# Fertilization and Soil Microbial Community: A Review
## 3 Results and Discussion
### Negative Effects of Chemical Fertilizers on Soil Ecosystem  
The application of chemical fertilizers alone generally improves crop production; however, concerns have been raised not only about the severe environmental problems posed by such practices but also about the long-term sustainability of such systems [143]. It was also highlighted that synthetic fertilizers can increase disease incidence [144; 145]. In some cases, the availability of some micronutrients (e.g., zinc) is reduced below the critical value, probably due to zinc precipitation by high concentrations of available soil P [146]. Long-term mineral fertilizer applications result in a significant loss in SOM, as found in monocultures performed for long periods without any addition of organic fertilizers and without crop rotation [90; 91; 92; 147]. Mineral fertilization has also been found to cause decreases in porosity and nutrient availability of soil [110]. Moreover, mineral fertilization strongly affects the number of microorganisms and the qualitative selection of entire communities of soil microorganisms [59]. The study by [PERSON] et al. [148] indicates that the use of synthetic fertilizers and herbicides changes interactions within and between below- and above-ground components of the soil microbial community and ultimately increases the negative environmental impacts of agriculture by reducing internal biological cycles and pest control.  
The long-term use of mineral fertilizers may be harmful, particularly at high rates of nitrogen fertilization, as it leads to increased gaseous nitrogen losses and to the deterioration of physical, chemical and biological soil properties [149,150]. Other studies (e.g., [PERSON] et al. [59]) indicate that agricultural chemicalization, especially in the form of high rates of N fertilizer application on arable, grassland and horticultural soils, might not only risk the biological productivity and ecological stability of agroecosystems but also threaten surface and groundwater through the accumulation of nitrates, nitrites and many other organic nitrogen compounds [151].  
Elevated concentrations of soil P have also been implicated in the P enrichment of shallow groundwater feeding coastal, lake and river ecosystems [152,153].  
Fungi and their enzymes are less sensitive to the action of chemical fertilizers [154]. In particular, in the study by [PERSON] [155], only protease activity was affected by fertilization in the case of the enzymes studied.  
[PERSON] et al. [156] suggested that the use of organic fertilizer or organic amendments can potentially mitigate the deleterious environmental impacts of inorganic fertilizers in agroecosystems, but they can also affect soil microorganisms that have not been well defined. They found that soil amendment such as biochar or the incorporation of other organic fertilizer for about two years affected microbial community biomass, composition and crop yield.  
A possible combination of chemical and organic fertilization was found to be a good way to not only improve soil fertility, but also for enhancing crop yield, in particular for soils with low N, P and organic carbon content [157].