Effects of biochar input on nitrogen absorption and growth of maize at seedling stage

doi:10.21203/rs.3.rs-4543430/v1

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Effects of biochar input on nitrogen absorption and growth of maize at seedling stage

https://doi.org/10.21203/rs.3.rs-4543430/v1

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Nitrogen (N) is an important nutrient for the yield of maize, farmers persue the higher yield by puting more N fertilizer to the soil leading more environmental pressures. Thus, reduced N feitilizer input is urgent. Biochar (BC), a carbon-rich product, affects N effectiveness, yet, the mechanism behind remains unclear, especially for the textures of soils. Therefore, three N levels, five applicated rates and three textures soils were used to evalute the seeds germiantion of maize, the N uptake under BC addition and reduced N input. The three N fertilizer levels were the control, 0 N fertilizer (N0), 30% reduction based in the local N input, 196 kg/hm² (N1) and local N application amount 280 kg/hm² (N2). The rates for BC were 0%, 2.5%, 5.0%, 7.5%, and 10.0% (wieght ratio), and the soil textures were loamy, loamy clay, and loamy sandy, which the bulk density was 1.38g/cm³, 1.42g/cm³, and 1.47g/cm³, respectively. The results showed that there was an interaction between BC and soil texture on maize growth and N uptake at seedling stage, there was a dose effect of BC on maize seed germination, plant height and storage material transfer efficiency, with a varied optimal BC dosage for the three textured soils. The growth of maize in the three soils showed different trends, and the growth of maize in loamy and loamy clay soil was better than that in loamy sandy soil, and BC had no effect on this trend. The optimal BC rate for the loamy sandy, loamy, and loamy clay soils was 2.5%, 7.5%, and 10%, respectively. Further research using relatively sensitive loamy found that BC addition under reduced N (N2) increased the total N, nitrate N contents and the microbial biomass of N by 12.0%, 9.99%, 11.3%, respectively and decreased the contents of ammonium N by 62.7%. Meanwhile, the uptake of N in maize seedling was increased, 11.1% for the N contents of aboveground and 11.4% for that of underground. The results certisfied that the dose-effect of BC changed for the soil texture and optimal BC application should be considered when the BC was added to the soil.

dose-effect

soil texture

germination

reduced fertilizer

Biochar (BC) is a product of pyrolysis reaction of biomass feedstock ^[1]. BC has a wide range of usesages, including adsorption, catalysis and energy storage ^{[2, 3, 4]}. It improves the physical and chemical properties of the soil as well as reduces the loss of nurtrients, for example, nitrogen (N) ^{[5, 6]}. That was because BC has strong adsorption properties due to its loose and porous structure ^[7]. It can adsorb the mineral N in the soil, thus it effectively reduces the volatilization of N in the soil result in the soil N contents remained ^{[7, 8, 9]}. Recently, the amount of BC was found to related with the effects on N effectiveness. The adsorption of N and potassium in crops increased along with the increasing appliaction rates of BC ^[10] Meanwhile, it has also been shown that BC applied alone has no significant effect on dry matter accumulation in both aboveground and belowground maize ^[11]. That means more further experiments needed to detect the nature relationship between BC and N ^[12].

N is one of the most important nutrients for crops, promoted the yields and changed the growth of maize especially the early growth period ^[13]. The farmers applicated much more chemical N fertilizers than the maize need to persue the high yields. In 2022, China's agricultural N fertilizer application is up to 16,541,800 tons, and the amount of N fertilizer applied to farmland globally is up to 120 million tons per year(China Fertilizer Network). Excessive N fertilizer causes a decline in the quality of agricultural products, as well as leads to soil problems like acidification ^[14]. It is recommended that the N input stay a resonable level ^[15].

Seedling stage is the critical period for chlorophyll synthesis, and when maize seedlings are deficient in N, plants with blocked chlorophyll synthesis will show yellowish green color and slow growth ^[16]. When N was applied at the seedling stage at a rate of 0.100 g/plant, the highest yield of strawberry in the early stage and the total yield were achieved ^[17]. Therefore, the rational use of N fertilizer in the seedling stage of crops can promote crop growth and development ^[18].

It was therefore hypothesized that the application rate of BC interact with the soil texture to change the N effectiveness for maize seedling, changed the germination and growth of maize. Due to the significant differences in abiotic factors such as pH value, nutrient availability, and soil physical properties in different soils, BC works differently for the soil textures ^{[19, 20]}. Secondly, the dose-effects of BC existed and varied for the soil textures. BC can adsorb and immobilize excess N in the soil during the early stages of crop growth ^{[21, 22]}. Subsequently, BC slowly releases adsorbed and immobilized N in the later stages of crop growth, extending the effective period of fertilizer and continuously providing nutrients for crop growth ^{[23, 24]}. Third, N reduction with BC can meet maize demand and stabilize maize biomass. BC has abilities including absorption capacity, preventing the loss of nutrients ^{[25, 26]}.

Maize seed germination and seedling growth experiment

Basic properties for soil and BC

The BC origined form rice husk, purchased from Nongken Guangyuan Bioenergy Co Pyrolysis temperature 400 ℃ (Fig. 1). Three types of soil were used, which are loam, loamy clay, and loamy sandy soil according to the U.S. Soil Texture Classification Criteria. The loamy, loamy clay, and loamy sandy soil was collected separately from Wuzhan Village (45o54'13" N, 126o17'31" E), Wangbian Waitun, Jiefang Village (46o0'40" N, 125o26'5" E), and Linjiang Village, Dongfa Township (45o42'37" N, 126o15'3" E), all located in Zhaodong City, Heilongjiang Province, China. The soils were cleared of surface weeds, then they were air-dried and passed through 2 mm sieve. The basic physical and chemical properties of the soils and BC were showed as Table 1.

Table 1

Basic physical and chemical properties of soils and BC
	Loam	Loamy clay	Loamy sand	BC
pH	6.85	7.12	6.73	7.75
Bulk density (g/cm³)	1.38	1.42	1.47	/
Organic matter (g/kg)	29.7	25.4	9.69	347.5
Total nitrogen (g/kg)	1.83	1.65	1.47	/
Clay content (%)	12.1	28.9	0.25	/
Silt content (%)	43.7	44.04	13.1	/
Grit content (%)	44.2	27.1	86.7	/
C content (%)	/	/	/	39.8
N content (%)	/	/	/	1.38
C:N ratio	/	/	/	33.3
Ash content (%)	/	/	/	33.1

Experimental device

The standard germination box as 13 cm (long)×19 cm (width)×12 cm(height) was used and filled with test soil to a depth of 10 cm. For each box, the weight of loam, loamy clay, and loamy sandy soil were 3.4 kg, 3.5 kg, and 3.6 kg, respectively. The application rates of BC quality ratio were 0%, 2.5%, 5.0%, 7.5%, and 10.0% (The ratio of BC weight to soil weight), evenly mixed with the soil. Maize seeds were soaked in a 10% H₂O₂ solution for 10 min, rinsed three times with tap water and deionized water, respectively, and then they were soaked in deionized water for 2 h, and then blotted with filter paper. 25 seeds were planted in each box and watered daily to maintain 60% of the soil field water holding capacity. The boxes were cultured at 25 ^oC with a photoperiod of 12 h, an average light intensity of 234 µmol/m²·s1 in a light incubator. Each treatment had four individual replications. The seed germination and maize seedling growth were detected daily.

Sampling and analysis

Daily germination was counted from the 3rd to 7th day after planting (DAP). The height and root length was measured at the 10th DAP. Then, plant was separated into three parts, seedlings, roots, and residues. All of them dried to a constant weight at 80oC and the weight was calculated. The formulas used to calculate the relevant indices were as follows:

Germination rate (GR) = n/N×100%, where the n is the number of germination seeds at the Seventh day; N is the total number of test seeds;

Germinpotential (GP) = n/N× 100%, n is the number of germination seeds on 3th; N is the total number of test seeds;

Germination Index (GI) =Σ (Gt / Dt), where Gt is the number of germination seeds on day n, and Dt is the germination days corresponding to Gt (d);

Viability index (VI) = GI×SH, including: SH is the seedling height (cm) on the Seventh day; Storage material transfer efficiency (STR)=(SDW + RDW)/(SDW + RDW + KRDW)×100%, where: SDW is the dry weight of seedlings (g); RDW is the dry weight of roots (g); KRD W is the grain residue dry weight (g).

Pot experiment

Soil type and experimental site

Based on the seedling experiment in incubator, the loam soil was chosen for the pot experiment, which was carried out at the potting site of Northeast Agricultural University(45o44'40" N, 126o43'10" E). The average annual temperature of about 4.8 ℃, an effective cumulative temperature of 2850 ℃, an average number of days in the frost-free period of 139 d, and an average rainfall of 448 mm.

Experimental design

Two factors were designed including the application rate of BC, namely: 0% (B0), 2.5% (B1), 5.0% (B2), 7.5% (B3) and 10.0% (B4) (weight to weight) and the amount of N fertilizer, no N fertilizer (N0), 30% reduction based in the local N input, 196 kg/hm² (N1) and local N application amount 280 kg/hm² (N2). The amounts of superphosphate and potassium chlorider were 100 kg/hm² and 120 kg/hm², respectively. The detail amounts of fertilizer and BC per pot for each treatment were shown in Table 2.

The soil (the bulk density is 1.38 g/cm³ and the weight is 8.7 kg) was evenly mixed with BC and fertilizer, then it were loaded into a plastic pot with a height of 25 cm and a diameter of 20 cm. The soil was irrigated to the 60% of the soil maximum field water holding capacity within planting. Each treatment was repeated 4 times .

Table 2

Amount of fertilizer and BC for each treatment in pot test
Treatment codes		Urea (g /pot)	Superphosphate (g /pot)	Potassium chloride (g /pot)	BC (g /pot)
N level	BC level	Urea (g /pot)	Superphosphate (g /pot)	Potassium chloride (g /pot)	BC (g /pot)
N0	B0	0.00	0.66	0.60	0.00
	B1	0.00	0.66	0.60	217.5
	B2	0.00	0.66	0.60	435.0
	B3	0.00	0.66	0.60	652.5
	B4	0.00	0.66	0.60	870.0
N1	B0	1.83	0.66	0.60	0.00
	B1	1.83	0.66	0.60	217.5
	B2	1.83	0.66	0.60	435.0
	B3	1.83	0.66	0.60	652.5
	B4	1.83	0.66	0.60	870.0
N2	B0	1.28	0.66	0.60	0.00
	B1	1.28	0.66	0.60	217.5
	B2	1.28	0.66	0.60	435.0
	B3	1.28	0.66	0.60	652.5
	B4	1.28	0.66	0.60	870.0

Sampling and analysis

At 30th DAP, destructive sampling was conducted to sample the soil and plant. The height of maize was measured using a meter ruler and vernier caliper. A Φ50.46×50 mm ring knife with a volume of 100 cm³ was used to collect soil surface samples to determine soil bulk density and moisture content. Soil samples were extracted using 2 mol/L KCl solution for 1 hour, and the extractable NH₄⁺-N and NO₃^--N were determined using a Seal AA3 continuous flow analyzer ^[27]. The H₂SO₄-H₂O₂ digestion method was utilized to digest leaf samples, and the Kjeldahl method was applied to determine the total N contents of soil and leaves. The soil microbial biomass of N were detected by chloroform fumigation extraction-Kjeldahl method ^[28].

Statistical analyses

All the test results were expressed as the mean of four replicated tests, and the data were processed and graphed using Excel 2016 software. IBM SPSS Statistics 23.0 software was used for the analysis of variance of the data (the significance level of difference was 0.05). Graphs were prepared with Origin Pro (Version 2021, Origin lab corporation, Wellesley Hills, Wellesley, MA, USA).

Effects of BC and soil texture on the seed germination of maize

The addition of BC stimulated the germination of maize seeds (Fig. 2). At the same texture soil, the germination percentage, germination potential, vigor index and germination index of maize seeds showed a bell curve along the increasing amount of BC. BC increased the germination percentage of maize seeds by 1.50–5.50% (loamy soil), 1.50–7.50% (loamy clay soil), 2.50–12.00% (loamy sandy soil), respectively (Fig. 2I). BC increased the germination potential of maize seeds by 1.00–5.00% (loamy), 3.00-5.50% (loamy clay soil), 7.00-14.50% (loamy sandy soil), respectively (Fig. 2II). BC increased the germination index of maize seeds to 0.67–3.26 (loamy), 1.83–3.41 (loamy clay soil), 4.19–9.21 (loamy sandy soil), respectively (Fig. 2III). BC improves the vigor index of maize seeds 133.5-222.6 (loamy), 100.3-207.2 (loamy clay soil), 44.1-165.2 (loamy sandy soil), respectively (Fig. 2IV). However, the summit of the indexes was different for the three textures. There was 7.5% BC for loamy soil, 5% and 10% BC for loamy clay soil and 2.5% for the loamy sandy soil. Compared to the control, germination rate, germination potential, germination index and vigor index increased by 6.0%, 6.3%, 9.6% and 71.3%, respectively, for the 7.5% BC addition to the loamy soil (Fig. 2). While the germination rate and vigor index increased by 8.3% and 47.1% for 10% BC addition to loamy clay soil (Fig. 2I, IV), the germination potential and germination index increased by 6.9% and 9.4% for 5% BC addition to loamy clay soil (Fig. 2II III). Differently, 2.5% BC addition gave the best improvement for the maize seedling in loamy sandy soil, the germination rate, the germination potential, the vigor index and the germination index increased by 15%, 21.80%, 66.42%, and 32.61%, respectively (P < 0.05) (Fig. 2).

At the same BC application level, germination rate were higher in loamy soil than that in loamy clay soil and in loamy sandy soil (except the B0 and B4 in loamy clay soil) (Fig. 2I), germination potential were higher in loamy soil and loamy clay soil than in loamy sandy soil (except the B1) (Fig. 2II). And the germination index of maize seeds were higher in loamy clay soil than that in loamy and loamy sandy soil (except the B1 in three texture soil and B2 in loamy soil) (Fig. 2III). And the vigor index of maize seeds were higher in loamy clay soil than that in loamy and loamy sandy soil (Fig. 2IV).

Note

Lower case letters in the graphs for the same soil texture indicate significant differences (P < 0.05) between biochar additions. Capital letters indicate significant differences (P < 0.05) between soil textures under the same biochar addition conditions. * represents a significant level of 0.05, ** represents a significant level of 0.01, S represents the soil texture, B represents the application amount of biochar. S×B:** indicates a highly significant interaction between soil texture and biochar.

Effects of BC and soil texture on plant height and root length of maize seedlings

The plant height and root length was increased by BC addition in all texture soils compared to that without BC (except B4 in loamy sandy soil) (Fig. 3). In loamy soil and loamy sandy soil, plant height and root length showed a bell-shaped curve with BC addition. While, the maximum value of plant height and root length in different textured soils appeared in different amounts of BC. In loamy soil with 7.5% BC addition plant height and root length reached the maximum value increasing by 51.2% and 60.6%, respectively, compared with that without BC(P < 0.05). In loamy sandy soil with 2.5% BC, the maximum value of plant height and root length increased by 27.8% and 29.8%, respectively, compared with that without BC (P < 0.05). Differently, in loamy clay soil, there was no peak when the amount of BC reached 10%, though plant height and root length increased by 49.15% and 55.18%, respectively, compared with that without BC(Fig. 3)(P < 0.05). At the same level of BC application, plant height and root length of maize seedlings grown on loamy soil and loamy clay soil,were overall higher than that in loamy sandy soil (Fig. 3)(P < 0.05).

Note

Lower case letters in the graphs for the same soil texture indicate significant differences (P < 0.05) between different biochar additions. Capital letters indicate significant differences (P < 0.05) between soil textures under the same biochar addition conditions. * represents a significant level of 0.05, ** represents a significant level of 0.01, S represents the soil texture, B represents the application amount of biochar. S×B:** indicates a highly significant interaction between soil texture and biochar.

Effects of BC and soil texture on the efficiency of storage material transport in maize seedlings

Compared to B0, the addition of BC increased the efficiency of storage material transport (except B3, B4 in loamy sandy soil and B1 in loamy soil) (Fig. 4). BC improved the transport efficiency of maize storage materials at 2.46%-7.75% (loamy), 3.24–8.13% (loamy clay soil) and 3.49–5.97% (loamy sandy soil), respectively, and the optimal dosage of BC was 7.5% for loamy soil, 10% for loamy clay soil and 5% for loamy sandy soil (Fig. 4). At the same level of BC addition, loamy soils consistently had higher transfer efficiencies than that in loamy clay and loamy sand soils (except B1 in loamy sandy soil). In summary, loamy soil results were relatively stable, so loamy soil was utilized for subsequent studies.

Note

Effects of N reduction with BC application on loamy soil N

The addition of BC promoted soil total N (TN), nitrate N (NO₃⁻-N) and microbial N (MBN) contents and inhibited ammonium N (NH₄⁺-N) contents of loamy soil (Fig. 5). B2, B3 and B4 increased the TN contents of soil with little differences between the N rates, with 0.16–0.28 g/kg increase for N0, 0.17–0.34 g/kg increase for N1 and 0.32–0.40 g/kg increase for N2. B1 significantly promoted soil TN by 0.32 g/kg for N2 (Fig. 5-I). B1-B4 treatment had no significant effect on NH₄⁺-N content under N2, BC except B5 reduced NH₄⁺-N contents by 0.82–3.07 mg/kg combined without N.(N0). B3 and B4 reduced NH₄⁺-N contents by 2.54 mg/kg and 4.17 mg/kg, respectively, meanwhile, B1 and B2 had no effects on NH₄⁺-N contents for N1(Fig. 5-II). B2, B3 and B4 promoted NO₃⁻-N contents, with a increase of 0.93-7.11mg/kg for N0, a increase of 3.18-6.71mg/kg for N1, and a increase of 3.55-4.55mg/kg for N2. B1 promoted NO₃⁻-N by 0.25mg/kg and 1.48mg/kg for N0 and N1(Fig. 5-III). B2, B3 and B4 promoted soil MBN contents, among which the MBN contents increased by 14.9–17.8 mg/kg for N0, MBN contents increased by 11.28-18.48mg/kg for N1, and increased by 8.01-15.18mg/kg for N2. B1 increased the soil nitrate N contents by 12.7mg/kg and 6.18mg/kg for N0 and N1 (Fig. 5-IV).

TN contents peaked at 7.5% BC addition for N0 and N1, which was 0.28g/kg and 0.35g/kg higher than that without BC, respectively, and peaked at 5% BC for N2, which was 0.41g/kg higher than that without BC (P < 0.05)(Fig. 5-I). NH₄⁺-N contents showed a decreasing trend along with the rates of BC and reached the lowest value at 10% BC for all N input level, which was 3.07mg/kg, 4.16mg/kg, and 2.43mg/kg lower than that without BC addition, respectively (P < 0.05)(Fig. 5-II). NO₃⁻-N content peaked at 10% BC addition under N0 condition and increased by 7.11mg/kg compared to without BC addition, peaked at 7.5% BC addition under N1 condition and increased by 6.71mg/kg compared to unadded BC, and peaked at 5% BC addition under N2 condition and increased by 4.56mg/kg compared to unadded BC (P < 0.05)(Fig. 5-III). MBN content peaked at 10% BC addition under N0 condition and increased by 17.77mg/kg compared to unadded BC, peaked at 7.5% BC addition under N1 condition and increased by 18.48mg/kg compared to unadded BC, and peaked at 5% BC addition under N2 condition and increased by 15.18mg/kg compared to unadded BC (P < 0.05)(Fig. 5-IV).

Note

Different uppercase letters in the graphs indicate differences between different nitrogen fertilizer levels at the same biochar level; different lowercase letters indicate differences between different biochar levels at the same nitrogen fertilizer level (P < 0.05)

Effect of N reduction with BC application on seedling biomass of maize

The biomass content of each part of the maize seedling was related to the amount of N fertilizer applied. At the same level of BC application, the highest biomass of both aboveground and belowground parts of maize was at the level of conventional N application (N1), followed by the level of 30% N reduction (N2) (except N2B2), and the differences were more significant (P < 0.05), indicating that N reduction alone resulted in the reduction of biomass of maize seedling in each part at the same level of BC, the decrease range is 0.17-0.40g and 0.21-0.48g of aboveground and belowground (Fig. 6).

At the conventional N application (N1) level, the biomass of aboveground and belowground parts of maize increased gradually with the increase of BC application at lower BC application rate, and reached the maximum value when the BC application rate reached 7.5% (N1B3), which was 0.23g and 0.67g higher than that of N1B0, respectively (P < 0.05), and the aboveground and belowground biomass of maize were both reduced when the BC application rate increased from 7.5–10.0%. when N was reduced by 30% (N2) level, the highest biomass of both aboveground and belowground parts of maize was in N2B2 treatment, which was 0.49g and 0.65g higher than that of N2B0 treatment, respectively(P < 0.05), even slightly higher than N1B0.

Under N2B0 conditions, the biomass of the aboveground and underground parts decreased by 0.37g and 0.21g compared to N1B0, respectively. After adding BC, the biomass of maize aboveground and underground increased by 0.10-0.49g and 0.24-0.65g, respectively. And when N2B2 reaches its maximum value, the aboveground and underground biomass of corn is 0.12g and 0.43g higher than N1B0, respectively. This indicates that BC can regulate N supply to meet the needs of maize growth in the case of reduced N fertilizer.

Note

Effect of N reduction with BC application on TN content of plants of maize at seedling stage

BC addition affected the N contents in all parts of maize at seedling stage. Under the same N fertilizer level, the TN content of aboveground and underground parts of maize increased gradually with the increase of BC application at the conventional N application (N1) level and reached the maximum value when the BC application reached 7.5% (N1B3), which was 4.32 mg/g and 0.88 mg/g higher than that of the N1B0 treatment, respectively. And the TN content of both aboveground and underground parts of maize decreased when the BC application was increased from 7.5–10.0%, the total N content of both aboveground and belowground parts of maize decreased (Fig. 7).

The N content in maize seedlings under the application of reduced N fertilizer combined with BC is equivalent to the level of sufficient N fertilizer (Fig. 7). N2B0 has a 1.16 mg/g and 3.97 mg/g lower N content in the aboveground and underground parts of maize seedlings than N1B0, respectively. N2B2 has a 4.56mg/g and 5.84mg/g higher N content in the aboveground and underground parts of maize seedlings than N2B0, and N2B2 has a 3.39 mg/g and 1.87 mg/g higher N content in the aboveground and underground parts of maize seedlings than N1B0, respectively. Adding BC will increase the N content in maize seedlings to compensate for the decrease in N content under N reduction conditions.

Figure 7. Effect of TN content in various parts of maize seedling using BC

Note

Effects of BC on soil N effectiveness and corn seed germination and seedling growth

We certified the first hypothesis that the BC addition combined the soil texture improved the germination and growth of maize, including germination rate, germination potential, germination index of maize seeds, and the maize seedling length, root length and storage material transport efficiency (Fig. 2–4). That is similar to the results of Dorak, who found that the addition of BC increased the germination rate of mallow seeds by more than 20% ^{[29, 30]}, because BC has a holding capacity of moisture, increased in soil water content from 45.8–61.9%, which is necessary for seed germination ^{[30, 31]}. Moreover, the addition of BC sequestered Na⁺ in the soil solution, enhanced the potassium utilization with K⁺/Na⁺ content of wheat seedlings increased, thus increasing the biomass of winter wheat seedlings and promoting their growth and development ^[32]. The seed germination increased by 16.7% and 8.33% under 50-fold dilution of pear BC and wine BC treatments, respectively, and BC increased the height and root vigor of oilseed rape seedlings ^[33]. Besides, BC increased soil nutrient sequestration ^[34], and facilitate the retention of soil nutrients ^[35], stimulate the talk between roots and soil ^[36], thus favoring seed development and seedling growth.

BC incorporation improved soil N content and thus promoted seed germination and seedling growth (Fig. 2–5). First, BC can adsorb and retain N in soil and fertilizer, thus effectively reducing N loss and increasing the total amount of available nutrient isolates in soil ^[37]. Secondly, the N absorbed and held into the BC can be slowly released in soil, extending the effective period of the fertilizer, and then supplementing the nutrients needed for the growth period of the crop ^[38]. Furthermore, BC increase soil aeration by improving soil bulk density and porosity, thereby affecting the microbial activity, inhibiting the denitrification of N microorganisms such as nitrifying bacteria, and reducing the formation and emission of N2, and ultimately increasing the TN content in soil ^[39]. The BC (6g/L) extract promoted the germination rate of rice seeds to 9%, because BC significantly increased the activity of the antioxidant system in the seeds, weakened the degree of membrane lipid peroxidation, reduced the deterioration of seeds, and improved the germination rate ^[40].

Dosage effects of BC in different textured soils

We found a dose-effect in BC application, though the optimal amounts were different for the three texture soils (Fig. 2–4), which certified the second hypothesis. Similar results also found in the growth of agate red cherry seedling, at 30 g/kg of BC application, the plant height, stem thickness, new shoot length and leaf number of onyx cherry seedlings reached the maximum values, and the above indexes decreased when the dosage of BC was increased again, which indicated that there was a dosage effect of BC in promoting the aboveground growth of onyx cherry seedlings ^[41]. When the BC application rate was 1%, the dry matter accumulation of tobacco seedlings increased by 28.5%; when the BC application rate was more than 4%, the dry matter decreased by 7.1% ^[42]. The moderate amounts (12.5 g/kg, 25.0 g/kg, and 50.0 g/kg) of BC additions significantly promoted root vigor and improved physiological traits in maize seedlings, while higher BC additions (100 g/kg) adversely affected seedling antioxidant systems ^[43]. The high amount of BC has an inhibitory effect on growth because since BC is alkaline, excessive BC addition will cause changes in the pH of the soil, which will have an inhibitory effect on seed germination ^[44].

In addition, the promotion of maize seed germination and seedling growth by BC in this study was affected by soil texture, adding BC under all three soils promotes seed growth and development (Fig. 2–4). But the optimum BC addition varied under different textures, where the most suitable BC addition for maize seed germination and seedling growth was 7.5% in loamy soil, 10.0% in loamy clay soil, and 2.5% in loamy sandy soil (Fig. 2–4). This difference may be due to the differences in properties between the different textures of the soils ^[45]. When BC is applied to loamy sand, the refined BC filled up the pores between soil grains, producing numerous intergranular pores ^[46]. This results in a 10.4% decrease in bulk density (BD) and a 12.3% increase in total porosity as shown by a drop in saturated hydraulic conductivity ^[47], the reduction in soil aeration pore space slows the flow of water and solutes in loamy sand, improving their ability to retain water and raising capillary water content. Thus it.promote the growth and germination of seedlings and seed ^[48]. As an organic binder, BC promotes the binding of micro aggregates to form larger aggregates, thus reducing the proportion of micropores and increasing the proportion of mesopores in loamy soil, allowing plants to absorb more water ^[49]. High BD or high soil compaction of loamy clay is not conducive to soil moisture exchange and microbial activity, thereby preventing roots from penetrating downward and obtaining nutrients ^[50]. Thus, BC promoted the seed germination in loamy soils much than that in loamy clay soils (Fig. 2–4). In situ experiments confirmed that BC alterd the pore size distribution of loamy clay soils, with 0.1–4 µm pores replacing the previously dominant 0.05–0.06 µm micropores, promoting air circulation and accelerating microbial decomposition of organic matter, providing nutrients for seed germination and seedling growth ^[51]. The moderate addition of BC (67.5 t/hm²) to sandy soils had a significant effect on improving the microbial environment of sandy soils and the directional transformation of plant growth ^[52]. The application of BC into sandy soil could effectively increase the content of rapidly available N, rapidly available phosphorus, rapidly available potassium and organic matter in the soil, and could promote the growth of mung bean seedlings ^[53].

Effects of BC under reduced N input on maize growth and biomass

The nutrient content of each part of the maize can reflect the fertilizer uptake of that crop, while the fertilizer utilization rate can visually reflect the fertilizer uptake of the crop ^[54]. The results showed that N2B2 increased the N content and biomass of aboveground and belowground parts of maize seedlings compared to N1, which proved that N reduction with BC can meet maize demand and stabilize maize biomass (Fig. 6–7). A similar result that BC inceased the N contents of rice under a reduced N by 20% compared to the full N input ^[55]. Applying BC and reducing 25% N input increased the N content of maize leaves even higher than that of normal N application ^[56]. Our findings were similar with them which means BC can fulfill the needs of maize under reduced N conditions to some extent ^[57]. Xuan et al. found that under the condition of reducing N, the application of BC could ensure that the N content of maize stems and leaves was not reduced, and the N demand of maize could be met ^[58]. That is because, BC application can also increase soil water content and organic matter as a way to retain soil nutrients ^{[59, 60]}. In addition the porous structure of BC can adsorb fertilizer nutrients, as fertilizer slow-release carrier nutrient "temporary storage", delay the release of nutrients, to make up for the rapid release of nutrients from chemical fertilizers, gives the soil the ability to continue supplying fertilizer to improve the efficiency of fertilizer and benefit the growth of crops ^[61]. N fertilizer, as an indispensable fertilizer for crop growth, has a significant impact on crop yields ^[62]. Compared with conventional fertilization treatments, controlled-release N fertilizer reduction application treatments could significantly improve N recovery, agronomic utilization rate and bias productivity, and the controlled-release N fertilizer reduction of 30% of the total amount of controlled-release N fertilizer (193 kg/hm²) can achieve a simultaneous increase in N utilization ^[63]. N fertilizer uptake and utilization efficiency is a key indicator of whether N is effectively utilized. That is because chemical N fertilizer reduction can significantly increase the level of corn root secretion, provide a good inter-root environment for the corn root system, and ensure that the corn growth N requirements. provide a good inter-root environment for maize root system to ensure the growth of maize N and chlorophyll content. and chlorophyll content, and can significantly improve the agronomic efficiency and apparent utilization of N fertilizer ^[64]. And BC application into the soil can increase the inorganic N content of the soil, so that the maize root system absorbs more N nutrients, and the nutrients absorbed by the root system are gradually transferred to the aboveground part of the maize, resulting in the aboveground part of the N uptake and utilization is also enhanced ^[65]. At the same time, crops in BC-amended soils have a larger inter-root zone and crop root hairs are more likely to adhere to the surface of the BC or even enter the BC macropores, which improves soil nutrient utilization and root uptake by crops, thus stimulating plant growth and accumulate nutrients ^[66]. Therefore, BC application under N-reducing conditions can increase corn biomass and aboveground and belowground N content of corn and satisfy corn's N requirements. Hypothesis 3 in the above quote is correct.

The effects of BC on maize seed germination and seedling growth is significantly associated with its application rate and the soil texture. In this study, adding BC was found to enhance the germination and growth of maize seedlings, and there is a dose effect, the optimal application rates varied with the texture of black soil. Specifically, the optimal BC application rates for maize seed germination and seedling growth were 7.5%, 10.0%, and 2.5% for loam, clay loam, and sandy loam soils, respectively. Addition of 5% BC (w/w) at 30% (196 kg/hm²) N fertilizer reduction increased the total N content of above and below ground parts of maize and increased the above and below ground biomass of maize. Compared with N2B0, the TN content of aboveground and underground parts of maize was increased by 15.46% and 47.03% (P < 0.05), and biomass was increased by 52.51% and 59.22% (P < 0.05) under N2B2 treatment. It was even higher than the TN and biomass of corn under conventional N application without adding BC. Therefore, it was concluded that N reduction by BC could meet the demand of corn and stabilize corn biomass.

Acknowledgments

We would like to express our gratitude to Mrs Mengrui Sun for her invaluable assistance.

Author contributions

The study’s conception and design were conducted by Yingjie Dai. Yang Yang and Haiyang You completed the construction of the database. Junyan Chu, Jingru Zhang, Hongling Qi and Siyuan Li sampled the materials for sequencing and helped in the preparation of the manuscript. The initial draft of the manuscript was authored by Zhihua Liu and Likun Hou, Haotian Wu, with input and feedback provided by all the authors on earlier versions of the paper. All authors have reviewed and endorsed the final version of the manuscript.

Funding

This work was Supported by the Strategic Priority Research Program of the Chinese Academy of Sciences of China (Grant No. XDA28070301). This work was Supported by the project of the Key Laboratory of germplasm innovation and physiological ecology of grain crops in cold regions of the Ministry of Education (CXSTOP2021008) and the scientific research project of Mudanjiang Normal University (YB2021005).

Data availability

The raw data of our project have been deposited in the Strategic Priority Research Program of the Chinese Academy of Sciences of China (Grant No. XDA28070301).

Ethics approval and consent to participate

This study did not involve the use of human or animal tissue materials, as such, it did not necessitate ethical approval.

Consent for publication

Not applicable.

Competing interests

The authors have no relevant financial or non-financial interests to disclose.

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Effects of biochar input on nitrogen absorption and growth of maize at seedling stage

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Version 1

Abstract

Figures

Introduction

Materials and methods

Maize seed germination and seedling growth experiment

Basic properties for soil and BC

Experimental device

Sampling and analysis

Pot experiment

Soil type and experimental site

Experimental design

Sampling and analysis

Statistical analyses

Results

Effects of BC and soil texture on the seed germination of maize

Effects of BC and soil texture on plant height and root length of maize seedlings

Effects of N reduction with BC application on loamy soil N

Effect of N reduction with BC application on seedling biomass of maize

Discussion

Effects of BC on soil N effectiveness and corn seed germination and seedling growth

Dosage effects of BC in different textured soils

Effects of BC under reduced N input on maize growth and biomass

Conclusions

Declarations

References

Additional Declarations

Status:

Version 1