Stakeholder-generated questions addressed in this chapter include the following:
- From a systems perspective, where are the control points for better management of N?
- Are there trade-offs between reduced N application and other cropping considerations? Will deviating from current N applications affect product quality, increase pest pressure, etc.?
- Are there current management practices that would increase N use efficiency and reduce N pollution?
Today, countless technologies and practices are available to optimize reactive nitrogen (N) use and change the way Californians interact with the nitrogen cascade. Knowledge and tools to limit the introduction of new reactive N into the cascade; mitigate the exchange of Namong the bio-, hydro-, and atmospheres; and adapt to the increasingly N -rich environment are already widely available for agriculture, transportation, industry, water treatment, and waste processing. With current technology, we estimate that strategic actions could reduce the amount of reactive N in the environment significantly.
Limiting the introduction of new reactive N—through improving agricultural, industrial, and transportation Nefficiency—is the most certain way to create win-win outcomes. Increasing efficiency would decrease the amount of Nper unit activity (potentially decreasing costs) and decrease emissions. Fortunately, practices are available to increase fertilizer and feed N use efficiency for virtually every agricultural commodity. Our conservative estimate suggests gains in efficiency could result in an estimated 36 Gg less fertilizer N use yr-1 and 82 Gg less feed N demand yr-1 without compromising productivity. By comparison to agricultural practices, the efficacy of engineering solutions to increase efficiency is well established.
Because a single source category is generally responsible for the majority (>50%) of each N transfer among environmental systems, priorities to mitigate Nemissions are clear. These include: manure management (to reduce ammonia (NH3) to air), soil management (to reduce nitrate (NO3-) to groundwater), fertilizer management (to reduce nitrous oxide (N2O) to air), fuel combustion (to reduce nitrogen oxide (NOx) to air), and wastewater treatment (to reduce ammonium (NH4) to surface water). Though these activities are the most culpable, a diverse number of additional actions also contribute to these transfers and it will take a systemic perspective to reign in N emissions. Further, because reactive N is intrinsically mobile in the environment, a narrow focus on a specific mitigative action will have the tendency to cause secondary emissions, thereby simply transferring the burden oftentimes with more harmful environmental and human health outcomes.
Reactive N is already changing California’s air, water, soils, and climate, and dynamics of the N cascade dictate that further degradation will continue to occur for some time. Moving forward, Californians will have to adapt systems and behavior to the new state of resources to maintain productivity, minimize exposure, and relieve further pressure on the environment. Adaptation will be especially important as populations grow further and concentrations of reactive N in the environment increase. There is already a need to treat drinking water to the regulated level of safe NO3- (45 mg per L) in many parts of the state, with this need projected to increase in the future. Ozone, groundwater NO3-, and increased deposition may all cause changes in productivity and management.