Nitrogen Transformations in Manure Amended Soils As Affected By Biochar Application.

Localization of confined animal feeding operations (CAFOs) has brought about a massive production of animal manures. Traditional management practices have applied manure to crops as a fertilizer; yet long-term manure applications can cause nutrient imbalances (such as N) in soils far in excess of what crops can assimilate. As a repercussion, excess soil nitrogen (N) can leach into ground water or be lost as N₂O. The situation is so severe in areas with multiple CAFOs, that producers must have nutrient management plans or manure application can be restricted if soils are over-saturated with respect to N. There is a clear need for alternative animal waste management methods with respect to N.

Biochar, a pyrolysis by-product, holds promise as a material that can influence soil N transformations in manure amended soils.  Biochar has been shown to both increase and decrease soil NO₃-N concentrations when applied to manure amended soils.  However, given high enough biochar application rates, soil NO₃-N may be maintained at lower concentrations in manure amended soils.  Increasing biochar application rates have also been shown to reduce soil NO₃-N leaching (in some instances up to 75%), suggesting nitrate capture by biochar.  Furthermore, it has been speculated that biochars can sorb soil NH₄-N, temporarily removing it from microbial processes.  This could be important when utilizing manure amended soils containing excessive organic N.

Applying compost and biochar has been shown to increase retention of fertilizer-applied N.  Biochar blending with manures and co-composting, or blending with liquid dairy wastes, has been shown to enhance the agronomic nutrient value of the final product while helping to reduce N₂O emissions and improve plant productivity; biochar alone has, in some instances, also been shown to reduce soil N₂O emissions.  Overall, biochar application to manure amended soils could potentially benefit producers who often observe excessive soil N accumulation.  Specific results and mechanisms will be discussed.