Soil Carbon Sequestration Affected by Cropping Changes from Upland Maize to Flooded Rice Cultivation

Abstract

The effects of cropping changes from upland maize to flooded rice cultivation on soil organic carbon (SOC) were studied. Three treatments of field experiments; continuous maize (M treatment), continuous paddy rice (R treatment) and maize-rice rotation (RM treatment) were made. Cropping change from maize to flooded rice resulted in an increase in soil bulk density and SOC content when compared to that of maize-rice rotation and continuous maize. The total SOC after two croppings was 16.50, 20.88 and 19.35 ton C ha -1 in the M, R and RM treatments, respectively. The effects of these short-term cropping changes were observed at both the aggregate level and in the humic substances of soil organic matter. The majority of SOC (ca. 65%) was present in association with the macro-aggregate (>250 m), of which the fraction size of 250-500 m contained the highest carbon concentration. After two croppings, the  13 C values of SOC and humic substances were shifted towards the  13 C values of rice straw when soil was incorporated with rice straw. The shift of  13 C values towards maize straw's  13 C values was also observed in cases when maize straw was incorporated into soil. The results demonstrate that a shift from upland maize to flooded rice could enhance soil carbon sequestration, and decomposition and incorporation of organic materials (maize and rice straw) into SOC and humic substances (himic acid, fulvic acid and humin) was detectable within a short time period.