Abstract
We monitored the composition of the soil air in native grassland and cultivated fields over several years on upper, middle, and lower slope sites on an Orthic Dark Brown Chernozemic soil. Soil carbon dioxide concentrations approximated 0.1 percent, volume per volume, in late April, started to increase in early May, reached maximum values of 1 to 2 percent, volume per volume, in June and July, and by late September had decreased to the same levels as in late April. The CO2 concentrations varied considerably from year to year and were affected more by slope position than by vegetative cover. Comparison between CO2 and O2 gradients indicated that anaerobic respiration rarely occurred.The annual course of CO2 evolution appeared related to climatic conditions during the growing season. Regression equations between CO2 evolution, and water content or temperature of the 0− to 10-cm soil layer were rarely significant, but monthly mean CO2 evolution correlated well with the mean temperature and total precipitation of that month. Carbon dioxide evolution increased markedly down the slope, reflecting increased productivity and possibly erosion, and was about twice as large under native grassland as on the cultivated fields that were fallowed every second year. Differences in CO2 evolution were small between cropped and fallowed sites on similar slope positions. Average CO2 evolution of the cultivated fields was estimated at 1900 kg C per hectare per year during the crop year and at 1800 kg C/ha/yr in the fallow year; the mean dry matter input was in the order of 1700 kg C/ha/yr.Accumulation of NO3-N in fallow fields was highest in the years with the lowest CO2 evolution. The low accumulation of NO3-N appeared mainly due to immobilization of mineral nitrogen during periods of high soil respiration rates. We monitored the composition of the soil air in native grassland and cultivated fields over several years on upper, middle, and lower slope sites on an Orthic Dark Brown Chernozemic soil. Soil carbon dioxide concentrations approximated 0.1 percent, volume per volume, in late April, started to increase in early May, reached maximum values of 1 to 2 percent, volume per volume, in June and July, and by late September had decreased to the same levels as in late April. The CO2 concentrations varied considerably from year to year and were affected more by slope position than by vegetative cover. Comparison between CO2 and O2 gradients indicated that anaerobic respiration rarely occurred. The annual course of CO2 evolution appeared related to climatic conditions during the growing season. Regression equations between CO2 evolution, and water content or temperature of the 0− to 10-cm soil layer were rarely significant, but monthly mean CO2 evolution correlated well with the mean temperature and total precipitation of that month. Carbon dioxide evolution increased markedly down the slope, reflecting increased productivity and possibly erosion, and was about twice as large under native grassland as on the cultivated fields that were fallowed every second year. Differences in CO2 evolution were small between cropped and fallowed sites on similar slope positions. Average CO2 evolution of the cultivated fields was estimated at 1900 kg C per hectare per year during the crop year and at 1800 kg C/ha/yr in the fallow year; the mean dry matter input was in the order of 1700 kg C/ha/yr. Accumulation of NO3-N in fallow fields was highest in the years with the lowest CO2 evolution. The low accumulation of NO3-N appeared mainly due to immobilization of mineral nitrogen during periods of high soil respiration rates. © Williams & Wilkins 1981. All Rights Reserved.