Interactive priming of soil N transformations from combining biochar and urea inputs: A 15N isotope tracer study
In this study we investigated the priming effect of combined biochar and urea inputs on soil inorganic N pools through an isotope tracer approach. Biochar was applied in combination with urea in two complementary laboratory experiments: (i) in the first one, three 15N-labeled organic amendments (wheat straw (WS), its biochars produced at 350 °C (B350) and at 550 °C (B550) were added to soil in combination with unlabeled urea; (ii) in the second experiment the three same, but unlabeled, amendments were added to soil in combination with 15N labeled urea. This system allowed partitioning between three N sources: native soil N, biochar-derived N and urea-derived N. In addition, CO2 fluxes were measured to follow total C mineralization in soil and N2O emissions were monitored. The proportion of N that mineralized from biochar was always below 0.5% of the added N. The co-addition of urea increased the concentration of NH4+ derived from B350, but not from B550, demonstrating the lower mineralization of N in biochars produced at 550 °C. Whereas the addition of WS led to a rapid immobilization of N, we found that despite their high C:N, none of the biochars, applied at a rate of 1.5%, immobilized inorganic N in soil. On the contrary, significantly higher NH4+concentrations derived from native soil organic N (SON) and urea were found throughout the incubation when B550 was added. This effect can be attributed to an apparent priming effect since a net decrease in CO2 fluxes was...
Source: Soil Biology and Biochemistry - Category: Biology Source Type: research
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