# Fertilization and Soil Microbial Community: A Review
## 3 Results and Discussion
### Effects of Chemical Fertilizers on Biomass, Activity and Diversity of Soil Microorganisms  
It has been generally shown that both chemical and organic fertilizers can directly stimulate the growth of specific microbial populations by supplying nutrients [70], leading to an increase in total microbial numbers [71; 72; 73; 74], improving microbial activity [75] and determining a switch in microbial diversity. A high soil microbial diversity is crucial for the productivity and stability of the agroecosystems [76]. In several studies, mineral fertilization has been found to reduce microbial diversity, including the plant-beneficial microbial taxa [76]. Meta-analysis of microbial communities, based on 107 datasets from 64 long-term trials from around the world, concluded that mineral fertilizer application (in particular N fertilizer treatment) leads to a 15.1% increase in microbial biomass compared to unfertilized control plots; moreover, N application (urea and ammonia fertilizers) can have a temporary or stable effect in increasing pH [77; 78; 79]. However, the use of a chemical fertilizer alone does not lead to a remarkable increase in soil microbial abundance. This was observed in a rice-wheat cropping system [80], in a drip-irrigated cotton systems [74] and in paddy field soils [81]. Long-term mineral fertilization, and in particular N addition, increases microbial biomass bec.use soil microorganisms may be carbon- or N-limited. The increase is significant if soil pH is \(>\)5; in other cases, fertilization reduce microbial biomass [77]. Soil-available P and total N are the most important factors influencing the abundance of microbial communities involved in the nitrogen cycle [82]. However, chemical fertilization, in particular N addition, was found to decrease bacterial alpha-diversity [83], although a recent study found that soil fertility and plant yield was mainly due to bacterial and archaeal abundance and community structure rather than bacterial, archaeal or fungal alpha-diversities [84]. In fact, the increase in microbial biomass has been attributed to better plant growth, which results in higher rhizdeposition [85]. The latter was found to be more active in determining a shift in the fungal community [86]. That is, soil bacteria were more sensitive than fungi to fertilization practices [87; 88]. In addition, the plant composition and \begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Subject** & \multicolumn{3}{c}{**Articles Distribution by Countries (Continents)**} \\ \hline
**General** & **Europe** & **China** & **North America** & **Others** \\ \hline Effects of chemical fertilizers on biomass, activity and diversity of soil microorganisms & 1 & 7 & 2 & 2 \\ \hline Types of fertilizers used and their influence on soil microbial community & 8 & 3 & 1 & 4 \\ \hline Bacterial and fungal species affected by chemical or organic fertilizers & 3 & 6 & 1 & 3 \\ \hline Negative effects of chemical fertilizers on soil ecosystem & 5 & 1 & 2 & 5 \\ \hline Total & 18 & 17 & 4 & 13 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Relevant data from the articles distributed on countries (continents) and research topics. carbon substrate utilization patterns of rhizobacterial communities were more diversified in unfertilized plots than in chemical fertilized plots in grasslands [89]. Long-term NPK applications have been found to result in a loss in soil organic matter (SOM), especially in arid and semi-arid areas or where a monoculture is performed (e.g., corn) [90; 91; 92]. An increase in SOM by mineral fertilizers has been found only when they are applied in combination with organic amendments [93; 94]. SOM quality greatly influences soil microbial community composition [95]. Soil quality and crop yield also depend on SOM content [4]. The latter affects the availability of micronutrients, with higher micronutrient amounts in higher SOM content [4].