Effect of CO2 enrichment on growth and competitiveness of soybean and millet against lambs quarters and pigweed

In order to study the effects of CO2 enrichment on growth and competitiveness of soybean (Glycine max) and millet (Panicum miliaceum) against redroot pigweed (Amaranthus retroflexus) and lambsquarter (Chenopodium albam) an experiment was conducted using two CO2 concentrations (350 and 700 ppm). For evaluating effects of CO2 variation on inter-and intra-specific competition plants were grown in monoculture and intercropping in greenhouse as factorial experiment based on the completely randomized design. The results indicated that with increasing CO2, chlorophyll index increased in all species but in average higher increase observed in C3 plants in mixture (20% increase) compare to C4 plants (12% increase). By increasing CO2 concentration root weight, leaf weight and stem weight in C3 species increased 0.75, 2.61 and 2.43 g respectively while, in C4 species these values were 0.04, 1.18 and 0.40 g respectively. Shoot dry weight of C4 species decreased in competition with C3 in high CO2 concentration. Comparison of plants PRY indicated that by increasing CO2 concentration soybean PRY increased by 8.9 and 9.6 against millet and pigweed respectively while, millet PRY decreased against C3 plants. This means that competition interaction of crop-weed could be affected by variation of CO2 in environment.