Nitrogen is fundamental to all living things, but nitrates in groundwater represent a serious health and environmental risk. Where do nitrates in groundwater come from and what is the role of a responsible agriculture to reduce contamination, starting from the nitrogen cycle (Global Cycle)?
The fundamental process that releases nitrogen from the atmosphere and makes it accessible to the biosphere is fixation which can be abiotic (by the energy of lightning), biotic (by nitrogen-fixing organisms) or anthropic (Haber-Bosch cycle).
The final product of fixation is represented either by NH3 or by NH4+, the latter can be either absorbed directly by plants, entering the food chain, and then be easily recycled and subjected to the decomposition process, or undergo nitrification processes (oxidation), producing NO2- and NO3- which in turn can be assimilated by plants.
Nitrogen re-enters the atmosphere through a dissimilative process called denitrification.
Several nitrogenous compounds released into the atmosphere are oxidized to nitric acid (HNO3), which forms a water condensation core, facilitating cloud formation and returning with dry depositions, in the form of dust in areas close to eruptions or with wet deposition thanks to the phenomenon of “acid rain”.
Also animals participate in the global nitrogen cycle by releasing excrements: ammonia from invertebrates and uric acid from vertebrates.
Finally, nitrogen in the terrestrial environment is often a limiting factor, so is provided through fertilization to increase agricultural production.
To produce fertilizers, the anthropic fixation of nitrogen occurs through the Haber-Bosch cycle.
In the nitrogen cycle are also important volcanic eruptions, volatilization processes and human intervention (fires, industries, and combustion).
Biological events that allow the release of nitrogen for the mineral nutrition of plants suggest industrial applications to control the process of nitrification at soil level, increase the use efficiency of fertilizers and reduce nitrogen leaks by volatilization and leaching.
RESPONSIBLE AGRICULTURE TO SAVE GROUNDWATER.
As mentioned above, fertilizers make extensive use of nitrogen to increase crop yield. The intake of these elements must be properly adjusted to avoid an overabundance of nitrates on the soil as well as leaching phenomena.
This is well known to Apulian farms that have been ascribed in the NVZ (Nitrate Vulnerable Zones) and that are required by the NAP (Nitrates Action Plan) to adopt agricultural behavior aimed at limiting contamination.
For these farms, and in general for all farms, it is good to undertake responsible agriculture, optimizing fertilizer inputs through proper planning of interventions based on plant monitoring data (to identify the correct needs) and soil (to detect possible too high nitrate concentrations).
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