Soil organic matter response to cropping system and nitrogen fertilization

Management to improve soil C and N storage is necessary to increase soil quality. Continuous corn (Zea mays L.) (CC) and a corn-soybean [Glycine max (L.) Merr.] rotation (CS) in a chisel plow tillage system with six N fertilizer rates in corn were sampled aft er 8 yr in Illinois. Soil organic carbon (SOC) and total nitrogen (TN) varied with cropping system at DeKalb, but not at Dixon Springs or Urbana. At DeKalb, SOC in the 0-to 30-cm depth was 98.6 and 81.4 Mg C ha ^-1 following CC and CS, respectively. Similarly, TN to a depth of 30 cm at DeKalb was 7.91 Mg N ha ^-1 with CC and 6.91 Mg N ha ^-1 with CS. Particulate organic matter (POM) C (POM-C) and POM N (POM-N) were also greater following CC in the 0- to 30-cm depth at DeKalb and in the surface 15 cm at Dixon Springs. At DeKalb, POM-C in the 0- to 30-cm depth was 6.5 Mg C ha ^-1 following CC and 5.1 Mg C ha ^-1 following CS, while POM-N was 0.41 and 0.34 Mg N ha ^-1, respectively. At Dixon Springs, where POM-C was 4.9 Mg C ha ^-1 and POM-N was 0.34 Mg N ha ^-1 in the 0- to 15-cm depth following CS, POM-C and POM-N were 10 and 9% greater with CC, respectively. These results indicate that cropping system infl uences soil C and N more than N fertilization, and that this infl uence is greater in the labile fraction of soil organic matter (SOM) than in total SOM.