# Can Biochar Improve the Sustainability of Animal Production?
## 6 Land Application
### Biochar Bioretention Systems to Treat Agricultural Run-Off  
Nitrates from manure and fertilizer land application are a primary pollutant of concern from agricultural fields. Nitrates move through the soil in soluble form and can pose health concerns when present in drinking water and in foraging biomass. Nitrates in waterways cause rampant growth of algae depleting available oxygen for aquatic life [128]. Biochar has been explored as a water biofilter extensively in stormwater applications. However, less research has been done to utilize the power of biochar to reduce contaminants from manure land application on agricultural fields. The following examples demonstrate the limited attempt to use biochar biofilters to treat agricultural run-off pollutants.  
[PERSON] et al. [129] used wood-chip biochar pyrolyzed at 900 \({}^{\circ}\)C in an existing bioretention cell (run-off treatment) to evaluate nitrogen removal of dairy wastewater mixed with stormwater. Bioretention cells were constructed to compare pure sand (S) versus a biochar sand combination (B). Each treatment was also tested with an established Muhly grass version (SP and BP) to see if the plants contributed to increased treatment giving a total of four treatments. The highest TAN removal was observed from both biochar systems at about 91% removal compared to the sand systems at 68%.  
This was attributed to the high CEC of the biochar (10.57 kmol kg\({}^{-1}\)) allowing more time for nitrification compared to the pure sand biofilters. The biochar amended filters also resulted in lower NOx concentrations (0.72-1.18 mg L\({}^{-1}\) vs. 2.09-3.15 g L\({}^{-1}\)) likely due to the total organic carbon (TOC) retained due to the high adsorption of the biochar. This was used as an electron donor for denitrification. The biochar's high surface area (537 m\({}^{2}\) g\({}^{-1}\)) and porosity enhanced the microbial communities in the filter resulting in greater adsorption and ammonification. The overall high moisture and nutrient retention also contributed to better plant growth.  
[PERSON] et al. [129] used biochar-amended vegetated filter strips for the treatment of nitrates in silage bunker (feed storage) runoff. Information was not given about the biochar feedstock or addition rate to the system. Biochar addition increased the subsurface effluent nitrogen from 49 to 64% compared to influent. Specifically, subsurface effluent nitrate was reduced by 40% compared to the control. Overall, the biochar addition reduced nitrogen soil leaching by 15%, increased soil nitrogen retention by 25% and reduced nitrogen lost through gaseous emissions by 10%. The authors suggested that increasing oxygen functional groups on the biochar would increase nitrogen retention.  
It is unclear why more studies have not been conducted in this area given the positive results reported by [PERSON] et al. [129] and [PERSON] et al. [129]. Going forward, reviewing the performance of stormwater biochar biofilters will be the best starting point to design and optimize off-site water filtration systems for agricultural run-off and pollutants.