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Berseem Production Boosted by Elevated CO2
Pal, M., Karthikeyapandian, V., Jain, V., Srivastava, A.C., Raj, A. and Sengupta, U.K.  2004.  Biomass production and nutritional levels of berseem (Trifolium alexandrium) grown under elevated CO2Agriculture, Ecosystems and Environment 101: 31-38.

What was done
The principle investigators of this study grew well-watered and fertilized berseem (Trifolium alexandrium L. cv. Pusa Jayant) - an important forage legume crop that is grown in the winter throughout India - from germination onwards in open-top chambers maintained at atmospheric CO2 concentrations of ambient (360 ppm) and 600 ppm for a period of 80 days.

What was learned
The scientists recorded the following percentage increases in the following plant growth parameters at 40, 60 and 80 days, respectively, after initial exposure to the 67% increase in the air's CO2 content: plant height (47%, 36%, 42%), stem dry weight (77%, 50%, 51%), total shoot mass (98%, 42%, 40%), leaf area (98%, 79%, 47%), number of leaves (23%, 30%, 43%), leaf dry weight (118%, 29%, 12%).  With respect to leaf nutrient concentrations, however, they recorded reductions of 29%, 27% and 33% for nitrogen, but increases of 12%, 8% and 9% for phosphorus, and no significant changes in calcium and iron.

What it means
The single negative aspect of this study - the decrease in leaf nitrogen concentration - may not be as serious as it appears when viewed in another light.  Pal et al. report, for example, that "if calculated on a unit land area basis, an increase of 20-25% in nitrogen content occurs."  Then there is another positive implication not revealed in the data themselves.  In addition to the intrinsic value of the huge increases in growth produced by the increase in atmospheric CO2 concentration, Pal et al. note that this "acceleration in biomass (fodder) production" may "lead to more than one cutting of berseem fodder if plants are grown under high CO2 conditions throughout the crop season," which would provide an even bigger additional boost (perhaps by a multiplicative factor of 2) to the total growing-season production of both harvestable biomass and nitrogen.

Reviewed 28 January 2004