Long Term Atmospheric Carbon Dioxide Exchange of No-Tilled Soils.

In the past, intensive agricultural practices have greatly increased crop production and food supply in the world. However, future intensification of agriculture as business as usual practice may become questionable. Experimental data necessary to understand both the influence of key environmental variables and soil management practices of intensive agriculture and atmospheric CO2 are limited. The objective of this study is to examine the soil-atmosphere carbon exchange of winter wheat/soybean cropping systems for northern Alabama soils under a no-till system. The daily, seasonal and integrated sum of net ecosystem carbon exchange was determined using 7500 open path IRGA and CSAT. Preliminarily data indicate that the seasonally integrated CO2 exchange (net ecosystem production, NEP) winter wheat/soybean canopies exhibited marked difference with soybean crop fixed more carbon than winter wheat canopy. Overall, the typical daily NEE in rainfed soybean ranged from - 10 to -25 mmolm-2 s-1 and - 18 to -30 mmolm-2 s-1 in 2007 and 2008, respectively. The longest diurnal carbon uptake rates were observed during the warmer months (May to August) although the summer of 2007 was one of the driest periods in northern Alabama in more than 150 years. The cool season winter wheat crop gained daily maximum NEE values ranged from - 4mmolm-2 s-1 in January to -12.5 mmolm-2 s-1 in March of 2007. The spatial integrated ecosystem C magnitude and detailed results of our study will be presented.