The objective of this study was to examine the effects of tillage on soil microbial biomass carbon under a crop of corn(Zea mays L.) Soil microbial biomass carbon was measured every two weeks and every month in conventional tillage(CT),1-year no-tillage(SNT),and long-term(>15 years) no-tillage (LNT) plots using the chloroform fumigation-extraction technique.The plots are located near Guelph,Ontario,Canada on a Typic Hapludalf(loam) soil.Sampling sites were in the corn row,directly between corn rows(interrow),and half way between the row and interrow(quarter row).Systematic spatial differences in soil microbial biomass carbon within and between tillage treatments were observed throughout the entire growing season of crop.The major changes in the biomass occurred as a large increase between the time of planting and the time of Bilking and were correlated with predicted and expetted root growth.Spatial variations of LNT biomass carbon were significantly correlated to spatial variations in soil water content over the crop growth season.