Introduction

Amidst escalating global climate crises, China has legislated its Dual Carbon Agenda through the National Climate Change Adaptation Plan (2022–2035), mandating systemic decarbonization pathways to peak CO2 emissions by 2030 and achieve carbon–neutral development by 2060. One-third of greenhouse gas (GHG) emissions are attributed to agricultural activities11,2. Therefore, reducing carbon dioxide (CO2) emissions and increasing carbon sequestration in agriculture and rural areas are key measures and potential opportunities for achieving carbon peaking and neutrality3. CR is an important zero-carbon biomass resource and a current research hotspot. The random disposal and ineffective use of crop residue (CR) result in economic losses and environmental pollution4. Consequently, this issue is receiving increasing attention, especially under the “dual carbon” and global 1.5 °C target framework.

The comprehensive utilization of CR resources has been highly emphasized by governments and academia in recent decades. How to utilize CR is a global issue5,6. The utilization using CR for various applications, such as fertilizer production7, animal feed development8, energy generation9, raw materials, and culture substrate10, can foster a synergistic enhancement in agricultural carbon mitigation and sequestration, thus contributing to the advancement of sustainable agriculture. However, the marketization and industrialization of straw utilization, or the commercialization of the “straw economy,” still faces many dilemmas, such as technical bottlenecks, an incomplete system of collecting and storing, non-sustainable practice, low farmers’ enthusiasm and economic benefits, etc. The dynamic assessment of theoretical and available straw yields, along with spatiotemporal distribution characteristics of CR, is an essential foundation for the collection, storage, transportation, and comprehensive utilization of straw resources11. Studies on China’s CR yield and utilization have been extensively reported12,13, but few research studies have focused on the regional situation. At present, regional CR utilization is diverse, stimulating the development of various CR industries. Thus, it is necessary to evaluate the overall situation of CR utilization and its potential for CO2 mitigation for a region.

CO2 mitigation and carbon sequestration depend on CR management, which is essential for achieving green and low-carbon agricultural development14,15. Utilizing CR for purposes such as fertilizer, feed, and energy can foster a synergistic advancement of agricultural carbon mitigation and sequestration, contributing to the development of sustainable agriculture. Based on this background, many researchers focused differently on the carbon mitigation effects of comprehensive CR utilization. Zhao16 reported that extensive CR utilization in China could offset carbon emissions by 62.6 × 106 t C eq yr−1, equivalent to 27.7% of the national agricultural carbon emissions. Of those contributions, CR used as fertilizer, feed, and energy accounted for 58.3%, 22.2%, and 19.5%, respectively. The contribution value of CR comprehensive utilization to reduce CO2 emissions in 2020 in China was estimated as 7.0 × 107 t by Huo17. Shi18 comprehensively assessed the environmental impacts of CR utilization during the 1950–2021 period, which indicated that developing bioenergy is an effective strategy for reducing CO2 emissions and sustainable utilization of CR. However, studies on the potential of carbon mitigation from regional CR comprehensive utilization are still limited.

There are variations in the types of crop residue (CR), the levels of CR utilization, and CO2 mitigation across different regions of China. The strengths of regional CR utilization and carbon reduction research lie in the availability of richer and more precise fundamental data, which provide favorable conditions for subsequent carbon accounting. Investigating regional CR utilization and carbon reduction from a local to global perspective serves as a crucial complement to China’s overall CR utilization and carbon reduction efforts. Currently, while there are numerous reports on straw-based carbon mitigation through CR utilization in China, studies at the regional level remain scarce16,18. As a key agricultural province in China, Sichuan Province possesses abundant straw resources. Therefore, this study adopted ArcGIS 10.1 to perform the spatial distribution of CR yield, their utilization, and CO2 potentials in Sichuan Province and analyzed their dynamic variation, to clarify the contribution of regional comprehensive utilization of CR to the potential for CO2 mitigation. This study provides a theoretical basis and data support for achieving full-scale, scientific, efficient CR utilization and CO2 mitigation in Sichuan Province. Additionally, it can enrich the ledger of CR comprehensive utilization in China.

Methodology

CR yields estimation

Crop production varies across Sichuan province due to differences in pedoclimatic conditions, crop types, and management practices. Four main agriculture regions and identified in Sichuan: West Sichuan( including cities of Aba(AB), Ganzi (GZ), Liangshang (LSH), Panzhihua (PZHH)), Chengdu Plain(including cities of Chengdu(CHD), Deyang(DY), Mianyang(MY), Meishan(MSH), Yaan(YAN), Suining(SN)), Northeast Sichuan(including cities of Guangyuan(GY), Bazhong(BZH), Dazhou(DZH), Nanchong(NCH), Guangan(GAN), Southern Sichuan(including cities of Ziyang(ZY), Zigong(ZG), Neijiang(NJ), Yibin(YB), Leshan(LS), Luzhou(LZH)).

The data on crop sowing areas and crop yields were obtained from the “Sichuan Statistical Yearbook (1990–2022).” The comprehensive utilization rate of crop straw for 2015 was sourced from the “Sichuan Province Crop Straw Comprehensive Utilization Plan (2016–2020).” The data for 2016 and 2017 were extracted from the “Sichuan Rural Yearbook,” while the 2018 data were derived from the “Sichuan Statistical Yearbook.” Finally, the 2019 data were retrieved from the “Compilation of Common Data on Comprehensive Utilization of Crop Straw (2020).”

The theoretical CR yield (CY) is estimated using formula (1), while the available CR yield (TY) is calculated according to formula (2).

$${\text{CY}} = \sum\limits_{{{\text{i}} = 0}}^{{\text{n}}} {Xi*Ai}$$
(1)
$${\text{TY}} = \sum\limits_{i = 0}^{n} {Xi*Ai*Bi}$$
(2)

As shown in formulas (1) and (2), CY represents the CR theoretical yield, TY indicates the available CR yield, Xi is the yield of the i-th crop, Ai denotes the CR-to-grain ratio of the i-th crop, and Bi is the collection coefficient of the i-th CR. Ai and Bi were obtained from the letter updating the CR index and collectible coefficient from the Ministry of Agriculture and Rural Affairs of China (MARAC, 2019)19, as listed in Table S.1. This study used rice, maize, rapeseed, wheat, potato, soybeans, and peanut CR to estimate the CY and TY in Sichuan Province.

The GHG emission from CR burning

Burning CR in the field generates many GHGs, primarily CO2, CH4, and N2O. The amount of GHG emissions from CR burning in this study was estimated according to the methods outlined in the IPCC 2006 National GHG Inventories Guidelines, as shown in formula (3).

$$RGHGE_{ sbj} = \sum {TY_{i} *Cf_{i} *Gef_{j} }$$
(3)

where TYi represents the available CR yields of different crops, Cfi is the burning factor of the i-th CR, and Gefj indicates the emission factor of the j-th GHG (including CO2, CH4, and N2O), RGHGHsbj denotes the aggregate of the j-th GHG emissions generated from CR burning in the field. Cfi and Gefj were obtained from IPCC 200620 as shown in Table S.2.

CR utilization as fertilizer and its CO2 mitigation

CR nutrient quantity (SN) is crucial for estimating CO2 mitigation potential from being used as fertilizer, represented by the net content values of N, P2O5, and K2O in CR. The theoretical and actual SNs were calculated using formulas (4) and (5), respectively. The CO2 mitigation was calculated according to formula (6).

$$SN_{ij} = \sum {SY_{j} *C_{ij} *\zeta_{i} }$$
(4)
$$SN_{ia} = { }SN_{ij} {*}f { }$$
(5)
$${\text{RGHGE}}_{SN} = SN_{ia} *F_{i}$$
(6)

where SNij is the sum of different SN of N, P2O5, and K2O, respectively. TYj is the CR yield of different crops; ζi denotes the conversion coefficients of N, P, and K to N, P2O5, and K2O, respectively; SNia indicates the actual SN of different CR; f is the coefficient of CR used as fertilizer; RGHGESN is CO2 reduction by replacing fertilizer with CR nutrients; ζi and f were obtained from the Magazine21 listed in Table S.3. Fi is CO2 emission coefficients of N, P2O5, and K2O contained in CR replacing those nutrients in fertilizer, respectively, which is derived from Chen22 as shown in Table S.4.

CR utilization as feed and its CO2 mitigation

CR serves as an important coarse feed for animals. Utilizing CR as feed not only addresses the feed shortage for herbivores but also reduces GHG emissions, helping to alleviate the speed of global warming. The potentials of CR utilization for feed and its CO2 mitigation can be estimated with formulas (7) and (8), respectively.

$${\text{SF}} = {\text{TY}}/{\text{N}}$$
(7)
$${\text{RGHGE}}_{feed} = TY*CL_{feed} *f_{g}$$
(8)

where SF is the theoretical sheep-carrying capacity of CR, which is quoted from Hong23; TY indicates the available CR yield; N is sheep-carrying capacity fed by each kilogram CR; RGHGEfeed represents CO2 mitigation from CR used as feed; CLfeed is utilization coefficient of CR feed; fg indicates CO2 emission coefficients, which is obtained from Huo17.

CR utilization as energy and its CO2 mitigation

CR is an important source of biomass energy. The amount of standard coal can express the energy value of CR. The potentials of CR utilization as energy and its CO2 mitigation can be calculated with formulas (7) and (8), respectively.

$${\text{SCE}} = \sum {TY_{i} *CF_{i} }$$
(9)
$${\text{RGHGE}}_{{ {\text{en}}}} = {\text{SCE*CE *}}44/12{ }$$
(10)

where SCE represents the sum of the amount of standard coal from different crops; TYi is available to CR yields of various crops; CFi denotes the conversion factors of standard coal equivalent for different CR; RGHGEen indicates CO2 mitigation from CR used as energy; CE is standard coal carbon emission factor.

CR comprehensive utilization and its CO2 mitigation

The comprehensive utilization of CR significantly reduces carbon emissions and achieves carbon neutrality. This study primarily analyzed the CO2 mitigation from CR used as fertilizer, feed, energy, raw material, and culture substrate, which was calculated based on formula (11).

$${\text{RGHG}} = RGHGE_{SN} + RGHGE_{{{\text{feed}}}} + RGHGE_{en} + RGHGE_{rm} + RGHGE_{cs}$$
(11)

where RGHG represents the sum of CO2 mitigation from CR used as fertilizer, feed, energy, raw material, and culture substrate, RGHGESN, RGHGEfeed, RGHGEen, RGHGErm, and RGHGEcs indicate CO2 mitigation from CR used as fertilizer, feed, energy, raw material, and culture substrate, respectively.

Data analysis

Data processing and drawing figures were conducted using Origin 2021. We used arcgis10.1 to perform the spatial distribution of CR, CR comprehensive utilizations and associated CO2 mitigation potential, which mainly includes data preparation, data connection, symbolic setting of maps and export of mind maps, etc. The URL is GIS Software for Mapping and Spatial Analytics | Esri.

Results

Spatiotemporal characteristics of CR

CR species and temporal characteristics

The dynamic evaluation of theoretical and utilizable CR constitutes a critical precondition for optimizing comprehensive CR utilization strategies24. This study systematically analyzed the average proportional distribution of CR yields (Fig. 1a) and cultivated area allocations (Fig. 1b) in Sichuan Province between 1990 and 2022. As illustrated in Fig. 1a, rice CR (36.3%) and maize CR (25.5%) predominated in theoretical production, collectively accounting for 61.8% of total yields. Subsequent contributions originated from wheat (13.7%), potato (11.2%), and rapeseed CR (8.0%). These quantitative findings demonstrate that rice and maize consistently served as the principal CR sources across the three-decade observational period.

Fig. 1
figure 1

The average proportion of different CR yields (a) and crop sown areas (b) in Sichuan Province from 1990 to 2022.

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The crop planting areas are presented in Fig. 1b, with rice having the largest share at 21.5%, maize at 15.4%, wheat at 13.1%, potato at 12.8%, and rapeseed at 9.8%. Different CR yield positively correlates with their respective planting areas.

Longitudinal analysis of temporal variation patterns in cultivated land allocation (total/individual crop types) and CR productivity metrics (theoretical/available yields) was systematically conducted for the 1990–2022 timeframe (Fig. 2). As shown in Fig. 2a., during the 30 years, the total crop sown area ranged from 9.05 to 10.20 Mha, which represented a gradually increasing trend overall. The total theoretical and available CR yield showed similar trends ranging from 34.23 to 45.52 and 25.96 to 35.70 Mt, respectively. However, it is observed that the sown areas in 1993, 2005, and 2007 decreased significantly, which was probably due to the policies promoting reforestation and grassland restoration. Specifically, the sown areas of rice and wheat, as well as their available CR yields, showed apparent decreasing trends from 1990 to 2022 (Fig. 2b and c). Conversely, those of maize, rapeseed, soybeans, potato, and peanut generally represented increasing trends during the past 30 years. Therefore, the conclusion can be obtained that the available CR yield is also positively correlated with the crop sown area, similar to the theoretical CR yield.

Fig. 2
figure 2

Variation trend of total crop sown area, theoretical and available CR yield (a), available CR yields (b) and crop sown areas (c) of different CRs from 1990 to 2022.

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Spatial distribution characteristics of CR yields

Clarifying the spatial distribution of CR is crucial for its harvest, storage, transportation, and utilization. The spatial distribution of available CR yield in 2022 is shown in Fig. 3. Generally, CR was mainly distributed in northeastern Sichuan, the Chengdu Plain, and southern Sichuan, while fewer were concentrated in the western plateau. Specifically, the available CR collected from DZH, NCH, and MY ranked first, second, and third in yields, respectively, which ranged from 2.87 to 3.34 Mt.

Fig. 3
figure 3

Spatial distribution of available and individual CR yields in 2022. (Version number: arcgis10.1, URL link: GIS Software for Mapping and Spatial Analytics | Esri).

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The spatial distribution of individual CR yield in 2022 is represented in Fig. 3. As mentioned above, the CR of rice, maize, rapeseed, and wheat were the four crop primary CRs in Sichuan province. Concretely, rice CR was mainly distributed in CHD, YB, NCH, and DZH, with yields ranging from 0.90 to 1.06 Mt, which was followed by DY, MY, GAN, and LZH, with yields ranging from 0.70 to 0.82 Mt. Maize CR was mainly distributed in MY, NCH, DZH, and LSH, with yields ranging from 0.90 to 1.01 Mt. Similarly, rapeseed CR was mainly distributed in MY, NCH, and DZH, with yields from 0.59 to 0.72 Mt. Wheat CR was distributed primally in MY, DY, and NCH, with yields from 0.43 to 0.57 Mt.

Status of CR comprehensive utilization

The comprehensive utilization of CR is beneficial for improving the rural ecological environment, and also plays a crucial role in promoting green and low-carbon agricultural development. From 2015 to 2019, the CR utilization rates in Sichuan Province showed remarkable progress, as illustrated in Fig. 4. In 2008, the comprehensive utilization rate of CR was less than 40%, yielding 40.56 Mt. However, by 2015, this rate had significantly increased to 81.3%. This growth was primarily due to the vigorous promotion of returning CR to fields and implementing key projects to maximize CR utilization. Overall, the utilization rates continued to rise steadily from 2015 to 2022, reaching 93.17% by 2022, even higher than the national average. These figures indicate that significant progress has been made in the comprehensive utilization of CR in recent years.

Fig. 4
figure 4

Comprehensive utilization rate and the proportion of CR utilization methods in recent years.

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Additionally, we investigated the proportions of various CR utilization methods over this period, as illustrated in Fig. 4. The primary method of CR utilization in China involves its application as fertilizer. In line with national trends, the predominant use of crop residue (CR) in Sichuan Province has consistently been as fertilizer throughout the study period. Utilization as feed and energy ranked second and third, respectively, followed by uses as cultural substrates and raw materials.

CO2 mitigation from CR comprehensive utilization

The comprehensive utilization of CR is crucial in mitigating climate change, as carbon sequestration and GHG mitigation depend on CR management25,26. This approach is considered one of the key strategies for achieving carbon neutrality in agricultural and rural areas. With technological advancements and supportive government policies in China, mitigating GHG emissions through effective CR utilization can yield even more significant results.

The GHG emissions from the open field burning of CR

Open field burning of CR produces a large number of GHGs, primarily including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). According to the IPCC 2006 methodology, the average total emissions of CO2, N2O, and CH4 from open-field burning of CR (wheat, maize, and rice) from 2015 to 2022 in Sichuan Province were 30.548 Mt, 4.033 thousand tons, and 0.137Mt, respectively (Table 1). Specifically, open field burning of maize and rice CR significantly contributed to GHG emissions. Assuming a CR burning rate of 5%, GHG emissions from CR burning in Sichuan Province amount to 2.98 Mt of CO2 equivalent. Burning in open air wastes valuable resources and causes climate change and severe environmental pollution, posing risks to human health. Comprehensive CR utilization can help reduce GHG emissions while providing economic benefits. Shi18 demonstrated that if the energy released from unnecessary utilization of CR (such as cooking and heating, open field burning, and other activities) is converted into bioenergy, it could reduce 122 Mt of GHG emissions.

Table 1 Average GHG emissions from open field burning of CR from 2015 to 2022 in Sichuan Province.
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CO2 mitigation from CR utilization as fertilizer

To address the large-scale degradation of farmland due to excessive chemical fertilizer use and the loss of nutrient resources from fields caused by CR abandonment, which exacerbates the long-term degradation of farmland quality and soil productivity, assessing the potential of nutrient resources from CR is crucial27. Returning CR to the fields can offset all K2O, most of the P2O5, and a portion of the N found in fertilizers27,28. This practice promotes the recycling of nutrients from CR, which can further reduce the excessive use of fertilizer and lower CO2 emissions. Overall, nutrient contents from CR in Sichuan Province showed an increasing trend year by year (Fig. 5a), with rice CR contributing the most, followed by maize CR (Fig. 5b). The theoretical total nitrogen (N), phosphorus (P2O5), and potassium (K2O) content of CR are 0.25, 0.19, and 0.62 Mt per year, respectively, which can offset all K2O in fertilizers, 58.29% of P2O5, and 31.85% of N, respectively. The theoretical CO2 mitigation from CR replacing chemical fertilizers was 2.93 Mt, while the actual and potential values were 1.49 and 1.44 Mt, respectively. It implied a significant CO2 emission reduction potential from CR replacing chemical fertilizers. Specifically, maize CR provided the most considerable potential when used as fertilizer, followed by rice CR (Fig. 5b).

Fig. 5
figure 5

Chang trends of CR nutrient resources from 2006 to 2022 (a) and CO2 mitigation from CR replacing chemical fertilizer (b).

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CO2 mitigation from CR utilization as feed

In China, both the quantity and quality of feed are facing shortages29,30. CR, rich in minerals and organic matter, is an important source of roughage for herbivorous livestock31. According to the “National Report on Comprehensive Utilization of CR” released by the Ministry of Agriculture and Rural Affairs in 2021, CR utilized as feed accounted for the highest proportion in the market, reaching 76.9%. It indicates that CR utilization as feed has tremendous market potential in China. Specifically, about 5.36 Mt of CR was used as feed per year in Sichuan Province from 2015 to 2022.

Table 2 represents the average livestock carrying capacity from CR utilization as feed from 2015 to 2022. Generally, CR’s theoretical and actual carrying capacity represented an increasing trend during the period. Notably, the average theoretical carrying capacity was 100.66 million SU per year, much higher than the actual carrying capacity. It indicates the significant potential of using CR as feed. Additionally, the CO2 mitigation potential from CR utilized as feed from 2015 to 2022 was analyzed, as illustrated in Table 2. In line with potential carrying capacity, CO2 mitigation potentials of CR used as feed also showed a generally increasing trend from 2015 to 2022, with average actual and potential values of 0.31 and 1.67 Mt of CO2 equivalent per year, respectively.

Table 2 The average livestock carrying capacity from CR utilization as feed and its CO2 mitigation potential from 2015 to 2022.
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CO2 mitigation from CR utilization as energy

As an alternative energy, bioenergy is receiving increasing attention for targeting carbon neutrality and mitigating climate change32,33,34. CR is a vital biomass resource that can potentially reduce CO2 emissions35. Enhancing CR utilization for energy is essential for lowering CO2 emissions. Policy changes can boost energy crop yields, encouraging the use of CR resources for energy36. Consequently, optimizing the methods and efficiency of CR utilization for energy, along with implementing supportive policy, will significantly impact its share in the energy landscape of Sichuan Province.

This study calculated the theoretical standard coal equivalents of CR used for energy and their corresponding CO2 mitigation from 2015 to 2022 (Table 3). Maize and rice CR ranked first and second in CO2 mitigation, respectively, followed by rapeseed and potato CR. It is known that CO2 mitigation is positively correlated with the yield and heat value of CR. As indicated in Table 3, the total theoretical CO2 mitigation potential from CR used as energy is 41.21 Mt of CO2 equivalent per year, significantly higher than the actual mitigation value of 5.71 Mt of CO2 equivalent per year. This discrepancy suggests that only a tiny portion of CR is currently utilized for energy, indicating a substantial opportunity for CO2 mitigation through increased CR use in Sichuan Province.

Table 3 The average standard coal equivalents of CR used as energy and their CO2 mitigations from 2015 to 2022.
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CO2 mitigation from CR utilization as raw materials and culture substrate

The utilization of raw materials and culture substrates from CR is a critical component of CR comprehensive utilization and holds relatively high economic value. The utilization of CR as a raw material in the production of various materials is highly extensive, particularly in applications such as papermaking, foaming buffer materials, artificial boards, nanocellulose, tableware, and packaging containers. CR culture substrate production involves utilizing CR as the primary raw material, supplemented with auxiliary materials, to develop culture media according to specific production formulas. This process is applicable not only for the cultivation of edible fungi but also for plant seedling propagation and general plant cultivation. The quantities of CR used as raw material and base material in the study area were 1.01 and 0.62 Mt, respectively. The CO2 mitigation from CR utilization as raw materials and culture substrate in the research region was 0.41 and 0.47 Mt per year, respectively.

Spatial distribution characteristics of CR comprehensive utilization and its CO2 mitigation

To further know about the CR resources in Sichuan Province, spatial characteristics of CR comprehensive utilization and its CO2 mitigation in 2022 were also investigated, as shown in Figs. 6 and 7. Generally, the extensive utilization of CR, including utilization as fertilizer, feed, and energy, is predominantly distributed in Northeastern Sichuan, the Chengdu Plain, and Southern Sichuan, which are consistent with that of CR yields. Specifically, DZH and NCH rank first and second in theoretical total nitrogen (N), phosphorus (P2O5), potassium (K2O), standard coal equivalent, and livestock carrying capacity from CR, ranging from 30.57 to 31.26, 54.94 to 58.67, 67.96 to 69.31 thousand tons (Fig. 6a and b), 1.98 to 2.49 Mt (Fig. 6c), and 6.34 to 8.03 million sheep (Fig. 6d), respectively.

Fig. 6
figure 6

Spatial distribution of CR utilization as fertilizer (N (a), P2O5 and K2O replaced by CRs (b)), Energy (c) and feed (d) in 2022.

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Fig. 7
figure 7

Spatial distribution of CO2 mitigation from CR comprehensive utilization (a), utilization as fertilizer (b), energy (c) and feed (d) in 2022.

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In line with spatial distribution characteristics of CR comprehensive utilization, those of their CO2 mitigation are also mainly distributed in the Chengdu Plain, Northeastern and Southern Sichuan, as shown in Fig. 7. Specifically, DZH and NCH rank first and second in CO2 mitigation from CR comprehensive utilization, utilization as fertilizer, energy, and feed, ranging from 1.08 to 1.09 Mt (Fig. 7a), 220.31 to 221.39 (Fig. 7b), 835.33 to 846.65 (Fig. 7c) and 22.93 to 24.71 thousand tons (Fig. 7d), respectively. The total CO2 mitigation from the comprehensive utilization of CR was up to 8.40 Mt per year, in which CR utilization as fertilizer, energy, feed, raw materials, and culture substrate were 1.49, 5.72, 0.31, 0.41, and 0.47 Mt per year, respectively. The CO2 mitigation achieved through CR utilization is calculated as the net difference between the CO2 mitigation from comprehensive utilization and the emissions generated by CR burning, which is 5.42 Mt per year.

Discussion

The sown area, the theoretical and available CR yields in Sichuan Province from 1990 to 2022 exhibited a sustained upward trajectory. This trend aligns with the findings of Wang13 and is primarily driven by the rapid expansion of sown areas for maize and rapeseed37. The increase in the sown area of crops can be attributed to the government’s supportive policies aimed at enhancing food security. CR is a valuable resource for farmers’ livelihoods and agricultural development. The comprehensive utilization of CR in Sichuan Province primarily involves three main pathways: fertilizer production, feed processing, and energy generation. Chemical fertilizers can enhance crop yields, but excessive use will cause the loss of N and P from soils, soil acidification, and non-point source pollution38. Returning CR to the field as a substitute for chemical fertilizers can improve soil fertility and increase crop yields39,40, thereby alleviating environmental problems caused by excessive use of chemical fertilizer. Moreover, the nutrient contents of CR in Sichuan Province have also shown an increasing trend in recent years, which can potentially substitute for all K2O and part of N and P, indicating significant potential for CR to replace chemical fertilizers. As to CR utilization as feed, the average capacity of CR used as livestock feed in Sichuan Province from 2015 to 2022 was 15.76 million SU equivalents annually, implying significant potential for CR utilization as feed. CR is also an important biomass energy source. China’s biomass energy potential is estimated at approximately 232.67 Mt of standard coal annually, accounting for 8.27% of the national energy consumption in 200941. The average biomass energy potential from CR in Sichuan Province was 2.33 Mt of standard coal annually from 2015 to 2022, highlighting the substantial potential for energy utilization.

Widespread ineffective utilization of CR, such as arbitrary dumping and open field burning, not only wastes resources but also generates large amounts of GHG emissions and atmospheric pollutants, affecting climate change and posing health hazards to humans42,43. The comprehensive utilization of CR was officially listed as an important component of carbon sequestration and mitigation in agriculture and rural areas in 2022. The average GHG emissions from open-field burning of all rice, maize, and wheat CR were 30.54 Mt of CO2, 4.033 thousand tons of N2O, and 0.137 Mt of CH4 from 2015 to 2022, in which burning of maize CR contributed the highest CO2 emissions. As a biomass energy source, the CO2 emitted into the atmosphere by the combustion of CR is equal to the CO2 absorbed from the atmosphere during the biomass growth. Therefore, CR is regarded as a zero-carbon emission fuel, and its carbon reduction is equivalent to the carbon emissions from replacing coal. It has enormous potential for CO2 mitigation from CR comprehensive utilization in Sichuan Province, with energy utilization reducing CO2 emissions by 5.72 Mt, which was followed by feed and fertilizer in sequence. It is inconsistent with the results of Zhao16 due to the different accounting perspectives on CO2 mitigation from comprehensive CR utilization. In this study, the calculation of CO2 mitigation mainly focuses on substituting CR nutrients for chemical fertilizers, temporarily neglecting the effects of CR returning to the soil for carbon sequestration and its impact on GHG (CH4 and N2O) emissions from agricultural fields. The exclusion of soil carbon storage and GHG emissions in the calculations is mainly due to the lack of precise baseline data. For example, the CH4 emission coefficients for paddy fields and the N2O emission coefficients for dry fields vary significantly depending on the soil characteristics of different farmlands. Given the absence of corresponding accurate data, these factors have not been integrated into the scope of carbon reduction associated with the return of CR to the field. It may lead to potentially underestimated CO2 mitigation from CR fertilizer utilization. This study adopts the fertilizer utilization rate of CR without classification, as there is currently a lack of official survey data in this area. It may influence the accuracy of assessment results. The CO2 mitigation from energy utilization was calculated from the perspective of replacing standard coal with CR, temporarily omitting calculations from the perspectives of CR energy utilization, such as biogas, ethanol, pyrolysis gas from CR, and CR solidification into shaped materials for CO2 reduction processes.

The straw economy faces many dilemmas, such as technical bottlenecks, an incomplete system of collecting and storing, non-sustainable practice, low farmers’ enthusiasm and economic benefits, etc. It is challenging to alter farmers’ crop residue management practices. This can only be achieved by modifying the cost–benefit relationship of CR utilization for farmers44. Such modification primarily occurs through government subsidy policies targeting farmers and CR utilization enterprises, and advancements in new CR utilization technologies. Government subsidies for straw utilization encompass several measures, including subsidies for CR returning machinery, a 100% immediate VAT refund for CR comprehensive utilization enterprises, permission for qualified CR comprehensive utilization enterprises to issue bonds for financing purposes, and electricity price subsidies for CR-based power generation. The research region has earnestly implemented the national tax incentives and other supportive policies for the comprehensive utilization of CR, accelerated the implementation of key projects for the comprehensive utilization of CR, established demonstration bases for comprehensive utilization, and researched and promoted new technologies and equipment. Municipal and county governments have been actively exploring and formulating a series of award and subsidy policies, covering “collection, transportation, and the entire industrial chain of “storage, addition and utilization” has achieved positive results.

Recommendations and implications

The comprehensive utilization of CR continues to play an increasingly important role in the sustainable development of agriculture and the rural economy, remaining challenging41. The Ministry of Agriculture and Rural Affairs released the market situation of the comprehensive utilization of CR in China in 2021. CR utilization as feed accounted for the highest proportion at 76.9% of market utilization, followed by fertilizer, energy, culture substrate, and raw materials, which showed relatively lower enthusiasm, accounting for 7.8, 8.9, 3.8, and 2.6%, respectively. It reflects ineffective development and utilization of CR, with uncertainties remaining in the efficiency, environmental performance, and added value of fertilizer, energy, culture substrate, and raw material utilization45. Different CRs possess distinct physicochemical properties requiring tailored utilization approaches. Joint efforts among industry, academia, and research are essential to develop core technologies for efficient and high-value utilization of various CRs, enhancing their economic value and promoting enthusiasm in the CR comprehensive utilization market.

Comprehensive CR utilization is important for CO2 mitigation in agriculture and rural areas. Efforts in CO2 mitigation from CR comprehensive utilization should prioritize agricultural use and local processing, focusing on intensification, industrialization, and high-value-added utilization of CR. It is essential to continue promoting CR utilization as fertilizer, feed, and raw materials, leveraging its role in conserving arable land and integrating crop farming with animal husbandry. Progress should be made in CR utilization as energy, adapting locally to develop biomass energy for gas, heating, and electricity supply. Additionally, ways for utilizing CR as raw materials should be expanded, supporting the substitution of CR pulp for wood pulp in papermaking and transforming CR into environmentally friendly panels, carbon-based products, etc.

Conclusions

Over the past 30 years, the sown areas of crops and the available yields of CR in Sichuan Province showed a generally increasing trend year by year, mainly driven by the rapid expansion of maize and rape sown areas. In line with sown areas of crops and available CR yield, the CR comprehensive utilization rate also represented a gradually increasing trend in recent years. It has generally formed a pattern for CR comprehensive utilization where utilization as fertilizer is the primary method, with steady progress in its use as feed and energy, while utilization as cultural substrate and raw materials plays a supporting role. Importantly, from 2015 to 2022, the average CO2 mitigation from CR comprehensive utilization was up to 8.40 Mt per year, in which energy utilization contributed the most. Consistent with the distribution of CR yields, the CO2 mitigation potentials of CR comprehensive utilization in Sichuan Province are primarily concentrated in the Chengdu Plain, northeastern and southern Sichuan, such as CHD, DZH, NCH, MY, YB, etc.