Microbial biomass c and n dynamics, and15 n 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 isotope15N was used to trace the incorporation of15N 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, and15N incorporated into the flush N fraction and15N excess varied with treatments. Among three approaches of calculating flush N, we found that NH+4 in fumigated less the nonfumigated soils yielded the best results, NH+4 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.