Estimating C inputs retained as soil organic matter from corn (Zea Mays L.)

In agroecosystems, the annual C inputs to soil are a major factor controlling soil organic matter (SOM) dynamics. However, the ability to predict soil C balance for agroecosystems is limited because of difficulties in estimating C inputs and in particular from the below-ground part. The objective of this paper was to estimate the proportion of corn residue retained as SOM. For that purpose, the results of a (13)C long-term (15 yr) field study conducted on continuous silage corn and two silage corn rotations along with data from the existing literature were analyzed. The total amount of corn-derived C (0-30 cm) was about 2.5 to 3.0 times higher for the continuous corn treatment (445 g m(-2)), compared to the two rotational treatments (175 and 133 g m(-2) for the corn-barley-barley- wheat and corn-underseeded barley hay-hay rotations, respectively). Assuming that the C inputs to the soil from silage-corn was mainly roots and would have been similar across treatments on an annual basis, the total amount of corn-derived C for the two rotational treatments was approximately proportional to the number of years the silage-corn was present in the rotation (4 yr). The results from the current study indicate that about 17% of root-derived C is retained as SOM. This value is higher than those reported in the literature for long-term studies on shoot-derived C (range of 7.7 to 20%, average of 12.2%), which is in agreement with previous studies showing that more C is retained as SOM from roots than from shoots.