Climate change is one of the biggest problems the world is now experiencing and it severely threatens human life and productivity (Wu et al., 2023; Zhao et al., 2023). Energy use, industry, transport and agriculture are essential drivers of climate change (Leitão and Balogh, 2020). Agriculture is a pivotal contributor to greenhouse gas emissions, accounting for approximately one-third of all such emissions (Fuentes Ponce et al., 2022). In agricultural production, greenhouse gases are generated directly during the sowing and growing of crops (Fan et al., 2022), and agriculture requires direct energy inputs in the form of fuels to power agricultural machinery, and equipment and to heat or cool buildings. In addition, the production of agricultural fertilizers and other chemicals contributes indirectly to greenhouse gas emissions (Wang et al., 2017; Ghimire et al., 2024). This is due to the fact that N₂o is created in part by soil nitrification and in part as an intermediate product of soil denitrification during the breakdown and absorption of nitrogenous fertilizers by the soil (He and Loffler, 2024). It is therefore important that we increase our efforts to reduce the use of chemical fertilizers and promote green and high-quality agriculture to mitigate the effects of climate change and ensure sustainable food production in the future (Lin TY. et al., 2022). As global demand for agricultural products is anticipated to quadruple by 2050, owing primarily to rising living standards, we must address the environmental implications of our food production and consumption (Rojas-Downing et al., 2017).

Research indicates that the use of organic fertilizers can improve the ammonification process and harmonize the nitrification and denitrification processes, which in turn lowers the production of N₂o and ammonia volatilization (Chen et al., 2020). Thus, there is a significant potential that using organic fertilizers will lower greenhouse gas emissions (Muller et al., 2017). Increased crop yields are another obvious benefit of using organic fertilizers, and this benefit is mostly derived from better soil conditions (Wang et al., 2019; Ye et al., 2020). Organic fertilizer has two main effects: on the one hand, organic fertilizer can supply crops with the essential nutrient sources, boost soil nutrients (Fu et al., 2024), and enhance soil structure (Liu et al., 2019). The structure and function of the soil microbial community can be optimized by using organic fertilizers (Sun et al., 2023), on the other hand, which can also encourage the growth and reproduction of microorganisms (Jiang et al., 2022). This increases the soil’s metabolic capacity and nutrient conversion efficiency, making it easier for crops to absorb and utilize soil nutrients (Li et al., 2020). It is noteworthy that cake fertilizer, as a type of organic fertilizer, has also received attention from researchers (Mirpoor et al., 2021).

Cake fertilizer, which is high in nitrogen, carbohydrates, and protein, is the byproduct of oil extraction from oilseed crop seeds (de Almeida Junior et al., 2011). Globally, the main oilseed crops are soybean, rapeseed, peanut and sunflower are the main oilseed trade varieties (Alzamel et al., 2022). Therefore, soybean cake fertilizer, rapeseed cake fertilizer, peanut cake fertilizer and sunflower cake fertilizer are used all over the world. Noteworthily, India, being the largest producer of oilseeds globally, manufactures more than 25 million metric tons of oilseed cakes every year (Singh et al., 2022). In the global market, soybean cake stands out as the most prominent oilcake/meal product, accounting for 54% of total production. Rapeseed cake/meal follows closely, making up 10% of the total output (Vichare and Morya, 2024). It has been discovered that cake fertilizers are primarily utilized as supplements for animal feed and soil (Mirpoor et al., 2021), and they are also used to medications (Zhao et al., 2017), films (Aramwit et al., 2022), and lubricants (Sahin et al., 2017). When applied directly to animals as feed, cake fertilizer has reportedly been shown to be poisonous (Worbs et al., 2011). Still, it can only be used as feed after detoxification of the cake fertilizer by chemical, physical, biological, or combined processes (Gomes et al., 2018). Currently, cake fertilizers are not only used as feed for poultry but are also fully utilized in fisheries (Mredul et al., 2022; He et al., 2024). However, cake fertilizer can be used directly as a soil fertilizer after fermentation to provide nutrients to the soil (Song et al., 2023). It is commonly recognized that the use of cake fertilizer in medications, flicks, additives, etc. necessitates the extraction of compounds unique to the fertilizer, which is an expensive and difficult procedure to carry out (Jingura and Kamusoko, 2018). However, cake fertilizer can be used directly as a soil fertilizer to provide nutrients to the soil (Jung and Choi, 2020). In addition, different cake fertilizers have varying chemical compositions, qualities, growth conditions, extraction techniques, and storage parameters (Martin et al., 2010). They also exhibit significant instability in the process of extracting the necessary substances. Furthermore, it is sufficient to apply fertilizer in accordance with the kind of cake fertilizer manufactured locally; it is not essential to take the type of cake fertilizer into consideration. This is due to various cake fertilizers can all increase soil fertility, they can only do so by enhancing the various nutrients already present in the soil (Xu et al., 2020).Therefore, when compared with the application of cake fertilizer in other aspects, the application of cake fertilizer as soil fertilizer has a significant advantage.

Cake fertilizer has the highest soil enzyme activity of any organic fertilizer when compared to amino acid eco-fertilizer and chicken type fertilizer treatments. Soil dormant enzyme activity, soil acid phosphatase, soil sucrase and soil dehydrogenase were all significantly increased after 150 days of cake fertilizer treatment (Li et al., 2014). AdeOluwa et al. studied the effects of Jatropha seed cake (JSC), Tithonia (Tithonia diversifolia), compost, and the other most common compound inorganic fertilizers in Nigeria-NPK on cucumber (AdeOluwa et al., 2021). This proved that the cake fertilizer was significantly increased. According to Wang et al., the nine-year average rice yield of cake fertilizer treatment was 60.0% higher than no fertilizer, and the total nitrogen content was 0.23-0.85 g kg^-1 higher than other treatments, respectively, based on a field experiment (Wang et al., 2023). Shan et al. demonstrated that the application of canola cake fertilizer together with straw mulching treatment had a significant effect on the soil fertility of the tea plantation. Soil organic matter content, total nitrogen content, effective phosphorus content, and the number of microorganisms, such as aminobacteria, aerobic autochthonous nitrogen-fixing bacteria, and smoky autochthonous nitrogen-fixing bacteria were significantly higher than that produced during the treatment of purely applying chemical fertilizer (Shan et al., 2010). Cake fertilizer provides an appropriate organic matter and fungal development environment in the soil, efficiently enhances its soil ecological balance, and serves as an excellent material basis for additional cake fertilizer for soil improvement.

In summary, the benefits of returning cake fertilizer to the field include: 1. increasing soil enzyme activity and nutrient content; 2. increasing crop yield and quality; 3. optimizing the soil microbial community. The drawbacks of returning cake fertilizer to the field include: 1. the need for chemical or biological detoxification of some cake fertilizers due to their natural toxins; 2. the wide variation in nutrient ratios and toxin contents among different cake fertilizers, which affects the consistency of the fertilizer application effect.

At this point, some academics are interested in the impact of cake fertilizer on agricultural greenhouse gas emissions. For example, Zhang et al. conducted a comparative analysis of the effects of different types of organic fertilizers and chemical fertilizers on greenhouse gas emissions, and confirmed that in the wheat-soybean replanting system, the distribution of cake fertilizer and chemical fertilizer significantly reduce the net greenhouse effect (Zhang et al., 2020). Furthermore, Meng discovered that mixing cake fertilizer could significantly reduce the cumulative emissions of soil N₂o (Meng, 2021). Although the great potential of cake fertilizer in reducing agricultural greenhouse gas emissions has been demonstrated, key technologies such as the regulatory mechanisms and causes of inhibition of cake fertilizer have not been systematically analyzed. Therefore, enhancing research on agricultural greenhouse gases from cake fertilizer and directing the technical system for regulating these gases can aid in comprehensively grasping the regulatory mechanism for cake fertilizer in agricultural greenhouse gas emissions. This endeavor is essential for advancing the sustainable development of cake fertilizer in managing agricultural greenhouse gases.

Little has been reported on its systematic sorting and visual analysis. In view of this, this paper is based on the core database of Web of Science (WoS), and through CiteSpace, the number of articles, countries, research institutions, published journals, and keyword analysis of greenhouse gases in cake fertilizer agriculture and soil improvement are analyzed. The analysis is aimed at further exploring the research contents, status and hotspots of greenhouse gas regulation and soil improvement in cake fertilizer agriculture, tapping the potential of this research field, and pointing out the direction for future research and development.

The above has been analyzed from keyword co-occurrences, keyword clusters, and keyword emergence to derive the research hotspots and research frontiers in different time frames, but there is no clear indication about the research content. Based on this, the above results are further discussed and some insights are provided for future research.

According to the keyword analysis, the research area of greenhouse gases and soil improvement in cake fertilizer agriculture is wide-ranging, and the main content doesn’t remain consistent. A range of influencing factors, including region, policy, science, and technology, have played a role in this transformation of agriculture over the past 20 years. The research process in the field of cake fertilizer application in agriculture over the last 20 years can be divided into three cycles, namely the pioneering period (2000-2007), the slow development period (2008-2016), and the rapid development period (2016-2023).

During the pioneering period, since excessive phosphorus can lead to degradation of water quality, the Water Quality Improvement Act in Maryland mandates P-based nutrient management for manures and biosolids by 2005 (Elliott et al., 2002). In order to regulate phosphorus in the soil, the research focused on the effects of different types of organic fertilizers applied alone or in combination with inorganic fertilizers on soil nitrogen and phosphorus transport (Withers et al., 2001; Elliott et al., 2002; Bousselhaj et al., 2004; Kaur et al., 2005) and yield quality of the crop broad bean (Abdelhamid et al., 2004). Moreover, in order to change the environmental impacts of sewage sludge, the UK pioneered the use of grassland to absorb sludge in order to reduce carbon dioxide and nitrous oxide emissions during this period. Using sludge reduces grassland greenhouse gas emissions, laying the groundwork for regulating cake fertilizers, but no mention has been made of the impact on cropland (Scott et al., 2000).

During the slow development period, The FAO’s Voluntary Guidelines for Sustainable Soil Management (Montanarella and Panagos, 2021), adopted in 2016, and China’s National Plan for Sustainable Agricultural Development (2015–2030) (Bryan et al., 2018), released in 2015, both make it clear that the development of organic agriculture should be accelerated in order to stop soil degradation and that the use of chemical fertilizers should be reduced without reducing soil fertility. Therefore, a number of studies were conducted on the effects of organic fertilizers mixed with compound fertilizers or organic fertilizers mixed with mineral fertilizers on soil microbial communities and soil improvement (Gilbert et al., 2008; Rigby et al., 2009; Dinesh et al., 2012; Murugan and Kumar, 2013; Srivastava et al., 2016), as well as the yields and quality of cash crops, including onions (Lee, 2010), sugarcane (Santos et al., 2011), and sweet oranges (Ghosh et al., 2014). A reduction in chemical fertilizer use was observed during this period, and Wang et al. conducted field experiments in southeastern China to demonstrate that organic fertilizers paired with chemical fertilizers did increase crop yields, but also significantly increased the risk of methane emissions (Wang et al., 2013). This paper examined the effects of three organic fertilizers combined with composite fertilizers on methane, nitrogen oxide, and grain yields in rice paddies. Combining chemical and organic fertilizers may increase greenhouse gas emissions for different crops, but the impact of cake fertilizer on GHG emissions has not been demonstrated and needs to be explored.

During the rapid development period, in addition to the expansion of the research content of the first two phases, research scope is widened, as well as the increasing limitations of traditional materials. The development of the new energy and new material industries, as well as the increased demand for new materials and energy, has led to the emergence of new materials into agricultural research of cake fertilizer application. Meanwhile, the Chinese government has issued a series of legal and policy documents to promote the replacement of chemical fertilizers with organic fertilizers (Lin B. et al., 2022). For example, the Action Plan for Replacing Chemical Fertilizers by Organic Fertilizers in Fruits, Vegetables, and Tea Plantations and the Opinions on Innovating System and Mechanism to Promote Agricultural Green Development, both released in 2017. And in December 2019, the European Commission published the European Green Deal (EGD) (Dupont and Torney, 2021). Research demonstrating that using environmentally friendly products along with agricultural management increases productivity while also improving crop yields and soil fertility. For example, Zhang et al. studied agronomic measures to improve rice yield and nitrogen use efficiency by adding rapeseed cake fertilizer, increasing the frequency of fertilizer application and increasing the frequency of irrigation (Zhang et al., 2017); Mortierella elongata, a dominant fungal strain, was studied for its phosphorus uptake, its response to organic fertilizer, and its role in growth promotion by (Li et al. (2018); Zhang et al. studied the optimization of integrated cultivation management to improve crop yield and nitrogen use efficiency by exploring different planting densities, irrigation levels, rapeseed cake fertilizer amounts and other management practices (Zhang et al., 2019); Manzoor et al. addressed the effect of biochar, rapeseed cake meal and chemical fertilizer formulation on root growth, nutrient utilization and yield of tea tree (Manzoor et al., 2022). Therefore, more in-depth investigation of the above new materials and agronomic practices is needed to explore the potential of the effects on crop quality and soil fertility, and to provide more possibilities for soil improvement in cake manure agriculture.

Despite rapid development, research on the impact of cake fertilizers on greenhouse gas regulation in agriculture has continued. For example, A study conducted by Zhou et al. examined the effects of rapeseed cake fertilizer and green manure fertilizer on citrus orchard yields and nitrogen oxide emissions. Based on these findings, citrus orchards can achieve sustainable productivity and protect their environment if they apply rapeseed cake fertilizer and reduce fertilizer use by 30% (Zhou et al., 2022). Grutzmacher et al. demonstrated the potential of biochar to reduce fertilizer-induced nitrous oxide emissions by exploring the effects of biochar with chicken manure, sewage sludge, press tree chips and filter cake on nitrous oxide emissions, with sludge cake fertilizer with biochar reducing soil fertilizer emissions by 87% (Grutzmacher et al., 2018). Furthermore, the Life Cycle Assessment (LCA) evaluation technique has demonstrated that biochar significantly reduces greenhouse gas emissions (Osman et al., 2024). This is owing to the fact that biochar may stabilize carbon in soil used in agriculture (Osman et al., 2022). However, there is a lack of using LCA on cake fertilizer to assess the impact of cake fertilizer on environmental factors, as well as resource consumption and environmental emissions during the production and use of cake fertilizer. Therefore, it’s critical to improve research on GHG emissions and consumption during the manufacture and application of cake fertilizer in addition to investigating the effects of mixing cake fertilizer with environmentally friendly products on GHGs.

Based on the above content research, cake fertilizer should be applied in a way that maximizes its benefits for crop growth and soil management. First, Cake fertilizers should be used in conjunction with biochar to meet environmental criteria, followed by the application of chemical fertilizers to maximize nutrient uptake and reduce the danger of nutrient imbalances, according on local soil and crop needs. Second, in terms of fertilizer amount and timing, the initial application is made one week before the planting of the crop. Depending on the soil type, crop type and management type in different areas, the amount of fertilizer applied varies. It is recommended to calculate the appropriate ratio of nitrogen, phosphorus and potassium based on the nutrients in the cake fertilizer. In circumstances where crop fertilizer demand is high and previous soil nutrient loss is excessive, a second application might be applied to ensure crop yield and quality and should be carefully managed to avoid potential environmental pollution. It is suggested to conduct soil tests before applying cake fertilizer to determine the appropriate application rate. Finally, adopting precision agriculture tools (e.g., IoT-based soil sensors, drone mapping) can optimize cake fertilizer application by dynamically adjusting doses based on real-time soil nutrient status and crop phenology.

Moreover, numerous experiments have shown that cake fertilizers significantly improve soil and reduce greenhouse gas emissions. However, there is a lack of potential mechanisms caused by chemical reactions or physical processes. Advances in chemistry and allied subjects, as well as a thorough understanding of molecular systems, can result from the combination of experimental data and computational chemistry approaches, according to certain research (Ahmed et al., 2020). For instance, the intricate impacts of pH on phosphorus binding and transport in soil were demonstrated, by Ahmed et al.’s molecular modeling and simulation studies (Ahmed et al., 2023a). Shaheen et al. revealed the complex effects of metal oxides on phosphorus morphology and transport in soil using soil spectroscopic and molecular methods(quantum chemical calculations (QCC)), providing more detailed theoretical principles for phosphorus management in soil (Shaheen et al., 2022). In addition, there are studies on the use of predictive modeling in machine learning to assess soil fertility and productivity (Helfer et al., 2020), as well as combining computational chemistry and machine learning to explore the effects of variables on biochar (Osman et al., 2023). Nevertheless, there isn’t much research on machine learning and computational chemistry in relation to cake fertilizer. In order to investigate the chemical reactions and physical processes of cake fertilizers on soils, it is crucial that future study on the topic combine cake fertilizers with adjacent fields like computational chemistry. Additionally, machine learning models should be utilized to assess and forecast experimental data.

Bibliometrics was used to systematically summarize the study. WOS database, which contains articles, citations, etc., was used for literature bibliometrics. As a result, the results of this study may vary based on the type of database, the keywords used, and the time of the search. In order to assure the accuracy of the data and minimize any bias, this article offers a thorough reading and screening of the chosen data in addition to a precise account of the search method and duration of the study. Furthermore, in order to present a complete picture, this work integrates expert opinion in addition to using bibliometrics for research. This study aims to impartially and objectively analyze the field’s developmental dynamics over a certain time period using these metrics.

The research on greenhouse gases and soil improvement in cake fertilizer agriculture during 2000-2023 is intensifying, with India ranking first in terms of the number of published articles. Having a certain degree of international influence on greenhouse gases and soil, China is more active in international collaborative research. The most influential journal is Journal of Plant Nutrition and Soil Science, Caione, Gustavo and Basak, B B as core authors. The development trend is as follows. In the pioneering period, organic fertilizers alone or in combination with inorganic fertilizers are being studied for their effects on soil nitrogen and phosphorus transport, as well as soil fertility. In the slow development period, the main focus is on the effects of organic fertilizers and mineral fertilizers on soil microbes and soil improvement. In the rapid development period, the scope of research expands; in addition to the research content of the previous two phases, there are new materials, as well as setting different water, soil conditions and other agronomic conditions.

We make the following recommendations about the development of cake fertilizers for soil improvement and greenhouse gas reduction based on the information and debates in the article.