Influence of the irrigation technique and strategies on the nitrogen cycle and budget: A review

The objective of this review is to remedy the lack of knowledge about the expected relationship between the irrigation techniques (flood irrigation, sprinkler irrigation, surface and subsurface drip irrigation) and the nitrogen transformations (fixation, mineralization, immobilization and nitrification) or fluxes (denitrification, runoff, volatilization and lixiviation) in agricultural contexts. This study investigates thus the various controls on the nitrogen cycle and budget, either site-specific (soil C/N ratio, pH, salinity, texture and temperature) or corresponding to deliberate strategies in water and nitrogen management. The comprehensive view gained from the gathered literature elements identifies the local variations (in space and time) of soil water content profile as both the strongest control and the control most directly related to the irrigation technique and to the practitioner's decisions. In the overall picture, flood irrigation and sprinkler irrigation are the techniques in which most transformations or fluxes may be enhanced or reduced, also with the risks associated with non-optimal practices. By contrast, subsurface drip irrigation seems the technique with the least unwanted impacts. Besides the academic aspects (bringing together scattered literature elements) an outcome of this review is thus to facilitate decision-making regarding the choice and/or use of irrigation-fertilization techniques and strategies (doses and scheduling) for given agro-pedoclimatic contexts, also for combined agricultural production, economic and site preservation objectives.