Effects of 49 years of fertilization on the distribution and accumulation of soil carbon under corn cultivation. Can. J. Soil Sci. 92: 835Á839. The effects of 49 yr of monoculture corn (Zea mays L.) production with/without chemical fertilizer addition on the origin and distribution of soil organic carbon (C) among the sand (53Á2000 mm), silt (2Á53 mm), and clay (B2 mm) particle size fractions in the top 20 cm of a clay loam soil were evaluated using the carbon-13 isotope abundance technique. The C derived from corn (newly formed C4-plant C) was greater under chemical fertilization relative to no fertilization in all three size fractions. However, the resident (old) C derived from C3-plants grown prior to corn was similar between the fertilized and unfertilized treatments for each size fraction. Fertilization of monoculture corn had little impact on the amount of native-formed C3-plant C, particularly in the silt and clay fractions, but did increase the amount of newly formed C4-plant C.