*3.2.1 Effects of biochar on soil nitrous oxide emissions*

The physicochemical properties of biochar and soil can interactively influence soil N2O emissions [98]. However, the effects of biochar on soil N2O emissions varied, including positive effects [99], negative effects [100], and no effects [101].

Biochar addition increased soil N2O emissions with the release of N from biochar [102]. By contrast, biochar reduced soil N2O emissions with (1) increased NO3 <sup>−</sup>-N immobilization [103]; (2) increased copy numbers of *nos*Z gene [104, 105]; and (3) increased toxic effects of polycyclic aromatic hydrocarbons and other toxic substances (pyrolysis by-products) on N-cycle microorganisms [106].

## *3.2.2 Effects of biochar on soil pH buffer capacity*

Biochar that increased soil pH buffer capacity may predominantly correlate with biochar riches in oxygen-containing functional groups in surface. The anions of weakly acidic functional groups can associate with H+ , hence increasing soil pH. Meanwhile, exchangeable base cations can release into the solution, thus increasing soil pH buffer capacity [107, 108]. In addition, soluble silicon (Si) such as H3SiO4 <sup>−</sup> (present at a high pH) can combine with H+ and generate H2SiO3 precipitation [107, 108].

### **3.3 Nitrification inhibitor**

Nitrification inhibitors are a class of organic compounds that can inhibit the activity of nitrifying bacteria.

Nitrification inhibitors, especially synthetic nitrification inhibitors (e.g*.*, dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP)), were widely used in agriculture for improving N use efficiency. Ammonia-oxidizing bacteria and AOA are the major microbial communities in nitrification and denitrification, and both contain *amo* enzyme that can catalyze ammonia oxidation (NH4 + -N → NH2OH). Synthetic nitrification inhibitors such as DCD and DMPP mainly inhibit nitrification by suppressing the activity of *amo* enzyme (a Cu-copper cofactor enzyme). In addition, biological nitrification inhibitors also can inhibit soil nitrification [109, 110]. In the mid-1980s, researchers found that *Brachiaria humidicola* cv. Tully (CIAT 679), a single community forage, had lower nitrification rates than a single legume community or bare land [111]. This phenomenon stimulated further studies on biological nitrification inhibitors. The first biological nitrification inhibitor (methyl 3-(4-hydroxyphenyl) propionate: MHPP) was identified from the root exudate of *Sorghum bicolor* in 2008, which mainly inhibited the activity of *amo* enzyme [112]. Subsequently, biological nitrification inhibitor (brachialactone) from the root exudate of *Brachiaria humidicola* was found to inhibit the activity of *amo* enzyme [113]. The Nanjing Soil Research Institute of China firstly found and identified a biological nitrification, 1,9-decanediol, from the root exudate of rice, which can inhibit the activity of *amo* enzyme [114].

Ammonium N can be adsorbed by soil colloids, while soil NO3 <sup>−</sup>-N (the end product of nitrification) easily can be leached to groundwater by precipitation. In addition, microbial-mediated nitrification is closely related with soil N2O emissions [20–22]. Nitrification inhibitors can effectively inhibit soil nitrification, slowing the transformation of NH4 + -N to NO3 <sup>−</sup>-N and hence reducing the NO3 <sup>−</sup>-N leaching and N2O emissions.

An evaluation from 62 field studies showed that although nitrification inhibitors increased 20% NH3 emissions, they reduced 48% inorganic N leaching, 44% N2O emissions, and 24% NO emissions and increased 58% plant N utilization, 9% grain yield, 5% straw yield, and 5% vegetable yield [115]. Consistently, other studies evaluated that nitrification inhibitors decreased by 38% [116], 50% [117], or 73% [118] N2O emissions and decreased by 0.3 t CO2e ha<sup>−</sup><sup>1</sup> yr<sup>−</sup><sup>1</sup> [119]. Similarly, DCD did not increase crop yields but reduced 35% N2O emissions [120]. A metaanalysis showed that DCD rather than DMPP significantly increased 6.5% crop yield as well as DCD and DMPP decreased N2O emissions by 44.7% and 47.6%, respectively [121].

Therefore, application of nitrification inhibitors could reduce N2O emissions and mitigate environmental pollution after intensive N inputs.

#### **3.4 Urease inhibitors**

Urease inhibitors are a class of compounds that can slow soil urease activity (**Figure 2**). Addition of urease inhibitors after urea input can inhibit the hydrolysis

**11**

and NO3

*Nitrogen Cycling and Soil Amelioration in* Camellia oleifera *Plantations*

a tridentate ligand [122], hence inhibiting the activity of urease.

inhibit NH3 volatilizations. For example, 530 mg NBPT kg<sup>−</sup><sup>1</sup>

NBPT dosage in the range of 0–1000 mg NBPT kg<sup>−</sup><sup>1</sup>

N2O emissions with NBPT (250 mg NBPT kg<sup>−</sup><sup>1</sup>

) soil [126].

oat yield and 33% crop N uptake [120].

of urea via inhibiting the activity of urease, hence reducing NH3 volatilizations and N2O emissions. Additionally, the application of urease inhibitors also contributes

Urease, a Ni-copper enzyme, has two Ni−O bidentate ligands, specifically catalyzing urea into NH3 and CO2. Urea only can bind with one specific Ni−O ligand of urease, but NBPT can bind with two Ni−O bidentate ligands of urease and generate

Presently, a meta-analysis reported that a nonlinear response was presented in soil NH3 volatilizations and N input [123]. Application of NBPT can effectively

NH3 volatilizations and decreased accumulation of NH3 volatilizations compared with the control treatment. NH3 volatilizations were linearly related with the

The effects of NBPT on N2O emissions were controversial. For example, NBPT can reduce 80% N2O emissions [117]. No effects of NBPT (0.07%, NBPT/Urea-N, w/w) on N2O emissions were observed [125]. Similarly, there was no change of

Additionally, NBPT can reduce N2O emissions from alkaline soils but has no effects on acidic soils [127], which indicated that pH plays a key role in the regulation of NBPT effects on N2O emissions. Further laboratory study showed that NBPT inhibited nitrification, stimulating N2O emissions from alkaline soils (pH 8.05) but not affecting N2O emissions from acid soils (pH 4.85). This finding suggested that the effect of NBPT on soil N2O emissions is not only influenced by pH but also by

Generally, urease inhibitors correlated with nitrification inhibitor could mitigate

from banana plantation, but did not affect the yield of

N2O emissions. A meta-analysis showed that urease inhibitors and nitrification inhibitors interactively reduced 30% N2O emissions [116]. For example, a field study reported that the combination of NBPT (0.3%, NBPT/Urea-N, w/w) and DCD (0.3%, DCD/Urea-N, w/w) reduced 32.1% soil N2O emissions with the addi-

**4. Sustainable management in** *Camellia oleifera* **plantations**

able management of oil safety in *C. oleifera* plantations.

Our previous incubation study found that although biochar application increased N2O emissions, DCD addition decreased soil N2O emissions under urea fertilization from *C. oleifera* field [88]. Our field study showed that N2O emission rates were inhibited by biochar or DCD application and the effects of biochar application on mitigation of cumulative N2O were comparable to DCD addition in *C. oleifera* plantations [1]. Compared with control treatment, available N (NH4

treatment [1]. In addition, the seed yield of *C. oleifera* was higher in NH4NO3 or NH4NO3 + biochar treatment than that in control or NH4NO3 + DCD treatment (**Figure 3**). Soil amelioration is necessary and improves N use efficiency and pH, mitigating N2O emissions. Soil amelioration plays an important role in the sustain-

<sup>−</sup>-N) was not affected by NH4NO3, NH4NO3 + DCD, or NH4NO3 + biochar

Urea) [124]. Other study reported that NBPT increased 27%

thiophosphoric triamide (NBPT) is one of the most wide and effective urease

<sup>−</sup>-N leaching. *N-*(*n-butyl*)

urea treatment delayed

+ -N

Urea (0, 530, 850, 1500, and

Urea) addition from urea-fertilized

*DOI: http://dx.doi.org/10.5772/intechopen.92415*

inhibitors.

2000 mg NBPT kg<sup>−</sup><sup>1</sup>

(50 kg Urea-N ha<sup>−</sup><sup>1</sup>

other unknown factors [127].

tion of 519 kg Urea-N ha<sup>−</sup><sup>1</sup>

banana [128].

to increase N utilization efficiency and reduce NO3

**Figure 2.** *The chemical equation of urea hydrolysis with urease catalysis.* *Advances in Forest Management under Global Change*

which can inhibit the activity of *amo* enzyme [114].

+

*The chemical equation of urea hydrolysis with urease catalysis.*


or 73% [118] N2O emissions and decreased by 0.3 t CO2e ha<sup>−</sup><sup>1</sup>

and mitigate environmental pollution after intensive N inputs.

Ammonium N can be adsorbed by soil colloids, while soil NO3

product of nitrification) easily can be leached to groundwater by precipitation. In addition, microbial-mediated nitrification is closely related with soil N2O emissions [20–22]. Nitrification inhibitors can effectively inhibit soil nitrification, slowing the

An evaluation from 62 field studies showed that although nitrification inhibitors increased 20% NH3 emissions, they reduced 48% inorganic N leaching, 44% N2O emissions, and 24% NO emissions and increased 58% plant N utilization, 9% grain yield, 5% straw yield, and 5% vegetable yield [115]. Consistently, other studies evaluated that nitrification inhibitors decreased by 38% [116], 50% [117],

DCD did not increase crop yields but reduced 35% N2O emissions [120]. A metaanalysis showed that DCD rather than DMPP significantly increased 6.5% crop yield as well as DCD and DMPP decreased N2O emissions by 44.7% and 47.6%,

Therefore, application of nitrification inhibitors could reduce N2O emissions

Urease inhibitors are a class of compounds that can slow soil urease activity (**Figure 2**). Addition of urease inhibitors after urea input can inhibit the hydrolysis

<sup>−</sup>-N and hence reducing the NO3

Nitrification inhibitors are a class of organic compounds that can inhibit the


<sup>−</sup>-N (the end

yr<sup>−</sup><sup>1</sup>

<sup>−</sup>-N leaching and

[119]. Similarly,

Nitrification inhibitors, especially synthetic nitrification inhibitors (e.g*.*, dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP)), were widely used in agriculture for improving N use efficiency. Ammonia-oxidizing bacteria and AOA are the major microbial communities in nitrification and denitrification, and both contain *amo* enzyme that can catalyze ammonia oxidation

**3.3 Nitrification inhibitor**

activity of nitrifying bacteria.

transformation of NH4

N2O emissions.

respectively [121].

**3.4 Urease inhibitors**

(NH4 +

**10**

**Figure 2.**

of urea via inhibiting the activity of urease, hence reducing NH3 volatilizations and N2O emissions. Additionally, the application of urease inhibitors also contributes to increase N utilization efficiency and reduce NO3 <sup>−</sup>-N leaching. *N-*(*n-butyl*) thiophosphoric triamide (NBPT) is one of the most wide and effective urease inhibitors.

Urease, a Ni-copper enzyme, has two Ni−O bidentate ligands, specifically catalyzing urea into NH3 and CO2. Urea only can bind with one specific Ni−O ligand of urease, but NBPT can bind with two Ni−O bidentate ligands of urease and generate a tridentate ligand [122], hence inhibiting the activity of urease.

Presently, a meta-analysis reported that a nonlinear response was presented in soil NH3 volatilizations and N input [123]. Application of NBPT can effectively inhibit NH3 volatilizations. For example, 530 mg NBPT kg<sup>−</sup><sup>1</sup> urea treatment delayed NH3 volatilizations and decreased accumulation of NH3 volatilizations compared with the control treatment. NH3 volatilizations were linearly related with the NBPT dosage in the range of 0–1000 mg NBPT kg<sup>−</sup><sup>1</sup> Urea (0, 530, 850, 1500, and 2000 mg NBPT kg<sup>−</sup><sup>1</sup> Urea) [124]. Other study reported that NBPT increased 27% oat yield and 33% crop N uptake [120].

The effects of NBPT on N2O emissions were controversial. For example, NBPT can reduce 80% N2O emissions [117]. No effects of NBPT (0.07%, NBPT/Urea-N, w/w) on N2O emissions were observed [125]. Similarly, there was no change of N2O emissions with NBPT (250 mg NBPT kg<sup>−</sup><sup>1</sup> Urea) addition from urea-fertilized (50 kg Urea-N ha<sup>−</sup><sup>1</sup> ) soil [126].

Additionally, NBPT can reduce N2O emissions from alkaline soils but has no effects on acidic soils [127], which indicated that pH plays a key role in the regulation of NBPT effects on N2O emissions. Further laboratory study showed that NBPT inhibited nitrification, stimulating N2O emissions from alkaline soils (pH 8.05) but not affecting N2O emissions from acid soils (pH 4.85). This finding suggested that the effect of NBPT on soil N2O emissions is not only influenced by pH but also by other unknown factors [127].

Generally, urease inhibitors correlated with nitrification inhibitor could mitigate N2O emissions. A meta-analysis showed that urease inhibitors and nitrification inhibitors interactively reduced 30% N2O emissions [116]. For example, a field study reported that the combination of NBPT (0.3%, NBPT/Urea-N, w/w) and DCD (0.3%, DCD/Urea-N, w/w) reduced 32.1% soil N2O emissions with the addition of 519 kg Urea-N ha<sup>−</sup><sup>1</sup> from banana plantation, but did not affect the yield of banana [128].
