Diurnal and Seasonal Carbon and Energy Flux Over No-Tillage Farming.

This research seeks to understand diurnal and seasonal carbon, water, and energy flux and its function of soil-vegetation-atmosphere dynamics. A long term investigation of energy and water balance, and carbon dioxide (CO2) measured under a no-tilled system on humid environment for the southeastern part of the United States is limited. Our objectives are to quantify carbon, water and energy partition for no-tillage system and understand the carbon, water and energy change as a function of environmental and biological controls for a soybean and winter wheat crops. The study was conducted at the Winfred Thomas Agricultural Research Station located at Hazel Green, AL. A micrometeorological station was installed at the center of 18 ha field and included eddy covariance system, and open path gas analyzer were used to make long-term continuous measurements during two complete soybean and winter wheat growing seasons. Our preliminary results indicate that the longest diurnal carbon uptake rates were observed during the warmer months (May to August, 2007). Large differences in daily CO2 uptake were observed during the cooler months (January to April) over winter wheat canopy while differences were small during summer time. The trend in CO2 uptake was consistent with changes in day length. Over a winter wheat canopy, the carbon assimilation values ranged from a maximum of -14.5 umol m-2 s-1 in March, to a minimum of about - 5 umol m-2 s-1 in January. During the warmer months, soybean CO2 flux reached a maximum of -15.5 umol m-2 s-1 in May during early morning hours and to a minimum of -8.5 umol m-2 s-1 in August. Mid-summer drought occurred during the main growing season (June-August) of the study period in 2007 and had a strong impact on canopy CO2 uptake which resulted in a reduction of day time carbon assimilation.