Biochar Affects An Eroded Calcareous Soil.

Erosional effects due to furrow irrigation in the Intermountain West have caused loss of shallow surface soils and exposure of calcareous subsoils.  When cultivated, these subsoils tend to produce lower crop yields and result in lost revenue for the producer.  Therefore, we explored the potential of biochar or biochar+manure to improve the fertility status of exposed subsoil. 

In a microcosm study conducted at 20^oC, increasing amounts of Dynamotive biochar (0, 1, 2, or 10% by weight) were added to a calcareous soil (pH 8.3) containing either 0 or 2% manure.  Both materials were thoroughly mixed into soil, microocosms were bought to field capacity twice per week with reverse osmosis water, and then destructively sampled at 1, 2, 3, 4, and 6 months.  Soil NO₃-N, pH, plant-available nutrients (as measured by DTPA), total C, organic C, total bacterial population (RT-PCR assay), and substrate induced respiration (measured via CO₂ evolution) response were measured.

In general, increasing biochar application rate caused a decrease in soil NO₃-N concentration, and an increase in total C and N content, organic C content, soil pH, bacterial population, and plant-available Fe, Mn, and Ni content.  The reduction in soil NO₃-N concentration, coupled with the increase in organic C content, suggested that N immobilization was occurring.  Increases in plant nutrients suggested biochar contained these elements and may serve as a micronutrient source when added to calcareous, exposed subsoil.           

Over time, however, the soil NO₃-N concentration generally increased, while the total C content and plant-available Fe, Mn and Ni content decreased.  These temporal effects appeared to result from normal nitrification and soil nutrient sorption processes, and were not biochar related.  When added to manure-amended soils, biochar application results were similar to the biochar only applications.  Findings suggest that biochar may improve the short-term micronutrient status of eroded calcareous soils and can increase the soil C content, yet excessive biochar applications may cause immobilization of soil NO₃-N.