AbstractThe global atmospheric CO2‐concentration is increasing and there has been an increase in Germany of about 30 ppm from 340 ppm to 370 ppm CO2during the last two decades. The hectare yield of many crops has also increased during this time period. The objective of the present study was to estimate whether the past and future change in the atmospheric composition significantly contributes to the increase in hectare yield.Different crop species (beans,Phaseolus vulgaris, cv Pfälzer Juni; spring barley,Hordeum vulgareL., cvs. Alexis and Arena; spring wheat,Triticum aestivumL., cvs. Star and Turbo; maize,Zea maysL., cvs. Bonny and Boss) were grown at ambient (372 ppm) and at slightly elevated CO2‐concentrations (459 ppm and 539 ppm) in open‐top chambers and the effect of the different CCVconcentrations on the growth and yield of the plants was measured. The past and future CO2‐effect was estimated from the slope of a linear CO2‐yield curve (percentage increase in yield per ppm CO2′100 at 370 ppm) fitted to the data and those from previous studies on wheat and maize. The percentage increase in yield per ppm CO2is insignificant for beans, of borderline significance for silage maize (0.06 per ppm), and 0.35 per ppm and 0.26 per ppm for barley and wheat, respectively. The COj‐elevation primarily decreases the tiller dieback of the cereals. Considering the increase in CO2of 30 ppm and in the hectare yield of 25 (barley) and 28 (wheat) from 1970 to 1990, the contribution of CO2to the increase in the agricultural production is estimated to be one fourth up to one half of the increase in hectare yield of spring cereals. Given a recent yearly increase of 2 ppm the future CO:‐related increase in hectare yield is estimated to be about 0
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