Fertilization Effects on Soil Organic Matter Turnover and Corn Residue C Storage

Abstract Soil organic matter turnover is influenced by N; thus long‐term fertilization of corn ( Zea mays L.) may significantly affect soil organic matter levels. Effects of fertilization on soil organic matter turnover and storage of residue C under continuous corn were evaluated using soils from a long‐term field experiment in Ontario. Total organic C and natural 13 C abundance measurements indicated that fertilized soils had more organic C than unfertilized soils, the difference accounted for by more C 4 ‐derived C in the fertilized soils. About 22 to 30% of the soil C in the plow layer had turned over and was derived from corn in the fertilized soils; in unfertilized soils only 15 to 20% was derived from corn. Assuming that organic matter turnover follows first‐order kinetics, the half‐life of C 3 ‐derived C in the surface 10 cm of both soils was the same, about 19 yr. Natural 13 C abundance measurements and estimates from a soil organic matter model indicate that 10 to 20% of the added residue C was retained in the soil. Fertilized soils had more light fraction (LF) C than unfertilized soils. More than 70% of the C in the LF of fertilized soils was derived from corn; in unfertilized soils only 41% was derived from corn. The half‐life of C 3 ‐derived C in the LF was shorter than 10 yr. These results indicate that adequate fertilization increases crop yields, in turn leading to greater C storage, and that fertilization does not significantly alter the rate of turnover of native soil organic matter.