Biochar Application for Soil Quality Improvement: An Overview

*Hassan Ali, Shahzaib Ali, Sadia Baloch, Fahmeeda Naheed, Emaan Amjad, Qudsia Saeed, Muhammad Naveed and Adnan Mustafa*

### **Abstract**

Soil as a renewable resource has a key role to play in sustainable crop production, soil management, and combating food insecurity. The overapplication of fertilizers in this regard has resulted in decreased soil health and productivity. Biochar application in this respect has received increasing attention of the scientific community due to its role in soil quality improvement. This is especially true in the face of global climate change and to the nature of biochar being a carbon (C)-rich compound. In this chapter, the potential of biochar to enhance soil quality attributes, particularly those pertaining to soil's physical, chemical, and biological properties, is comprehensively reviewed. Special attention is directed toward the distinctive properties of biochars sourced from various feedstocks, elucidating their subsequent effects on soil quality. This sheds light on potential directions for future studies in this field.

**Keywords:** biochar, soil health, sustainable environment, soil improvement, soil quality

#### **1. Introduction**

Climate change negatively impacts crop growth. Salinized, weak alkaline soils; temperature fluctuations; and latitudinal factors require urgent scientific attention [1, 2]. Soil, a complex ecosystem, plays a vital role in agriculture, ecosystem services, climate change mitigation, landscape protection, and human development [3, 4]. Long-term cultivation can lead to degradation, resulting in reduced soil organic matter, severe erosion, and diminished aggregate stability [5, 6]. Soil quality directly impacts ecosystems, affecting crop production, biota, and human well-being, contributing to a healthy environment [7, 8]. Various factors, including pollution levels, bacterial activity, climate, and land use, can alter soil characteristics [9]. Green approaches, like soil amendment, offer effective means to reduce salinity by enhancing physical and chemical properties and nutrient distribution. These approaches also promote microorganism growth and restore soil health [10–13]. The application of additives is a promising method to enhance soil characteristics. In recent years, biochar (B) has gained significant interest as a versatile soil fertilizer, owing to its high porosity, abundant surface functional groups, strong adsorption capacity, and recalcitrant carbon content [14].

Biochar (BC) is plant-derived charcoal used to absorb carbon dioxide when incorporated into soil [15, 16]. It plays a crucial role in long-term climate change mitigation [17] and enhances soil biochemical properties [18]. BC also facilitates large-scale disposal of waste biomass [19]. Studies highlight its significance as a carbon source and soil enhancer, sequestering pollutants and enhancing fertility [20]. Its elemental composition includes essential elements like C, N, and H, alongside lower-nutrient elements [21]. Adding BC improves soil properties such as porosity, bulk density, and water availability [22]. Pyrolysis releases volatile compounds, increasing BC's surface area and creating pores akin to honeycombs, enhancing water and nutrient retention [23, 24].

BC incorporation enhances soil structure, aeration, nutrient availability, and alters microbial communities, fostering crop growth and yield [25–27]. It raises soil pH and enhances cation exchange capacity [28, 29]. Amended soils exhibit heightened fertility and nutrient retention [30], with significantly boosted extractable nutrient levels [31]. BC increases hydraulic conductivity, base saturation, and nutrient levels and reduces erosion rate [32, 33]. It halts the leaching of nitrate nitrogen from soils [34]. The diverse pore sizes of BC influence microorganism habitats, promoting beneficial bacterial survival and enhancing bacterial structure [35–41]. BC's effects on soil microorganisms are influenced by nutrient availability, microbial community composition, plant–microbe signaling, and habitat creation [42].

Climate change disrupts the vital carbon storage in soil, impacting global food production and greenhouse gas emissions [43–46]. Methane (CH4) and nitrous oxide (N2O), potent greenhouse gases, primarily from agricultural land, have a significant warming effect [47]. Biochar is pivotal in curbing emissions and averting climate change by enhancing soil quality, reducing pollution, and stabilizing carbon [48–50]. It is technically and economically feasible for carbon capture and storage [51], disrupting the carbon cycle and preventing emissions from reentering the atmosphere [52, 53]. This fosters soil health, lowers emissions, and boosts carbon sequestration [54–56].

#### **2. Literature review methodology**

A set of thematic keywords were used for exploring the relevant research articles and review papers, such as biochar, feedstock, soil quality, soil fertility, soil pH, soil physicochemical properties, biochar amendments, soil organic matter, carbon sequestration, the role of biochar amendment, plant growth and yield attributes, crop performance, and so forth. In this regard, five different databases were used, namely, Research Gate, Google Scholar, Science Direct, Web of Science, and Scopus. These databases comprise extensively used huge collections of related mainstream research articles. Following this, multiple research and review articles were selected within the era 2000–2022. Furthermore, related research articles referenced in the abovementioned papers were also reviewed.

#### **3. Application of biochar in soil quality improvement**

Biochar is considered as a potential soil amendment, as its addition improves the C accumulation (60–80%) in the soil, which is central to the enhancement in the soil properties, and hence, biochar technology could be very effective for soils having low organic matter contents (OM) [22]. The following sections discuss the role of biochar as a potential amendment to enhance soil quality.

#### **3.1 Improvement in soil bulk density**

Soil bulk density, a critical indicator of soil physical properties, is closely linked to soil tightness [57]. It reflects soil compaction and health and influences crucial aspects of the plant life cycle [58]. Enhanced soil porosity and aeration, facilitated by biochar, lead to reduced bulk density [59]. Biochar's lower bulk density contributes to decreased soil bulk density and improved water holding capacity due to its larger surface area [60–62]. Numerous studies have reported a significant negative impact of biochar addition on soil bulk density [63, 64]. Głąb et al. [65] found a 35% reduction in bulk density with the incorporation of 4% biochar. Similarly, Qin et al. [66] documented a decrease in bulk density with an increase in overall soil porosity after introducing biochar. The influence of biochar on soil bulk density is closely tied to soil texture; coarser-textured soils experience more pronounced reductions compared to finer-textured soils [67]. This may be attributed to the higher bulk density of coarsetextured soils (~1.6 g cm−3) compared to biochar (~ 0.6 g cm−3), allowing interactions between the biochar and soil particles, resulting in a decline in the final bulk density of the soil. Additionally, biochar's high porosity and sandy soils' lower porosity contribute to decreased bulk density [68]. Furthermore, the nature of feedstock material and pyrolysis temperature significantly influence bulk density, with higher pyrolysis temperatures leading to lower bulk density [69]. The rate of biochar application also affects bulk density, generally showing a negative correlation with application rate [58].

#### **3.2 Improvement in surface area and soil porosity**

Biochar significantly influences soil porosity through its pore distribution, particle size, and connectivity [57]. Studies have reported an increase in soil porosity following biochar addition, ranging from 14% to 64% [22]. Higher pyrolysis temperatures enhance soil porosity, potentially due to organic matter decomposition and the formation of micropores [70, 71]. The impact of biochar on soil porosity depends on soil texture and type, with coarse-textured soils showing a greater increase compared to fine-textured soils, likely due to their lower inherent porosity [72]. In sandy soils, biochar improves porosity by enhancing mechanical interactions with soil particles, leading to notable improvements [73]. Increased porosity positively affects soil microbial activities, and different pore size distributions may influence specific microbial species [74]. Additionally, Seyedsadr et al. [75] found that biochar addition increased total porosity and reduced bulk density compared to compost. They suggested several mechanisms for improved soil porosity, including direct pore effects within biochar, accommodation pores formed between soil aggregates and biochar, and enhanced persistence of soil pores through increased aggregate stability [76].

#### **3.3 Improvement in soil aggregate stability**

Soil aggregate stability is crucial for resisting mechanical stresses like surface runoff, water erosion, and precipitation effects [58, 77]. Disintegration of aggregates leads to fine particles susceptible to erosion, potentially forming a soil crust upon

re-sedimentation [78]. Biochar application significantly impacts aggregate stability through interactions with soil mineral surfaces, facilitated by oxidized carboxylic groups on biochar particles [79]. This interaction fosters aggregate formation, creating stable microaggregates and larger pores, ultimately enhancing stability and structure [80]. Studies have reported an increase in soil aggregate stability ranging from 6 to 217% after biochar addition [32, 81]. This improvement may be attributed to the high carbon content of biochar, forming bonds with various oxides, and organic matter providing a food source for microorganisms. This leads to increased microbial activity and the secretion of mucilage, contributing to stable aggregates [82]. Additionally, biochar may enhance aggregate resistance against clay swelling and slaking [83].

#### **3.4 Improvement in soil consistency**

Soil consistency attributes, such as plastic limit, liquid limit, and plasticity index, are crucial for designing stable slope systems [84]. Understanding soil consistency is vital for engineering applications and agronomic contexts, including tillage operations and compaction. Additionally, biochar application can enhance soil consistency by increasing organic carbon concentrations [85]. Different types of biochar applied to sandy soils at various rates resulted in significant improvements in plasticity index (48–99%) and liquid limits (8–22%) [85]. This improvement is primarily attributed to biochar's larger surface area and increased porosity [86, 87]. Laboratory experiments by Choudhary et al. [88] showed that biochar addition improved soil consistency limits up to a specific weight limit, leading to enhanced physical properties of the soil.

#### **3.5 Improvement in cation exchange capacity (CEC)**

The CEC indicates the ability of soil to absorb, retain, and exchange cations, and enhancing the number of exchange sites for cations can augment the soil CEC contents. Soils having a high CEC can readily absorb K+ , NH4 + , Mg2+, and Ca2+ and improve the utilization of nutrient ions in soils [89]. The CEC is largely pH-dependent particularly on tropical soils, and some biochars can raise the pH of the soil as well as soil CEC [90–92]. Use of peanut shell-derived biochars in an acidified soil increased the soil pH, CEC, SOM, as well as plant biomass [93]. Biochar application increases soil charge and cation exchange capacity (CEC) by 20–40% compared to control conditions [94]. Non-wood feedstock biochar exhibits higher CEC than wood-derived biochars [95, 96]. Feedstock type, application rate, and pyrolysis temperature are crucial factors influencing soil CEC regulation [97].

#### **3.6 Biochar application on soil EC and pH modulation**

Soil acidity is a significant challenge for upland agriculture, affecting approximately 30% of potential arable lands globally [98]. Factors such as aluminum (Al) toxicity, as well as deficiencies in calcium (Ca), magnesium (Mg), and phosphorus (P), act as constraints on crop production in acidic soils [99]. The alkaline properties of specific biochars play a crucial role in enhancing crop productivity in acidic and highly weathered soils [100]. However, the addition of pine sawdust biochar in sandy desert soil has been observed to decrease soil pH [101]. Hence (**Figure 1**),

*Biochar Application for Soil Quality Improvement: An Overview DOI: http://dx.doi.org/10.5772/intechopen.114192*

**Figure 1.**

*Conceptual scheme on the effect of biochar amendment on the physicochemical, biological properties, and greenhouse gas emissions (adapted from Li et al. [102, 103]).*

it is imperative to exercise caution in selecting the appropriate acidic or alkaline biochar capable of modifying the soil rhizosphere accordingly for optimal plant growth. Electrical conductivity (EC) is closely related to the concentration of salts dissolved in water and is a critical factor influencing upland crop growth (**Table 1**). Biochar derived from agricultural waste and woody feedstock typically exhibits low to moderate EC, while manure-derived biochar tends to have higher EC [116–118]. Biochar application has been shown to improve the growth and yield of crops in saline conditions, attributed to higher concentrations of essential ions in the biochar [118]. Most biochars have higher soluble salt content and, consequently, higher EC compared to agricultural soils [119]. However, excessive salt content is detrimental to plants due to reduced osmotic potential. Therefore, maintaining low soil EC is crucial for optimal nutrient availability and plant growth. It is worth noting that the EC of soil may increase with higher application rates of biochar [102, 103, 120, 121]. Rice husk biochar, however, did not significantly impact soil EC [122]. Biochar pH ranges from 4 to 12 and directly influences soil pH upon application. Biochar interacts with aluminum ions (Al3+) and hydrogen ions (H+ ) in soil, leading to reduced ion concentrations [123]. Higher pyrolytic temperatures can result in biochar with alkaline pH [124]. In acidic soils, biochar additions raise soil pH to varying degrees [92, 125, 126]. The pH increases gradually with higher biochar application rates, but the impact on alkali soils is less pronounced [94]. Biochar additions lead to a 25% increase in crop yield in tropical regions, attributed to lower acidity, whereas effects are less significant in temperate zones [127]. Biochar addition also affects soil pH and the activity of essential ions involved in phosphorus (P) complexation and sorption [128]. Research by Lu et al. [129] demonstrated that various types of biochars enhance soil pH and buffering capacity, correlating with improved soil pH buffering capacity.


#### *Soil Contamination – Recent Advances and Future Perspectives*


**Table 1.** *Effect of biochar addition on soil physicochemical properties and plant growth.*

## *Biochar Application for Soil Quality Improvement: An Overview DOI: http://dx.doi.org/10.5772/intechopen.114192*

#### **3.7 Improvement in soil organic matter (SOM)**

Soil organic matter (SOM) is a vital factor reflecting soil fertility and providing nutrients for soil life [130]. Biochar application increases SOM, with effectiveness dependent on biochar quantity and stability [131, 132]. Biochar contains essential plant nutrients, enriching soil nutrient levels upon application [57]. It also catalyzes the formation of soil organic matter from small organic molecules [82, 133]. Biochar enhances soil fertility and crop yields by boosting SOM content [134]. Elevated SOM content improves crop growth and productivity due to increased soil porosity and nutrient availability [135]. In coastal regions, biochar.

addition increases corn yields while reducing soil salinity [136]. It also enhances root microbe activity and organic matter uptake by plant roots. Chen et al. [133] found that applying biochar at 15 and 30 t ha−1 increased SOM content. Additionally, Liu et al. [137] showed that biochar application reduced organic matter mineralization by inhibiting the β-glucosidase enzyme.

#### **3.8 Improvement in soil biological properties**

The effects of biochar application on soil microbial biomass are diverse, with some studies indicating positive impacts [138] and others showing no significant changes [139]. Additionally, biochar can enhance soil microbial biomass carbon, nitrogen, C-mineralization, and enzyme activities [140, 141]. Barman et al. [142] observed an increase in different enzyme types with freshly prepared biochar. Moreover, biochar has been found to mitigate toxic contaminants and modify soil enzymes [143]. Furthermore, biochar application has been associated with increased root colonization and spore germination of mycorrhizal fungus, attributing to improvements in soil properties [144, 145]. It has also shown potential to enhance biological nitrogen fixation in various crops [146–148]. Shifts in microbial community structures and functions after biochar supplementation are influenced by physicochemical attributes of biochar, organic matter content, nutrient availability, and water retention capacity [149]. Additionally, dominant bacterial groups like *Alphaproteobacteria, Betaproteobacteria, Proteobacteria, Gammaproteobacteria, and Rubrobacteridae* have been reported to increase after biochar addition [150]. Tang et al. [151] observed that soil microorganisms, including those in the rhizosphere, utilize various carbon sources after biochar amendment. In a 30-month experiment, Somerville et al. [152] found that the addition of organic matter, including biochar, improved soil biological properties, attributing it to increased porosity supporting microbial biomass, particularly mycorrhiza [153]. Kolton et al. [154] noted that biochar has the potential to enhance the diversity and metabolic potential of microbiota in the tomato rhizosphere. Pei et al. [155] reported that biochar amendment increased C mineralization, microbial respiration, and microbial communities. Additionally, nutrient-enriched biochar stimulated microbial activities responsible for pesticide degradation [156, 157], indicating a close interaction between microbial activities and pesticides in soils [158]. Biochar application also enhanced the alpha diversity of various microbial communities, particularly fungal species [159]. While numerous studies have focused on improving soil biological attributes with biochar application (see **Table 2**), there is still much to learn about the dynamics of soil microbial communities and the enhancement of soil biological properties in relation to biochar application.

#### *Biochar Application for Soil Quality Improvement: An Overview DOI: http://dx.doi.org/10.5772/intechopen.114192*



**Table 2.** *Effect of biochar prepared from different sources on the soil biological properties.*

#### *Soil Contamination – Recent Advances and Future Perspectives*
