Agriculture accounts for approximately 14% of greenhouse gas emissions, which has a high potential for reduction (Cichorowski et al, 2015). The adoption of conservation agriculture aims to promote a more sustainable and environmental friendly management system compared to conventional agriculture (Habbs et al, 2008). Crop rotation and soil conservation are principles of conservation agriculture, which have shown 18.9% reduction in carbon emissions in crop rotation compared to monoculture systems, and 14.7% reduction in no-till system compared to conventional tillage (Yin et al, 2017). Cultivation as a crucial agricultural management technique impacts the dispersion and conversion of soil organic carbon (SOC), stability of soil particles, water retention capacity, and soil temperature by regulating pathways for air and water exchange between the soil surface and the atmosphere (Bregaglio et al, 2022). So selecting proper cultivation system is essential to meet sustainability goals and farm productivity.
Proper selection of agricultural operations can lead to a decrease in pollutant gases. Soil management is one of the most influential operations affecting carbon storage and carbon dioxide emissions in agricultural systems (Page et al, 2014). Compared to soilless agriculture, soil-based agriculture has a 58% higher CO2 emissions. CO2 emission from soil have a direct relationship with soil and air temperature, and intensive soil tillage, heavy rainfall, or extra irrigation increase CO2 emission from the soil. In a study on alfalfa and wheat crops in North Dakota, irrigation and intensive tillage have resulted in a 27% and 58% increase in CO2 emission compared to non-irrigated and soilless conditions, respectively (Sainju et al, 2006). Irrigation and soil surface cover also potentially affect carbon and nitrogen cycling, and as a results affect the emissions of CO2 and NO2 gases from the soil. Kallenbach et al. (2010), demonstrated that soil covered with residues had 40% and 15% higher CO2 emission compared to bare soil under surface and drip irrigation methods, respectively. In covered soil with residues, CO2 and NO2 emissions increased by 425 milligrams and 60 micrograms per square meter per hour compared to bare soil, respectively. Fossil fuels are also significant contributors to emission of greenhouse gases from the farm, and their consumption is directly related to the number of operations carried out on the farm. Therefore, by managing these operations, fuel and other related inputs reduce and as a results greenhouse gas emissions decrease. Another important factor in the emission of greenhouse gases is the way in which agricultural residues is managed. Burning residues as a managing way releases particulate matter and pollutants into the air. In many developing countries, burning residues is a common practice, and in Iran, unfortunately it is a common way to manage the residues for many farmers. Burning crop residues significantly increases the emission of fine particles in the atmosphere, affecting the air quality in the surrounding areas of the fields and even distant locations. In this regard, a study by Dhammapala et al. (2006), in eastern Washington and northern Idaho reported that 4% of particles smaller than 2.5 microns and 34.5% of carbon emissions were related to burning residues in the agricultural sector. In Iran, there are also numerous cases of burned farmlands, for example in the Khuzestan province as one of the most important province of crops productions, approximately crop residues of 195,000 ha agricultural lands were set on fire in 2019 (Bogari et al, 2023). Therefore, recommending a production pattern that reduces environmental pollutants is essential for sustainable agriculture, and this requires replacing current production methods with new patterns and practices in agriculture.
The impact of different land uses in agriculture on the emission of greenhouse gases was investigated using a closed chamber and gas chromatography method (Mahdipour and Landi, 2010). In this study, CO2 emission from wheat, canola, citrus orchards, and fallow were estimated as 4.47, 3.72, 3.38, and 1.89 t/ha/y, respectively. Dong et al. (2017), examined the effect of tillage on short-term and long-term CO2 emission in dry regions of China. In this study, three tillage treatments including conventional tillage with a moldboard plow, no tillage with wheat straw mulching, and no tillage without crop residues were studied for their impact on CO2 emission. Their results showed that immediately after tillage and up to 48 hours, the CO2 emissions from conventional tillage were significantly higher, but the annual emissions from the wheat straw mulching treatment were higher than the other two tillage methods. The highest emission were estimated as 0.2 grams per square meter per hour in winter, while the lowest emission were 0.04 grams per square meter per hour in summer. CO2 emission from soil is an important part of the terrestrial ecosystem cycle. Tillage is an influential operation in carbon storage and CO2 emission in agricultural ecosystems (Page et al, 2014). Increasing concerns about global warming and changes in soil management in agriculture can have significant effects on CO2 emissions (Sheehy et al, 2015). Research has shown varied results on the impact of tillage on CO2 emissions, with some studies reporting lower levels (Shahidi et al, 2014) and others indicating higher emissions (Fuetes et al, 2012), while some studies have reported that tillage had no significant effect on gases emission (Aslam et al, 2000).
The effect of soil managements on CO2 emission from soil depends on factors such as soil temperature, soil moisture content, or the interaction between these two factors (Lu et al, 2015). Research suggests that soil temperature and moisture can cause variations of 76 to 96 percent in CO2 emission from soil (Xu and Qi, 2001). The release of NO2 and CO2 from agricultural soils is a result of complex interactions between water, biological, chemical, and physical properties of the soil (Oorts et al, 2007). The agricultural soils in Khuzestan province are often characterized by poor organic matter content and low stability, which can lead to soil structure degradation with excessive flooding irrigation. Implementing drip irrigation with reduced speed and quantity of water can help maintain soil stability (Bougari et al, 2021). Water management can influence these mentioned properties and have an impact on the emission of greenhouse gases (Kallenbach et al, 2010). An increase in greenhouse gas emissions can occur during irrigation hours and several hours after irrigation (Khalil and Bags, 2005).
Soil management practices have the potential to reduce CO2 emission from the soil (Mangalassery et al, 2014 and Abdalla et al,. 2016). In a study, CO2 emission were examined in different farming systems in sugarcane cultivation, including conventional tillage, minimum tillage, and reduced tillage with residue retention. The highest CO2 emission was observed in conventional tillage, followed by minimum tillage and reduced tillage, with values of 350, 51.7, and 5.5 grams per square meter, respectively. CO2 emission in conventional tillage can lead to up to an 80% reduction in soil carbon, emphasizing the need for conservative tillage (Silva-olaya et al, 2013). Wei et al. (2018), investigated the effects of surface and subsurface irrigation on the potential for global warming through the emissions of NO2 and CO2 in a laboratory-scale study using soil that had been prepared after tomato harvest. The results of this study showed that the emissions of NO2 and CO2 in surface irrigation were 28.9% and 19.4% lower, respectively, compared to subsurface irrigation at 72 and 168 hours after irrigation. In a study conducted in China, it was found that no-tillage resulted in less CO2 emission compared to conventional tillage, while the use of residue mulching in each tillage led to an increase in the emission (Yao et al,. 2023). In general, sustainable agriculture has the potential to reduce greenhouse gas emissions, without a bad side effect on yield (Zhong et al,. 2022). However, no study has been conducted to examine the effects of tillage, irrigation, residue, planting and their interactions on the emission of CO2 from the soil and CO2 eq emission from the inputs in wheat-maize rotation. Therefore, this study was carried out to examine CO2 emission from the soil, CO2 eq emission from the inputs and the total CO2 emission in different farming systems, aiming to suggest the best system and estimate effect of each change and their interactions.