Crop Growth Analysis: Carbon Flux Measurements vs. Plant Sampling

The traditional method of crop growth analysis involves the destructive sampling of plants within a canopy. Changes in above ground plant biomass is determined by comparing the dry weights of plants collected during consecutive weeks. These data are then used to estimate the rate photosynthesis and growth. The recent development of the open-path infrared gas analyzer (IRGA) provides a mechanism to continuously monitor carbon dioxide fluxes from crop canopies using the eddy-covariance method. As part of the National Oceanic and Atmospheric Administration's (NOAA) contribution to the Global Energy and Water Cycle Experiment (GEWEX) a long term energy/carbon flux tower system was established on a no-till corn and soybean field in central Illinois. Flux measurements have been collected continuously since August of 1996. During the summers of 1998, 1999, and 2000 weekly crop growth measurements were obtained by destructively sampling plants in a one meter length of crop row. Crop growth rate from the destructively sampled plants were compared to that measured with the IRGA. This paper will discuss the differences observed in the two growth analysis measurement methods, and compare the growth rates estimated for soybean in 1998 and 2000, and for corn in 1997 and 1999.