Fig. 2. Mean values for the nitrogen pools and rates of nitrogen transformations of the rototilled and control Pico silt loam soils. (a) NO₃-N, (b) nitrification potential, (c) MBN, and (d) denitrification rate with acetylene block. Day zero is the time of tillage. The sample at 0.04 d was obtained in the field immediately after tillage, while later samples were taken from intact cores incubated in the 20°C growth chamber. The error bars are the standard error of the mean. The Least Significant Difference (LSD) based on a Student's t-test between tilled and control soil is shown