Biochar application at different rates and their co-application with CF improved soil nutrient status as compare to control (Murtaza et al. 2021). We observed that application of biochar improved the nutrient status of soil, and at the same time, enhanced C, N and P availability for microbial utilization as reported by previous studies (Bu et al. 2019; Naeem et al. 2019; Zhu et al. 2017a). However, no significant change was observed in soil pH under all the applied BC rates, as previously stated by (Rashid et al. 2020) and (Zhu et al. 2017b), who reported that alkaline soils have large buffering capacity, which resist towards any change in pH brought by BC application. (Griffin et al. 2017) found a little increment in soil pH after BC application, but significant enhancement in soil macro nutrients (K, NO3-N, Olsen P and NH4-N), as observed under current study, which indicate the direct role of BC on soil nutrient stock. Few other studies have indicated that the increase in soil nutrient levels is due to BC's labile C, N, P, and K contents which are continuously released in soil, and are readily available for plant uptake. In simple words, rise in soil nutrients can be attributed to the direct effects of BC on the soil (Aziz et al. 2023; Qayyum et al. 2017; Song et al. 2018a). Moreover, BC contains larger surface area, negative surface charge and higher number of functional groups which play a key role against nutrients leaching (Yuan et al. 2016). Additionally, presence of oxonium functional groups on BC surface make increase its anion exchange capacity (AEC) which help to retain NO3-N and phosphate (Banik et al. 2018; Sorrenti et al. 2016), while the negative surface charge of BC can retain cations like NH4+ and K+ by sorption (Choudhary et al. 2021).
It was observed that biochar-based treatments had a key role in improving soil enzyme activities as observed by (Song et al. 2019) and (Oladele 2019), who examined that presence of organic C, MBC and MBN pools of BC provided organic substrates for enzymes which lead towards higher enzymatic activity. Although, it has also been reported that BC addition lead to a reduction in soil enzyme activities because of synthetic C mineralization (El-Naggar et al. 2015). Moreover, few studies revealed that BC can adsorb a range of organic and inorganic molecules, this adsorption causes the blockage of reaction sites which decreases soil enzyme activities (He et al. 2021a; Lehmann et al. 2011). Contrastingly, our study did not support this observation as results revealed that BC addition significantly increased the activity of all enzymes, as supported by the results of (Bailey et al. 2011) and (Ameloot et al. 2013a), who revealed that BC has few volatile compounds which increase soil enzyme activity such as urease, protease, dehydrogenase phosphatase and β-glucosidase under alkaline conditions. Furthermore, BC can also increase enzymatic activity by absorbing soil toxic substances (Salam et al. 2019; Song et al. 2022) however, there was no sign of toxicity observed in the soil of current study. BC alters the soil biochemical properties (Elzobair et al. 2016) and nutrient availability (Lu et al. 2015), which lead to higher enzyme activities and therefore, significant correlation between BC concentration and soil enzymatic activity may directly support this suggestion. Interaction between soil enzymes and organic matter in soil determines the biogeochemical stability, which is manifested by the relative proportions of enzymes involved in CNP cycles. The balance between the ratio of microbial biomass and elemental composition of organic matter is essential for maintaining this stability (Waring et al. 2014; Wei et al. 2020). Inclusively we can suggest that, soil enzyme activity was improved with the increment in BC application rates although sometimes, it is based on the soil nutrients availability and climatic conditions (Waring et al. 2014).
Generally, it has been reported that BC has the potential to improve soil biological properties, which leads to better soil microbial abundance because of BC's special structure and properties (Lucheta et al. 2016; Ren et al. 2022; Zhang et al. 2021). In current study, a significant increment was observed in soil total PLFA, bacterial and fungal in BC treated soils but this activity increased as the BC application rate increased with CFs. Our findings are closely related to the results of (Chen et al. 2017), where they reported that application of 3–9% of BC significantly improved the soil total PLFA content as compare to control. Moreover, the labile C and N pools of BC serve as a suitable habitat (i.e., energy and nutrient sources) for better growth and development of soil microbes (Zhao et al. 2016). Previous literature has proved that soil supplementation with biochar and animal manure marginally improves microbial community which lead towards better soil structure and C content (Bowles et al. 2014; Cheng et al. 2017). Bacterial and fungal biomass was increased with the BC application rate in current study but these results are distinct to the meta-analysis of (Xu et al. 2021), as they observed reduction in soil bacterial and fungal community which was proved by previous 107 research studies. Similarly, (Chen et al. 2013) also found some negative impacts of wheat straw derived BC on soil bacterial and fungal activity. This variation indicates that BC effects are based on its feedstock type, pyrolysis temperature, soil type and application rate (Xu et al. 2021). Further, it has also been revealed that soil microbial biomass is based on BC feedstock type as each feedstock have its own physicochemical characteristics and nutritious values (Luo et al. 2017). Additionally, soil pH is also influenced by the BC type, and this increase lead towards better soil microbial abundance. It has also been observed that porous structure of BC can be substantially affected by pyrolysis temperature (He et al. 2021b), as the temperature rises, BC surface area and pore volume is increased, which provide desired habitat to microorganisms whilst lower BC pore volume and surface area favors the growth of fungal hypha (Muhammad et al. 2016). Conclusively, elevated BC pyrolysis temperature and pore spaces could be less conducive for fungal better growth and abundance.
Bacterial fungal ratio indicate soil C sequestration capability, as the fungal content upsurges soil, carbon storage potential also increases which plays a pivotal role in environment safety (Malik et al. 2016). In our study, soil that received BC20 and BC20 + CF treatments had maximum fungal bacterial ratio, which reflects that application of BC alone or with chemical fertilizers could improve soil C sequestration potential and ecosystem stability. Moreover, in our findings, soil MBC, MBN and MBP were also increased i.e., particularly, at higher dose of BC application. Study of (Bhaduri et al. 2016) as well as (Biederman and Harpole 2013) support our results, where they observed that application of BC significantly increased soil MBC and MBP respectively. Similarly study of (Zhang et al. 2014b) also revealed that application of corncob BC significantly increased soil MBC and MBN. Generally, MBC carries approximately 3–7% of the total soil organic carbon while MBN and MBP consist of 1–5% of total soil nitrogen and phosphorus respectively (Oladele et al. 2019). These shifts in soil microbial biomasses indicates the soil carbon mineralization, growth and mortality ratio of microbes (Fang et al. 2020).
Our study revealed that poultry manure derived BC had significant positive effects on wheat crop growth and yield parameters. According to our results, crop growth was significantly improved as the BC application increased with NPK fertilizers. Our results are supported by (Khan et al. 2021) and (Aziz et al. 2023), as they applied different feedstock based biochars on alkaline soils, and observed a significant increment on crop growth, nutrients uptake and grain yield. Furthermore, it has also been examined that plant response to BC is based on feedstock type, pyrolysis temperature and soil type as each feedstock has its own properties (Choudhary et al. 2021). In our previous experiment, we applied three different types of BCs i.e., poultry litter biochar, Acacia modesta wood biochar and Dalbergia sissoo wood biochar, where we discovered that poultry litter biochar significantly influenced wheat growth along with their yield (Aziz et al. 2023). Being an organic amendment, BC reduces soil compaction, nutrients loss and increases water holding capacity along with nutrient use efficiency which leads toward improvements in crop agronomic and yield parameters (Khan et al. 2021). Generally, BC affect soil nutrients availability by two ways: directly, by providing nutrients (work as nutrient and reduces the nutrient release and leaching) indirectly, by increasing nutrient and water holding capacities of soil as well as by causing variations in soil pH, CEC and soil microbial abundance (Azeem et al. 2021). Moreover, BC has large surface area and high porosity, which provide suitable habitat to microbes for survival, which is very critical to nutrient solubilization, for instance, P solubilization leads to higher P uptake, which plays a significant impact on root growth, and ultimately increase nutrients uptake (Azeem et al. 2021; Wahid et al. 2020). Consequently, better nutrient uptake lead towards higher root-shoot growth and crop yield (Guo et al. 2019).