Inﬂuence of Rice Husk Biochar and Lime in Reducing Phosphorus Application Rate in Acid Soil: A Field Trial with Maize

: Biochar has been suggested for application in acidic soils for increasing agricultural productivity, as it may result in the beneﬁts of sustainable carbon offset into soils and of increasing soil fertility improvement. However, the role of biochar in enhancing nutrient bioavailability and plant performance is manifested through the complex interactions of biochar-soil-plant. Moreover, it is not yet known how a crop-residue-derived biochar would perform in acidic soil when applied with a reduced rate of lime and phosphorus. Here, we examined the performance of maize with different combinations of biochar, lime, and phosphorus (P) application rates under ﬁeld conditions. Speciﬁcally, rice husk biochar (10 t ha − 1 ) was applied with 75% of the required lime and three rates of phosphorus fertilizer (100%, 75%, and 50%). The results showed that incorporation of biochar and lime, irrespective of the rates of P application, signiﬁcantly increased soil nutrient (nitrogen and P) availability, while aluminum (Al) and iron (Fe) concentrations in soil were reduced. Furthermore, when biochar was combined with a lower amount of lime (75% of the recommended amount) and half of the required P, maize production increased by 62.38% compared to the control. Similarly, nutrient uptake in plants increased signiﬁcantly in the same treatment (e.g., P uptake increased by 231.88%). However, soil respiration (CO 2 emission) increased with lime only and the combined application of lime with biochar compared to the control; these treatments resulted in a higher carbon loss, as CO 2 from the soil (84.94% and 67.50% from only lime treatment (T 2 ), and rice husk biochar (RHB) and lime with 50% triple superphosphate (TSP) (T 5 ), respectively). Overall, our ﬁndings imply that biochar application may sustain productivity in acid soils even when lime and P fertilizer applications are made at a reduced rate.


Introduction
Maize is one of the multipurpose crops used as food for humans, fodder for animals, and raw materials for industries throughout the world [1]. In tropical and subtropical zones, maize cultivation is largely hampered by acidic soil, since high rainfall occurs in this region [2]. Soil acidification can be both natural and anthropogenic, through changes in land use and application of chemical fertilizers [3]. While the extent of acidified soil is quite large, estimated at 30% of the global land area and 50% of arable lands, its coverage may increase in the future. Therefore, soil acidification can be one of the major limitations responsible for poor soil fertility and agriculture productivity, consequently reducing crop Previously, studies have been conducted to evaluate the biochar-mediated effects on soil acidity and plant performance [32,33]. These studies reported significant effects of biochar and lime on maize productivity [34]. However, these studies were conducted in pots with a small amount of soil and only a few plants. Since the interactions of biochar and lime with soils in field conditions can be quite different than pot culture due to the interactions of biochars and plants with a large volume of soil, changes in nutrient inputs and outputs, and environmental conditions, it is important to examine the combined application of biochar under field conditions. Therefore, the study aimed to examine the performance of maize after the application of biochar with lime and with variable rates of P fertilizer. Moreover, we also present data on changes in soil property and the emission of CO2.

Experimental Site
The research was performed at Universiti Putra Malaysia, Serdang, Selangor, from January 2021 to April 2021. The study location was 2°98′57.5″ N latitude and 101°73′56.7″ E longitude. According to the United States Department of Agriculture (USDA) soil classification system, the research site's soil was designated as a sandy clay texture (sand 50%, silt 14%, and clay 36%), and soil particle-size distribution was examined by the hydrometer technique [35]. It was fine, kaolinitic, isohyperthermic, typic Paleudult, Order: Ultisol, and belongs to the Bungor Series. The climate is tropical, hot, and humid in the region. The average temperature for the experimental time was 28 °C, the monthly average rainfall was 241.42 mm, and the relative humidity was 78% ( Figure 1).

Soil Properties
The initial and final soil samples were collected before applying the treatments and after harvesting, respectively, and then air-dried at room temperature. Then, they were crushed and sieved to less than 2 mm, prior to chemical characterization.
Soil pH was recorded using a glass electrode pH meter in a 1:2.5 (weight/volume basis) soil: distilled water proportion [36]. A LECO TrueSpec CNS auto analyzer was utilized to measure soil's total carbon, nitrogen, and sulfur content through the dry combustion method, using air-dried and ground soil. The exchangeable cations K, Ca, and Mg were extracted using a 1:5, soil: ammonium acetate (NH4OAc) buffered solution at pH 7

Soil Properties
The initial and final soil samples were collected before applying the treatments and after harvesting, respectively, and then air-dried at room temperature. Then, they were crushed and sieved to less than 2 mm, prior to chemical characterization.
Soil pH was recorded using a glass electrode pH meter in a 1:2.5 (weight/volume basis) soil: distilled water proportion [36]. A LECO TrueSpec CNS auto analyzer was utilized to measure soil's total carbon, nitrogen, and sulfur content through the dry combustion method, using air-dried and ground soil. The exchangeable cations K, Ca, and Mg were extracted using a 1:5, soil: ammonium acetate (NH 4 OAc) buffered solution at pH 7 [37], and their concentrations were evaluated using inductively coupled plasma optical emission spectroscopy (PerkinElmer, Inc., Waltham, MA, USA). Soil exchangeable Al was subsequently extracted using 1 M KCl [38], and ICP-OES was used for analyzing the extract. An atomic absorption spectrometer (AAS) was used to determine the concentrations of Fe and Mn in the soil sample, which was extracted using Mehlich No. 1 double acid [39]. Available P was analyzed by the Bray and Kurtz II method [40]. The collected soil sample had a moisture content of 25.71% (by mass), a soil pH of 4.56, total carbon (TC) of 1.05%, total nitrogen (TN) of 0.08%, exchangeable K, Ca, Mg, and Al of 0.34, 0.97, 0.41, and 2.63 cmol c kg −1 , respectively, available P of 3.68 mg kg −1 , extractable Fe of 128.45 mg kg −1 , and extractable Mn of 2.71 mg kg −1 .

Characteristics of Rice Husk Biochar (RHB)
In this trial, the rice husk biochar was collected from Sendi Enterprise (Sungai Burong, Selangor, Malaysia), which was pyrolyzed from rice husk at 300 • C. First, the RHB pH was determined using a 1:2.5 ratio of air-dried biochar sample to distilled water [41]. Next, biochar's total C and total N content were measured by a TrueMac CNS analyzer, biochar's CEC, base cations were determined using 1 M NH 4 OAc buffered solution at pH 7 [39], and the K, Ca, and Mg extraction was analyzed using AAS. Next, biochar's total P content was determined by the dry ash method, followed by ICP-OES [42]. Finally, the dry combustion technique was used to determine the ash content of RHB. The collected RHB had an ash content of 32.40%, with a pH of 8.15, CEC of 48.12 cmol c kg −1 , total carbon and nitrogen of 24.86% and 1.13%, respectively, exchangeable K, Ca, and Mg of 17.45 cmol c kg −1 , 19.46 cmol c kg −1 , and 13.96 cmol c kg −1 , respectively, total P of 3098.40 mg kg −1 , and extractable Fe and Mn of 43.06 mg kg −1 and 23.51 mg kg −1 , respectively.
The chemical fertilizers were applied in all treatments by following the recommendation rate of Pedram [43]. Urea, triple superphosphate (TSP), and muriate of potash (MoP) were used at 140 kg ha −1 N, 100 kg ha −1 P 2 O 5 , and 120 kg ha −1 K 2 O, respectively. Based on the recommendation rate, urea, TSP, and MoP were scaled and applied at 304.35 g, 217.39 g, and 200.00 g per plot. Further, the amount of P fertilizer was lowered to 75% (163.04 g) and 50% (108.70 g) and applied to the respective treatment combination. On the day before sowing, the entire dose of P and potassium (K) based chemical fertilizer was administered as a baseline dose in all treatments. The N fertilizer was applied in two equal portions at 10 and 28 days after planting to prevent nutrient loss through volatilization and leaching. Biochar at the amount of 10 kg (10 t ha −1 ) and dolomitic limestone at 1.70 kg and 1.28 kg (1.28 t ha −1 ) were applied on plots. The lime rates corresponded to 100 and 75% of the dose established by the lime requirement test [44].

Agronomic Practice
After ploughing to a depth of 30 cm, the cultivated area was rotovated. The total area was 200 m 2 (40 m × 5 m), with four replicates, and each sub-plot was 10 m 2 (4 m × 2.5 m). The RHB and dolomitic limestone were applied once into the soil, mixed thoroughly, and moistened with water to 60% of the maximum water holding capacity before 14 days of the maize seeds sowing. The maize variety of F1 hybrid sweet corn (Zea mays L.) seeds were soaked with water for 10 to 12 h before sowing for good germination. After two weeks of biochar and lime treatment, on 3 February 2021, two seeds were manually sown in holes at 25 cm plant-to-plant and 75 cm row-to-row distance, and then all the holes were filled with loose soil. Later, the plant was thinned to one after one week of planting. Preemergence herbicide Adol (metolachor, 960 g/L), and post-emergence herbicide, Kenbast (glufosinate-ammonium), were applied manually for weed control. Pegasus (diafenthiuron, 250 g/L) was used as an insecticide to protect plants from insects. Water supply to plants was maintained by a sprinkler irrigation system when necessary.

Plant Analysis
On 18 April 2021, maize was harvested and sampled for nutrient analysis. Five plants were taken from the center row of every plot. The plant was cut above the soil surface, partly placed in an envelope, and dried in the oven for 72 h at 60 • C [45]. The elements of the grain were extracted using the single dry ashing process [42]. An AAS was used to determine the concentration of P, K, Ca, and Mg. Total N was analyzed by the TrueMac CNS analyzer. After the determination of nutrient concentration, the value of grain uptake was found using the following calculation [46]: A portable chlorophyll meter (SPAD-502 Konica Minolta, Inc., Tokyo, Japan) was utilized to measure the leaf chlorophyll content. The average of five SPAD measurements from completely expanded leaves was calculated for each plant [47]. The maize plant's third fully expanded leaf was carefully chosen to measure photosynthetic rate, stomatal conductance, and transpiration rate by LICOR LI-6400XT Portable Photosynthesis System (Li-Cor, Inc., Lincoln, NE, USA). Two plants per plot were used for measurement in the morning. The readings were taken automatically by the device. At harvest, dried biomass (g), cob length (cm), number of grains per cob, and other yield components were also measured.

Determination of Protein Content
The protein content was determined from the percent N determined in the grain [48].

Soil CO 2 Gas Measurement
Soil CO 2 emission was analyzed with a portable LI-8100 automated soil CO 2 flux system (LI-COR Biosciences, Lincoln, NE, USA), started on 21 January 2021 as day 1, and it continued on days 2, 3, 4, 5, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, and 75. To avoid the disturbance to the soil surface, the chamber of the instrument device was placed on the polyvinyl chloride (PVC) cylinder, which had a height of 11.5 cm and a diameter of 20 cm, and was inserted 7 to 8 cm into the soil one day before the first measurement and left throughout the whole experiment. In each plot, there were three PVC collars installed. To minimize gas leakage, the soil along the outer side of the PVC collars was compacted thoroughly. The measurement of soil CO 2 flux was monitored from 9:00 a.m. to 11:00 a.m. [49]. Cumulative soil CO 2 emission was calculated by linear interpolation [50].

Statistical Analysis
The data were assessed by SAS 9.4 software (SAS Institute Inc., Cary, NC, USA), and the statistical difference between the treatments was verified using analysis of variance. In addition, Tukey's Honestly Significant Difference (HSD) test was performed to separate the treatment means at a 5% level of confidence. To better understand the interactions and implications of various factors in maize productivity, principal component analysis (PCA) was used.

Effect of RHB, Lime, and Varying Doses of Phosphorus on Soil Properties at Harvest
The pH of the post-harvest soil varied significantly for various treatments ( Figure 2). The maximum soil pH (6.37) was noted from T4. The pH was increased by 1.90 units in this treatment compared to the control treatment. However, soil pH was similar in T 3 , T 4 , and T 5 treatments. the treatment means at a 5% level of confidence. To better understand the interactions and implications of various factors in maize productivity, principal component analysis (PCA) was used.

Effect of RHB, Lime, and Varying Doses of Phosphorus on Soil Properties at Harvest
The pH of the post-harvest soil varied significantly for various treatments ( Figure 2). The maximum soil pH (6.37) was noted from T4. The pH was increased by 1.90 units in this treatment compared to the control treatment. However, soil pH was similar in T3, T4, and T5 treatments. Soil available phosphorus was significantly increased by adding RHB, dolomitic limestone, and varying rates of TSP compared to the control treatment (Table 1). However, the available soil P was statistically similar in the T3, T4, and T5 treatments, although it was increased 291.53% in the T5 compared to the control. At harvest, the highest soil exchangeable K (1.32 cmolc kg −1 ) was observed in T4, estimated at a 428% increase compared to the control. The highest soil exchangeable Ca (3.32 cmolc kg −1 ) was exhibited in T3, and T4. The values were greater by 257% compared to the Soil available phosphorus was significantly increased by adding RHB, dolomitic limestone, and varying rates of TSP compared to the control treatment (Table 1). However, the available soil P was statistically similar in the T 3 , T 4 , and T 5 treatments, although it was increased 291.53% in the T 5 compared to the control.  At harvest, the highest soil exchangeable K (1.32 cmolc kg −1 ) was observed in T 4 , estimated at a 428% increase compared to the control. The highest soil exchangeable Ca (3.32 cmolc kg −1 ) was exhibited in T 3 , and T 4 . The values were greater by 257% compared to the control treatment. However, in both cases, there were no significant differences among T 3 , T 4 , and T 5 .
The RHB, lime, and varying rates of P fertilizer significantly decreased the exchangeable Al. In comparison to the control (T 1 ), there were statistical changes in T 3 , T 4 , and T 5 ; however, there were no significant differences among T 3 , T 4 , and T 5 . By applying treatments, the lowest soil exchangeable Al, 0.07 cmol c kg −1 , was determined in T 4 . At harvest, the minimum Fe (71.50 mg kg −1 ) was recorded in T 5 , which was 71.19% lower than the control. The maximal Mn concentration (4.84 mg kg −1 ) was found in T 3 and T 5 , although T 3 , T 4 , and T 5 had no significant differences.

Effect of RHB, Lime, and Varying Doses of Phosphorus on the Growth and Yield Components of Maize
The plant height, stem diameter, and dry biomass of maize were enhanced significantly by various treatments (Table 2). A longer but statistically similar plant was observed in T 3 , T 4 , and T 5 (up to 233.85 cm), while the shortest plant was observed in T 1 (190.30 cm). The maximum stem diameter and dry biomass were noted in T 4 (2.81 cm and 93.79 g, respectively), while the control treatment provided the lowest value. There were significant increments in cob length, fresh cob weight, No. of grains per cob, and yield of maize in T 3 , T 4 , and T 5 compared to T 1 and T 2 ( Table 2). The highest cob length (24.88 cm), fresh cob weight (360.13 g), and the No. of grains per cob (644) were obtained from T 3 . The greater and identical cob yield produced by T 3 , T 4 , and T 5 (up to 19.21 t ha −1 ) was 62.38% higher than control, i.e., T 1 (11.83 t ha −1 ).

Effect of RHB, Lime, and Varying Doses of Phosphorus on Concentration and Nutrient Uptake by Maize
The RHB, dolomitic limestone, and TSP fertilizer application had a significant increase in concentration and nutrient uptake by maize (Tables 3 and 4). The maximal nitrogen concentration (0.45%), uptake (86.06 kg ha −1 ), and protein content (2.83%) of maize were recorded in T 4 , the highest phosphorus concentration (0.175%) and uptake (33.42 kg ha −1 ) and potassium concentration (0.177%) and uptake (34.17 kg ha −1 ) were from T 3 , and the highest calcium concentration (0.235%) and uptake (44.81 kg ha −1 ) and magnesium concentration (0.115%) and uptake (21.95 kg ha −1 ) were from T 5 . However, there were no statistical differences for T 3 , T 4 , and T 5 for all the parameters, except P uptake by maize.  The influence of treatments on the relative chlorophyll content (SPAD), photosynthetic rate, stomatal conductance, and transpiration rate of maize plants in the maturing stage revealed significant differences ( Figure 3). The maximum SPAD value (49.68) was found from T 3 , indicating a maximum increase of 16.21% relative to control. The highest photosynthetic rate (36.81 µmol m −2 s −1 ) was observed in T 4 , which increased 39.17% compared to the control. The highest stomatal conductance (0.49 mol m −2 s −1 ) and transpiration rate (9.75 mmol m −2 s −1 ) of maize plants were obtained from T 3 and T 5 , respectively. There were no significant alterations in SPAD value, photosynthetic rate, stomatal conductance, and transpiration rate among the treatments of T 3 , T 4 , and T 5 .

Effect of RHB, Lime, and Varying Doses of Phosphorus on Soil CO 2 Emission from the Maize Field
The effect of treatments on daily emission rates of soil CO 2 and their cumulative emissions are presented in Figure 4; Figure 5, respectively. It can be observed that adding dolomitic limestone (T 2 ) into the soil showed the highest cumulative soil CO 2 emission compared to adding organic amendments with lime (T 3 , T 4 , and T 5 ) or the control soil (T 1 ). The soil CO 2 flux emission was significantly increased on day 4 in the amended treatments. However, no significant differences were observed in the cumulative CO 2 emission of T 3 , T 4 , and T 5 . The highest magnitude (12.32 µmol CO 2 m −2 s −1 ) and cumulative CO 2 flux (111.37 µmol CO 2 m −2 ) were noted in T 2 . A moderate CO 2 emission was seen from all the amended treatments from 15 days after sowing (DAS), and it continued up to the last measurement. Compared to the control, the cumulative CO 2 emission was significantly increased by 84.94%, 74.19%, and 67.50% from only lime treatment (T 2 ), RHB and lime with 100% TSP amended soil (T 3 ), and RHB and lime with 50% TSP amended soil (T 5 ), respectively, but T 3 , T 4 , and T 5 showed the same statistical values.

Principal Component Analysis
The principal component analysis (PCA) of different variables is presented in Figure 6. The first and second PCA explained most of the variations of the variables, estimated at 84% and 6%, respectively. All variables had positive loading on the first component, except soil Al and Fe, while variables varied along with positive and negative loading. As a result, the association between variables was created. Specifically, grain yield and biomass production were closely associated with plant nitrogen (i.e., protein and chlorophyll) and Ca concentration. Moreover, biochar and lime treatments were closely associated with most of the plant parameters.
stage revealed significant differences (Figure 3). The maximum SPAD value (49.68) was found from T3, indicating a maximum increase of 16.21% relative to control. The highest photosynthetic rate (36.81 μmol m −2 s −1 ) was observed in T4, which increased 39.17% compared to the control. The highest stomatal conductance (0.49 mol m −2 s −1 ) and transpiration rate (9.75 mmol m −2 s −1 ) of maize plants were obtained from T3 and T5, respectively. There were no significant alterations in SPAD value, photosynthetic rate, stomatal conductance, and transpiration rate among the treatments of T3, T4, and T5.

Effect of RHB, Lime, and Varying Doses of Phosphorus on Soil CO2 Emission from the Maize Field
The effect of treatments on daily emission rates of soil CO2 and their cumulative emissions are presented in Figure 4; Figure 5, respectively. It can be observed that adding dolomitic limestone (T2) into the soil showed the highest cumulative soil CO2 emission compared to adding organic amendments with lime (T3, T4, and T5) or the control soil (T1). The soil CO2 flux emission was significantly increased on day 4 in the amended treatments. However, no significant differences were observed in the cumulative CO2 emission of T3, T4, and T5. The highest magnitude (12.32 μmol CO2 m −2 s −1 ) and cumulative CO2 flux (111.37 μmol CO2 m −2 ) were noted in T2. A moderate CO2 emission was seen from all the amended treatments from 15 days after sowing (DAS), and it continued up to the last measurement. Compared to the control, the cumulative CO2 emission was significantly increased by 84.94%, 74.19%, and 67.50% from only lime treatment (T2), RHB and lime with 100% TSP amended soil (T3), and RHB and lime with 50% TSP amended soil (T5), respectively, but T3, T4, and T5 showed the same statistical values.

Effect of RHB, Lime, and Varying Doses of Phosphorus on Soil CO2 Emission from the Maize Field
The effect of treatments on daily emission rates of soil CO2 and their cumulative emissions are presented in Figure 4; Figure 5, respectively. It can be observed that adding dolomitic limestone (T2) into the soil showed the highest cumulative soil CO2 emission compared to adding organic amendments with lime (T3, T4, and T5) or the control soil (T1). The soil CO2 flux emission was significantly increased on day 4 in the amended treatments. However, no significant differences were observed in the cumulative CO2 emission of T3, T4, and T5. The highest magnitude (12.32 μmol CO2 m −2 s −1 ) and cumulative CO2 flux (111.37 μmol CO2 m −2 ) were noted in T2. A moderate CO2 emission was seen from all the amended treatments from 15 days after sowing (DAS), and it continued up to the last measurement. Compared to the control, the cumulative CO2 emission was significantly increased by 84.94%, 74.19%, and 67.50% from only lime treatment (T2), RHB and lime with 100% TSP amended soil (T3), and RHB and lime with 50% TSP amended soil (T5), respectively, but T3, T4, and T5 showed the same statistical values.

Principal Component Analysis
The principal component analysis (PCA) of different variables is presented in Figure  6. The first and second PCA explained most of the variations of the variables, estimated at 84% and 6%, respectively. All variables had positive loading on the first component, except soil Al and Fe, while variables varied along with positive and negative loading. As a result, the association between variables was created. Specifically, grain yield and biomass production were closely associated with plant nitrogen (i.e., protein and chlorophyll) and Ca concentration. Moreover, biochar and lime treatments were closely associated with most of the plant parameters.

Principal Component Analysis
The principal component analysis (PCA) of different variables is presented in Figure  6. The first and second PCA explained most of the variations of the variables, estimated at 84% and 6%, respectively. All variables had positive loading on the first component, except soil Al and Fe, while variables varied along with positive and negative loading. As a result, the association between variables was created. Specifically, grain yield and biomass production were closely associated with plant nitrogen (i.e., protein and chlorophyll) and Ca concentration. Moreover, biochar and lime treatments were closely associated with most of the plant parameters.

Impact of RHB, Lime, and Different Doses of Phosphorus on Soil Nutrients
The application of lime and biochar can buffer soil pH [51]. In our study, mixed application of RHB (10 t ha −1 ) and lime (75%) increased soil pH compared to the control and 100% lime treatment (Table 1). These results suggest that biochar amendment at 10 t ha −1 is more effective than 25% lime application in increasing soil pH.
The proton consumption after biochar application might be the reason for the increased value of soil pH [32,52]. As the RHB is alkaline (pH = 8.15), and there is a huge amount of ash in RHB (~32%), during the hydrolysis process, it releases OH − by its base cations, which may assist in increasing soil pH [53]. Furthermore, the presence of acid functional groups on biochar's surface may also contribute to the proton consumption [31], since the CEC of biochar was relatively high at~48 cmol c kg −1 biochar. Panhwar et al. [54] also reported the same finding, where they used RHB and bio-fertilizer of 4 t ha −1 each, and soil pH increased by 1.39 units. However, biochar's immediate impacts on soil pH might be short-lived, since the basic cations in the biochar's ash can be lost from the soil through different mechanisms, particularly by leaching in areas with high rainfall levels. In contrast, pH buffering through oxygenated functional groups of biochar may increase with time, suggesting a long-term effect of biochar.
In acidic soil, applying soil amendments, including lime and biochar, can increase nutrient availability [55,56]. In this study, the highest available P (17.11 mg kg −1 ) was observed in T 3 (75% lime + 10 t ha −1 RHB + 100% TSP), representing a three-fold rise in P in comparison to the control. Moreover, it was significantly higher than 100% lime treatment. However, all the biochar and lime-receiving treatments had similar P concentrations, although they received variable amounts of P, ranging from 50 to 100% of the recommended rate. These findings imply that the application of RHB with lime can significantly increase P bioavailability, and this is more pronounced when the P application rate is low. We believe that these changes mostly occurred due to an increase in soil pH, and the addition of P from biochar, while P bioavailability might have increased due to the replacement of fixed phosphate with biochar-derived small molecules [30]. Furthermore, since the CEC of the biochar was high, its role in the competitive interactions may be significant. Incorporating biochar into the soil can also function as a phosphate adsorbent and a source of readily accessible phosphorus [14,28,57]. However, these roles of biochar may be minimal, since the anion exchange capacity of our biochar may be low [28]. Nevertheless, our findings were consistent with Panhwar et al. [55], who reported a 99.82% increase of available P using biochar and bio-fertilizer.
Applying biochar or lime can increase the availability of nutrients in acidic soil [56][57][58]. Compared to the control treatment, the exchangeable cations (Ca 2+ , Mg 2+ , and K + ) increased significantly after the addition of soil amendments in our study (Table 1). Several experiments have reported an enhancement of exchangeable bases considering the use of biochar and lime in tandem [59,60]. In addition, lime may increase Ca and Mg concentration in the soil [56]. On the other hand, the inclusion of RHB added Ca 2+ , Mg 2+ , and K + . As a result, biochar reduces soil acidity, hence increasing the supply of vital plant nutrients [51]. Moreover, biochar may increase the retention of these nutrients in its ion exchange sites [61,62].
In acidic soils, biochar can minimize Al toxicity in various ways, including Al adsorption, absorption, complexation, cation exchange, and electrostatic interactions [63]. In this study, the exchangeable Al significantly decreased when using RHB and lime in combination with various P fertilizer rates compared to the control and sole lime treatment (T 1 and T 2 ). The use of biochar and lime to elevate the soil's pH might help reduce the toxicity of Al [64]. Moreover, biochar-mediated complexation of Al may also have contributed to reducing Al toxicity [65]. Our result is consistent with Ch'ng et al. [64], who reported reduced Al concentration with increased pH by adding chicken litter biochar in acid soil.

Impact of RHB, Lime, and Different Doses of Phosphorus on Plant Growth Variables
The plant dry weight of control and only lime treatments (T 1 and T 2 ) were significantly lower than the biochar amended treatments (T 3 , T 4 , and T 5 ). Due to the lack of enough nutrient supply in the control soil, the growth and development of the plant were reduced. Al toxicity, as well as a lack of Ca, Mg, and P in acidic soil, can limit plant development and productivity [66]. According to Akinrinde et al. [67], usually in acid soil, the hydroxide of Al and Fe fixes P, which is responsible for poor plant development. Moreover, soil pH is an essential means for growing plants [68]. Applying biochar, lime, and chemical fertilizer increased plant growth, root development, cob length, fresh cob weight, grain per cob, and maize yield due to biochar's ability to improve the bioavailability of essential nutrients and their uptake by the maize plant. This outcome is compatible with the findings of Ndor et al. [69] and Gandahi et al. [70], who investigated the influence of biochar on maize plant growth, nutrient uptake, and yield with RHB.

Impact of RHB, Lime, and Different Doses of Phosphorus on Plant Nutrient Concentration and Grain Uptake
Applying RHB, lime, and various levels of TSP considerably increased the maize plant nutrient concentration and uptake over the control treatment and lime-only treatment (T 1 and T 2 ). Specifically, the relative chlorophyll content (SPAD) of the maize plant significantly changed by applying organic amendments relative to control treatment. We believe that applying RHB, lime, and different rates of P enhanced the N concentration in the plant (Table 3), since SPAD values were higher in these treatments and were also associated with plant N concentration in the PCA analysis ( Figure 6). This higher concentration of N was then partitioned to the grain, providing a higher protein concentration (Table 3). Similarly, concentrations and uptakes of other nutrients, including P, K, Ca, and Mg, were significantly increased when biochar was mixed with lime, irrespective of P treatments. In addition, Al 3+ toxicity, one of the common problems identified in the acid soil associated with the root zone, resulted in poor plant development and reduced uptake of essential nutrients in the plot that received biochar and lime treatments [71]. Our findings are consistent with Ndor et al. [69], who obtained increased nutrient uptake and yield of maize by applying rice husk and sawdust biochar. Furthermore, biochar's high surface area and the functional carboxylic and phenolic group binds with ions, preventing the leaching loss of the nutrients [62]. Subsequently, it helps to increase the nutrient uptake by maize.
In this study, the relative chlorophyll content (SPAD) of the maize plant significantly changed by applying organic amendments relative to the control. The SPAD value is an important biochemical indicator for identifying the plant's development and yield parameter [72], where a higher value may indicate the higher yield of crops [73] and also a higher photosynthetic rate [74]. Furthermore, the enrichment of essential nutrients to the acid soil may result in a significant increase in the SPAD value, which may later exhibit proper plant development and growth rate along with chlorophyll content [75,76].

Impact of RHB, Lime, and Different Rates of Phosphorus on Soil CO 2 Emission
Applying biochar has a considerable impact on the soil organic matter mineralization and CO 2 emissions. In our field research, the emission of soil CO 2 gas was influenced by RHB, lime, and different rates of P fertilizer. Higher soil CO 2 emissions were noted with only lime treatment (T 2 ) because of the dissociation of carbonates [77] and mineralization of organic carbon enhanced by the microbial communities [78][79][80].
In general, the rise in soil CO 2 emissions due to biochar addition could be described by the increase of labile soil organic carbon (SOC) pools from the biochar addition and mineralization of biochar-induced priming of native SOC [81]. This increase may also have been accelerated by the stimulated growth of soil microorganisms [78]. Although it has been reported that soil CO 2 emissions may be suppressed by applying biochar, as biochar may inhibit or reduce the C-degrading enzymatic activity [82] and precipitation of CO 2 onto the biochar surface [83], we did not observe these phenomena in our experiment. Possibly, the CO 2 production was much higher than the trapping capacity of biochar, while biochar's pores might have filled with clay minerals in our soil for CO 2 adsorption.
Our findings reveal that the lime-C was reduced from the treatment with co-application of RHB and lime (T 3 , T 4 , and T 5 ) compared with the lime-only treatment (T 2 ), which may be explained as more sequestration of lime-C into the soil in the organic amended treatment [84]. Furthermore, biochar's aromatic compounds are mostly chemically stable, and it has high resistance to decomposition [85,86]. Consequently, biochar can remain in the soil for centuries or millennia [87].

Conclusions
Our findings demonstrate that using RHB and lime in combination with a P fertilizer boosts the soil available P, nutrient uptake, and maize production. This occurred as a result of a rise in soil pH and reduction of the Al toxicity through organic modifications and using lime. Additionally, the combined application of RHB, lime, and varying rates of chemical P fertilizer resulted in enhanced soil nutrients, P-use efficiency, and dry matter yield of maize compared to the control treatment. Biochar application at 10 t ha −1 with 75% lime application provided a similar harvest in a range of P applications from 50 to 100%, whereas the emission of CO 2 gas increased 74.19% and 67.50% from 75% lime + 10 t ha −1 RHB + 100% TSP (T 3 ) and 75% lime + 10 t ha −1 RHB + 50% TSP (T 5 ), respectively. Therefore, our results suggest that 75% lime + 10 t ha −1 RHB + 50% TSP (T 5 ) can be one of the sustainable means for maize cultivation in acidic soil conditions, since it can be more profitable to farmers while reducing total soil CO 2 emission compared to a lime-only treatment.