## 3 Results
### Power Generation or Biofertilizer: Energy and Carbon Dioxide Footprint Comparison  
There are some forms of straw use, such as straw-to-energy and straw return-to-field. [PERSON] et al. [51] studied the benefits of straw return-to-field. Straw retained in arable lands can increase organic nitrogen, phosphates, and potassium, which enhance crop yield [81; 82; 83]. Researchers found a number of disadvantages of straw return-to-field technology, such as nitrous emissions, methane emissions, and the possible reduction in crop yield (in the case of high levels of straw retained) [84; 85; 86; 87; 88]. In this study, we evaluated the environmental and energy indicators of straw use as biofertilizers compared with power generation. Crop residues can be used for power generation and use as fertilizers. The use of agricultural residues as a substitute for mineral fertilizers can reduce the energy consumption and carbon dioxide emissions of agricultural practice. That is why the comparison of different pathways for crop residues is of scientific and practical interest. The use of crop residues as fertilizers saves the following amount of energy:  
\[FES=\sum_{i=1}^{n}\left(\frac{NG_{i}\cdot EEq_{i}}{100}\right)-\Delta H,\ \text{MJ/kg}, \tag{27}\]  
Figure 8: Energy specific costs. where \(NG_{i}\) is the content of the \(i^{th}\) nutrient component in a crop residue, %; \(EEq_{i}\) is the energy equivalent of the \(i^{th}\) nutrient component, MJ/kg. An organic fertilizer produced from crop residues can reduce carbon dioxide emissions caused by the production process of mineral fertilizers as such:  
\[CDEFS=\sum_{i=1}^{n}\left(\frac{NG_{i}\cdot CDFP_{i}}{100}\right)-\frac{CDET \cdot SR}{Ys},\ \text{kgCO}_{2}/\text{kg}, \tag{28}\]  
where \(CDFP_{i}\) is the carbon dioxide emissions caused by the production of the \(i^{th}\) nutrient component in a mineral fertilizer, kg CO\({}_{2}/\text{kg}\). The carbon dioxide emissions and energy used by the production process of mineral fertilizers are presented in Table 3[62; 63; 64]. As an example, corn stover was considered. Corn stover has the following composition of nutrient components: nitrogen--5.95; phosphorus--0.56; potassium--7.91 g/kg [89]. In our study, we used the data reported by [PERSON] et al. [90; 91]. The energy used for straw formation is around 8.81% of the total energy potential of straw (Figure 9). The embodied energy of mineral fertilizers substituted by straw is at least four-fold compared with the energy used for straw formation. Therefore, the use of straw for energy generation is more energy-efficient. Carbon dioxide emissions were analyzed too. The total carbon dioxide emissions of corn production are around 1895 kg CO\({}_{2}\)/ha. The energy associated with straw formation is 1048 kg CO\({}_{2}\)/ha of straw. Therefore, WTT is equal to 0.112 kg CO\({}_{2}\)/kg. In our calculation, the following emission factor (power generation) was assumed: average--0.578; minimum--0.146; maximum--1.593 kg CO\({}_{2}\)/kWh [90]. Our study revealed that the use of straw for power generation saves more carbon dioxide emissions compared with the straw return-to-field technology (Figure 10). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Fertilizer Product**} & **Primary** & **Percentage (by** & **Consumption,** & **Carbon Dioxide** & **Emissions, g** \\  & **Component** & **Weight)** & **MJ/kg (Primary** & **CO\({}_{2}\)/kg (Primary** \\  & & & **Component)** & **Component)** \\ \hline Ammonium nitrate & N & 33.5 & 90.30–121.21 & 2298–7108 \\ Urea & N & 46 & 52.02–112.17 & 913–4018 \\ Ammonia & N & 82 & 1491–2637 \\ Single superphosphate & P & 21 & 61.90 & \(-\)238–1051 \\ Triple superphosphate & P & 48 & 16.50–63.02 & \(-\)416–1083 \\ Potassium chloride & K & 60 & 16.77 & 583 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Carbon dioxide emissions and energy used by production processes. Figure 9: Energy parameter of straw production and utilization. Energy saving was analyzed too.