**5. Management of nitrogen and phosphorus pollution and challenges faced**

 Generally, it has been much easier to manage point sources of both N and P however, non-point sources have been a challenge to control and are the main sources of pollution in the marine ecosystem [51, 52]. Nitrogen has higher mobility in the environment compared to P since N flows easily through both ground water and atmosphere [51]. It has been generally indicated that management practices for reducing N pollution in most cases are also effective in phosphorus control, however the converse is not true (**Table 2**) [51, 53]. Due to high N mobility and volatility, in some cases it might need different/additional mitigation strategies compared with P. In United States and Europe major progress has been made in reducing N pollution from municipal waste water sources which is a point source but very little progress has been made in reducing non-point source N and P pollution [51, 54]. The following are some technical solutions for N and P management.

*Nitrogen and Phosphorus Eutrophication in Marine Ecosystems DOI: http://dx.doi.org/10.5772/intechopen.81869* 


#### **Table 2.**

*Relative effectiveness of some representative best management practices (for reducing nitrogen and phosphorus pollution of surface and groundwater. Modified from Howarth [51].* 

#### **5.1 Leaching and runoff from agricultural fields**

In United States, N inputs to agricultural fields doubled from 8 to 17 million metric tons per year between 1961 and 1997 [55]. Approximately 20% of the new N inputs to agricultural fields is leached to ground or surface water [55, 56]. Climate has an influence on N losses, whereby, losses are higher under high rainfall intensities and wetter years [57]. Significant amount of P from agricultural fields is lost through leachate and runoff to rivers, lakes and reservoirs and eventually finds its way to the marine ecosystem [38].

#### *5.1.1 Growing perennial crops*

 Growing grasses or alfalfa rather than annuals such as soybeans or corn is presented here as a potentially beneficial practice to control N and P nonpoint source pollution. Perennials are known to maintain N in the rooting zone, thereby reducing losses to groundwater. Previous work has shown that fields planted with perennial alfalfa lost ~30–50 times less nitrate compared to fields planted with soybeans and corn in Iowa and Minnesota, USA [57, 58].

#### *5.1.2 Planting winter cover crops*

 Winter cover crops provide a range of services that are beneficial to managing N and P pollution since these crops protect the soil during this vulnerable season with lower evapotranspiration rates and higher antecedent soil moisture conditions. Cover crops provide cover to soils vulnerable to accelerated erosion losses and reduce soil erosion, which is the primary mechanism whereby nutrients are transported to surface water systems. In particular, N and P are attached to soil particles that are transported via storm water runoff directly to receiving surface waters such as streams, rivers, lakes, wetlands, and oceans. Further, winter cover crops reduce nutrients transported such as leaching of nitrate into groundwater during winter and spring, this is the period that most leaching occurs in many climates [51] as a result of the antecedent moisture conditions due to reduced plant soil water and nutrient uptake. The previous literature reports that long term winter cover crops have the capability of reduced nitrate loss as much as 3-fold [59].

#### *5.1.3 Effective N and P application*

Nitrogen and P fertilizer application timing is critical to managing nonpoint source pollution in cropping systems. Fertilizer application as close as possible to the time of crop need during the growing season is presented as a viable control for pollution challenges related to N and P. In particular, fall fertilizer application is often not the most agronomically, economically, or environmentally efficient or sustainable practice since much of this amendment would be either have direct connectivity to receiving surface waters through storm water runoff during the dormant season or eventually leach to ground waters since plant uptake is limited to negligible amounts because, with the exception of fall or winter cash crops, growth begins in the spring. The previous literature has found that fall application of fertilizer can result in as much as 30–40% leaching of the fertilizer [57].
