CARBON-DIOXIDE BUDGET OF MAIZE

Measurements made during 1982, 1983 and 1984 were used to study the CO2 budget of maize (Zea mays L.). Above-canopy CO2 flux density, which represents most of the CO2 absorption by crops, was monitored throughout each growing season using the eddy correlation technique. Intercepted solar radiation was calculated on an hourly basis using measurements of incident solar radiation, leaf aura index and solar elevation. The observed relationships between above-canopy CO2 flux densities and intercepted solar radiation, for each growing season, were then used to estimate hourly above-canopy CO2 flux densities. Assimilation of soil-respired CO2 and nighttime losses of plant respiratory CO2 flux densities to determine net photosynthesis. Although clear short term relationships between above-canopy CO2 flux density and intercepted solar radiation have been observed for maize, a great variability in CO2 flux density as a function of estimated intercepted solar radiation is observed over the whole growing season. Comparison of estimated CO2 budget based on gaseous exchange estimates agreed within .+-.1 standard error while for 1984 the estimates based on gaseous exchanges were consistently lower. The relative magnitudes of gross phootosynthesis, soil and plant respiration are presented and techniques for improving our ability for closing the CO2 budget using gaseous exchanges estimates are discussed.