**1.** *Camellia oleifera*

*Camellia oleifera* Abel*.* as a native edible oil tree has a long cultivation history in subtropical China [1]. It is a perennial and evergreen species with synchronous flowers and fruits. The cultivation area and total product value of *C. oleifera* have reached 4.47 million ha and 102.4 billion Chinese yuan, respectively [2]. With rapid development, the *C. oleifera* oil accounted for 80% domestic high-end vegetable edible oils in 2018 from China. High habitat suitability area for *C. oleifera* cultivation in China has been up to 4.94% [3].

Specially, *C. oleifera* oil and oils derived from palm, olive, and coconut are the four major woody edible oils in the world [4]. The *C. oleifera* oil is characterized by remarkable antioxidant activity [5] and high content of unsaturated fatty acids (about 83%) [6].

*Camellia oleifera* can survive and adapt to low-fertility acid soil. Generally, it usually is used in the conservation of soil and water as well as afforestation in barren hill. Therefore, *C. oleifera* is an excellent species with both ecological and economic advantages. Development of *C. oleifera* industry would be beneficial for the safety of edible oil and the conservation of soil and water in China.

As a typical economic tree, intensification such as water management, fertilization, and trimming takes an important part in the management of *C. oleifera* plantations. Notably, organic matter, available phosphorus, and pH value was low in *C. oleifera* plantation soils [7], constraining the yield of *C. oleifera* oil. Therefore, intensive management with fertilization is often performed in *C. oleifera* plantations [1].

#### **2. Challenges**

Fertilization is the major way of intensive management, efficiently improving the yield of oil in *C. oleifera* plantations. However, a large amount of nitrogen (N) input increased the risk of soil N leaching and gaseous N (e.g*.*, nitrous oxide (N2O), nitric oxide (NO), ammonia (NH3)) losing [8]. In addition, excessive N input induced soil acidification [9].

#### **2.1 Nitrous oxide emissions**

Nitrous oxide, as the major ozone-depleting substance [10], has been recognized to be an important greenhouse gas. Especially, the potential of N2O for global warming is 265 times than that of carbon dioxide [11]. The concentration of N2O is ranging from 270 ppb in pre-industrial period to 329.9 ppb in 2017 [12].

Soil systems contributed the largest source of N2O emissions (13 Tg N2O-N yr<sup>−</sup><sup>1</sup> ), of which human activities accounted for 54% [13]. Nitrogen input such as N deposition and N fertilization often increased N2O emissions and altered the process of N transformation [14–17]. Generally, soil N2O emissions had a positive and linear relationship with N input [18]. About 120 Tg N was contributed by human activities per year [13]. Therefore, intensive N input often leads to high emissions of soil N2O [19].

#### *2.1.1 Nitrification and denitrification*

Nitrification and denitrification are the two main pathways of N2O emissions (**Figure 1**) [20–22], which produced global 70% soil N2O emissions [13].

**5**

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

moisture, temperature, oxygen (O2), and pH condition [23, 24].

WFPS conditions than that under flooded conditions [26].

Soil N2O emissions can be influenced by soil environmental factors such as soil

Soil moisture is a vital factor that affects soil N2O emissions. Generally, soil N2O

Effects of soil temperature on N2O emissions were more complex than that of soil moisture. For example, warming increased soil N2O emissions from boreal peatland [27] and alpine meadow [28]. Soil N2O emissions had an exponential increased relationship with incubation temperatures [29]. A significant positive correlation was presented in N2O emissions and soil temperature from different soil types (paddy, orchard, forest, and mountain) [30]. Although warming did not affect soil N2O emissions from northern peatlands, it suppressed N2O emissions under N addition conditions [31]. By contrast, the effects of warming on soil N2O emissions from alpine meadow soil were not observed [32]. Consistently, no significant increase of soil N2O emissions was found with increasing incubation temperatures [33]. Previous study reported that soil moisture and temperature can

Soil O2 concentration was closely related with soil moisture and soil mechanical composition. Generally, soil with higher water content and larger clay fraction had lower soil O2 concentrations. Lower soil O2 concentrations mainly promoted soil N2O emissions via denitrification [20, 35]. The production of N2O and NO was increased when O2 concentration decreased from 21% to 0.5% in a laboratory study [36]. Similarly, field study reported that soil N2O emissions increased with increas-

pH played an important role in the activity of microbes [38]. Indeed, soil acidification [39] and soil pH amelioration [40] significantly influenced soil N2O emissions. However, other researchers reported that there was no significant correlation

pH influenced the activity of nitrification- and denitrification-related enzymes [42]. Generally, soil acidification increased N2O emissions [42]. Compared with ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) were higher in activity and resistance from acid soil [43]. However, the domination of AOB was increased by increasing soil pH [44]. Additionally, archaeal *amoA* genes had a wide pH range of about 3.7–8.65, which had high activity in extreme environ-

emission rates reached the peak when soil water-filled pore space (WFPS) was 60–70% [25]. For example, soil N2O emissions were significantly higher under 60%

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

*2.1.2 Influence factors*

*2.1.2.1 Soil moisture*

*2.1.2.2 Soil temperature*

explain 86% of soil N2O emissions [34].

ing soil O2 concentrations in wetland [37].

between N2O emissions and pH [41].

ments such as high temperature and extreme acid [45].

*2.1.2.3 Soil O2 concentration*

*2.1.2.4 Soil pH*

**Figure 1.** *Nitrification- and denitrification-related pathways [20–22].*
