*5.1.4 Optimal fertilizer application rates*

 Application of the right quantity of the fertilizer is critical to responsible nutrient management in most all ecosystems. Prudent nutrient management and sound economics requires that fertilizer amendment to the point of optimal yield without excess application that results in increased nutrient export via surface runoff or leaching. Incremental application rates above the point where more fertilizer application increases crop yield and N and P are no longer limiting has no effect on production [60] and can actually have negative return on yields as well as the excessive fertilizer is susceptible to surface storm water runoff and leaching to groundwater (**Figure 5**).

## *5.1.5 Effective buffer strips and/or forest buffers*

Buffers in the form of grass hedges, stiff grass hedges, field buffers, riparian forests, forest buffers, and wetland forests are commonly applied to minimize the effects of agricultural and urban land uses. Forested conditions are optimal for control of nonpoint source pollutions due to a range of characteristics that minimize the storm runoff and subsequent soil and nutrient transport that can result [61]. These characteristics include increased infiltration rates, increased vegetative cover, a thick organic layer, increased surface roughness, and higher evapotranspiration rates among other attributes. Each of these characteristics singularly reduces the quantity of surface water available to transport nutrients as well as nutrients

#### **Figure 5.**

*Schematic representation of crop yield and reactive nitrogen export to surface and groundwater as a function of reactive nitrogen inputs to agricultural field. Arrows indicate level of fertilization recommended by extension agents (1) and actual levels applied on average by farmers (2). Modified from Howarth et al. [55].* 

available to leach to groundwater. Uptake of grass and/or tree species can remove excess nutrients as a means of production of a component crop whether it come in the form of biomass, wildlife habitat, timber, or hay among other economic benefits.
