Biochar decreases and nitrification inhibitor increases phosphorus limitation for microbial growth in a wheat-canola...

Agricultural management practices affect microbial populations and ecoenzymatic activities; however, the effect of these practices on ecological stoichiometry relating the elemental ratio of resources to microbial biomass is poorly understood. In a 2-year field study, we assessed the effects of biochar and nitrapyrin (a commonly used nitrification inhibitor (NI)) on the ecological stoichiometry and microbial nutrient limitation in a wheat (Triticum aestivum L.)-canola (Brassica juncea L.) rotation. This study used a 3 × 2 factorial design that included two treatments: (i) biochar with three levels: no biochar addition (BC0), and biochar added at 10 (BC10) and 20 t ha^-1 (BC20), and (ii) NI with two levels: without (NI0) and with NI (NI1). Soil microbial biomass carbon (C), nitrogen (N) and phosphorus (P) were increased by biochar application, regardless of the application rate, but were not affected by NI application. Biochar increased and NI decreased β-1,4-glucosidase, β-1,4-N-acetyl glucosaminidase and acid phosphatase (P < 0.05) with subsequent changes in ecoenzymatic stoichiometry. Ecoenzymatic stoichiometry analysis showed microbial P limitation relative to N in the studied area irrespective of the treatment, with contrasting effects of biochar (decreasing) and NI (increasing) on the vector angle of ecoenzymatic stoichiometry (P = 0.037 and 0.043, respectively). Biochar applied at 20 t ha^-1 decreased the threshold elemental ratio of C:P at which microbial growth switches between nutrient and C limitations, suggesting a shift towards C relative to nutrient (P) limitation. This study concludes that biochar produced from manure compost can be useful in increasing microbial growth by alleviating P limitations in a wheat-canola rotation.