Abstract

JOHN, B., LUDWIG, B., POTTHOFF, M., and FLESSA, H.

J. Plant Nutr. Soil Sci. 167:270-276 (2004)

The sequestration of carbon in soil is not completely understood, and quantitative information about the rates of soil organic carbon (SOC) turnover could improve understanding. We analysed the effects of the uneven distribution of crop residues after harvest of silage maize on C and N losses (CO2-C, dissolved organic carbon (DOC) and nitrogen (DON) and NO3-) from a Haplic Phaeozem and on the occurrence of priming effects induced by the decomposition of accumulated maize residues. Soil columns were taken from a continuous maize (since 1961) field after harvest i) between maize stalk rows (Mbare), ii) within the maize rows including a standing maize stalk (Mstalk), and iii) from a continuous rye (since 1878) field after tillage (rye stalk and roots were mixed into the Ap horizon). The soil columns were incubated for 230 days at 8°C with an irrigation rate of 2 mm 10-2 M CaCl2 per day. Natural 13C abundance was used to distinguish between maize-derived C (in SOC and maize residues) and older C originating from former C3 vegetation.
The uneven distribution of maize residues resulted in a considerably increased heterotrophic activity within the maize rows as compared with soil between seed rows. Cumulative CO2 production was 53.1 g CO2-C m-2 for Mstalk and 23.3 g CO2-C m-2 for Mbare. The contribution of maize-derived C to the total CO2 emission was 83% (Mstalk) and 67% (Mbare). Calculated as difference between CO2-C release from Mstalk and Mbare, 19% of the maize residues (roots and stalk) in Mstalk were mineralised during the incubation period. There was no or only a marginal effect of the accumulation of maize residues in Mstalk on leaching of DOC, DON and NO3-. Total DOC and DON leaching amounted to 2.5 g C m-2 and 0.16 g N m-2 for Mstalk and to 2.1 g C m-2 and 0.12 g N m-2 for Mbare. The contribution of maize-derived C to DOC leaching was about 25% for Mstalk and Mbare. Nitrate leaching amounted to 3.9 g NO3--N m-2 for Mstalk and to 3.5 g NO3--N m-2 for Mbare. There was no priming effect induced by the decomposition of fresh maize residues with respect to CO2 or DOC production from indigenous soil organic carbon derived from C3 vegetation.