Microbial biomass C and N dynamics, and 15N incorporation into microbial biomass under faba bean, canola, barley, and summer fallow in a Gray Luvisol

Abstract

Microbial biomass C and N dynamics was studied of the soils cropped to faba bean, canola, barley and summer fallow in the Breton Plots in Canada. Stable isotope ¹⁵N was used to trace the incorporation of ¹⁵N into microbial biomass fraction. Flush N was calculated in three ways to compare discrepancies that may exist in results widely published. Crop and cropping had significant effects on microbial biomass C and respiration C of treated soils. Microbial biomass C estimated in faba bean plots was higher than that in canola, barley or summer fallow by 44, 39 and 167% on the average of four samplings. A peak was observed for canola, barley and summer fallow around July 24, but it was not evident for faba bean. Flush N was not significant upon treatments, and 15N incorporated into the flush N fraction and ¹⁵N excess varied with treatments. Among three approaches of calculating flush N, we found that NH₄⁺ in fumigated less the nonfumigated soils yielded the best results, NH₄⁺ in fumigated without control resulting in deviation from considering a control by 1-2% in faba bean, 1-6% in barley and 1% in canola and summer fallow.