of crop residues in agroecosystems seems to be a rational ecological approach for sustainable management of wheat agroecosystems with a consequence of the reduction in greenhouse gases and mitigation of climate change. This could make a significant contribution to improving agricultural sustainability and stability in arid and semiarid regions.