Biochar and its effects on soil properties and evapotranspiration: A sustainable solution for plant growth

Abstract

A pressing need has come to the fore to improve sustainability as well as the use of low-cost agricultural organic materials that boost both poor soil characteristics, leading to better plant growth, while at the same time developing resilience to climate change effects. To achieve this purpose, biochar (BC), a carbon-rich by-product of organic matter pyrolysis under high temperatures and partial or complete hypoxia known for its porous nature, affects both soil physiochemical properties and evapotranspiration (ET). In this article, the history and definition of BC were investigated. Current knowledge about BC’s production process, how BC alters soil’s physical and chemical properties, and the most recent studies on BC soil amendment interaction with various plants’ ET were examined. This review concludes that BC is a paramount carbonaceous material that improves both physical and chemical properties of soils, depending on biochar dose, soil texture and initial soil pH, leading to better moisture and macronutrient availability which possibly be the reason behind increasing ET at low doses of BC amended soils.

Keywords:

• biochar
• soil physical properties
• soil chemical properties
• evapotranspiration

1. Introduction

Worldwide, drought, fertilizer leaching, soil deterioration, and a lack of food security are consequences of climate change and unsustainable agriculture (Glaser & Birk, 2012). Drought stress occurs due to a low soil water content and an improper balance between soil surface evaporation (E) and plant transpiration (Lamaoui et al., 2018). On the other side, lands degradation and nutrients leakage from agricultural soils may be caused by the excessive and illogical application of inorganic fertilizers (Adnan et al., 2020; Laird et al., 2010) as well as the growth in the plantation area and less reclamation (Fearnside, 2005). Biochar (BC) is considered a viable option for addressing the abovementioned problems and is being researched across the globe for its potential benefits (Nair et al., 2017; Vijay et al., 2015). It is noticeable that there are not enough recent comprehensive reviews that have yet evaluated BC’s effects on soil available nutrients, along with some of the physical and chemical soil properties and some plantsˈ ET (explains water and energy transfer among soil, land surface, and atmosphere). BC is produced by pyrolysis, the thermal decomposition of waste biomass under high temperatures and partial or complete hypoxia (Lehmann, 2007). However, it is commonly produced at temperatures between 250 to 1200 °C in industrial settings or simple furnaces (Das & Sarmah, 2015; Kinney et al., 2012; Liu et al., 2017; Omondi et al., 2016; Sohi et al., 2010). It has a moisture absorption capacity that is 1–2 orders of magnitude higher than that of soil organic matter (Accardi-Dey & Gschwend, 2002), and has intrinsic chemical recalcitrance to biodegradation, thereby, the carbon compounds from BC are not easily degraded (Singh et al., 2012; Solomon et al., 2007) due to the high content of stable carbon (Cross & Sohi, 2011; Kimetu & Lehmann, 2010; Sohi et al., 2010). Considering the favourable features of BC, including high porosity, high specific surface area, low density, and others; it has been shown to improve the chemical, and physical properties of soils (Sohi et al., 2010), causing improvements in both soil nutrients and water use (Atkinson et al., 2010; Basso et al., 2013; Faloye et al., 2019; Jeffery et al., 2011; Karhu et al., 2011).

Although soil water retention capacity was not affected by woody BC amendments of 0.5% and 1% on silty clay soil (Wang et al., 2019), switch-grass (Panicum virgatum) BC maximized soil-water retention of loamy sand (Novak et al., 2009). Moreover, BC application can reduce bulk density (BD) (the weight of dry soil divided by the total soil volume) by 14.2% in coarse-textured soils and 9.2% in fine-textured soils (Blanco-Canqui, 2017) as was the case with loamy sand soil using peanut hulls (Arachis hypogaea) BC application (Githinji, 2013). According to Razzaghi et al. (2020), BC reportedly enhanced the soil-available water (SAW) (the difference between field capacity, FC, and wilting point, WP) to plants in coarse-, medium-, and fine-textured soils by 45%, 21%, and 14%, respectively. The soil amendment of corn stover BC increased total porosity (TP) (the ratio of nonsolid volume to the total volume of soil) in silt loam soil (Herath et al., 2013). Consequently, BC boosts water retention in fine and coarse soils, enabling more effective use of irrigation or precipitation (Fischer et al., 2019) as it could eventually increase ET and total dry matter yield in drought conditions (Bruun et al., 2022). Additionally, mineral N (nitrogen), available phosphorus (AP), and available potassium (AK) (the amounts of soil nutrients in chemical forms accessible to plant roots) were increased when corn straw BC was amended with N fertilizer to silt loam soil (Li et al., 2022). The combined improvements in the physical and chemical properties of soil caused by BC encourage different plants growth.

This study aimed to overview previous results dealing with BC interactions with physical and chemical properties of different types of soils that could cover the gap with the numerous effects on some plantsˈ ET-biochar interaction.

2. What is BC?

BC is a carbon-rich substance with unique physicochemical characteristics (Jeyasubramanian et al., 2021). The type of feedstock, pyrolysis temperature, residence duration, and reactor design all significantly influence the previous features of the final BC product (Mimmo et al., 2014). Mainly depending, on the initial BC biomass, BC porosity ranged from 55 to 86% (Brewer et al., 2014). Similarly, true BC densities recorded high values, ranging from 1.5 to 2.1 g cm^_3 for a variety of feedstocks (Brewer et al., 2009), while bulk densities typically range from 0.09 to 0.5 g cm^_3 (Bird et al., 2008; Karaosmanoglu et al., 2000; Özçimen & Karaosmanolu, 2004; Spokas et al., 2009). BC’s CEC (cation exchange capacity) is between 6.4 and 46.62 cmol kg⁻¹ (Li et al., 2021). The main chemical distinction between BC and other organic matters is a remarkably more significant proportion of aromatic C and condensed aromatic forms, in contrast to other aromatic structures of soil organic matter, such as lignin (Hedges et al., 2000; Keiluweit et al., 2010; Schmidt & Noack, 2000). There are two major structural components that make up the generally acknowledged structure of BC: stacked crystalline graphene sheets and randomly ordered amorphous aromatic structures (Lehmann & Joseph, 2009). Due to its multiple advantages in climate change, agriculture, wastewater treatment, and soil health, it has attracted much interest in the last ten years (Yu et al., 2019).

2.1. Origin of BC

At least 2000 years ago, BC was used for agricultural purposes (Hunt et al., 2010). The actual use of BC may date back even further than the mid-19th century, when western agriculture first became aware of it (Abiven et al., 2014). The earliest origins of BC are linked to the American Indian communities of the Amazon basin (Han et al., 2020; Lehmann, 2009; Lehmann & Joseph, 2009). A long-ago indigenous society produced the incredibly productive soils known as terra preta, or “the black soils of the Indians,” showing signs of intensive usage of BC (Lehmann, 2009; Lehmann & Joseph, 2009). Their textures range from sandy to clay-dominant and A horizons are thicker (up to 2 m in thickness) and darker (black to very dark grayish brown: Munsell colors 5 YR 2.5/1, 7.5 YR 2/0 to 3/1, 10 YR 2/0 to 3/2) than adjacent soils (Kern et al., 2017). In these soils, the nutrients, i.e., K, P, and N elements, were extremely high (Chen et al., 2019). Despite hundreds of years of leaching induced by intense tropical rain, this region remains exceptionally fertile because of its dark, rich soil qualities (Hunt et al., 2010).

2.2. How is BC produced?

BC, activated carbon, and charcoal are three pyrogenic carbonaceous materials that share many characteristics and have highly similar compositions and production processes (Břendová et al., 2016). It is mainly created from organic biomass (Sun, 2008), including wood chips, crop residues, manure, and animal waste, as well as municipal sludge (Diatta et al., 2020) to be used for carbon sequestration (Certificate, 2017; Lehmann & Joseph, 2015), and soil amendment (Lehmann & Rondon, 2006). Activated carbon is a sorbent to eliminate impurities from gases and liquids (Marsh & Reinoso, 2006; Smisek & Cerny, 1970). It is expensive because developing adsorption characteristics requires energy for intensive thermal activation (Bayer et al., 2005). Globally, charcoal is made of woody materials (Straka, 2017) by blazes and earth mounds (Brown et al., 2015; Kaltschmitt et al., 2009) as well as industrial reactors (Straka, 2017), and used as a fuel for cooking, heating, and steel production (Brown et al., 2015). They are produced through pyrolysis, the thermochemical degradation of biomass under anaerobic or oxygen-limited conditions (Lehmann, 2007).

Pyrolysis converts aliphatic carbon into more stable aromatic carbon and discharges combustible gases (H₂, CH₄, and CO) (Mlonka-Mędrala et al., 2021). The former procedure can be classified into several groups; gasification > 800 °C, fast pyrolysis ~ 500 °C, and slow pyrolysis 450–650 °C (Sohi et al., 2009), as well as the same according to the degradation temperatures for hemicelluloses (220–315 °C), cellulose (315–400 °C), and lignin (˃400 °C) (Yang et al., 2006). The products of pyrolysis are oil (a mixture of hydrocarbons), synthetic gas (mixed hydrocarbon gases), and BC (Lewandowski et al., 2010; Verheijen et al., 2010). The quantities of these specific products vary according to the temperature, pressure, duration, etc (Brewer, 2012; Cheah et al., 2016; Lewandowski et al., 2010). Slow pyrolysis is the most optimal pyrolysis process for the production of BC over other products (Duku et al., 2011; Sohi et al., 2010). The most effective way for generating biofuels is fast pyrolysis (Brown et al., 2010; Yadav, 2019); it produces up to 75 wt% bio-oil (Czernik & Bridgwater, 2004), and gasification is the most effective method of generating syngas and is so commonly utilized to create heat and energy (Cheah et al., 2016) like thermal power generation and liquid fuel production (Sircar & Wang, 2014). Furthermore, under certain conditions, such as feedstock type, pollution in the feedstock, and pyrolysis parameters; biomass pyrolysis may lead to the production of phytotoxic and possibly carcinogenic chemicals (Ndriangu et al., 2019). As a result of the pyrolysis process, certain heavy metals are converted into less hazardous forms, and infections are eradicated (Paz-Ferreiro et al., 2018).

3. What can BC be applied for?

BC is attracting significant interest in sustainable agriculture with possible advantages such as improvements in soil physical and chemical fertility, and increased soil carbon sequestration (Sohi et al., 2010).

3.1. Soil physical properties

BC had a pronounced role in improving BD, TP, and SAW across different types of soils, amendment rates, different feedstock types, and pyrolysis temperatures of biochar (Lentz et al., 2019) (Tables 1–3).

Table 1. Impact of BC application on BD

Soil type	Initial pH	Duration	Study type	Plant	BC feedstock	Pyrolysis tempera-ture °C	Residence time in the reactor (min)	Application rate (%/Mg andt ha^−1)	BD (g cm^−3)	References
Sand	8.16	288 d	Laboratory		Wheat straw	600	60	0 1 3 5%	1.54 1.40^a 1.22^b 1.05^c	(Chen et al., 2018)
Sandy Loam	5.69	2 consecutive years	Field	Cocoyam	Hardwood	500	720	0 10 20 30 t ha^−1	1.59^a 1.38^b 1.20^c 0.91^d	(Adekiya et al., 2020)
Sand	8.33	2 years	Lysimeter	Wheat	Citrus trees		-	0 1.50 Mg ha^−1 S 5 Mg ha^−1 1.50 Mg ha^−1 S 5 Mg ha^−1	1.60* 1.57* 1.51* 1.47*	(EL-Gamal et al., 2020)
Clay Loam	7.9	70 days	Pot	Lentil	Rice husk	250–500	30–225	With fertilizer 0 0.4 0.8 1.6 2.4 3.3%	1.39^a 1.37^a 1.29^b 1.17^c 1.14^c 1.14^c	(Abrishamkesh et al., 2016)
Alkaline soil	8.25	5 months	Pot	Soybean	Corn straw	450	120	With fertilizer 0 2.5 5 10%	1.26^a 1.23^b 1.22^b 1.18^c	(Liu et al., 2020)
Clay	8.27	2 years	Lysine-ter		Citrus trees		-	0 1.50 Mg ha^−1 S 5 Mg ha^−1 1.50 Mg ha^−1 S 5 Mg ha^−1	1.22* 1.18* 1.15* 1.11*	(EL-Gamal et al., 2020)
Entic Halpudept	6.5	Field	4 months	Rice	Wheat straw	350–550	-	i. Without N 0 t ha^−1 10 t ha^−1 40 t ha^−1 ii. With N 0 t ha^−1 10 t ha^−1 40 t ha^−1	1.01^a 0.98^ab 0.89^c 0.99^ab 0.96^ab 0.89^c	(Zhang et al., 2010)

S: Sulfur, N: Nitrogen fertilizer, *:data are significantly different.

Table 2. Impact of BC application on TP

Soil type	Initial pH	Duration	Study type	Plant	BC feedstock	Pyrolysis temperature °C	Residence time in the reactor(min)	Application rate (%/Mg and t ha^−1)	Porosity (%)	References
Alkaline soil	8.25	5 months	Pot	Soybean	Corn straw	450	120	with inorganic fertilizer 0 2.5 5 10%	52.67^c 53.18^b 54.85^ab 55.35^a	(Liu et al., 2020)
Sand	8.27	2 years	Lysimeter		Citrus trees		-	0 1.50 Mg ha^−1 S 5 Mg ha^−1 1.50 Mg ha^−1 S +5 Mg ha^−1	39.62* 40.75* 43.02* 44.53*	(EL-Gamal et al., 2020)
Loamy sand		4 months	Incubation		Winter wheat and Miscanthus	300	15	0 0.5 1 2 4%	32.2 39.5^d 41.4^c 44.2^b 48.9^a	(Głąb et al., 2016)
Sandy Loam	5.69	2 consecutive years	Field	Cocoyam	Hardwood	500	720	0 10 20 30 t ha^−1	40.0^d 47.9^c 54.7^b 66.0^a	(Adekiya et al., 2020)
Silt loam	5.71	2 seasons	Field	Zea mays L.	Mixture of paper fiber sludge and cereal husks	550	30	Spring 0 10 20 t ha^−1 10+160 kg N ha^−1 20+160 kg N ha^−1	35.4^a 37.7^b 37.5^b 37.1^b 39.8^c	(Igaz et al., 2018)
Silt loam	5.71			Zea mays L.	Mixture of paper fiber sludge and cereal husks	550	30	Autumn 0 10 20 t ha^−1 10+160 kg N ha^−1 20+160 kg N ha^−1	38.4^b 37.7^ab 36.7^a 38.6^b 38.2^ab	(Igaz et al., 2018)
Clay	8.27	2 years	Lysimeter		Citrus trees		-	0 1.50 Mg ha^−1 S 5 Mg ha^−1 1.50 Mg ha^−1 S +5 Mg ha^−1	53.96* 55.47* 56.60* 58.11*	(EL-Gamal et al., 2020)

*data are significantly different.

Table 3. Impact of BC application on SAW

Soil type	Initial pH	Duration	Study type	Plant	BC feedstock	Pyrolysis temperature °C	Residence time in the reactor(min)	Application rate (%/t and Mg ha^−1)	SAW (v/v)	References
Sand	8.54	4 months	Laboratory		Cotton stalks	400	180	0 1 2 4 6%	0.0382^d 0.0397^cd 0.0406^c 0.0498^b 0.0522^a	(Shenghai et al., 2019)
Loamy sand		90 days	Pots	Vigna unguiculata (L.)	Chipped woody green waste	550	-	0 1 2%	0.224 0.239 0.262*	(Pudasaini et al., 2016)
Silty clay loam		6 years	Field	Vineyard	Walnut shell	900	-	Organic 0 10 t ha^−1 Conventional 0 10 t ha^−1	0.141^a 0.138^a 0.147^a 0.156^a	(Wang et al., 2019)
Clay loam		3 years	Field		Corn straw and peanut hulls		-	0 8 Mg ha^−1	10.6^b 13.7^a	(Ma et al., 2016)
Clay	8	180 d	Incubation		Sugarcane bagasse	800	120	0 1 3 5 10%	0.04^c 0.05^bc 0.06^b 0.08^ab 0.09^a	(Kameyama et al., 2016)

3.1.1. Soil bulk density (BD)

In regards to the magnitude of variations in bulk density caused by BC incorporation, fine-textured soil (clay) is less influenced than coarse-textured soil (sandy) (Głąb et al., 2016), but medium and fine-textured soil displayed negligible impacts in certain trials (Abrishamkesh et al., 2016). However, by increasing the application rate of BC, BD was also noticeably reduced (Githinji, 2013). Since most BC have BDs that are between 0.3 and 0.6 g.cm⁻³ lower than those of common agricultural soils and highly stable organic carbon BC (Gwenzi et al., 2015), BC additions are expected to decrease the BD of the majority of mineral agrarian soils. Furthermore, BC may indirectly impact BD through affecting aggregation (Verheijen et al., 2019).

3.1.2. Soil total porosity (TP)

Using different BC (doses, feedstock and pyrolysis temperature) as a soil amendment significantly increased soils porosity in both short-term and long-term studies of coarse-textured soil (sandy). The increase of macropores (they are large soil pores, usually between aggregates, that are generally greater than 0.08 mm in diameter) (Lei & Zhang, 2013), and the development soil micropores (<0.03 mm) in the soil (Brewer, 1965) could be attributed to three ways in which BC may improve soil porosity. Reduced soil bulk density comes first, followed by increased soil aggregation, interaction with mineral soil particles in third, and finally, decreased soil packing. The porosity of BC particles ranges from 70 to 90%. BC can increase soil porosity, improving the soil’s ability to transfer gases, heat, and water (Blanco-Canqui, 2017).

3.1.3. Soil-available water (SAW)

All BC rates markedly increased SAW in both sandy and clay soils (Kameyama et al., 2016; Ma et al., 2016; Shenghai et al., 2019), while loamy sand soil responded significantly at the highest rate (Pudasaini et al., 2016). This can be translated into the BC interaction with organic particles or parent soil minerals (Lehmann et al., 2011), which can occur through the change of the soil structure matrix by BC particles capable of absorbing water strictly due to their porous character (BC intrapores). BC can increase SAW by increasing intraparticle porosity (between particles), particularly intra-particle mesopore (0.08–0.03 mm diameter), and macropore volume. BC amendment can affect both interparticle and intraparticle pore structures, while interparticle (within the particles) pore structures are created by irregularly shaped BC particles (Liu et al., 2017), that can be easily occupied by soil particles (Lehmann & Joseph, 2015).

3.2. Soil chemical properties

BC amendment is known as a soil improvement approach that is thought to improve plant growth by affecting soils nutrient availability while using different sources of biochar with different pyrolysis conditions (Jjagwe et al., 2021; Lusiba et al., 2017; Purakayastha et al., 2019) (Tables 4–9).

Table 4. Impact of BC application on an

Soil type	Initial pH	Duration	Study type	Plant	BC feedstock	Pyrolysis temperature °C	Application rate (%/Mg and t ha^−1)	AN (mg kg^−1)	References
Sandy loam	7.53	20 months	Pot	-	Forest logging residues	500	0 2 4%	81.63^d 109.85^bc 123.68^ab	(Zhou et al., 2019)
Sandy loam	5.27	4 years	Field	Maize and Soybean	Ponderosa pine wood	650	0–7.5 cm 0 10 Mg ha^−1 7.5–15 cm 0 10 Mg ha^−1	43930^b 34770^c 8270^a 5970^a	(Abagandura et al., 2021)
Sandy loam	8.50	90 days	Incubation		Conocarpus wood	400	0 1%	13.1^e 15.1^d	(El-Naggar et al., 2015)
Sandy loam	6.27	6 years	Field	Peanuts	Corn stalks	500	0 225 0.75 t ha^−1 +NPK 0.25 t ha^−1+NPK	46.5^d 70.1^c 74.6^bc 80.8^a 78.1^ab	(Gao et al., 2021)
Loam	7.05		Pot	Oryza sativa L	Rice husk	500	0 1%	60.90 61.83^ns	(Wen et al., 2022)
Loam	7.05		Pot	Oryza sativa L	Wood	500	0 1%	60.90 64.63*	(Wen et al., 2022)
Clay loam	5.93	4 years	Field	Maize and soybean	Ponderosa pinewood	650	0–7.5 cm 0 10 Mg ha^−1 7.5–15 cm 0 10 Mg ha^−1	5290^b 51030^b 16170^a 16270^a	(Abagandura et al., 2021)
Acid purple	5.52	110 days	Pot	Brassica campestris L.	Rice husk	500	0 0.8 2 4 %	70980^a 69620^a 61700^b 63880^b	(Li et al., 2021)
Weathered granites and gneisses	7.15	90 days	Pot	Wheat	Corn straw	400–500	0 0.5 1 2 4%	8.64^c 9.63^c 13.60^b 13.73^b 17.41^a	(Hu et al., 2023)
Black loessial loose texture	8.19	8 years	Field	Winter wheat	Corn straw	400	0 N0 0 N90 0 N120 20 t ha ^−1N90 20 t ha ^−1N120 PK	30.44^a 35.84^b 30.84^a 34.00^b 34.29^b	(Yuan et al., 2023)

Table 5. Impact of BC application on AP

Soil type	Initial pH	Period	Study type	Plant	BC feedstock	Pyrolysis temperature °C	Application rate (%/Mg ha^−1)	AP (mg kg^−1)	References
Clay loam	7.9	70 days	Pot	Lentil	Rice husk	250–500	With NPK 0 0.4, 0.8 1.6 2.4 3.3%	108.00^f 121.33^e 140.00^d 176.67^c 218.67^b 256.00^a	(Abrishamkesh et al., 2016)
Sandy loam	7.97	90 days	Incubation		Sheep manure	300 500	0 5 5%Without NPK	9.06^e 26.33^a 22.33^b	(Boostani et al., 2020)
Sandy loam	7.97	90 days	Incubation		Vermicompost	300 500	0 5 5%Without NPK	9.06e^e 16.66^c 17.16^e	(Boostani et al., 2020)
Acid purple	5.52	110 days	Pot	Brassica campestris L. cv.	Rice husk	500	0 0.8 2. 4 %	30.88^d 45.23^c 73.27^b 115.50^a	(Li et al., 2021)
Sandy loam	5.27	4 years	Field	Maize and Soybean	Ponderosa pinewood	650	0–7.5 cm 0 10 Mg ha^−1 7.5–15 cm 0 10 Mg ha^−1	66000^a 52670 ^a 18330^a 16000^a	(Abagandura et al., 2021)
Clay loam	5.03	4 years	Field	Maize and Soybean	Ponderosa pinewood	650	0–7.5 cm 0 10 Mg ha^−1 7.5–15 cm 0 10 Mg ha^−1	113000 ^a 99670^a 42000^a 21000^a	(Abagandura et al., 2021)
Sandy loam		20 months	Pot		Forest logging residues	500	Without NPK 0 2 4%	9.64^d 25.50^bc 24.65^bc	(Zhou et al., 2019)

Table 6. Impact of BC application on AK

Soil type	Initial pH	Duration	Study type	Plant	BC feedstock	Pyrolysis temperature °C	Application rate (%/t and Mg ha^−1)	AK (mg kg^−1)	References
Acid purple	5.52	110 days	Pot	Bras-sica cam-pestris L	Rice husk	500	0 0.8 2 4 %	30.88^d 45.23^c 73.27^b 115.50^a	(Li et al., 2021)
Sandy Loam	7.97	90 days	Incubation		Sheep manure	-300 500	0 5 5%Without NPK	172.3^g 2428.3^a 1906.2^b	(Boostani et al., 2020)
Sandy Loam	7.97	90 days	Incubation		Vermicompost	-300 500	0 5 5%Without NPK	172.3^g 486.7^d 440.2^e	(Boostani et al., 2020)
Clay Loam	7.9	70 days	Pot	Lentil	Rice husk	250–500	With NPK 0 0.4 0.8 1.6 2.4 3.3%	16.51^a 11.91^c 10.89^c 14.80^abc 15.42^ab 12.78^bc	(Abrishamkesh et al., 2016)
Ultisols	5.94	11 months	Field	Noodle rice	Cassava straw	300–500	135 kg N ha^−1 0 10 20 30 t ha^−1	237.53^d 253.67^c 275.26^ab 278.55^a	(Ali et al., 2022)
Ultisols	5.94	11 months	Field	Noodle rice	Cassava straw	300–500	180 kg N ha^−1 0 10 20 30 t ha^−1	253.32^c 269.66^b 277.37^a 277.71^a	(Ali et al., 2022)
Clay loam	5.03	4 years	Field	Maize and Soybean	Ponderosa pinewood	650	0–7.5 cm 0 10 Mg ha^−1 7.5–15 cm 0 10 Mg ha^−1	190670^a 157670 ^a 93330^a 95670^a	(Abagandura et al., 2021)

Table 7. Impact of BC application on soil pH

Soil type	Initial pH	Duration	Study type	Plant	BC feedstock	BC pH	Pyrolysis temperature °C	Application rate (%/Mg ha^−1)	pH	References
Loamy sand	4.68	254 days	Laboratory		Wheat straw	6.52	300	0 0.2 0.5 1 2%	4.65^a 4.70^bc 4.83^cd 4.97^de 5.29^gh	(Mierzwa-Hersztek et al., 2020)
Sandy loam	7.97	90 days	Incubation		Sheep manure	10.25 10.40	-300 500	0 5 5% Without NPK	8.01^e 8.15^c 8.37^a	(Boostani et al., 2020)
Sandy loam	7.97	90 days	Incubation		Vermicompost	9.78 10.50	-300 500	0 5 5% Without NPK	8.01^e 8.10^d 8.24 ^b	(Boostani et al., 2020)
Ultisol	4.31	90 days	Incubation		Canola straw Corn straw	6.48 9.39 10.76 9.37 10.77 11.32	0 300 500 700 300 500 700	1%	3.95^j 4.30^i 4.60^e 5.17^b 4.35^h 4.48^f 4.80^d	(Wan et al., 2013)
Sandy clay loam	5.10	90 days	Microcosm		Bamboo	10.26 10.35 10.57	350 500 700	2%	5.73^b 5.97^b 6.80^a 7.00^a	(Guo et al., 2020)
Loam	7.7	90 days	Incubation		Corn residue	8.17 9.19	350 500	0 1 2% 0 1 2%	7.60^d 7.63^cd 7.68^c 7.60^d 7.76^b 7.81^a	(Karimi et al., 2019)
Silt loam	6.37	28 days	Incubation		Chicken manure	9	500	0 15 Mg ha^−1 30 Mg ha^−1 (OCk) Under 300 ha^−1 urea	6.35^a 7.67^b 6.87^ab	(Widowati et al., 2011)
Silt loam	6.37	28 days	Incubation		Organic city waste (OCW)	9.6	500	0 15 Mg ha^−1 30 Mg ha^−1 (OCW) + 300 ha^−1 urea	6.35^a 7.70^b 6.73^ab	(Widowati et al., 2011)
loam	7.05	5 weeks	Pot		Rice husk		500	0 1%	7.10 7.27***	(Wen et al., 2022)
loam	7.05	5 weeks	Pot		Wood		500	0 1%	7.10 7.40***	(Wen et al., 2022)
Clay loam	5.03	4 years	Field	Maize and soybean	Ponderosa pinewood	9.3	650	0–7.5 cm 0 10 Mg ha^−1 7.5–15 cm 0 10 Mg ha^−1	5.03^a 5.30^a 5.67 ^a 5.93^a	(Abagandura et al., 2021)
Clayey	6.5cacl2	35 days	Pot	Raphanus sativus L	Sewage sludge	6	300	0 1 2 3 4 5%	6.20^a 6.18^a 6.48^a 6.55^a 6.45^a 6.35^a	(Sousa & Figueiredo, 2016)

OCK: Organic Chicken Manure, OCW: Organic city waste.

Table 8. Impact of BC application on soil pH in different climatic regions

Soil type	Climatic region	Initial pH	Duration	Study type	Plant	BC feedstock	BC pH	Pyrolysis temperature °C	Application rate (%/Mg ha^−1)	pH	References
Sandy Ultisol	Tropical and subtropical	5	180	Incubation		Straw Woodchips Waste water sludge	8.6 8.4 8.3	500	0 2 4 6% 2 4 6% 2 4 6%	5.01^b 4.95^c 5.01^b 5.15^a 5.67^c 6.51^b 7.34^a 5.24^b 5.31^a 5.29^ab	(Zong et al., 2015)
Silty clay loam	Tropical and subtropical	7.09	180	Incubation		Wood (WB) Rice husk (RHB)	7.79 8.86	600	0 2%WB 2%RHB	7.08b^C 7.14b^B 7.20b^A	(Lee et al., 2022)
Weathered sandy loam	Tropical		2 years	Field		Corn cobs	10.2	500–550	0 15 30 t ha^−1	5.4^c 6.2^b 6.6^a	(Amoakwah et al., 2022)
Highly weathered Silty clay	Humid subtropical and tropical	3.95	105	Incubation		Wood	9.94	700	0 2.5 5%	3.95^a 4.65^b 5.07^c	(Jien & Wang, 2013)
Sandy loam Ultisol	Humid tropics	3.7	1 season	Field	Maize	Cacao shell	9.8	400–500	0 5 15 t ha^−1	a b c^+	(Cornelissen et al., 2018)

+: increase.

Table 9. Impact of BC application on EC

Soil type	Initial pH	Duration	Study type	Plant	BC feedstock	Pyrolysis temperature °C	Application rate (%/Mg ha^−1)	EC (mS cm^−1)	References
Loamy sand	5.67	254 days	Laboratory		Wheat straw	300	0 0.2 0.5 1 2%	0.130^b 0.617^i 0.627^i 0.651^ij 0.748^j	(Mierzwa-Hersztek et al., 2020)
Sandy loam	7.97	90 days	Incubation		Sheep manure	-300 500	0 5 5% Without NPK	0.14^f 0.81 ^b 1.01 ^a	(Boostani et al., 2020)
Sandy loam	7.97	90 days	Incubation		Vermicompost	-300 500	0 5 5%Without NPK	0.14^f 0.63^c 0.81^b	(Boostani et al., 2020)
Sandy loam	5.27	4 years	Field	Maize and Soybean	Ponderosa pinewood	650	0–7.5 cm 0 10 Mg ha^−1 7.5–15 cm 0 10 Mg ha^−1	0.33^a 0.29^a 0.11^a 0.10 ^a	(Abagandura et al., 2021)
Clay loam	5.03	4 years	Field	Maize and Soybean	Ponderosa pinewood	650	0–7.5 cm 0 10 Mg ha^−1 7.5–15 cm 0 10 Mg ha^−1	0.57^a 0.54^a 0.24^a 0.22 ^a	(Abagandura et al., 2021)
Clay loam	7.9	70 days	Pot	Lentil	Rice husk	250–500	0 0.4 0.8 1.6 2.4 3.3%With NPK	0.593^bc 0.535^bc 0.498^c 0.543^bc 0.620^ab 0.695^a	(Abrishamkesh et al., 2016)

C: Controlled irrigation, F: Flooding irrigation.

3.2.1. Soil-available nitrogen (AN)

Alkaline and neutral (sandy loam and loam soils) exhibited substantial increases in AN but the increments were not significant when rice husk biochar was added for neutral loam soil (El-Naggar et al., 2015; Wen et al., 2022; Zhou et al., 2019) while acidic sandy loam followed a substantial downward trend (Abagandura et al., 2021). Similarly, AN decreased significantly after BC addition of 2% in acidic purple soil. In contrast in both neutral weathered granites and gneisses and medium alkaline Black loessial loose soils, they started to increase significantly at a 1% and 20 t ha⁻¹ BC amendment rate (Hu et al., 2023; Li et al., 2021; Yuan et al., 2023). However, acidic clay loam displayed insignificant increases. AN decline in soil could be attributed to two reasons: (1) higher N absorption by plant or (2) use and immobilization of N by microorganisms during BC breakdown of mineralizable fractions with low N contents (Parton et al., 2007). In the same vein, BC application boosted soil particle CEC and anion exchange capacities (AEC) (Mavi et al., 2018), causing reductions in the nitrogen leaching from the soil and increasing the nitrogen concentrations of (NO₃⁻ -N) and (NH₄⁺ -N) (Abbruzzini et al., 2019; Vaccari et al., 2011).

3.2.2. Soil-available phosphorus (AP)

Medium alkaline (clay and sandy loam) soils showed a significant gradual increasing trend in soil AP after biochar amendment (Abrishamkesh et al., 2016; Boostani et al., 2020) whereas highly acidic (sandy and clay loam) soils revealed insignificant decreases (Abagandura et al., 2021). However, soil AP becomes progressively greater in acidic purple soil when supplied with gradual doses of biochar (Li et al., 2021). BC’s effects on P have multifold mechanisms. First, BC liming’s impact on acidic soil causes Al (aluminum) and Fe (iron) to precipitate as Fe (OH)₃ and Al (OH)₃, increasing P availability in the soil system. Second, BC has a significant amount of soluble P salts generated during the charring of organic materials (Deluca et al., 2009); thus, both mechanisms increase P availability, which is greatest in the pH range of 5.5–6.0. On the other hand, BC amendment significantly decreased P levels in leachate solutions and increased its retention in the soil in an incubation study (Novak et al., 2009).

3.2.3. Soil-available potassium (AK)

AK experienced a significant reduction in medium alkaline clay loam soil after biochar addition (Abrishamkesh et al., 2016) while AK in highly acidic clay loam showed an insignificant reduction when biochar was introduced (Abagandura et al., 2021). However, medium alkaline sandy loam revealed a significant upturn trend in AK soil content as a response to biochar amendment (Boostani et al., 2020). A significant increase in AK with increasing rates of biochar was observed by Li et al. (2021) and Ali et al. (2022) in (medium acidic ultisol and acidic purple) soils. Strong carboxylic and phenolic functional groups on the surface of the BC particles could be the reason behind the K upward trend (Tian et al., 2017) or due to the presence of cation exchange sites on their surface. The increase in K may be due to BC’s porous structure, large surface area, and negative surface charge, which can increase the soil’s CEC and allow for the retention of nutrients, including K (Alkharabsheh et al., 2011).

3.2.4. Soil pH

Light acidic and highly acidic (clayey and clay loamy) soils revealed no significant effect under BC application rates (Abagandura et al., 2021; Sousa & Figueiredo, 2016). However, highly acidic to light alkaline (medium and coarse-textured) soils showed a considerable increase with the gradual increments in doses regarding pH values (Boostani et al., 2020; Mierzwa-Hersztek et al., 2020; Wen et al., 2022; Widowati et al., 2011). However, increasing the pyrolysis temperatures at the same dose of biochar significantly increased the soil pH for strongly acidic, acidic and light alkali soils (Guo et al., 2020; Karimi et al., 2019; Wan et al., 2013). Depending on the climatic regions and affected soils shown in Table 8, mostly gradual biochar amendment increased the pH value in all the regions (humid tropics and subtropic) and soil types (Amoakwah et al., 2022; Cornelissen et al., 2018; Jien & Wang, 2013; Lee et al., 2022; Zong et al., 2015). BCˈs effects on soil pH have multifold aspects depending on the initial status of the soil, BC feedstock and pyrolysis temperature. First, the rise in pH may be explained by the alkalinity of added BC, which can act as a liming agent in acidic soil (Alkharabsheh et al., 2011; Tian et al., 2017). According to Major et al. (2010) and Bedassa (2020), the beneficial impact of BC on raising soil pH is more visible in acidic soils with low soil organic matter content. On the contrary, acidic compounds generated by the oxidation and degradation of soil organic matter were responsible for the pH drop (Gul et al., 2015; Stewart et al., 2013). This may mitigate soil alkalinity and reduce soil pH (Zavalloni et al., 2011).

3.2.5. Soil EC (electrical conductivity)

EC grew significantly in medium acidic loamy sand and medium alkaline sandy loam soil with respect to the amendment rate (Boostani et al., 2020). On the other hand (Abagandura et al., 2021), indicated that EC in acidic sandy loam and highly acidic clay loam soils decreased non-significantly after BC amendment. A significant fluctuation EC trend started with decreasing then increasing with the biochar amendment in medium alkaline clay loam soil (Abrishamkesh et al., 2016). BC’s EC value has a great relation to BC’s ash content values (Abrishamkesh et al., 2016). Both of them depend on the feedstock and pyrolysis temperature. For example, compared to woody BC (camellia oleifera shells, garden waste), herbaceous plant biochar (rice straw, corn straw) exhibited a much higher EC, and ash content (Tu et al., 2022). According to the rise in pyrolysis temperature, Khanmohammadi et al. (2015) indicated that increasing the temperature from 300 to 700 °C, sewage sludge BCˈs EC rose by 1.4 dS m⁻¹. The integration of BC into acidic soil improved EC because BC’s weakly bound nutrients (cations and anions) are released into the soil solution, which are accessible for plant absorption (Chan et al., 2008).

4. ET under BC treatment in soils growing different plants

In agreement with the results of ET under soil BC treatment during growing different plants were presented in Table 10. Researchers had shown different trends in plant ET when BC was added to soil while dry plant weight showed a steady increasing trend in all treatments. The discrepancies could be attributed to the soil type, plant species, BC dose, irrigation level and fertilization. These results suggested that soybean ET increased significantly as a response to BC addition only at the first dose of 10 t ha⁻¹ in the incorporated application method and the lysimeters ET estimation method in a sandy loam soil (Reyes-Cabrera et al., 2017), while in using some other ET estimation methods with biochar, there was not a significance in ET increasing (Ahmed et al., 2019; Bruun et al., 2022; Yeboah et al., 2016). On the other hand, maize ET revealed a significant rise in a sandy clay loam under full irrigation with 300 kg N ha⁻¹ and biochar 20 t ha⁻¹. Still, maize ET grew markedly under 80 % irrigation and without N fertilizer in the same BC treatment (Faloye et al., 2019). This behaviour could not be noticed in other types of soils. However, ET response for plants growing in sandy loam and sandy clay loam soils was considerable under low BC doses (Faloye et al., 2019; Reyes-Cabrera et al., 2017). Table 9 indicated that the incorporated BC also increased soybean dry weight significantly after supplying gradual rates to the sandy loam soil. At the same time, topdressing distribution method responded seriously just at the highest rate 50 t ha⁻¹ (Reyes-Cabrera et al., 2017). Dry weight increased substantially when fertilization was used with full irrigation at 20 t ha⁻¹ BC rate, but decreasing the irrigation to 80% has a significant effect among the whole treatments (Faloye et al., 2019). On the other hand, dry weight rose significantly in loamy soil at 20 t ha⁻¹ biochar dose (Ahmed et al., 2019).

Table 10. Recent results for BC use and ET (mm) on different plants and soils

Soil type	Initial pH	Study duration and type	Plant	BC Feedstock	Pyrolysis temperature °C	Estimation methods	Application rate	ET (mm)		Dry plant weight (g)	References
Sandy loam	5.7	40 days lysimeter columns	Soybean	Wood	760	Lysimeters (depth: 35 cm) were weighed) twice a week to determine water losses	Incorporated 0 10 25 50 t ha^−1 Top-dressed 0 10 25 50 t ha^−1	87.6^b 94.3^ab 91.9^ab 95.6^ab 87.6 99.4^a 102.2^a 104.0^a	2.7^bc 3.0^abc 3.18^ab 3.20^a 2.7^abc 2.7^abc 3.0^abc 2.5^c		(Reyes-Cabrera et al., 2017)
Sandy clay loam	5.12	Field 1 season	Maize	Maize-cob residue	500	Water balance equation	F0B0I100 F0B20I100 F300B20I100 F300B0I100 F300B20I80 F0B20I80 F300B0I80 F0B0I80	433.55^a 439.64^a 447.54^b 444.43^b 427.91^a 416.03^b 424.44^a 411.79^b	14.80^ab 14.80^ab 17.57^a 16.85^a 17.24^a 12.46^bc 15.74^ab 11.33^c		(Faloye et al., 2019)
Loamy	8.15	2 seasons Column	Brassica Campestris Var.	Poultry manure (chicken litters and straw)	450	Lysimeters (circular PVC (Polyvinyl Chloride) tank of 30 cm diameter and 35 cm height)	Season-1 CK WB BC Season-2 CK WB BC	8.76^a 8.46^a 9.32^a 3.54^a 3.65^a 3.53^a	62.9^b 79.5^ab 87.4^a 44.45^b 61.95^ab 66.12^a		(Ahmed et al., 2019)
Sand	6.5	1 year Column	Winter wheat	Wheat straw	730	Based on changes in water content by PR2 probe 120°	2017 Control 1%	100^a 116^a	65.8^a 89^a		(Bruun et al., 2022)
Sand	6.5	2 years Column	Winter wheat	Wheat straw	730	Based on changes in water content by PR2 probe 120°	2018 Control 1%	100^a 133^a	37.5^a 118^b		(Bruun et al., 2022)
Sandy loam	8.3	2 consecutive seasons	Spring wheat	Maize straw	500	Calculated through the differences in water storage	2015 Control 50 kg(N) ha^−1 15 t ha^−1 B+50 kg(N) ha^−1 4.5 t ha^−1straw+50 kg(N) ha^−1	218.72^a 217.92^a 200.24^a 203.59^a	-		(Yeboah et al., 2016)

CK: no biochar and no fertilization, BC: biochar 20 t ha⁻¹and fertilization 300 kg N ha⁻¹, WB: fertilization without biochar addition, FIT: Irrigation percentage, F300B20: 300 kg ha⁻¹ fertilizer + 20 t ha⁻¹ biochar, F0B0: No Fertilizer + No Biochar, F0B20: No Fertilizer + 20 t ha-1, F300B0: 300 kg ha⁻¹ + no biochar, F0: No Fertilizer, B0: No Biochar, I100: 100%Full Irrigation, B20: 20 t ha⁻¹ of Biochar, I80: 80% irrigation, I60: 60% irrigation, F300: 300 kg ha⁻¹.

5. Summary and future perspective

This review emphasized several points related to BC: Firstly, its production and origin. Secondly, how BC application alters both the soil’s physical and chemical characteristics. Third, evaluating the last research papers on the interaction between BC and some plantsˈ ET. The combination of BC’s effect on both soil physical and chemical properties through rising water and macronutrient availability, either by supplying more nutrients or improving plant absorption, especially in coarse and medium texture soils, was reliably the cause of rising plantsˈ ET. BC is an inexpensive, eco-friendly material used to resist water loss due to climate change, especially in poor-quality soils. It seems like biochar is an encouraging organic alternative to control ET in the long run, focusing on factors such as BC particle size effect, long-term studies, and timing of re-application of different BC types.

List of abbreviations

Abbreviation	=	Definition
BC	=	Biochar is a carbon-rich by-product of organic matter pyrolysis under high temperature, partial or complete hypoxia.
ET (mm)	=	Evapotranspiration (explains water and energy transfer among soil, land surface, and atmosphere).
E(mm)	=	soil surface evaporation (the movement of water directly to the air from the soil surface).
BD (g cm−3)	=	Bulk density (The weight of dry soil divided by the total soil volume).
SAW (%)	=	Soil available water (The difference between field capacity, FC, and wilting point, WP).
TP (%)	=	Total porosity (the ratio of nonsolid volume to the total volume of soil)
AN, AP, AK (mg kg−1)	=	The amounts of soil macronutrients nitrogen, phosphorous and potassium respectively in chemical forms accessible to plant roots.
pH	=	is the measure of soil acidity or alkalinity, specifically the inverse log of the hydrogen ion concentration on a scale from 0-14
EC (mS cm−1)	=	Electrical conductivity measures the concentration of ions from water-soluble salts in soils, and the test results indicate soil salinity
CEC (meq/100g)	=	Cation exchange capacity measures ions in millequivalents per 100 grams of soil (meq/100g). A meq is the number of ions which total a specific quantity of electrical charges.
AEC (meq/100g).	=	Anion exchange capacity measures anions in millequivalents per 100 grams of soil (meq/100g).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Evan Bassam Dayoub

Evan Bassam Dayoub is a PhD candidate at Festetics Doctoral school, Hungarian University of Agriculture and Life Sciences (MATE), Keszthely, Hungary. He completed his MSc in 2020 from Tishreen University, Soil and Water Sciences Department. He completed his bachelor of Agricultural engineering in 2015 from Tishreen University, Soil and Water Sciences Department. He is interested in biochar applications and production in addition to its impacts on soil physical and chemical characteristics as well as plant growth and productivity.

Zoltan Tóth

Zoltan Tóth is a Doctor of Philosophy of plant breeding and botany from the University of Veszprém, Hungary, 2001. His Research area long-term field experiments. Effect of crop rotations, fertilization and soil tillage on productivity, as well as soil physical, chemical and biological properties. Soil management and land use. Head of Department of Agronomy https://doktori.hu/index.php?menuid=192&lang=HU&sz_ID=6823

Angela Anda

Angela Anda Hungarian agrometeorologist, educator. Recipient of Szechenyi I. professorship. MSc in Agricultural engineering at Agricultural University of Keszthely (1978). Special training in Meteorology on the basis of WMO Guide at Eötvös L. University, 1982. Doctor of Philosophy in Geography, 1993; Doctor of Sciences (DSc, Hungarian Academy of Sciences, 2001). Her research area is the members of the non-living environment; especially types of water losses (evaporation, transpiration); processes of the crop-atmosphere continuum Head of Festetics Doctoral School: https://doktori.hu/index.php?menuid=192&lang=HU&sz_ID=3641