1 Introduction

The botanical name for mung bean is Vigna radiata L., and it is classified within the Leguminosae (Fabaceae) family. Mung beans are cultivated in regions characterized by warm climates, which encompass both tropical and subtropical conditions [18]. Due to its property of prevent soil erosion, soil consolidation and its rapid growth, it is considered a better option compared to the other crops. Mung beans are really simple and easy to grow and have a enrich composition of proteins and carbohydrates. According to [15], mung beans are involved in many biological activities, including antimicrobial, antioxidant, lipid metabolism accommodation and antitumor effects. Mung bean is a beneficial legume crop. As mentioned above this little green bean has unique properties such as its enriched composition as well as its magnificent attainability. It is also capable of the famous legume trait known as biological nitrogen fixation. It forms an association with Rhizobium to fix nitrogen which in response can promote soil fertility.

Mung beans sometimes have a multi branched stalk with twining tips [30]. The crop has trifoliate leaves of alternate nature. The leaflets are elliptical. The length of the leaves 5–18 cm and the width ranged from 3 to 15 cm. It bears 4–30 flowers which are pale yellowish or green. It bears long, cylindrical pods. The seeds exhibit a range of colors, predominantly green but also including shades of yellow, olive, purple, brown, and black. Some of the obstacles that might limit mung bean growth are the damages caused by pests and some foliar diseases. The abiotic natural problems which includes a common problem i.e. drought and heat stress may also account for the poor productivity and growth of mung beans [22]. In Pakistan during the season mung bean is grown over a region of 220,000 ha with an all-out generating a yield of 157.4 tons, which translates to an average of 716 kg per hectare. However, mung bean is being developed throughout the country. Punjab is the significant maker of mung bean. In Khyber Pakhtunkhwa it is grown over an area of 8.5 ha, delivering yearly 5.1 tons and yielding 600 kg ha−1. In Punjab mung bean covers 88% of the cultivated area and produce 85% of the absolute mung bean production.

Biochar is charcoal produced from plant matter or animal waste and stored ground to of remove carbon dioxide from the atmosphere. In essence, it can be characterized as a soil amendment agent. The global assessment of biochar's impact on soil quality and its recognized potential to enhance soil fertility while addressing adverse climate conditions have garnered significant attention. However, its impact on soil biota have not been put under focus as compared to its effects on soil chemistry [24]. It also reduces the emission of dangerous N2O gas that can harm the environment. The studies of Cayuela et al. [12] shows that the proportion of N2O emitted from the soil is reduced by 54% after the applying bio-char. The updated version of Cayuela et al. [13] research revealed that the percentage of N2O is reduced by 49%. It is helpful in increasing the water holding capacity in soils which cannot retain moisture such as sandy soils. Research proposed by Reeta et al. [33] showed that the organic material added in soil, it has the potential to decrease the necessity for irrigation water, thereby enhancing the soil's water retention capacity. It makes the soil healthy in many aspects. In the study conducted by Downie et al. in 2009 [16], the use of biochar produced favorable outcomes in enhancing soil pore distribution. It is highly rich in carbon and it has the potential to persist in the soil for an extended period up to a thousand years. It is in a stabilized solid state. It is produced from biomass by pyrolysis. Pyrolysis is a process in which decomposition occurs under elevated temperatures within an oxygen-free environment. Biochar is known as an approach to sequestering carbon due to its ability to control climate change. Also the other geochemical properties of the soil and the black carbon significantly improves the Cation Exchange Capacity (CEC) of biochar production. It is known to be a tremendous protectant agent against soil borne diseases. However, there are still some gaps in the performance of biochar in terms of mung bean yield and NUE mung bean. Therefore, we investigate the influence of biochar on improving of NUE and quality of mung beans, increasing the nodule formation and improving mung bean yield.

2 Materials and methods

2.1 Site for experimentation

In 2018, experiments took place at the Agriculture Research Farm of Abdul Wali Khan University, situated in Mardan, Pakistan. This agricultural research facility is positioned at a latitude of 34.1989° N, a longitude of 72.0231° E, and an elevation of 310 m above sea level within the Mardan Valley. The soil found at the location consists of sandy clay loam, and it falls under the Mardan soil series, specifically classified as a fine Ustertic Camborthid. This soil type has developed in a filled basin and river bed, characterized by a grayish-brown color and a material of Holocene age, which is non to slightly calcareous in nature, as reported by Shafiq et al. in 2002. The soil at the experimental site exhibited characteristics of 3.2 g kg−1 organic matter, a pH level of 8.2, a total nitrogen content below 0.1 mg kg−1, 4.32 mg kg−1 of P2O5, and 72 mg kg−1 of K2O. The study site is situated within a semiarid region, experiencing an average seasonal rainfall of 250 mm during the summer months (May–September) and 300 mm in the winter season (October–April). Air temperature and precipitation data were gathered from a meteorological station and are depicted in Fig. 1.

Fig. 1
figure 1

Mean monthly precipitation and air temperature of the experimental year

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2.2 Experimental design and treatment

The experimental interventions involved various biochar application rates, namely BC1 at 0 tons per hectare, BC2 at 10 tons per hectare, BC3 at 20 tons per hectare, and BC4 at 30 tons per hectare. These treatments were organized in a randomized complete block design, with each treatment having four replications. Mung bean was sown as a test crop for grain purpose. After maturity, the harvest was analyzed for different nutrient contents. Mung bean NM-92 variety was used in the experiment. The planting of the crop took place in early April. The plot size 5 × 6 m2 with ten rows. All the agronomic and cultural practices were carried out as required. Soil samples were analyses for N, P, K, pH and EC before sowing and after harvest of the crop.

2.3 Measurements

Nodule density of the mung bean was measured by selecting randomly three plants from each plot, the nodules present at the root of plant were counted and averaged from nodule plant−1. Data of pods plant−1 was observed by selecting ten plants randomly from each plot at maturity after harvesting the pods were counted and converted into average number of pods plant−1. To record the data of grain pod−1 three plants were selected randomly from the central row, pods were detached and ten pods were selected, their grains were counted and converted into average number of grain pod−1. A random sampling of a thousand grains was performed from each plot of threshed mung beans, and their weight was measured using an electronic balance. From each subplot, three central rows were harvested at maturity and bundled separately. These bundles were then left to sun dry and weighed using a spring balance to determine the biological yield. The collected data was subsequently converted to kilograms per hectare (kg ha−1) using the following formula:

$${\text{Biological \,yield }}\left( {{\text{kg \,ha}}^{ - 1} } \right) \, = \frac{{\text{Grain \,weight \, of \,three \,central \,rows}}}{{{\text{Row \,length}} \times {\text{R}} - {\text{R \,distance}} \times {\text{no}} \,{\text{. of \,rows}}}} \, \times 10,000$$

To measure the grain yield, we harvested three central rows from each plot with a sickle. The collected samples were sun-dried, threshed, and weighed using an electronic balance. The resulting data was then converted into kilograms per hectare (kg ha−1) using the formula:

$${\text{Grain \,yield }}\left( {{\text{kg \, ha}}^{{ - {1}}} } \right)\, = \,\frac{{\left( {\text{Grain \, weight \,of \,three \,central \, rows}} \right)}}{{\left( {{\text{Row \,length }} \times {\text{ R}} - {\text{R \,distance }} \times {\text{ no}}. \,{\text{ of \,rows}}} \right)}} \, \, \times \,{1}0,000.$$

Straw and grain samples of the mung bean were both subjected to N content analysis using the Kjeldahl method as described by Bremner and Mulvaney in 1982 [9].

2.4 Statistical analysis

In this study, we used one-way analysis of variance (ANOVA) to examine the impact of varying biochar rates on the growth, yield, as well as nitrogen and quality parameters of legumes. To compare multiple means for variables in cases where the effects of experimental factors were statistically significant, Tukey's post-hoc test was utilized and also correlation coefficients was calculated. We also calculated correlation coefficients to explore the relationships among growth, yield, and quality variables using R Studio. Additionally, Principal Component Analysis was employed to assess the differences among the treatments for the variables under investigation, utilizing Canoco5. All statistical analyses were conducted using SPSS for Windows Software version 19.

3 Results and discussion

3.1 Grains and straw N content

The data concerning N-content in grain and straw (g kg−1) of mung bean are presented in Fig. 2. Analysis of the data revealed a significant effect of biochar on the amount of nitrogen in mung bean grain. A higher amount of nitrogen (25.2 g kg−1) was recorded in the plot where 30 tons ha−1 biochar was incorporated while in the control plot (22.2 g kg−1) N was recorded. The reason may be the improved soil fertility and the supply of the plant with essential nutrients by adding biochar to the soil. [5]. The addition of carbon (C), i.e., biochar incorporation to the soil can enhance crop yields [3], improve soil fertility nutrient cycling, reduce nutrient leaching from the soil, and stimulate microbial activity because of all these activities plant nitrogen also increases in the soil where biochar is being applied to soil [5]). Further, statistical analysis of the data revealed that the application of biochar was significantly influenced by the N content in the straw. Our results are consistent with the finding of Baiamonte et al. 2015 [7] and Spokas et al. 2012 [36] who stated that biochar soil improvement enhances soil quality and boosts plant productivity by improving various soil attributes such as nutrients holding capacity, larger availability of N, improved microbial population and activity, which might increase N-content in straw [27]).

Fig. 2
figure 2

Effect of biochar on N contents, uptake and use efficiency of mung bean

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3.2 N-uptake and nitrogen use efficiency (NUE) of mung bean

The significant difference in N-uptake and NUE was noted at different biochar levels (Fig. 2). Nitrogen uptake was 17.4, 5.2, and 2.5% higher at 30 t ha−1 of biochar compared with that of 0, 10, 20 t ha−1 bio-char. Additionally, 30 t ha−1 of biochar significantly increase nitrogen use efficiency of mung bean by 104.7, 45.5, and 18.5% than 0, 10, and 20 t ha−1 of bio-char. This phenomenon may be partially attributed to the influence of biochar on the soil environment, which enhances the uptake and utilization of inorganic nitrogen by plant roots. Additionally, biochar has the capacity to adsorb surface-level inorganic nitrogen within the soil, thereby mitigating nutrient loss [23, 29]. Liang et al. [26] have suggested that biochar enhances the soil environment by facilitating the absorption and utilization of inorganic nitrogen, leading to overall improvements in crop growth. Nevertheless, there are conflicting findings in the literature regarding the impact of biochar on soil inorganic nitrogen content, as reported by Zimmerman et al. [39], Singh and Cowie [35], and Bai et al. [6].

3.3 Biochemical properties of mung bean

3.3.1 Oil content (%)

The results of Table 1, revealed that different rates of biochar significantly affected the percent of oil content of mung bean grains. The data resulted that BC3 had the higher percent oil content followed by BC1 and BC0 whereas under BC2 the recorded oil content was lower compared to other treatments. This might be due to the higher nutrient content and carbon sequestration which is beneficial for percent oil content under enriched biochar soils. The applications of organic supplies were beneficial for the development of plants to produce seeds with higher percent oil content [32].

Table 1 Effect of different levels of biochar on chemical compositions of mung bean
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3.3.2 Saturated and unsaturated fatty acids

Data regarding saturated and unsaturated fatty acids are shown in Table 1. Significant variations in saturated fatty acids content was recorded under different levels of biochar treatments. Highest fatty acid content was observed in plots treated with BC3 followed by BC1 while the lowest saturated fatty acids were recorded under BC2. The possible reason for this result could be environmental conditions as well as type of soil (concentration of organic matter i.e. nutrients) which had significant effects on saturated fatty acid content [17, 31, 40]. Onemli [32] reported that higher organic matter results in higher concentrations of fatty acids which explains why our results were absolute under higher applications of bio-char.

3.3.3 Protein content

The information pertaining to protein content can be found in Table 1 showed significant variation in protein content caused by different levels of bio-char. The BC1 treatment achieved the highest protein content, with the application of 10 tons of biochar per hectare followed by BC3 (30 t ha−1) while BC2 had the lowest protein content in each case. Previous studies showed that applying biochar at ambient applications benefited the higher protein content grain. However, under elevated applications the protein content of the grains fell in decline. Blackwell et al. [8] reported that there was no effect of biochar recorded on the grains of wheat.

3.3.4 Stearic acid

Data concerning stearic acid is presented in Table 1. The statistical analysis demonstrated that all the treatments exerted a noteworthy influence on stearic acid content. Among the treated plots, BC2-treated plots exhibited the highest stearic acid content, followed by BC1 and BC3 treatments, while the control plots displayed the lowest stearic acid content. These findings align with the conclusions reached by Onemli in 2014 [32] who said that stearic acid and oil content has a positive correlation when it comes to organic applications. Both respond positively. The reason might be the rich nutritious supply of organic feed to the grains producing leaves which also makes the grains nutritious.

3.4 Yield and yielding attributes

Table 2 displays the data concerning mung bean plant nodules, indicating significant variations in the number of nodules of mung bean plant were caused by different biochar treatments. Highest density of nodules (17.8) was observed in plots treated by BC3 where biochar was applied at a rate of 30 t ha−1. Lowest density of nodules (7.3) was observed in control plots. Biochar application positively improved soil microorganisms’ population which in turn improved nodule density. Rondon et al. [34] also found comparable outcomes, revealing that common beans treated with biochar exhibited a higher number of nodes per plant and enhanced biological nitrogen fixation compared to those without biochar treatment. Data concerning to pod plant−1 are presented in Table 2. Statistical analysis of the data shows that different levels of biochar caused a significantly increased in the number of pod plant−1. Highest numbers of pods were recorded in BC3 treated plots (27.3), followed by BC2 (26.3) and BC1 (24.8). Fewer pod plant−1 were noted in control plots (21.8). The presence of nutrients, particularly nitrogen, throughout the growing season in plots treated with biochar application may be a contributing factor. Our findings align with those of Arif et al. [2], who observed increased plant height in biochar-applied plots. Similarly, Lehmann et al. [25] reported enhanced productivity when biochar was incorporated into the soil. Bishwoyog et al. [10] found that the application of various biochar sources can lead to an increased number of seeds per pod. The data regarding grain yield per pod under various biochar treatment conditions is presented in Table 2. Analysis of the data indicated a significant impact of biochar on grain yield per pod. Significant differences were recorded in grains pod−1 between different treatments of biochar. BC3 treatment produced significantly higher grains pod−1 (11.4) followed by BC2 (10.7) and BC1 (9.8) as compared to control (8.8), Previous studies [19,20,21, 38] have also reported similar findings, demonstrating the positive impact of biochar on soils with low quality. Moreover, there is a growing body of evidence suggesting that the inclusion of biochar can lead to increased crop yields. However, it's worth noting that most biochar research has been limited to temperate agricultural soils and often confined to pot-based experiments of short duration. Our own findings, however, highlight the potential of field-scale biochar applications to enhance the productivity of legume crops.

Table 2 Response of biochar on nodule and yielding traits of mung bean
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The biological yield results in Table 2 showed that all treatments had a significant effect on the biological yield of mung bean. The highest biological yield was observed in BC3 treated plots (6467 kg ha−1), followed by BC2 treated plots (6096 kg ha−1) and BC1 treated plots (5167 kg ha−1), whereas lowest biological yield was recorded in control plots (4772 kg ha−1). Possible reason for it could be the ability of biochar to deliver essential crop nutrient to the plant which resulted in more photosynthate formation as biomass was increased. Our findings align with the conclusions reached by multiple researchers who have documented that the most substantial enhancements in plant growth occur when charcoal and fertilizers are employed together, indicating a cooperative association [14]. Table 2 provides the data based on the weight of 1000 grains. A statistical examination of the data demonstrates that every treatment significantly influences the weight of 1000 grains. Heavier grains weights (64 g) were produced in BC2 treated plots followed by BC3 (63 g) and BC1 (61 g). Lighter gains were recorded in control plots. Biochar application improved the nitrogen and phosphorus available in the soil, and these nutrients were available in enough amounts to improve grain weight. Asai et al. [4] found that the use of biochar led to higher grain yields and improved responses to chemical nitrogen (N) and phosphorus (P) fertilizer treatments, particularly in areas with limited phosphorus availability. This observation is in line with the research by Cao et al. [11], who noted that as the application rate of biochar increased, there was a corresponding increase in seed weight. Higher biochar levels promoted the assimilation of nutrients and vegetative growth, extending the duration of grain filling. This, in turn, resulted in larger and better-filled grains, making them significantly heavier compared to scenarios without biochar application.

The application of biochar had a significant impact on grain yield, as demonstrated in Table 2. Increasing the quantity of biochar led to a notable improvement in grain yield. For instance, the highest grain yield of 1550 kg ha−1 was observed in BC3 plots, followed by BC2 (1474 kg ha−1) and BC1 (1353 kg ha−1), while control plots exhibited the lowest yield. Biochar's ability to enhance crop yield is attributed to its positive influence on soil nutrient availability, fostering improved crop growth and development [37]. Additionally, the application of biochar led to enhanced nitrogen-fixing organism activity and subsequently improved total crop biomass [37]. Consistent findings by Liang et al. [26] indicated that biochar, being a porous material with a substantial surface area, significantly influences soil moisture, nutrient dynamics, and crop yield characteristics, including the number of grains per ear and overall grain yield. Agegnehu et al. [1] reported similar outcomes, highlighting that the use of biochar made from nutrient-rich sources like poultry litter results in increased crop yield. Miranda et al. [28] and Asai et al. (2009) also observed that biochar not only enhances crop yield but also improves pollen development and anther dehiscence. Further, correlation rank co-efficient of biochemical properties, NUE and yield of mung bean presented in Fig. 3 showed that all biochemical properties have good relationship with NUE and yield of mung bean except, oil content, protein content, saturated and unsaturated fatty acid showed negative relationship with NUE, grain and straw N content, N uptake, Steric Acid, Palmitic acid and Linolenic acid contents. While, the Principal component analysis (PCA) among biochemical composition, NUE, nodules and yield characteristic of mung bean showed the explained variation on x-axis (90.5%), and y-axis (7.54%) in Fig. 4. Further explained that BC3 showed significant positive relationship with all variables and suggested a sustainable theoretical approach in the improvement of biochemical traits, NUE and yield of mung bean.

Fig. 3
figure 3

Correlation rank co-efficient of biochemical properties, NUE and yield of mung bean

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Fig. 4
figure 4

Redundancy analysis (RDA) among biochemical composition, NUE, nodules and yield characteristic of mung bean

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4 Conclusions

It can be concluded that through the application of biochar in 30 t ha−1 mung bean improved, biological yield (4421 kg ha−1), grain yield (653 kg ha−1) and N-content in grains (26.5 g kg−1). The use of biochar also has a positive impacts on the quality attributes of the mung bean. However, varying results are found under different levels but BC3 can be recommended because it has the best results as compared to the other levels. The quality attributes mentioned in this experiment are really important for a healthy diet. Further research should be conducted on the healthy attributes. Biochar is a soil amendment agent and it is environment friendly as well. As it is known that the world is facing crisis of a healthy environment the use of biochar should be taken into consideration for a better healthy planet and for life.