Nitrogen-Cycling Communities in Organically Amended Versus Conventionally Managed Agricultural Soil

Abstract

Productivity in agricultural ecosystems is often largely dependent on the input of nitrogen fertilizers such as urea, nitrate, and ammonia, despite the high financial costs and potential detrimental effects on the environment. Soil enrichment with organic matter, such as plant compost, straw, or manure, can enhance soil organic carbon and improve soil quality and increase aggregate stability, biological activity, and microbial diversity, including nitrogen cycles. The abundance of the nifH gene, thus nitrogen cycles, was found to be enhanced when organic fertilization was used and correlated mainly to the availability of organic carbon, potentially due to the presence of fuels required to run the energetically expensive nitrogen fixation process. On the other hand, readily available ammonia and nitrate, which are often associated with inorganic fertilization, tend to suppress the soil potential for nitrogen fixation. The impacts of fertilizers on denitrifying microbial communities are complex, due to the great diversity of the denitrifiers and the variation in their abundance in different environments. However, in general, the use of organic fertilizers increases denitrification potential and activity in soils when compared to inorganic fertilization. This is particularly important for increasing the abundance of those denitrifiers containing the nosZ genes and capable of the final step of the denitrification process, removing the potent greenhouse gas nitrous oxide by its conversion to dinitrogen. Bacterial and archaeal nitrifiers react differently to variations in soil conditions and to different fertilization management strategies. It is important to note that nitrogen fertilizers in access might turn into an ecosystem hazard where nitrifying microbes convert them to nitrate. This survey of the literature suggests that the addition of organic matter to agricultural soils, even where inorganic nitrogen fertilizers are used, enhances the soil potential for nitrogen cycling and soil sustainability.